Theme 1 – FLOW FRICTION<\/strong><\/h1>\n\n\n\n![\"Symbol](\"http:\/\/yvcharron.com\/wp-content\/uploads\/2020\/07\/image-7.png\")
Credit : https:\/\/www.karlsims.com\/fluid-flow.html<\/a><\/figcaption><\/figure><\/div>\n\n\n\n–<\/p>\n\n\n\n
1.1-General information on fluidic friction<\/strong><\/h3>\n\n\n\nAs the solid friction, resulting from the relative movement between two solid elements in contact, the fluidic friction, resulting from the relative movement between a solid element and a fluid, is of very great importance. This friction causes energy losses transformed into heat contributing twice to global warming<\/strong> (the losses themselves and the overconsumption of energy). This degraded energy is irrecoverable corresponding in thermodynamics to an increase in entropy<\/strong>. Fluid friction may be found, for instance, inside gas or liquid turbines driving electric generators or in gas or liquid pipelines which therefore require the use of large pressurizing stations. These two examples fall into the category of internal flows. It may also be found in means of transport like planes, trains, cars, trucks or boats. These latter examples fall into the category of external flows.<\/p>\n\n\n\nGiven the importance of this fluidic\nfriction, it is important to be able to predict it with sufficient accuracy in\nindustrial applications (lift and drag of a wing or pressure drops in a pipeline),\nto determine the importance of tiny wall surface deformations (roughness,\nundulations), to characterize the surface of these walls (or coatings in\ncontact with the flow), to develop measuring equipment to determine the\nhydraulic roughness (equivalent roughness on a fluidic basis) under all\nconditions of use, including the most severe (high density and high relative velocity\nof the fluid) also to develop techniques for reducing drag (in particular,\nreducing turbulent friction).<\/p>\n\n\n\n
It is important to distinguish two fundamentally different cases of flow: a) laminar flow<\/strong> characterized by a low value of the Reynolds number (product of the volumetric mass by the hydraulic diameter, the relative velocity and the inverse of the viscosity). In this case, the relative velocity presents a parabolic profile while the flow is not very sensitive to surface deformations; b) turbulent flow<\/strong> characterized by a medium or high value of the Reynolds number. In this case, the relative velocity presents a relatively flat profile beyond a certain distance from the wall referred to as the boundary layer<\/strong>. This latest includes a very thin viscous layer<\/strong> in contact with the wall and a turbulent transition layer<\/strong> in between the viscous layer and the main turbulent zone.<\/p>\n\n\n\n_<\/p>\n\n\n\n
1.2-Texture of a coated and an uncoated surface<\/strong><\/h3>\n\n\n\nThe texture of\na surface is extremely complex. It may be favourable or not to the displacement\nof a fluid. Fluid flow may be increased, relatively to a smooth surface, in the\ncase of a turbulent flow and by using organised structures at the wall surface.\nOn the contrary, it is reduced in the case of a turbulent flow and with walls\ncovered by asperities distributed randomly (size and interval). Fluid flow is\nunchanged in the case of a laminar flow whether the surface deformations are\ndistributed randomly or not.<\/p>\n\n\n\n
Surface\ntexture is the result of a manufacturing process, erosion, abrasion, corrosion\nor the application of a coating (internal in the case of a conduct). It can\nalso evolve over time and according to the environmental conditions\n(physicochemical action). The texture of a coating depends on many factors: the\nmaterial of the coating (epoxy, polyurethane), the mode of application (cold or\ndeposition of molten particles), the size of pigments and fillers (solid\nparticles), the type and concentration of a solvent (water, organic element).<\/p>\n\n\n\n
Numerous\nindustrial applications have made it possible to predict the surface topology\nof steels. Depending on the storage conditions, the operating time and the\naggressiveness of the environment, it is possible to estimate the amplitude of\nthe roughness. On this basis, the resulting friction factor may be roughly\nestimated.<\/p>\n\n\n\n
The case of internal coatings is significantly different<\/strong>. The surface characteristics are very dependent on the type of coating and its mode of application. It should be mentioned that certain coating surfaces presents very small local roughness suggesting a favourable friction factor but also ripples of larger amplitudes with long wavelength<\/strong> which have been ignored for a long time by the industry but which could sometimes be very penalizing.<\/p>\n\n\n\nThe surface characterization of a coating requires, therefore, the measurement of surface deformations using a sensor (often a roughness meter) from short to long wavelengths. The aerodynamic tests (presented below) make it possible to compare the results obtained in terms of hydraulic roughness (equivalent) and physical roughness.<\/p>\n\n\n\n
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1.3-Measurement of hydraulic roughness – Large boundary layer range<\/strong><\/h3>\n\n\n\nIt is\nimportant to have a good understanding of the fluidic friction in a wall –\nfluid interaction in order to design industrial systems with the best possible\nprecision. Fluidic friction is as well dependent on the wall material, in\nparticular, its physicochemical properties as on the surface topology. It is\nalso dependent on the physicochemical properties of the fluid as the flow\nconditions.<\/p>\n\n\n\n
Determining experimentally,\nthe characteristics of a low pressure and low velocity flow is relatively easy\nrequiring low testing volume, short equilibrium time, small establishing length\nand low investment cost. It is quite different when it is desired to carry out\ntests with gases of high density, high pressure (up to 500 bar) or high velocity\n(up to 20 m \/ s) representing a very small boundary layer thickness. This\nresults in high investment and operating costs.<\/p>\n\n\n\n
To solve this problem, a relatively compact device has been developed which can induce a flow with a very small boundary layer thickness, of the order of a micron<\/strong>. It consists of a cylindrical vessel (external part) designed to withstand a pressure of 100 bars in which a cylinder (drum – internal part), driven externally by an electric motor, is rotated with a peripheral velocity of the order of 40 m \/ s. The internal cylinder drives the gas in its rotation which is then slowed down by a fixed wall mounted inside the high pressure vessel. The flow brakeage is measured using either a torque meter or a Pitot probe mounted in the air gap between the outside of the rotating cylinder and the inside of the fixed wall. A preliminary calibration phase with several fixed walls of different roughness makes it possible to determine (by interpolation) the equivalent roughness (hydraulic or aerodynamic) of any fixed wall.<\/p>\n\n\n\nThe device has been used for testing the properties of pipeline internal coatings designed for gas transport. Tests have shown the occurrence of a wall sliding effect <\/strong>which appears, mainly, when the thickness of the boundary layer is very small (on the order of a micron meter).<\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/coating-aerodynamic-testing\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
1.4-Structured surfaces for turbulent friction reduction<\/strong><\/h3>\n\n\n\nIt\nhas long been believed that a rigid, straight, smooth surface was the optimum\nmedium for minimizing the effects of turbulent friction, hence drag (hydraulic\nor aerodynamic) that is the friction factor. By observing the displacement of\nsharks into water, it was noticed that their relatively high velocity was due\nto the presence on their skin of micro asperities, oriented in the direction of\ntheir displacement and forming channels in the inter-space of the skin\ndeformations. For this reason, these structures are commonly called “Riblets”.<\/strong><\/p>\n\n\n\nRectilinearly grooved surfaces\n– Two-dimensional or \u201c2D\u201d Shapes<\/strong><\/p>\n\n\n\nTests\ncarried out in the mid-twentieth century on this type of surface structure showed\nthat a reduction in hydraulic drag could be achieved within a range of 5 to 10%\ndepending on the geometry of the groove (equilateral or half elliptical) or\neven, according to some experiments, between 10 and 12% (razor blade shape).<\/p>\n\n\n\n
The\nexplanation for these results relates to the following observations. In the\ncase of a smooth surface, instabilities called \u201cLow Speed Streaks\u201d<\/strong>\n(kinds of longitudinal vortices, generally paired and rotating around themselves)\ndevelop near to the wall (at the limit of the viscous layer where viscous\nfriction occurs) to occasionally burst from the boundary layer and amplify in\nsize when escaping towards the flow core. This process is extremely\ndissipative. The use of micro grooves permits to control the “Low Speed Streaks”\nin their lateral displacement and to limit to some extend viscous dissipation\nnear to the wall. The optimum size of the grooves corresponds approximately to\nthe average diameter of the \u201cLow Speed Streaks\u201d. In this situation, these\nturbulent structures float on the tip of the solid structures explaining why\nthe razor blade shaped grooves provide the best performance.<\/p>\n\n\n\nThis physical explanation makes it possible to understand why the effect of the turbulent flow structures can be simulated with a RANS code <\/strong>(numerical simulation of fluids of the Reynolds Average Navier Stockes type), code in which the turbulence is modelled by equations and not simulated as in the case described below (three-dimensional structured surfaces). This code was used to verify the performance of grooves (solid structures) of different shapes (Triangular and knife blades) with several relative groove dimensions (width and height).<\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/two-dimension-structures\/<\/a><\/p>\n\n\n\nSinusoidal grooved\nsurfaces – Three-dimensional shape “3D1”<\/strong><\/p>\n\n\n\nIn\nturbulent flow, the energy dissipation is mainly of a turbulent nature and very\nlittle of a viscous nature. This turbulent dissipation represents a fraction of\nthe order of 90% for slightly or moderately turbulent flows reaching 99.9% for\nvery highly turbulent flows. These relative rates of turbulent dissipation\nprovide some insight into the potential for energy gain offered by structured\nsurfaces or any other means designed for turbulent friction reduction.<\/p>\n\n\n\n
To\nthis end, it should be noted the contribution of an oscillating transverse\nparietal movement<\/strong> characterized by a wall (a flat plate or the internal\nsurface of a cylinder) in periodic transversal displacement (right – left) to\nthe mean direction of the flow. For a given frequency, the energy gain is\nmaximum. The energy input is globally positive (taking into account the energy\nrequired to oscillate the wall) for a given oscillation amplitude. The\nelongation and stabilization of Low Speed Streaks are two parameters put\nforward to explain the benefit of an oscillating transverse movement.<\/strong><\/p>\n\n\n\nThe\ncombination of these two phenomena<\/strong> (rectilinear grooves\nand oscillating wall) has been used for the design of three-dimensional\nstructured (grooved) surfaces. In this configuration, the grooves present a\nsinusoidal shape in direction of the flow. This concept was analyzed, not by using\na numerical code of the RANS type but by using an LES code<\/strong> (Large Eddy\nSimulation) where the effect of turbulence is simulated and not modelled. The\nproperties of turbulence are not calculated at the smallest scale (called\nKolmogorov – DNS code) but at a larger scale related to the phenomenon to be\nanalyzed. This code allows taking into account the deformation generated on the\nLow Speed Streaks by the oscillating movement. The code was first validated on linear\ngrooves then used to determine the effect of a sinusoidal motion (amplitude and\nfrequency) applied to the basic groove shape (linear). Under optimal\nconditions, the reduction in turbulent friction is of the order of 20%,\nwhich is roughly the double of the previous case.<\/strong><\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/three-dimension-structured-surfaces-type-1\/<\/a><\/p>\n\n\n\nGrooved surfaces with\ntwo orthogonal transverse waves – three-dimensional shape “3D2”<\/strong><\/p>\n\n\n\nThe\nthree-dimensional shape “3D1”<\/strong> corresponds\nto grooves of constant dimensions (width and height) in the flow direction and\nwith a sinusoidal course oriented successively towards the left and the right<\/strong>\nrespectively to the wall or the mean direction of the flow.<\/p>\n\n\n\nThe\nthree-dimensional shape “3D2<\/strong>” is similar to\nthe shape “3D1” but with the addition of a sinusoidal displacement of\nthe flow oriented successively upwards and downwards<\/strong> with respect to the\nwall and to the mean direction of the flow. The two waves such oriented are\nsaid to be orthogonal.<\/strong><\/p>\n\n\n\nThe\nthree-dimensional shape \u201c3D2\u201d provides additional advantages compared to the\nshape \u201c3D1\u201d: a) additional stabilization and additional elongation of the Low\nSpeed Streak (LSS); b) more viscous loss reduction at the wall surface; c) less\nfrequent burst of the LSS towards the central core. In this \u201c3D2\u201d case, the\nwave normal to the wall is materialized by an increase in height of the grooves\nat the peak amplitude of the horizontal wave and a decrease in height of the\ngrooves at the inflection point of the horizontal wave.<\/p>\n\n\n\n
First\ncalculations have shown a reduction in turbulent friction of more than 25%.<\/p>\n\n\n\n
http:\/\/yvcharron.com\/index.php\/three-dimension-structures-type-2\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
1.5-Deformable or porous coatings and injection of materials<\/strong><\/h3>\n\n\n\nA\nreduction in turbulent friction can be obtained in a conduct (pipeline) based\non the mechanical properties and the\nconstitution of the wall<\/strong> in contact with the flow.<\/p>\n\n\n\nA\ndeformable coating<\/strong> providing an efficient reduction in\nturbulent friction relies on an optimum attenuation of pressure waves. In such\na case, a pressure wave directed towards the wall generates a second wave in phase\nopposition that counteracts the action of other waves directed towards the\nwall.<\/p>\n\n\n\nA porous\nand permeable coating<\/strong> providing an efficient reduction in\nturbulent friction relies on an optimum attenuation of the velocity waves. The\nprinciple is similar to the previous case: a velocity wave directed towards the\nwall generates a second wave in phase opposition which counteracts the action\nof other waves directed towards the wall.<\/p>\n\n\n\nA\nreduction in turbulent friction can be achieved by injecting liquids or particles into the flow<\/strong>.<\/p>\n\n\n\nFilm-forming\nagents<\/strong> injected into a flow (more generally\ngaseous) produce a reduction in aerodynamic drag on a plate in contact with\nthis flow or a reduction in pressure drops inside a pipeline. The action of\nthese agents which are deposited on a wall can be explained in several manners.\nIt may be caused either by a parietal sliding resulting by a kind of sliding of\nthe agents deposited along the wall (reduction in the relative velocity of the\nflow with respect to the wall) or a molecular force, normal to the wall, repelling\nthe molecules of the fluid from the wall thus causing less brakeage by the wall.<\/p>\n\n\n\nViscoelastic agents<\/strong> injected into a flow (more generally liquid) produce a reduction in pressure losses inside a pipe by a damping effect of the large turbulence structures in the flow core. The reduction in pressure drop can reach 75% in certain situations to the detriment of the particularly high injection cost of these agents.<\/p>\n\n\n\n_<\/p>\n\n\n\n
1.6-Parietal slip<\/strong><\/h3>\n\n\n\nWe\ncan distinguish at least two different cases of parietal sliding.<\/p>\n\n\n\n
The\nfirst case concerns the chemical compositions of the wall and of the moving\nfluid <\/strong>and the resulting molecular interaction<\/strong>\nbetween these two. Let\u2019s consider the molecular forces normal to the wall. In\nthe case of a force directed from the wall towards the flow core, the molecules\nof the fluid are so much less slowed down by the wall as they are more repelled\nby it. This results in an increase in the flow velocity which may be designated\nby \u201cWall slip\u201d.<\/strong> In the opposite case, the result is a reduction in the\nflow velocity which may be designated as a \u201cWall brake\u201d<\/strong>. Wall slip and wall\nbrake are characterized by a “slip length” measuring the distance\nbetween the physical wall and the zero velocity condition (after extrapolation\nof the velocity profile).<\/p>\n\n\n\nThe\nsecond case relates to the movement of movable walls within a fixed wall<\/strong> (for example, a conduct or a pipeline).<\/p>\n\n\n\nLet\nus imagine, firstly<\/em>,<\/strong> a fluid not circulating by itself in a conduct but a fluid confined in sealed containers<\/strong>\n(caissons) moving along the conduct. In this situation, the pressure drop is\nlimited to the viscous and turbulent losses produced between the fixed wall (conduct)\nand the moving one (container), i.e. over a very short distance (difference in\ndiameter of the conduct and the container). These losses being very small, the\nresult is a very low pressure drop along the conduct.<\/p>\n\n\n\nLet\nus imagine, secondly<\/em><\/strong> a mobile wall<\/strong>, rigorously circular, moving\ninside a fixed wall<\/strong> (pipeline), also rigorously circular and with a\ndiameter slightly greater than that of the mobile wall. In this situation,\nthere are two relative displacements, that of the mobile wall relative to the\nfixed wall and that of the flow inside the mobile wall. The energy loss\ncorresponding to the mobile wall is very low given the small distance between\nthe two walls and the lower relative velocity of the mobile wall compared to a\nfree flow in a fixed pipe. The same is true for the pressure drop of the flow\ninside the moving wall, the pressure drop being proportional to the square of\nthe velocity.<\/p>\n\n\n\nLet\nus imagine, thirdly,<\/em><\/strong> a somewhat more realistic situation concerning the\nmaterials used. Its principle, intermediate between the two preceding cases<\/strong>,\nwould be as follows. A flexible material is produced in situ or deployed\nupstream of the pipeline in the form of thin and flexible strips or bands,\nparallel to the wall of the pipe and entrained by a sort of shield located\ndownstream and pushed by the fluid. This system is reproduced along the pipe as\nmany times as required by the length of the pipeline and the length of the band\n– shield system. A complex flow of fluid is established in which the fluid is\npredominantly enclosed within the straps (bands), therefore, with very little\nmovement relative to them. The turbulence inside the bands is almost non-existent\nwhile the turbulence external to the bands evolves over very short distances\nbeing also largely attenuated by the flexible bands.<\/p>\n\n\n\n_<\/p>\n\n\n\n
Theme 2 – PIPELINES<\/strong><\/h1>\n\n\n\n![\"Symbol](\"http:\/\/yvcharron.com\/wp-content\/uploads\/2020\/07\/image-8.png\")
Credit : https:\/\/fr.depositphotos.com\/stock-photos\/pipeline.html<\/a><\/figcaption><\/figure><\/div>\n\n\n\n2.1-General information on pipelines<\/strong><\/h3>\n\n\n\nPipeline design and operation involve many sciences or\nspecialties and among them metallurgy,\nchemistry, geophysics, civil engineering, fluid mechanics, geopolitics and\neconomics<\/strong>. The problems encountered are numerous and of different kinds. In\nmetallurgy, the subjects are related to the quality and composition of steels to\nprovide enough resistance to pressure, temperature, depressurization and\ncorrosion. In chemistry, the preoccupation is related to the protection against\ncorrosion (and associated control systems), in particular, with the use of\ninternal and external coatings but also by the various causes of clogging\n(formation of hydrates or paraffin). Geophysics and civil engineering are\nconcerned with the behaviour of pipelines on their land or sea support. Fluid\nmechanics deal with hydraulic aspects including various types of two phase flow\n(from liquid bubbles to plugs, liquid accumulation) or various aerodynamic and\nhydraulic aspects determining the sizing of pipelines, compressor stations and\nterminal design. Geopolitics is involved in the pipeline routing regarding\ncustomer locations and frontiers. Economics is essential since it determines\nthe feasibility of a project for investors.<\/p>\n\n\n\nIn this topic,\nwe are particularly interested in some aspects relating to fluid mechanics<\/strong>:\nthe use of specific internal coatings, the impact of the aging of internal\ncoatings on the transmission factor, the degree of pressure loss linked to\nexternal welds with penetration inside a pipeline, a monitoring device for the\ncontinuous measurement of internal hydraulic roughness along a pipeline as well\nas the benefit of aerodynamic drag reduction techniques.<\/p>\n\n\n\n_<\/p>\n\n\n\n
2.2-Aging of pipe internal coatings<\/strong><\/h3>\n\n\n\nTheme 1 on\n“fluidic friction” focuses<\/strong> more\nparticularly on the surface characterization (roughness and undulations) of newly applied internal coatings<\/strong> as well\nas their aerodynamic performance measured with an aerodynamic test device\ncalled the “Rotating cylinder Unit\u201d (RCU).<\/p>\n\n\n\nTheme 2 on “pipelines” focuses on aged coatings<\/strong>, that is, coatings subjected to the various operating conditions of a production system to determine the impact on their aerodynamic performance. The aging conditions studied relate, in particular, to erosion, to a sudden decompression and to the physicochemical interactions between internal coatings and certain chemical agents encountered in gas transport, for instance, tri-ethylene glycol. Sometimes, tests show a sharp deterioration in the aerodynamic performance for certain coatings even when their surface topology has not been altered. This aerodynamic behaviour is apparently the result of a physicochemical interaction between the chemical agent and the coating material. In this situation, the degradation of performance can be interpreted by a “molecular brakeage” of the wall (the reverse of a wall slip). See \u201cParietal slip\u201d in theme 1.<\/p>\n\n\n\n_<\/p>\n\n\n\n
2.3-Impact of welds on gas transport<\/strong><\/h3>\n\n\n\nWelds carried out on the outside of a tube or a pipeline\ncan penetrate inside them with a greater or lesser impact depending on the\ncharacteristics of the weld (penetration height and routing inside a pipeline)\nas well as the flow most often represented by a Reynolds number<\/strong>. The higher this number (density, pressure and fluid\nvelocity), the greater the pressure drops. On the contrary, the smaller this\nnumber, the more the pressure drops can be neglected.<\/p>\n\n\n\nTo this end, it is necessary to distinguish three types of welding<\/strong> associated to three mechanical requirements corresponding each one to a specific shape.<\/p>\n\n\n\nLongitudinal\nwelds<\/strong> result from the manufacturing of forged tubes, rolled\nand then welded along a longitudinal direction. This weld, although very long,\nhas no effect on gas transport since it is in perfect alignment with the main flow.\nThe height of penetration also has very little impact on pressure drops.<\/p>\n\n\n\nRadial welds<\/strong>\nmet at regular intervals (generally every 12 m) are required for the assembly\nof tubes for the construction of a pipeline. Perpendicular to the flow, this\ntype of weld partially obstructs the flow. The magnitude of the corresponding\npressure loss is of the order of a few per cent. Magnitude of the pressure loss\nis determined, primarily, by the weld penetration height and by the thickness\nof the boundary layer, itself determined by flow conditions (primarily, the\nReynolds number). Calculations were made using a RANS (Reynolds Average Navier\nStockes) fluid mechanics code for several weld heights and shapes\n(semi-circular, elongated) and also several flow conditions.<\/p>\n\n\n\nSpiral welds<\/strong> are encountered during the manufacturing of tube sections of great length (18 to 24 m) and large diameter with a relatively low operating pressure (of the order of 100 bars). These tubes are made from coiled plates. This method of manufacture allows the production of tubes at a relatively low cost. Intermediate between the longitudinal weld and the radial weld, the pressure drop associated to a spiral weld is strongly dependent on the helix angle<\/strong> (spiral shape) but also on the penetration height inside the tube and the thickness of the boundary layer. The calculation of the pressure drop is particularly complex since it is necessary to perform flow simulations on asymmetric pipe sections<\/strong> and over great lengths. Calculations were made using RANS code for several weld heights and shapes, multiple helix angles and for various flow conditions.<\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/internal-pipeline-welds\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
2.4-Realization of structured surfaces inside a long tube<\/strong><\/h3>\n\n\n\nThe benefit of structured surfaces has been presented\nin Theme 1 and, in more detail, in the case of three geometrical shapes: a) a two-dimensional;\nb) a three-dimensional \u201ctype 1\u201d characterized by a transverse sine wave\nparallel to the wall and c) very succinctly, a three-dimensional \u201ctype 2\u201d characterized\nby two transverse sinusoidal waves, one of which being parallel and the other\northogonal to the wall.<\/p>\n\n\n\n
Achieving structured surfaces on a flat surface or\ninside a cylinder (for example, a pipeline tube) can be accomplished in several\nways. In the case of structures of large dimensions (of the order of a millimetre)\nand for a limited surface, it is possible to produce them mechanically. In the\ncase of structures with a small dimension (few tens of micron) to be produced\non large surfaces, another method should be selected. The method adopted in this document comprises three stages.<\/strong><\/p>\n\n\n\nIn a first step<\/em><\/strong>, structured surfaces are produced with a great accuracy\nby using a femto second laser<\/strong> on a\nrelatively rigid surface (surface erosion by laser ablation). These lasers\nallow the production of regularly shaped grooves in a periodic transverse\nmovement (3D-Type1) and with a periodically adjustable depth (3D-Type2).<\/p>\n\n\n\nIn a second step<\/em><\/strong>, it is proceeded to the manufacture of a flexible mould\non the eroded (ablated) surface mentioned above. The structures of the flexible\npart are, practically, the mirror image of the structures provided by laser\nablation.<\/p>\n\n\n\nIn a third step<\/em><\/strong>, the flexible part mentioned above is applied shortly\nafterwards an internal coating has been applied on the internal surface of a\ntube. After the time required for the coating to harden, the flexible part is\nremoved. The structures inside the tube are practically identical to those made\nin the first step.<\/p>\n\n\n\n_<\/p>\n\n\n\n
2.5-Measurement of hydraulic parameters inside a pipeline<\/strong><\/h3>\n\n\n\nDevices are sometimes introduced inside pipelines\nduring maintenance operations. These devices are divided into two main\ncategories: mechanical pigs<\/strong> which\nessentially aim to carry out cleaning inside a pipeline (displacement or\nremoval of paraffin deposits or liquid plugs). These pigs are strictly passive.\nThere is a second category, the purpose of which being to perform measurements\nsuch as the wall thickness of the pipeline to assess the effects of corrosion\nand adapt the flow rate and frequency of injection of anticorrosion products.\nThese pigs are equipped with electronics, batteries, transmitters and various\nsensors. They are said to be “Intelligent Monitoring Pig” or “Smart Monitoring Pig<\/strong>“.<\/p>\n\n\n\nIt is proposed in this section another type of \u201cSmart Monitoring\nPig\u201d whose objective is to continuously measure the hydraulic roughness along\nthe entire length of a pipeline. The device is inspired by the operation of the\n\u201cRotating Cylinder Unit<\/strong>\u201d described\nin Theme 1 (Fluidic friction). The device operates as follows: A cylinder is\nrotated with the aid of an electric motor near the wall of the pipeline. A Pitot tube<\/strong> installed in the air gap\nbetween the cylinder and the wall measures the velocity of the intermediate gas.\nFrom this measurement it is possible to interpolate the hydraulic roughness\nfrom a calibration curve (established following a calibration phase with\ndefined roughness) which is then stored in a digital device. The measurement\ncan also be done at several transverse angles (North, South, East, West or\nintermediate).<\/p>\n\n\n\nAssociated to pressure and temperature measurements,\nthe knowledge of the hydraulic roughness would provide a detailed survey of\ncorrosion and material deposit zones along the pipeline.<\/p>\n\n\n\n
http:\/\/yvcharron.com\/index.php\/pipeline-pig-monitoring\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
2.6-Technico economical studies<\/strong><\/h3>\n\n\n\nThe cost of a pipeline depends on a very large number\nof parameters, starting with the characteristics of the fluid transported. It\nalso depends on the quality of the steel, the diameter and the design pressure\nof the pipeline as well as the compression stations (including intermediate\nstations for pipeline of several thousands of kilometres). All these parameters\nare, of course, interrelated requiring in some cases some compromise.<\/p>\n\n\n\n
As the\ninvestment cost is considerable, it is important to minimize the pressure drop<\/strong>.\nFor a pipeline in a given configuration, a reduction in pressure losses can be\nobtained in different ways with sometimes high performance associated with a technological\ncomplexity.<\/p>\n\n\n\nTo facilitate understanding of the technical –\neconomic study, a few technical elements are recalled below. For a pipe of\ngiven diameter and a fluid of given viscosity, the thickness of the boundary\nlayer (approximately 5 times the thickness of the viscous layer) is inversely\nproportional to the density (for a gas, product of the molecular mass by the\nabsolute pressure and the inverse of the absolute temperature) and also the fluid\nvelocity. This thickness is also an inverse function of the Reynolds number.\nThe friction factor is a decreasing function of the Reynolds number up to a\nthreshold value where it is substantially determined by the relative roughness.\nPressure losses are proportional to the friction factor, the square of the fluid\nvelocity, the volumetric mass (or density), the length of the pipeline and the\ninverse of the diameter. For a given mass flow rate, the pressure drop varies with the inverse of the diameter to the power\nof 5<\/strong>.<\/p>\n\n\n\nPipeline\nuncoated internally<\/strong>: the internal roughness of the pipeline increases\nsignificantly over time. If the Reynolds number is low (thick boundary layer),\nthe pressure drop is not significantly dependent on the roughness magnitude.\nBeyond a certain Reynolds number, the pressure drop becomes relatively large.<\/p>\n\n\n\nInternally coated\npipeline<\/strong>: By applying an internal coating with a thickness approaching\none hundred microns, it greatly reduces the internal roughness of the pipeline.\nThis value is maintained at a relatively low level for several tens of years of\noperation. This solution makes it possible to greatly reduce the pressure drop\ncompared to an uncoated pipe.<\/p>\n\n\n\nPipeline\ncoated internally with smoothing of the coating<\/strong> before coating\nhardening (see corresponding section). This procedure allows a further\nreduction in the friction factor when the boundary layer is thin (large value\nof the velocity and pressure product that is high Reynolds number).<\/p>\n\n\n\nPipeline\ncoated internally with 2D structuring<\/strong> (see\ncorresponding sections: 2D application and performance) of the coating before\ncuring. This procedure allows a reduction in the friction factor of around 8%\ncompared to a strictly smooth surface, regardless of the thickness of the\nboundary layer. This method is easier to implement for an average dimension of\nstructures greater than 50 microns (average thickness of the boundary layer).\nNote that for water transport, the average dimension of structures is of the\norder of 100 microns.<\/p>\n\n\n\nPipeline\ncoated internally with 3D structuring<\/strong> (see\ncorresponding sections) of the coating before curing. This procedure allows an\nadditional reduction in the friction factor of around 16% compared to a\nstrictly smooth surface, regardless of the thickness of the boundary layer. As\nin the previous section, this method is easier to set up for an average\ndimension of structures greater than 50 microns. The realization of a\nstructured surface is slightly more expensive than that of a smooth surface\nconcerning the realization of the primary moulds.<\/p>\n\n\n\nThese technical elements make it possible to choose\nthe type and method of application of an internal coating, the operating\npressure, the average diameter of the pipeline, the size and the distance\nbetween the compression stations within the framework of economic optimization.<\/p>\n\n\n\n
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Theme 3 – TWO PHASE FLOW<\/strong><\/h1>\n\n\n\n![\"Symbol](\"http:\/\/yvcharron.com\/wp-content\/uploads\/2020\/07\/Site-Symbol-diphasique.png\")
Credit : https:\/\/www.thermal-engineering.org\/what-is-bubbly-flow-two-phase-flow-definition\/<\/a><\/figcaption><\/figure><\/div>\n\n\n\n–<\/p>\n\n\n\n
3.1-Two-phase compression – pumping<\/strong><\/h3>\n\n\n\nThe multiphase limits of single-phase\ncompression and pumping equipment<\/strong><\/p>\n\n\n\nSingle-phase compression expression is used to mean the compression of a\ngas phase (compressible) and single-phase pumping to mean the pumping of a\nliquid phase (incompressible). Hereinafter, the term compression or pumping is\nused indifferently when it concerns a two-phase mixture.<\/p>\n\n\n\n
The equipment required for single-phase compression or pumping is of the\nvolumetric type (pistons, gears, diaphragms) or of the rotodynamic part. In the\nfirst case, the energy transmitted by the pressurizing machine is directly\nconverted into pressure. These machines present many advantages including\nefficiency and the ability to compress a two-phase phase with a relatively high\n\u201cefficacy<\/strong>\u201d (this parameter measures\nthe ratio between efficiencies, respectively, in two-phase and single-phase\nflows). These machines, on the other hand, are heavy, bulky and require\nsignificant maintenance. In the second case, the energy transmitted by the pressurizing\nmachine is, firstly, converted into velocity (through a rotating wheel or\nimpeller) then into pressure (through a fixed diffuser or rectifier). These\nmachines present many advantages in terms of pressure (radial machines) and\nvolume flow (axial machines), reduced space and limited maintenance. On the\nother hand, the efficiency is largely dependent on the volume flow.\nFurthermore, these machines are totally unsuitable for two-phase compression or\npumping, whether in the presence of a small quantity of liquid associated with\na gas phase (erosion is an additional drawback) or of a small quantity of gas\nassociated with a liquid phase (gas plug at the entrance a radial wheel).\nBeyond a very low level of gas (for a pump) or liquid (for a compressor), the\ntwo-phase efficacy tends towards zero.<\/p>\n\n\n\nHelico – axial hydraulics – Poseidon type –\n1st generation hydraulic<\/strong><\/p>\n\n\n\nTo overcome the inability of conventional rotodynamic machines to\ncompress or to pump two-phase effluents, IFP has developed in the eighties a\nhelico axial hydraulic system called \u201cPoseidon\u201d. The impeller (the wheel)\nincludes vanes with a very small entry angle (often less than 10 degrees) and a\nvery small curvature. These blades are therefore relatively long (overlap ratio<\/strong> between 1.5 and 2.0)\ngenerating relatively high viscous losses. According to this design, the\naccelerations in the longitudinal, transverse and radial directions are\nrelatively low. These characteristics are obtained by a small variation of the\npassage section (the area) along the flow path, a small blade curvature and the action of a Coriolis force in the\nradial direction reducing the effect of the centrifugal force<\/strong>. For a low or\nhigh gas- liquid volume flow ratio represented by the GLR parameter<\/strong> (for \u201cGas – Liquid Ratio\u201d), the two-phase efficacy is\nclose to 1. On the other hand, for an intermediate GLR (between 2 and 10\ndepending on the geometry), the efficacy decreases significantly when the GLDR parameter<\/strong> (for \u201cGas – Liquid\nDensity Ratio\u201d) is reduced.<\/p>\n\n\n\nIn conclusion<\/strong><\/em> <\/strong>– Despite relatively good performance compared to single-phase machines, Poseidon hydraulics present several drawbacks: significant viscous losses and low two-phase efficacy at intermediate GLR\u2019s.<\/p>\n\n\n\nHelico – axial hydraulics with interfacial\nslip control – 2nd generation hydraulic<\/strong><\/p>\n\n\n\nThe operation of the Poseidon hydraulics is satisfactory at low GLRs,\nthe low orthogonal accelerations (longitudinal, transverse and radial) limiting\nto some extend the separation of the phases in the three main directions.\nBeyond a certain GLR (for example 2 – value dependent on many parameters\nincluding pressure, viscosity and surface tension), the two phases separate,\ngenerating strong interfacial losses. In strictly helico-axial hydraulics, the\nliquid phase is projected against the surface with the larger diameter slowing\nit down in its displacement towards the outlet (relatively large viscous forces)\nwhich in turn induces a braking of the gaseous phase (high energy dissipation\nat the interface of the two phases). The difference in velocity between the two\nphases is referred to as the interfacial\nslip<\/strong>. The parietal braking of the liquid film increases with a decrease of\nthe liquid film thickness.<\/p>\n\n\n\nTo remedy this situation, the external part of the impeller (larger\ndiameter) is tuned to provide it with a very slight radial shape including, at\nthe inlet, a convex curvature (centre of the curvature directed outwards)\nallowing a large acceleration of the liquid phase and, at the outlet, a concave\ncurvature (centre inward) allowing a reduction in the acceleration of the\nliquid phase. These two curvatures help to minimize the velocity difference\nbetween the two phases. This action is referred to as “interfacial slip control”.<\/strong> This action allows a relatively large increase in the two-phase efficacy\nfor any value of GLR, including, for low values of the GLDR parameter.<\/strong><\/p>\n\n\n\nThe control of the interfacial slip allows a certain “relaxation” of the impeller\nblade parameters<\/strong>. In particular, the blade length may be reduced (smaller overlap\nratio) limiting viscous losses, thus, providing higher single and two phase efficiencies.\nIn addition the blade curvature may be increased, consequently, providing a\ngreater manometric head coefficient (compression ratio).<\/p>\n\n\n\nIn conclusion<\/em> – This second-generation hydraulic system presents, compared to the first-generation, in single phase flow, a higher efficiency and a higher manometric head coefficient as well as a higher two-phase efficacy<\/strong>.<\/p>\n\n\n\nRadio – helico – axial hydraulics – Wet gas<\/strong><\/p>\n\n\n\nThe design of hydraulics suitable for compressing wet gas derives from\nthe design of the second generation helico axial hydraulics.<\/p>\n\n\n\n
The terminology \u201cwet gas\u201d<\/strong>\ndenotes a low level of liquid fraction within the gas phase corresponding to a\nsignificant braking of the liquid film along the surface with the larger\ndiameter. As a result, the external curvatures located, respectively, at the\ninlet and at the outlet of the impeller are accentuated so as to greatly\naccelerate the liquid film (small thickness) towards the outlet.<\/p>\n\n\n\nThis configuration results in a diameter significantly increased at the\noutlet, compared to the inlet, providing a more radial shape of the impeller.\nThis configuration presents two advantages: less droplet erosion at the\nimpeller inlet and a higher manometric head coefficient which is required in\nthe case of the compression of a gas with a lower volumetric mass compared to a\ntwo phase flow with medium GLR.<\/p>\n\n\n\n
Helico \u2013 radio – axial hydraulics – Bubbly flow and viscous liquid<\/strong><\/p>\n\n\n\nIn bubbly flow (very low GLR), separation forces (accelerations acting\nin the three main orthogonal directions) have a lesser effect compared to the\ndrag forces acting on bubbles submerged in the liquid phase.<\/p>\n\n\n\n
As the separation forces get smaller, it is possible to apply a certain\n“relaxation” on the design parameters defining the 1st generation\nhydraulic (Poseidon). It is, in particular, possible to design a hydraulic with\na more radial shape (Helico radio axial), to shorten the length of the blades\nand to bend them so as to increase as well the efficiency as the manometric\nhead coefficient of an impeller.<\/p>\n\n\n\n
In the presence of a viscous liquid, the drag forces acting on the\nbubbles increase further compared to a situation with a non-viscous liquid. As\na result, it is possible to apply a greater “relaxation” on the\ndesign parameters of the 1st generation hydraulic.<\/p>\n\n\n\n
http:\/\/yvcharron.com\/index.php\/two-phase-flow-pumps\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
3.2-Two-phase expansion – turbines<\/strong><\/h3>\n\n\n\nThe multiphase limits of single phase\nexpansion or turbine equipment<\/strong><\/p>\n\n\n\nBy single-phase expansion it is meant here the expansion of a gaseous\nphase (compressible) through an expander and by single-phase depressurization,\nthe let-down of a liquid phase (incompressible) through a turbine. These\nexpansions or let downs result in energy supply.<\/p>\n\n\n\n
It is generally easier to depressurize, with a single-phase equipment, a\nslightly two-phase mixture (low or high GLR) than to pressurize it. However,\nthese depressurizations generally take place through a single stage.<\/p>\n\n\n\n
The challenge is to design a two-phase\nmulti-stage turbine so as to respond to a high expansion rate<\/strong>.<\/p>\n\n\n\nHelico – axial hydraulics – 1st generation<\/strong><\/p>\n\n\n\nAccording to a simplified approach, an expansion impeller (wheel) of a\ntwo-phase multistage turbine looks similar to a compression impeller of a\ntwo-phase multistage pump, the inlet section of the compression impeller acting\nas the outlet section of the expansion impeller. The same principle goes for\nthe opposite sections. The same principle goes also for the static elements (diffuser\nand inducer). However, the outlet angle of the expansion inducer is\nsignificantly reduced compared to the inlet angle of the compression diffuser.<\/p>\n\n\n\n
This hydraulic expansion provides advantages similar to those of the pumping\none.<\/p>\n\n\n\n
Helical – axial hydraulics – 2nd generation<\/strong><\/p>\n\n\n\nThe control of the interfacial slip in the wheel of a two phase turbine\nis similarly carried out to the control described for a compression system. It provides\na significant improvement in both single and two-phase performance.<\/p>\n\n\n\n
Radio – helical – axial hydraulics – Bubbly\nflow and viscous liquid<\/strong><\/p>\n\n\n\nConsideration of the interfacial slip as well as the ratio of the forces\nof separation and drag of the bubbles in the liquid leads to the same\nconclusions as those made in the context of a compression or pumping system.<\/p>\n\n\n\n
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1.1-General information on fluidic friction<\/strong><\/h3>\n\n\n\nAs the solid friction, resulting from the relative movement between two solid elements in contact, the fluidic friction, resulting from the relative movement between a solid element and a fluid, is of very great importance. This friction causes energy losses transformed into heat contributing twice to global warming<\/strong> (the losses themselves and the overconsumption of energy). This degraded energy is irrecoverable corresponding in thermodynamics to an increase in entropy<\/strong>. Fluid friction may be found, for instance, inside gas or liquid turbines driving electric generators or in gas or liquid pipelines which therefore require the use of large pressurizing stations. These two examples fall into the category of internal flows. It may also be found in means of transport like planes, trains, cars, trucks or boats. These latter examples fall into the category of external flows.<\/p>\n\n\n\nGiven the importance of this fluidic\nfriction, it is important to be able to predict it with sufficient accuracy in\nindustrial applications (lift and drag of a wing or pressure drops in a pipeline),\nto determine the importance of tiny wall surface deformations (roughness,\nundulations), to characterize the surface of these walls (or coatings in\ncontact with the flow), to develop measuring equipment to determine the\nhydraulic roughness (equivalent roughness on a fluidic basis) under all\nconditions of use, including the most severe (high density and high relative velocity\nof the fluid) also to develop techniques for reducing drag (in particular,\nreducing turbulent friction).<\/p>\n\n\n\n
It is important to distinguish two fundamentally different cases of flow: a) laminar flow<\/strong> characterized by a low value of the Reynolds number (product of the volumetric mass by the hydraulic diameter, the relative velocity and the inverse of the viscosity). In this case, the relative velocity presents a parabolic profile while the flow is not very sensitive to surface deformations; b) turbulent flow<\/strong> characterized by a medium or high value of the Reynolds number. In this case, the relative velocity presents a relatively flat profile beyond a certain distance from the wall referred to as the boundary layer<\/strong>. This latest includes a very thin viscous layer<\/strong> in contact with the wall and a turbulent transition layer<\/strong> in between the viscous layer and the main turbulent zone.<\/p>\n\n\n\n_<\/p>\n\n\n\n
1.2-Texture of a coated and an uncoated surface<\/strong><\/h3>\n\n\n\nThe texture of\na surface is extremely complex. It may be favourable or not to the displacement\nof a fluid. Fluid flow may be increased, relatively to a smooth surface, in the\ncase of a turbulent flow and by using organised structures at the wall surface.\nOn the contrary, it is reduced in the case of a turbulent flow and with walls\ncovered by asperities distributed randomly (size and interval). Fluid flow is\nunchanged in the case of a laminar flow whether the surface deformations are\ndistributed randomly or not.<\/p>\n\n\n\n
Surface\ntexture is the result of a manufacturing process, erosion, abrasion, corrosion\nor the application of a coating (internal in the case of a conduct). It can\nalso evolve over time and according to the environmental conditions\n(physicochemical action). The texture of a coating depends on many factors: the\nmaterial of the coating (epoxy, polyurethane), the mode of application (cold or\ndeposition of molten particles), the size of pigments and fillers (solid\nparticles), the type and concentration of a solvent (water, organic element).<\/p>\n\n\n\n
Numerous\nindustrial applications have made it possible to predict the surface topology\nof steels. Depending on the storage conditions, the operating time and the\naggressiveness of the environment, it is possible to estimate the amplitude of\nthe roughness. On this basis, the resulting friction factor may be roughly\nestimated.<\/p>\n\n\n\n
The case of internal coatings is significantly different<\/strong>. The surface characteristics are very dependent on the type of coating and its mode of application. It should be mentioned that certain coating surfaces presents very small local roughness suggesting a favourable friction factor but also ripples of larger amplitudes with long wavelength<\/strong> which have been ignored for a long time by the industry but which could sometimes be very penalizing.<\/p>\n\n\n\nThe surface characterization of a coating requires, therefore, the measurement of surface deformations using a sensor (often a roughness meter) from short to long wavelengths. The aerodynamic tests (presented below) make it possible to compare the results obtained in terms of hydraulic roughness (equivalent) and physical roughness.<\/p>\n\n\n\n
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1.3-Measurement of hydraulic roughness – Large boundary layer range<\/strong><\/h3>\n\n\n\nIt is\nimportant to have a good understanding of the fluidic friction in a wall –\nfluid interaction in order to design industrial systems with the best possible\nprecision. Fluidic friction is as well dependent on the wall material, in\nparticular, its physicochemical properties as on the surface topology. It is\nalso dependent on the physicochemical properties of the fluid as the flow\nconditions.<\/p>\n\n\n\n
Determining experimentally,\nthe characteristics of a low pressure and low velocity flow is relatively easy\nrequiring low testing volume, short equilibrium time, small establishing length\nand low investment cost. It is quite different when it is desired to carry out\ntests with gases of high density, high pressure (up to 500 bar) or high velocity\n(up to 20 m \/ s) representing a very small boundary layer thickness. This\nresults in high investment and operating costs.<\/p>\n\n\n\n
To solve this problem, a relatively compact device has been developed which can induce a flow with a very small boundary layer thickness, of the order of a micron<\/strong>. It consists of a cylindrical vessel (external part) designed to withstand a pressure of 100 bars in which a cylinder (drum – internal part), driven externally by an electric motor, is rotated with a peripheral velocity of the order of 40 m \/ s. The internal cylinder drives the gas in its rotation which is then slowed down by a fixed wall mounted inside the high pressure vessel. The flow brakeage is measured using either a torque meter or a Pitot probe mounted in the air gap between the outside of the rotating cylinder and the inside of the fixed wall. A preliminary calibration phase with several fixed walls of different roughness makes it possible to determine (by interpolation) the equivalent roughness (hydraulic or aerodynamic) of any fixed wall.<\/p>\n\n\n\nThe device has been used for testing the properties of pipeline internal coatings designed for gas transport. Tests have shown the occurrence of a wall sliding effect <\/strong>which appears, mainly, when the thickness of the boundary layer is very small (on the order of a micron meter).<\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/coating-aerodynamic-testing\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
1.4-Structured surfaces for turbulent friction reduction<\/strong><\/h3>\n\n\n\nIt\nhas long been believed that a rigid, straight, smooth surface was the optimum\nmedium for minimizing the effects of turbulent friction, hence drag (hydraulic\nor aerodynamic) that is the friction factor. By observing the displacement of\nsharks into water, it was noticed that their relatively high velocity was due\nto the presence on their skin of micro asperities, oriented in the direction of\ntheir displacement and forming channels in the inter-space of the skin\ndeformations. For this reason, these structures are commonly called “Riblets”.<\/strong><\/p>\n\n\n\nRectilinearly grooved surfaces\n– Two-dimensional or \u201c2D\u201d Shapes<\/strong><\/p>\n\n\n\nTests\ncarried out in the mid-twentieth century on this type of surface structure showed\nthat a reduction in hydraulic drag could be achieved within a range of 5 to 10%\ndepending on the geometry of the groove (equilateral or half elliptical) or\neven, according to some experiments, between 10 and 12% (razor blade shape).<\/p>\n\n\n\n
The\nexplanation for these results relates to the following observations. In the\ncase of a smooth surface, instabilities called \u201cLow Speed Streaks\u201d<\/strong>\n(kinds of longitudinal vortices, generally paired and rotating around themselves)\ndevelop near to the wall (at the limit of the viscous layer where viscous\nfriction occurs) to occasionally burst from the boundary layer and amplify in\nsize when escaping towards the flow core. This process is extremely\ndissipative. The use of micro grooves permits to control the “Low Speed Streaks”\nin their lateral displacement and to limit to some extend viscous dissipation\nnear to the wall. The optimum size of the grooves corresponds approximately to\nthe average diameter of the \u201cLow Speed Streaks\u201d. In this situation, these\nturbulent structures float on the tip of the solid structures explaining why\nthe razor blade shaped grooves provide the best performance.<\/p>\n\n\n\nThis physical explanation makes it possible to understand why the effect of the turbulent flow structures can be simulated with a RANS code <\/strong>(numerical simulation of fluids of the Reynolds Average Navier Stockes type), code in which the turbulence is modelled by equations and not simulated as in the case described below (three-dimensional structured surfaces). This code was used to verify the performance of grooves (solid structures) of different shapes (Triangular and knife blades) with several relative groove dimensions (width and height).<\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/two-dimension-structures\/<\/a><\/p>\n\n\n\nSinusoidal grooved\nsurfaces – Three-dimensional shape “3D1”<\/strong><\/p>\n\n\n\nIn\nturbulent flow, the energy dissipation is mainly of a turbulent nature and very\nlittle of a viscous nature. This turbulent dissipation represents a fraction of\nthe order of 90% for slightly or moderately turbulent flows reaching 99.9% for\nvery highly turbulent flows. These relative rates of turbulent dissipation\nprovide some insight into the potential for energy gain offered by structured\nsurfaces or any other means designed for turbulent friction reduction.<\/p>\n\n\n\n
To\nthis end, it should be noted the contribution of an oscillating transverse\nparietal movement<\/strong> characterized by a wall (a flat plate or the internal\nsurface of a cylinder) in periodic transversal displacement (right – left) to\nthe mean direction of the flow. For a given frequency, the energy gain is\nmaximum. The energy input is globally positive (taking into account the energy\nrequired to oscillate the wall) for a given oscillation amplitude. The\nelongation and stabilization of Low Speed Streaks are two parameters put\nforward to explain the benefit of an oscillating transverse movement.<\/strong><\/p>\n\n\n\nThe\ncombination of these two phenomena<\/strong> (rectilinear grooves\nand oscillating wall) has been used for the design of three-dimensional\nstructured (grooved) surfaces. In this configuration, the grooves present a\nsinusoidal shape in direction of the flow. This concept was analyzed, not by using\na numerical code of the RANS type but by using an LES code<\/strong> (Large Eddy\nSimulation) where the effect of turbulence is simulated and not modelled. The\nproperties of turbulence are not calculated at the smallest scale (called\nKolmogorov – DNS code) but at a larger scale related to the phenomenon to be\nanalyzed. This code allows taking into account the deformation generated on the\nLow Speed Streaks by the oscillating movement. The code was first validated on linear\ngrooves then used to determine the effect of a sinusoidal motion (amplitude and\nfrequency) applied to the basic groove shape (linear). Under optimal\nconditions, the reduction in turbulent friction is of the order of 20%,\nwhich is roughly the double of the previous case.<\/strong><\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/three-dimension-structured-surfaces-type-1\/<\/a><\/p>\n\n\n\nGrooved surfaces with\ntwo orthogonal transverse waves – three-dimensional shape “3D2”<\/strong><\/p>\n\n\n\nThe\nthree-dimensional shape “3D1”<\/strong> corresponds\nto grooves of constant dimensions (width and height) in the flow direction and\nwith a sinusoidal course oriented successively towards the left and the right<\/strong>\nrespectively to the wall or the mean direction of the flow.<\/p>\n\n\n\nThe\nthree-dimensional shape “3D2<\/strong>” is similar to\nthe shape “3D1” but with the addition of a sinusoidal displacement of\nthe flow oriented successively upwards and downwards<\/strong> with respect to the\nwall and to the mean direction of the flow. The two waves such oriented are\nsaid to be orthogonal.<\/strong><\/p>\n\n\n\nThe\nthree-dimensional shape \u201c3D2\u201d provides additional advantages compared to the\nshape \u201c3D1\u201d: a) additional stabilization and additional elongation of the Low\nSpeed Streak (LSS); b) more viscous loss reduction at the wall surface; c) less\nfrequent burst of the LSS towards the central core. In this \u201c3D2\u201d case, the\nwave normal to the wall is materialized by an increase in height of the grooves\nat the peak amplitude of the horizontal wave and a decrease in height of the\ngrooves at the inflection point of the horizontal wave.<\/p>\n\n\n\n
First\ncalculations have shown a reduction in turbulent friction of more than 25%.<\/p>\n\n\n\n
http:\/\/yvcharron.com\/index.php\/three-dimension-structures-type-2\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
1.5-Deformable or porous coatings and injection of materials<\/strong><\/h3>\n\n\n\nA\nreduction in turbulent friction can be obtained in a conduct (pipeline) based\non the mechanical properties and the\nconstitution of the wall<\/strong> in contact with the flow.<\/p>\n\n\n\nA\ndeformable coating<\/strong> providing an efficient reduction in\nturbulent friction relies on an optimum attenuation of pressure waves. In such\na case, a pressure wave directed towards the wall generates a second wave in phase\nopposition that counteracts the action of other waves directed towards the\nwall.<\/p>\n\n\n\nA porous\nand permeable coating<\/strong> providing an efficient reduction in\nturbulent friction relies on an optimum attenuation of the velocity waves. The\nprinciple is similar to the previous case: a velocity wave directed towards the\nwall generates a second wave in phase opposition which counteracts the action\nof other waves directed towards the wall.<\/p>\n\n\n\nA\nreduction in turbulent friction can be achieved by injecting liquids or particles into the flow<\/strong>.<\/p>\n\n\n\nFilm-forming\nagents<\/strong> injected into a flow (more generally\ngaseous) produce a reduction in aerodynamic drag on a plate in contact with\nthis flow or a reduction in pressure drops inside a pipeline. The action of\nthese agents which are deposited on a wall can be explained in several manners.\nIt may be caused either by a parietal sliding resulting by a kind of sliding of\nthe agents deposited along the wall (reduction in the relative velocity of the\nflow with respect to the wall) or a molecular force, normal to the wall, repelling\nthe molecules of the fluid from the wall thus causing less brakeage by the wall.<\/p>\n\n\n\nViscoelastic agents<\/strong> injected into a flow (more generally liquid) produce a reduction in pressure losses inside a pipe by a damping effect of the large turbulence structures in the flow core. The reduction in pressure drop can reach 75% in certain situations to the detriment of the particularly high injection cost of these agents.<\/p>\n\n\n\n_<\/p>\n\n\n\n
1.6-Parietal slip<\/strong><\/h3>\n\n\n\nWe\ncan distinguish at least two different cases of parietal sliding.<\/p>\n\n\n\n
The\nfirst case concerns the chemical compositions of the wall and of the moving\nfluid <\/strong>and the resulting molecular interaction<\/strong>\nbetween these two. Let\u2019s consider the molecular forces normal to the wall. In\nthe case of a force directed from the wall towards the flow core, the molecules\nof the fluid are so much less slowed down by the wall as they are more repelled\nby it. This results in an increase in the flow velocity which may be designated\nby \u201cWall slip\u201d.<\/strong> In the opposite case, the result is a reduction in the\nflow velocity which may be designated as a \u201cWall brake\u201d<\/strong>. Wall slip and wall\nbrake are characterized by a “slip length” measuring the distance\nbetween the physical wall and the zero velocity condition (after extrapolation\nof the velocity profile).<\/p>\n\n\n\nThe\nsecond case relates to the movement of movable walls within a fixed wall<\/strong> (for example, a conduct or a pipeline).<\/p>\n\n\n\nLet\nus imagine, firstly<\/em>,<\/strong> a fluid not circulating by itself in a conduct but a fluid confined in sealed containers<\/strong>\n(caissons) moving along the conduct. In this situation, the pressure drop is\nlimited to the viscous and turbulent losses produced between the fixed wall (conduct)\nand the moving one (container), i.e. over a very short distance (difference in\ndiameter of the conduct and the container). These losses being very small, the\nresult is a very low pressure drop along the conduct.<\/p>\n\n\n\nLet\nus imagine, secondly<\/em><\/strong> a mobile wall<\/strong>, rigorously circular, moving\ninside a fixed wall<\/strong> (pipeline), also rigorously circular and with a\ndiameter slightly greater than that of the mobile wall. In this situation,\nthere are two relative displacements, that of the mobile wall relative to the\nfixed wall and that of the flow inside the mobile wall. The energy loss\ncorresponding to the mobile wall is very low given the small distance between\nthe two walls and the lower relative velocity of the mobile wall compared to a\nfree flow in a fixed pipe. The same is true for the pressure drop of the flow\ninside the moving wall, the pressure drop being proportional to the square of\nthe velocity.<\/p>\n\n\n\nLet\nus imagine, thirdly,<\/em><\/strong> a somewhat more realistic situation concerning the\nmaterials used. Its principle, intermediate between the two preceding cases<\/strong>,\nwould be as follows. A flexible material is produced in situ or deployed\nupstream of the pipeline in the form of thin and flexible strips or bands,\nparallel to the wall of the pipe and entrained by a sort of shield located\ndownstream and pushed by the fluid. This system is reproduced along the pipe as\nmany times as required by the length of the pipeline and the length of the band\n– shield system. A complex flow of fluid is established in which the fluid is\npredominantly enclosed within the straps (bands), therefore, with very little\nmovement relative to them. The turbulence inside the bands is almost non-existent\nwhile the turbulence external to the bands evolves over very short distances\nbeing also largely attenuated by the flexible bands.<\/p>\n\n\n\n_<\/p>\n\n\n\n
Theme 2 – PIPELINES<\/strong><\/h1>\n\n\n\nCredit : https:\/\/fr.depositphotos.com\/stock-photos\/pipeline.html<\/a><\/figcaption><\/figure><\/div>\n\n\n\n2.1-General information on pipelines<\/strong><\/h3>\n\n\n\nPipeline design and operation involve many sciences or\nspecialties and among them metallurgy,\nchemistry, geophysics, civil engineering, fluid mechanics, geopolitics and\neconomics<\/strong>. The problems encountered are numerous and of different kinds. In\nmetallurgy, the subjects are related to the quality and composition of steels to\nprovide enough resistance to pressure, temperature, depressurization and\ncorrosion. In chemistry, the preoccupation is related to the protection against\ncorrosion (and associated control systems), in particular, with the use of\ninternal and external coatings but also by the various causes of clogging\n(formation of hydrates or paraffin). Geophysics and civil engineering are\nconcerned with the behaviour of pipelines on their land or sea support. Fluid\nmechanics deal with hydraulic aspects including various types of two phase flow\n(from liquid bubbles to plugs, liquid accumulation) or various aerodynamic and\nhydraulic aspects determining the sizing of pipelines, compressor stations and\nterminal design. Geopolitics is involved in the pipeline routing regarding\ncustomer locations and frontiers. Economics is essential since it determines\nthe feasibility of a project for investors.<\/p>\n\n\n\nIn this topic,\nwe are particularly interested in some aspects relating to fluid mechanics<\/strong>:\nthe use of specific internal coatings, the impact of the aging of internal\ncoatings on the transmission factor, the degree of pressure loss linked to\nexternal welds with penetration inside a pipeline, a monitoring device for the\ncontinuous measurement of internal hydraulic roughness along a pipeline as well\nas the benefit of aerodynamic drag reduction techniques.<\/p>\n\n\n\n_<\/p>\n\n\n\n
2.2-Aging of pipe internal coatings<\/strong><\/h3>\n\n\n\nTheme 1 on\n“fluidic friction” focuses<\/strong> more\nparticularly on the surface characterization (roughness and undulations) of newly applied internal coatings<\/strong> as well\nas their aerodynamic performance measured with an aerodynamic test device\ncalled the “Rotating cylinder Unit\u201d (RCU).<\/p>\n\n\n\nTheme 2 on “pipelines” focuses on aged coatings<\/strong>, that is, coatings subjected to the various operating conditions of a production system to determine the impact on their aerodynamic performance. The aging conditions studied relate, in particular, to erosion, to a sudden decompression and to the physicochemical interactions between internal coatings and certain chemical agents encountered in gas transport, for instance, tri-ethylene glycol. Sometimes, tests show a sharp deterioration in the aerodynamic performance for certain coatings even when their surface topology has not been altered. This aerodynamic behaviour is apparently the result of a physicochemical interaction between the chemical agent and the coating material. In this situation, the degradation of performance can be interpreted by a “molecular brakeage” of the wall (the reverse of a wall slip). See \u201cParietal slip\u201d in theme 1.<\/p>\n\n\n\n_<\/p>\n\n\n\n
2.3-Impact of welds on gas transport<\/strong><\/h3>\n\n\n\nWelds carried out on the outside of a tube or a pipeline\ncan penetrate inside them with a greater or lesser impact depending on the\ncharacteristics of the weld (penetration height and routing inside a pipeline)\nas well as the flow most often represented by a Reynolds number<\/strong>. The higher this number (density, pressure and fluid\nvelocity), the greater the pressure drops. On the contrary, the smaller this\nnumber, the more the pressure drops can be neglected.<\/p>\n\n\n\nTo this end, it is necessary to distinguish three types of welding<\/strong> associated to three mechanical requirements corresponding each one to a specific shape.<\/p>\n\n\n\nLongitudinal\nwelds<\/strong> result from the manufacturing of forged tubes, rolled\nand then welded along a longitudinal direction. This weld, although very long,\nhas no effect on gas transport since it is in perfect alignment with the main flow.\nThe height of penetration also has very little impact on pressure drops.<\/p>\n\n\n\nRadial welds<\/strong>\nmet at regular intervals (generally every 12 m) are required for the assembly\nof tubes for the construction of a pipeline. Perpendicular to the flow, this\ntype of weld partially obstructs the flow. The magnitude of the corresponding\npressure loss is of the order of a few per cent. Magnitude of the pressure loss\nis determined, primarily, by the weld penetration height and by the thickness\nof the boundary layer, itself determined by flow conditions (primarily, the\nReynolds number). Calculations were made using a RANS (Reynolds Average Navier\nStockes) fluid mechanics code for several weld heights and shapes\n(semi-circular, elongated) and also several flow conditions.<\/p>\n\n\n\nSpiral welds<\/strong> are encountered during the manufacturing of tube sections of great length (18 to 24 m) and large diameter with a relatively low operating pressure (of the order of 100 bars). These tubes are made from coiled plates. This method of manufacture allows the production of tubes at a relatively low cost. Intermediate between the longitudinal weld and the radial weld, the pressure drop associated to a spiral weld is strongly dependent on the helix angle<\/strong> (spiral shape) but also on the penetration height inside the tube and the thickness of the boundary layer. The calculation of the pressure drop is particularly complex since it is necessary to perform flow simulations on asymmetric pipe sections<\/strong> and over great lengths. Calculations were made using RANS code for several weld heights and shapes, multiple helix angles and for various flow conditions.<\/p>\n\n\n\nhttp:\/\/yvcharron.com\/index.php\/internal-pipeline-welds\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
2.4-Realization of structured surfaces inside a long tube<\/strong><\/h3>\n\n\n\nThe benefit of structured surfaces has been presented\nin Theme 1 and, in more detail, in the case of three geometrical shapes: a) a two-dimensional;\nb) a three-dimensional \u201ctype 1\u201d characterized by a transverse sine wave\nparallel to the wall and c) very succinctly, a three-dimensional \u201ctype 2\u201d characterized\nby two transverse sinusoidal waves, one of which being parallel and the other\northogonal to the wall.<\/p>\n\n\n\n
Achieving structured surfaces on a flat surface or\ninside a cylinder (for example, a pipeline tube) can be accomplished in several\nways. In the case of structures of large dimensions (of the order of a millimetre)\nand for a limited surface, it is possible to produce them mechanically. In the\ncase of structures with a small dimension (few tens of micron) to be produced\non large surfaces, another method should be selected. The method adopted in this document comprises three stages.<\/strong><\/p>\n\n\n\nIn a first step<\/em><\/strong>, structured surfaces are produced with a great accuracy\nby using a femto second laser<\/strong> on a\nrelatively rigid surface (surface erosion by laser ablation). These lasers\nallow the production of regularly shaped grooves in a periodic transverse\nmovement (3D-Type1) and with a periodically adjustable depth (3D-Type2).<\/p>\n\n\n\nIn a second step<\/em><\/strong>, it is proceeded to the manufacture of a flexible mould\non the eroded (ablated) surface mentioned above. The structures of the flexible\npart are, practically, the mirror image of the structures provided by laser\nablation.<\/p>\n\n\n\nIn a third step<\/em><\/strong>, the flexible part mentioned above is applied shortly\nafterwards an internal coating has been applied on the internal surface of a\ntube. After the time required for the coating to harden, the flexible part is\nremoved. The structures inside the tube are practically identical to those made\nin the first step.<\/p>\n\n\n\n_<\/p>\n\n\n\n
2.5-Measurement of hydraulic parameters inside a pipeline<\/strong><\/h3>\n\n\n\nDevices are sometimes introduced inside pipelines\nduring maintenance operations. These devices are divided into two main\ncategories: mechanical pigs<\/strong> which\nessentially aim to carry out cleaning inside a pipeline (displacement or\nremoval of paraffin deposits or liquid plugs). These pigs are strictly passive.\nThere is a second category, the purpose of which being to perform measurements\nsuch as the wall thickness of the pipeline to assess the effects of corrosion\nand adapt the flow rate and frequency of injection of anticorrosion products.\nThese pigs are equipped with electronics, batteries, transmitters and various\nsensors. They are said to be “Intelligent Monitoring Pig” or “Smart Monitoring Pig<\/strong>“.<\/p>\n\n\n\nIt is proposed in this section another type of \u201cSmart Monitoring\nPig\u201d whose objective is to continuously measure the hydraulic roughness along\nthe entire length of a pipeline. The device is inspired by the operation of the\n\u201cRotating Cylinder Unit<\/strong>\u201d described\nin Theme 1 (Fluidic friction). The device operates as follows: A cylinder is\nrotated with the aid of an electric motor near the wall of the pipeline. A Pitot tube<\/strong> installed in the air gap\nbetween the cylinder and the wall measures the velocity of the intermediate gas.\nFrom this measurement it is possible to interpolate the hydraulic roughness\nfrom a calibration curve (established following a calibration phase with\ndefined roughness) which is then stored in a digital device. The measurement\ncan also be done at several transverse angles (North, South, East, West or\nintermediate).<\/p>\n\n\n\nAssociated to pressure and temperature measurements,\nthe knowledge of the hydraulic roughness would provide a detailed survey of\ncorrosion and material deposit zones along the pipeline.<\/p>\n\n\n\n
http:\/\/yvcharron.com\/index.php\/pipeline-pig-monitoring\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
2.6-Technico economical studies<\/strong><\/h3>\n\n\n\nThe cost of a pipeline depends on a very large number\nof parameters, starting with the characteristics of the fluid transported. It\nalso depends on the quality of the steel, the diameter and the design pressure\nof the pipeline as well as the compression stations (including intermediate\nstations for pipeline of several thousands of kilometres). All these parameters\nare, of course, interrelated requiring in some cases some compromise.<\/p>\n\n\n\n
As the\ninvestment cost is considerable, it is important to minimize the pressure drop<\/strong>.\nFor a pipeline in a given configuration, a reduction in pressure losses can be\nobtained in different ways with sometimes high performance associated with a technological\ncomplexity.<\/p>\n\n\n\nTo facilitate understanding of the technical –\neconomic study, a few technical elements are recalled below. For a pipe of\ngiven diameter and a fluid of given viscosity, the thickness of the boundary\nlayer (approximately 5 times the thickness of the viscous layer) is inversely\nproportional to the density (for a gas, product of the molecular mass by the\nabsolute pressure and the inverse of the absolute temperature) and also the fluid\nvelocity. This thickness is also an inverse function of the Reynolds number.\nThe friction factor is a decreasing function of the Reynolds number up to a\nthreshold value where it is substantially determined by the relative roughness.\nPressure losses are proportional to the friction factor, the square of the fluid\nvelocity, the volumetric mass (or density), the length of the pipeline and the\ninverse of the diameter. For a given mass flow rate, the pressure drop varies with the inverse of the diameter to the power\nof 5<\/strong>.<\/p>\n\n\n\nPipeline\nuncoated internally<\/strong>: the internal roughness of the pipeline increases\nsignificantly over time. If the Reynolds number is low (thick boundary layer),\nthe pressure drop is not significantly dependent on the roughness magnitude.\nBeyond a certain Reynolds number, the pressure drop becomes relatively large.<\/p>\n\n\n\nInternally coated\npipeline<\/strong>: By applying an internal coating with a thickness approaching\none hundred microns, it greatly reduces the internal roughness of the pipeline.\nThis value is maintained at a relatively low level for several tens of years of\noperation. This solution makes it possible to greatly reduce the pressure drop\ncompared to an uncoated pipe.<\/p>\n\n\n\nPipeline\ncoated internally with smoothing of the coating<\/strong> before coating\nhardening (see corresponding section). This procedure allows a further\nreduction in the friction factor when the boundary layer is thin (large value\nof the velocity and pressure product that is high Reynolds number).<\/p>\n\n\n\nPipeline\ncoated internally with 2D structuring<\/strong> (see\ncorresponding sections: 2D application and performance) of the coating before\ncuring. This procedure allows a reduction in the friction factor of around 8%\ncompared to a strictly smooth surface, regardless of the thickness of the\nboundary layer. This method is easier to implement for an average dimension of\nstructures greater than 50 microns (average thickness of the boundary layer).\nNote that for water transport, the average dimension of structures is of the\norder of 100 microns.<\/p>\n\n\n\nPipeline\ncoated internally with 3D structuring<\/strong> (see\ncorresponding sections) of the coating before curing. This procedure allows an\nadditional reduction in the friction factor of around 16% compared to a\nstrictly smooth surface, regardless of the thickness of the boundary layer. As\nin the previous section, this method is easier to set up for an average\ndimension of structures greater than 50 microns. The realization of a\nstructured surface is slightly more expensive than that of a smooth surface\nconcerning the realization of the primary moulds.<\/p>\n\n\n\nThese technical elements make it possible to choose\nthe type and method of application of an internal coating, the operating\npressure, the average diameter of the pipeline, the size and the distance\nbetween the compression stations within the framework of economic optimization.<\/p>\n\n\n\n
_<\/p>\n\n\n\n
Theme 3 – TWO PHASE FLOW<\/strong><\/h1>\n\n\n\nCredit : https:\/\/www.thermal-engineering.org\/what-is-bubbly-flow-two-phase-flow-definition\/<\/a><\/figcaption><\/figure><\/div>\n\n\n\n–<\/p>\n\n\n\n
3.1-Two-phase compression – pumping<\/strong><\/h3>\n\n\n\nThe multiphase limits of single-phase\ncompression and pumping equipment<\/strong><\/p>\n\n\n\nSingle-phase compression expression is used to mean the compression of a\ngas phase (compressible) and single-phase pumping to mean the pumping of a\nliquid phase (incompressible). Hereinafter, the term compression or pumping is\nused indifferently when it concerns a two-phase mixture.<\/p>\n\n\n\n
The equipment required for single-phase compression or pumping is of the\nvolumetric type (pistons, gears, diaphragms) or of the rotodynamic part. In the\nfirst case, the energy transmitted by the pressurizing machine is directly\nconverted into pressure. These machines present many advantages including\nefficiency and the ability to compress a two-phase phase with a relatively high\n\u201cefficacy<\/strong>\u201d (this parameter measures\nthe ratio between efficiencies, respectively, in two-phase and single-phase\nflows). These machines, on the other hand, are heavy, bulky and require\nsignificant maintenance. In the second case, the energy transmitted by the pressurizing\nmachine is, firstly, converted into velocity (through a rotating wheel or\nimpeller) then into pressure (through a fixed diffuser or rectifier). These\nmachines present many advantages in terms of pressure (radial machines) and\nvolume flow (axial machines), reduced space and limited maintenance. On the\nother hand, the efficiency is largely dependent on the volume flow.\nFurthermore, these machines are totally unsuitable for two-phase compression or\npumping, whether in the presence of a small quantity of liquid associated with\na gas phase (erosion is an additional drawback) or of a small quantity of gas\nassociated with a liquid phase (gas plug at the entrance a radial wheel).\nBeyond a very low level of gas (for a pump) or liquid (for a compressor), the\ntwo-phase efficacy tends towards zero.<\/p>\n\n\n\nHelico – axial hydraulics – Poseidon type –\n1st generation hydraulic<\/strong><\/p>\n\n\n\nTo overcome the inability of conventional rotodynamic machines to\ncompress or to pump two-phase effluents, IFP has developed in the eighties a\nhelico axial hydraulic system called \u201cPoseidon\u201d. The impeller (the wheel)\nincludes vanes with a very small entry angle (often less than 10 degrees) and a\nvery small curvature. These blades are therefore relatively long (overlap ratio<\/strong> between 1.5 and 2.0)\ngenerating relatively high viscous losses. According to this design, the\naccelerations in the longitudinal, transverse and radial directions are\nrelatively low. These characteristics are obtained by a small variation of the\npassage section (the area) along the flow path, a small blade curvature and the action of a Coriolis force in the\nradial direction reducing the effect of the centrifugal force<\/strong>. For a low or\nhigh gas- liquid volume flow ratio represented by the GLR parameter<\/strong> (for \u201cGas – Liquid Ratio\u201d), the two-phase efficacy is\nclose to 1. On the other hand, for an intermediate GLR (between 2 and 10\ndepending on the geometry), the efficacy decreases significantly when the GLDR parameter<\/strong> (for \u201cGas – Liquid\nDensity Ratio\u201d) is reduced.<\/p>\n\n\n\nIn conclusion<\/strong><\/em> <\/strong>– Despite relatively good performance compared to single-phase machines, Poseidon hydraulics present several drawbacks: significant viscous losses and low two-phase efficacy at intermediate GLR\u2019s.<\/p>\n\n\n\nHelico – axial hydraulics with interfacial\nslip control – 2nd generation hydraulic<\/strong><\/p>\n\n\n\nThe operation of the Poseidon hydraulics is satisfactory at low GLRs,\nthe low orthogonal accelerations (longitudinal, transverse and radial) limiting\nto some extend the separation of the phases in the three main directions.\nBeyond a certain GLR (for example 2 – value dependent on many parameters\nincluding pressure, viscosity and surface tension), the two phases separate,\ngenerating strong interfacial losses. In strictly helico-axial hydraulics, the\nliquid phase is projected against the surface with the larger diameter slowing\nit down in its displacement towards the outlet (relatively large viscous forces)\nwhich in turn induces a braking of the gaseous phase (high energy dissipation\nat the interface of the two phases). The difference in velocity between the two\nphases is referred to as the interfacial\nslip<\/strong>. The parietal braking of the liquid film increases with a decrease of\nthe liquid film thickness.<\/p>\n\n\n\nTo remedy this situation, the external part of the impeller (larger\ndiameter) is tuned to provide it with a very slight radial shape including, at\nthe inlet, a convex curvature (centre of the curvature directed outwards)\nallowing a large acceleration of the liquid phase and, at the outlet, a concave\ncurvature (centre inward) allowing a reduction in the acceleration of the\nliquid phase. These two curvatures help to minimize the velocity difference\nbetween the two phases. This action is referred to as “interfacial slip control”.<\/strong> This action allows a relatively large increase in the two-phase efficacy\nfor any value of GLR, including, for low values of the GLDR parameter.<\/strong><\/p>\n\n\n\nThe control of the interfacial slip allows a certain “relaxation” of the impeller\nblade parameters<\/strong>. In particular, the blade length may be reduced (smaller overlap\nratio) limiting viscous losses, thus, providing higher single and two phase efficiencies.\nIn addition the blade curvature may be increased, consequently, providing a\ngreater manometric head coefficient (compression ratio).<\/p>\n\n\n\nIn conclusion<\/em> – This second-generation hydraulic system presents, compared to the first-generation, in single phase flow, a higher efficiency and a higher manometric head coefficient as well as a higher two-phase efficacy<\/strong>.<\/p>\n\n\n\nRadio – helico – axial hydraulics – Wet gas<\/strong><\/p>\n\n\n\nThe design of hydraulics suitable for compressing wet gas derives from\nthe design of the second generation helico axial hydraulics.<\/p>\n\n\n\n
The terminology \u201cwet gas\u201d<\/strong>\ndenotes a low level of liquid fraction within the gas phase corresponding to a\nsignificant braking of the liquid film along the surface with the larger\ndiameter. As a result, the external curvatures located, respectively, at the\ninlet and at the outlet of the impeller are accentuated so as to greatly\naccelerate the liquid film (small thickness) towards the outlet.<\/p>\n\n\n\nThis configuration results in a diameter significantly increased at the\noutlet, compared to the inlet, providing a more radial shape of the impeller.\nThis configuration presents two advantages: less droplet erosion at the\nimpeller inlet and a higher manometric head coefficient which is required in\nthe case of the compression of a gas with a lower volumetric mass compared to a\ntwo phase flow with medium GLR.<\/p>\n\n\n\n
Helico \u2013 radio – axial hydraulics – Bubbly flow and viscous liquid<\/strong><\/p>\n\n\n\nIn bubbly flow (very low GLR), separation forces (accelerations acting\nin the three main orthogonal directions) have a lesser effect compared to the\ndrag forces acting on bubbles submerged in the liquid phase.<\/p>\n\n\n\n
As the separation forces get smaller, it is possible to apply a certain\n“relaxation” on the design parameters defining the 1st generation\nhydraulic (Poseidon). It is, in particular, possible to design a hydraulic with\na more radial shape (Helico radio axial), to shorten the length of the blades\nand to bend them so as to increase as well the efficiency as the manometric\nhead coefficient of an impeller.<\/p>\n\n\n\n
In the presence of a viscous liquid, the drag forces acting on the\nbubbles increase further compared to a situation with a non-viscous liquid. As\na result, it is possible to apply a greater “relaxation” on the\ndesign parameters of the 1st generation hydraulic.<\/p>\n\n\n\n
http:\/\/yvcharron.com\/index.php\/two-phase-flow-pumps\/<\/a><\/p>\n\n\n\n_<\/p>\n\n\n\n
3.2-Two-phase expansion – turbines<\/strong><\/h3>\n\n\n\nThe multiphase limits of single phase\nexpansion or turbine equipment<\/strong><\/p>\n\n\n\nBy single-phase expansion it is meant here the expansion of a gaseous\nphase (compressible) through an expander and by single-phase depressurization,\nthe let-down of a liquid phase (incompressible) through a turbine. These\nexpansions or let downs result in energy supply.<\/p>\n\n\n\n
It is generally easier to depressurize, with a single-phase equipment, a\nslightly two-phase mixture (low or high GLR) than to pressurize it. However,\nthese depressurizations generally take place through a single stage.<\/p>\n\n\n\n
The challenge is to design a two-phase\nmulti-stage turbine so as to respond to a high expansion rate<\/strong>.<\/p>\n\n\n\nHelico – axial hydraulics – 1st generation<\/strong><\/p>\n\n\n\nAccording to a simplified approach, an expansion impeller (wheel) of a\ntwo-phase multistage turbine looks similar to a compression impeller of a\ntwo-phase multistage pump, the inlet section of the compression impeller acting\nas the outlet section of the expansion impeller. The same principle goes for\nthe opposite sections. The same principle goes also for the static elements (diffuser\nand inducer). However, the outlet angle of the expansion inducer is\nsignificantly reduced compared to the inlet angle of the compression diffuser.<\/p>\n\n\n\n
This hydraulic expansion provides advantages similar to those of the pumping\none.<\/p>\n\n\n\n
Helical – axial hydraulics – 2nd generation<\/strong><\/p>\n\n\n\nThe control of the interfacial slip in the wheel of a two phase turbine\nis similarly carried out to the control described for a compression system. It provides\na significant improvement in both single and two-phase performance.<\/p>\n\n\n\n
Radio – helical – axial hydraulics – Bubbly\nflow and viscous liquid<\/strong><\/p>\n\n\n\nConsideration of the interfacial slip as well as the ratio of the forces\nof separation and drag of the bubbles in the liquid leads to the same\nconclusions as those made in the context of a compression or pumping system.<\/p>\n\n\n\n
Given the importance of this fluidic\nfriction, it is important to be able to predict it with sufficient accuracy in\nindustrial applications (lift and drag of a wing or pressure drops in a pipeline),\nto determine the importance of tiny wall surface deformations (roughness,\nundulations), to characterize the surface of these walls (or coatings in\ncontact with the flow), to develop measuring equipment to determine the\nhydraulic roughness (equivalent roughness on a fluidic basis) under all\nconditions of use, including the most severe (high density and high relative velocity\nof the fluid) also to develop techniques for reducing drag (in particular,\nreducing turbulent friction).<\/p>\n\n\n\n
It is important to distinguish two fundamentally different cases of flow: a) laminar flow<\/strong> characterized by a low value of the Reynolds number (product of the volumetric mass by the hydraulic diameter, the relative velocity and the inverse of the viscosity). In this case, the relative velocity presents a parabolic profile while the flow is not very sensitive to surface deformations; b) turbulent flow<\/strong> characterized by a medium or high value of the Reynolds number. In this case, the relative velocity presents a relatively flat profile beyond a certain distance from the wall referred to as the boundary layer<\/strong>. This latest includes a very thin viscous layer<\/strong> in contact with the wall and a turbulent transition layer<\/strong> in between the viscous layer and the main turbulent zone.<\/p>\n\n\n\n _<\/p>\n\n\n\n The texture of\na surface is extremely complex. It may be favourable or not to the displacement\nof a fluid. Fluid flow may be increased, relatively to a smooth surface, in the\ncase of a turbulent flow and by using organised structures at the wall surface.\nOn the contrary, it is reduced in the case of a turbulent flow and with walls\ncovered by asperities distributed randomly (size and interval). Fluid flow is\nunchanged in the case of a laminar flow whether the surface deformations are\ndistributed randomly or not.<\/p>\n\n\n\n Surface\ntexture is the result of a manufacturing process, erosion, abrasion, corrosion\nor the application of a coating (internal in the case of a conduct). It can\nalso evolve over time and according to the environmental conditions\n(physicochemical action). The texture of a coating depends on many factors: the\nmaterial of the coating (epoxy, polyurethane), the mode of application (cold or\ndeposition of molten particles), the size of pigments and fillers (solid\nparticles), the type and concentration of a solvent (water, organic element).<\/p>\n\n\n\n Numerous\nindustrial applications have made it possible to predict the surface topology\nof steels. Depending on the storage conditions, the operating time and the\naggressiveness of the environment, it is possible to estimate the amplitude of\nthe roughness. On this basis, the resulting friction factor may be roughly\nestimated.<\/p>\n\n\n\n The case of internal coatings is significantly different<\/strong>. The surface characteristics are very dependent on the type of coating and its mode of application. It should be mentioned that certain coating surfaces presents very small local roughness suggesting a favourable friction factor but also ripples of larger amplitudes with long wavelength<\/strong> which have been ignored for a long time by the industry but which could sometimes be very penalizing.<\/p>\n\n\n\n The surface characterization of a coating requires, therefore, the measurement of surface deformations using a sensor (often a roughness meter) from short to long wavelengths. The aerodynamic tests (presented below) make it possible to compare the results obtained in terms of hydraulic roughness (equivalent) and physical roughness.<\/p>\n\n\n\n _<\/p>\n\n\n\n It is\nimportant to have a good understanding of the fluidic friction in a wall –\nfluid interaction in order to design industrial systems with the best possible\nprecision. Fluidic friction is as well dependent on the wall material, in\nparticular, its physicochemical properties as on the surface topology. It is\nalso dependent on the physicochemical properties of the fluid as the flow\nconditions.<\/p>\n\n\n\n Determining experimentally,\nthe characteristics of a low pressure and low velocity flow is relatively easy\nrequiring low testing volume, short equilibrium time, small establishing length\nand low investment cost. It is quite different when it is desired to carry out\ntests with gases of high density, high pressure (up to 500 bar) or high velocity\n(up to 20 m \/ s) representing a very small boundary layer thickness. This\nresults in high investment and operating costs.<\/p>\n\n\n\n To solve this problem, a relatively compact device has been developed which can induce a flow with a very small boundary layer thickness, of the order of a micron<\/strong>. It consists of a cylindrical vessel (external part) designed to withstand a pressure of 100 bars in which a cylinder (drum – internal part), driven externally by an electric motor, is rotated with a peripheral velocity of the order of 40 m \/ s. The internal cylinder drives the gas in its rotation which is then slowed down by a fixed wall mounted inside the high pressure vessel. The flow brakeage is measured using either a torque meter or a Pitot probe mounted in the air gap between the outside of the rotating cylinder and the inside of the fixed wall. A preliminary calibration phase with several fixed walls of different roughness makes it possible to determine (by interpolation) the equivalent roughness (hydraulic or aerodynamic) of any fixed wall.<\/p>\n\n\n\n The device has been used for testing the properties of pipeline internal coatings designed for gas transport. Tests have shown the occurrence of a wall sliding effect <\/strong>which appears, mainly, when the thickness of the boundary layer is very small (on the order of a micron meter).<\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/coating-aerodynamic-testing\/<\/a><\/p>\n\n\n\n _<\/p>\n\n\n\n It\nhas long been believed that a rigid, straight, smooth surface was the optimum\nmedium for minimizing the effects of turbulent friction, hence drag (hydraulic\nor aerodynamic) that is the friction factor. By observing the displacement of\nsharks into water, it was noticed that their relatively high velocity was due\nto the presence on their skin of micro asperities, oriented in the direction of\ntheir displacement and forming channels in the inter-space of the skin\ndeformations. For this reason, these structures are commonly called “Riblets”.<\/strong><\/p>\n\n\n\n Rectilinearly grooved surfaces\n– Two-dimensional or \u201c2D\u201d Shapes<\/strong><\/p>\n\n\n\n Tests\ncarried out in the mid-twentieth century on this type of surface structure showed\nthat a reduction in hydraulic drag could be achieved within a range of 5 to 10%\ndepending on the geometry of the groove (equilateral or half elliptical) or\neven, according to some experiments, between 10 and 12% (razor blade shape).<\/p>\n\n\n\n The\nexplanation for these results relates to the following observations. In the\ncase of a smooth surface, instabilities called \u201cLow Speed Streaks\u201d<\/strong>\n(kinds of longitudinal vortices, generally paired and rotating around themselves)\ndevelop near to the wall (at the limit of the viscous layer where viscous\nfriction occurs) to occasionally burst from the boundary layer and amplify in\nsize when escaping towards the flow core. This process is extremely\ndissipative. The use of micro grooves permits to control the “Low Speed Streaks”\nin their lateral displacement and to limit to some extend viscous dissipation\nnear to the wall. The optimum size of the grooves corresponds approximately to\nthe average diameter of the \u201cLow Speed Streaks\u201d. In this situation, these\nturbulent structures float on the tip of the solid structures explaining why\nthe razor blade shaped grooves provide the best performance.<\/p>\n\n\n\n This physical explanation makes it possible to understand why the effect of the turbulent flow structures can be simulated with a RANS code <\/strong>(numerical simulation of fluids of the Reynolds Average Navier Stockes type), code in which the turbulence is modelled by equations and not simulated as in the case described below (three-dimensional structured surfaces). This code was used to verify the performance of grooves (solid structures) of different shapes (Triangular and knife blades) with several relative groove dimensions (width and height).<\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/two-dimension-structures\/<\/a><\/p>\n\n\n\n Sinusoidal grooved\nsurfaces – Three-dimensional shape “3D1”<\/strong><\/p>\n\n\n\n In\nturbulent flow, the energy dissipation is mainly of a turbulent nature and very\nlittle of a viscous nature. This turbulent dissipation represents a fraction of\nthe order of 90% for slightly or moderately turbulent flows reaching 99.9% for\nvery highly turbulent flows. These relative rates of turbulent dissipation\nprovide some insight into the potential for energy gain offered by structured\nsurfaces or any other means designed for turbulent friction reduction.<\/p>\n\n\n\n To\nthis end, it should be noted the contribution of an oscillating transverse\nparietal movement<\/strong> characterized by a wall (a flat plate or the internal\nsurface of a cylinder) in periodic transversal displacement (right – left) to\nthe mean direction of the flow. For a given frequency, the energy gain is\nmaximum. The energy input is globally positive (taking into account the energy\nrequired to oscillate the wall) for a given oscillation amplitude. The\nelongation and stabilization of Low Speed Streaks are two parameters put\nforward to explain the benefit of an oscillating transverse movement.<\/strong><\/p>\n\n\n\n The\ncombination of these two phenomena<\/strong> (rectilinear grooves\nand oscillating wall) has been used for the design of three-dimensional\nstructured (grooved) surfaces. In this configuration, the grooves present a\nsinusoidal shape in direction of the flow. This concept was analyzed, not by using\na numerical code of the RANS type but by using an LES code<\/strong> (Large Eddy\nSimulation) where the effect of turbulence is simulated and not modelled. The\nproperties of turbulence are not calculated at the smallest scale (called\nKolmogorov – DNS code) but at a larger scale related to the phenomenon to be\nanalyzed. This code allows taking into account the deformation generated on the\nLow Speed Streaks by the oscillating movement. The code was first validated on linear\ngrooves then used to determine the effect of a sinusoidal motion (amplitude and\nfrequency) applied to the basic groove shape (linear). Under optimal\nconditions, the reduction in turbulent friction is of the order of 20%,\nwhich is roughly the double of the previous case.<\/strong><\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/three-dimension-structured-surfaces-type-1\/<\/a><\/p>\n\n\n\n Grooved surfaces with\ntwo orthogonal transverse waves – three-dimensional shape “3D2”<\/strong><\/p>\n\n\n\n The\nthree-dimensional shape “3D1”<\/strong> corresponds\nto grooves of constant dimensions (width and height) in the flow direction and\nwith a sinusoidal course oriented successively towards the left and the right<\/strong>\nrespectively to the wall or the mean direction of the flow.<\/p>\n\n\n\n The\nthree-dimensional shape “3D2<\/strong>” is similar to\nthe shape “3D1” but with the addition of a sinusoidal displacement of\nthe flow oriented successively upwards and downwards<\/strong> with respect to the\nwall and to the mean direction of the flow. The two waves such oriented are\nsaid to be orthogonal.<\/strong><\/p>\n\n\n\n The\nthree-dimensional shape \u201c3D2\u201d provides additional advantages compared to the\nshape \u201c3D1\u201d: a) additional stabilization and additional elongation of the Low\nSpeed Streak (LSS); b) more viscous loss reduction at the wall surface; c) less\nfrequent burst of the LSS towards the central core. In this \u201c3D2\u201d case, the\nwave normal to the wall is materialized by an increase in height of the grooves\nat the peak amplitude of the horizontal wave and a decrease in height of the\ngrooves at the inflection point of the horizontal wave.<\/p>\n\n\n\n First\ncalculations have shown a reduction in turbulent friction of more than 25%.<\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/three-dimension-structures-type-2\/<\/a><\/p>\n\n\n\n _<\/p>\n\n\n\n A\nreduction in turbulent friction can be obtained in a conduct (pipeline) based\non the mechanical properties and the\nconstitution of the wall<\/strong> in contact with the flow.<\/p>\n\n\n\n A\ndeformable coating<\/strong> providing an efficient reduction in\nturbulent friction relies on an optimum attenuation of pressure waves. In such\na case, a pressure wave directed towards the wall generates a second wave in phase\nopposition that counteracts the action of other waves directed towards the\nwall.<\/p>\n\n\n\n A porous\nand permeable coating<\/strong> providing an efficient reduction in\nturbulent friction relies on an optimum attenuation of the velocity waves. The\nprinciple is similar to the previous case: a velocity wave directed towards the\nwall generates a second wave in phase opposition which counteracts the action\nof other waves directed towards the wall.<\/p>\n\n\n\n A\nreduction in turbulent friction can be achieved by injecting liquids or particles into the flow<\/strong>.<\/p>\n\n\n\n Film-forming\nagents<\/strong> injected into a flow (more generally\ngaseous) produce a reduction in aerodynamic drag on a plate in contact with\nthis flow or a reduction in pressure drops inside a pipeline. The action of\nthese agents which are deposited on a wall can be explained in several manners.\nIt may be caused either by a parietal sliding resulting by a kind of sliding of\nthe agents deposited along the wall (reduction in the relative velocity of the\nflow with respect to the wall) or a molecular force, normal to the wall, repelling\nthe molecules of the fluid from the wall thus causing less brakeage by the wall.<\/p>\n\n\n\n Viscoelastic agents<\/strong> injected into a flow (more generally liquid) produce a reduction in pressure losses inside a pipe by a damping effect of the large turbulence structures in the flow core. The reduction in pressure drop can reach 75% in certain situations to the detriment of the particularly high injection cost of these agents.<\/p>\n\n\n\n _<\/p>\n\n\n\n We\ncan distinguish at least two different cases of parietal sliding.<\/p>\n\n\n\n The\nfirst case concerns the chemical compositions of the wall and of the moving\nfluid <\/strong>and the resulting molecular interaction<\/strong>\nbetween these two. Let\u2019s consider the molecular forces normal to the wall. In\nthe case of a force directed from the wall towards the flow core, the molecules\nof the fluid are so much less slowed down by the wall as they are more repelled\nby it. This results in an increase in the flow velocity which may be designated\nby \u201cWall slip\u201d.<\/strong> In the opposite case, the result is a reduction in the\nflow velocity which may be designated as a \u201cWall brake\u201d<\/strong>. Wall slip and wall\nbrake are characterized by a “slip length” measuring the distance\nbetween the physical wall and the zero velocity condition (after extrapolation\nof the velocity profile).<\/p>\n\n\n\n The\nsecond case relates to the movement of movable walls within a fixed wall<\/strong> (for example, a conduct or a pipeline).<\/p>\n\n\n\n Let\nus imagine, firstly<\/em>,<\/strong> a fluid not circulating by itself in a conduct but a fluid confined in sealed containers<\/strong>\n(caissons) moving along the conduct. In this situation, the pressure drop is\nlimited to the viscous and turbulent losses produced between the fixed wall (conduct)\nand the moving one (container), i.e. over a very short distance (difference in\ndiameter of the conduct and the container). These losses being very small, the\nresult is a very low pressure drop along the conduct.<\/p>\n\n\n\n Let\nus imagine, secondly<\/em><\/strong> a mobile wall<\/strong>, rigorously circular, moving\ninside a fixed wall<\/strong> (pipeline), also rigorously circular and with a\ndiameter slightly greater than that of the mobile wall. In this situation,\nthere are two relative displacements, that of the mobile wall relative to the\nfixed wall and that of the flow inside the mobile wall. The energy loss\ncorresponding to the mobile wall is very low given the small distance between\nthe two walls and the lower relative velocity of the mobile wall compared to a\nfree flow in a fixed pipe. The same is true for the pressure drop of the flow\ninside the moving wall, the pressure drop being proportional to the square of\nthe velocity.<\/p>\n\n\n\n Let\nus imagine, thirdly,<\/em><\/strong> a somewhat more realistic situation concerning the\nmaterials used. Its principle, intermediate between the two preceding cases<\/strong>,\nwould be as follows. A flexible material is produced in situ or deployed\nupstream of the pipeline in the form of thin and flexible strips or bands,\nparallel to the wall of the pipe and entrained by a sort of shield located\ndownstream and pushed by the fluid. This system is reproduced along the pipe as\nmany times as required by the length of the pipeline and the length of the band\n– shield system. A complex flow of fluid is established in which the fluid is\npredominantly enclosed within the straps (bands), therefore, with very little\nmovement relative to them. The turbulence inside the bands is almost non-existent\nwhile the turbulence external to the bands evolves over very short distances\nbeing also largely attenuated by the flexible bands.<\/p>\n\n\n\n _<\/p>\n\n\n\n Pipeline design and operation involve many sciences or\nspecialties and among them metallurgy,\nchemistry, geophysics, civil engineering, fluid mechanics, geopolitics and\neconomics<\/strong>. The problems encountered are numerous and of different kinds. In\nmetallurgy, the subjects are related to the quality and composition of steels to\nprovide enough resistance to pressure, temperature, depressurization and\ncorrosion. In chemistry, the preoccupation is related to the protection against\ncorrosion (and associated control systems), in particular, with the use of\ninternal and external coatings but also by the various causes of clogging\n(formation of hydrates or paraffin). Geophysics and civil engineering are\nconcerned with the behaviour of pipelines on their land or sea support. Fluid\nmechanics deal with hydraulic aspects including various types of two phase flow\n(from liquid bubbles to plugs, liquid accumulation) or various aerodynamic and\nhydraulic aspects determining the sizing of pipelines, compressor stations and\nterminal design. Geopolitics is involved in the pipeline routing regarding\ncustomer locations and frontiers. Economics is essential since it determines\nthe feasibility of a project for investors.<\/p>\n\n\n\n In this topic,\nwe are particularly interested in some aspects relating to fluid mechanics<\/strong>:\nthe use of specific internal coatings, the impact of the aging of internal\ncoatings on the transmission factor, the degree of pressure loss linked to\nexternal welds with penetration inside a pipeline, a monitoring device for the\ncontinuous measurement of internal hydraulic roughness along a pipeline as well\nas the benefit of aerodynamic drag reduction techniques.<\/p>\n\n\n\n _<\/p>\n\n\n\n Theme 1 on\n“fluidic friction” focuses<\/strong> more\nparticularly on the surface characterization (roughness and undulations) of newly applied internal coatings<\/strong> as well\nas their aerodynamic performance measured with an aerodynamic test device\ncalled the “Rotating cylinder Unit\u201d (RCU).<\/p>\n\n\n\n Theme 2 on “pipelines” focuses on aged coatings<\/strong>, that is, coatings subjected to the various operating conditions of a production system to determine the impact on their aerodynamic performance. The aging conditions studied relate, in particular, to erosion, to a sudden decompression and to the physicochemical interactions between internal coatings and certain chemical agents encountered in gas transport, for instance, tri-ethylene glycol. Sometimes, tests show a sharp deterioration in the aerodynamic performance for certain coatings even when their surface topology has not been altered. This aerodynamic behaviour is apparently the result of a physicochemical interaction between the chemical agent and the coating material. In this situation, the degradation of performance can be interpreted by a “molecular brakeage” of the wall (the reverse of a wall slip). See \u201cParietal slip\u201d in theme 1.<\/p>\n\n\n\n _<\/p>\n\n\n\n Welds carried out on the outside of a tube or a pipeline\ncan penetrate inside them with a greater or lesser impact depending on the\ncharacteristics of the weld (penetration height and routing inside a pipeline)\nas well as the flow most often represented by a Reynolds number<\/strong>. The higher this number (density, pressure and fluid\nvelocity), the greater the pressure drops. On the contrary, the smaller this\nnumber, the more the pressure drops can be neglected.<\/p>\n\n\n\n To this end, it is necessary to distinguish three types of welding<\/strong> associated to three mechanical requirements corresponding each one to a specific shape.<\/p>\n\n\n\n Longitudinal\nwelds<\/strong> result from the manufacturing of forged tubes, rolled\nand then welded along a longitudinal direction. This weld, although very long,\nhas no effect on gas transport since it is in perfect alignment with the main flow.\nThe height of penetration also has very little impact on pressure drops.<\/p>\n\n\n\n Radial welds<\/strong>\nmet at regular intervals (generally every 12 m) are required for the assembly\nof tubes for the construction of a pipeline. Perpendicular to the flow, this\ntype of weld partially obstructs the flow. The magnitude of the corresponding\npressure loss is of the order of a few per cent. Magnitude of the pressure loss\nis determined, primarily, by the weld penetration height and by the thickness\nof the boundary layer, itself determined by flow conditions (primarily, the\nReynolds number). Calculations were made using a RANS (Reynolds Average Navier\nStockes) fluid mechanics code for several weld heights and shapes\n(semi-circular, elongated) and also several flow conditions.<\/p>\n\n\n\n Spiral welds<\/strong> are encountered during the manufacturing of tube sections of great length (18 to 24 m) and large diameter with a relatively low operating pressure (of the order of 100 bars). These tubes are made from coiled plates. This method of manufacture allows the production of tubes at a relatively low cost. Intermediate between the longitudinal weld and the radial weld, the pressure drop associated to a spiral weld is strongly dependent on the helix angle<\/strong> (spiral shape) but also on the penetration height inside the tube and the thickness of the boundary layer. The calculation of the pressure drop is particularly complex since it is necessary to perform flow simulations on asymmetric pipe sections<\/strong> and over great lengths. Calculations were made using RANS code for several weld heights and shapes, multiple helix angles and for various flow conditions.<\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/internal-pipeline-welds\/<\/a><\/p>\n\n\n\n _<\/p>\n\n\n\n The benefit of structured surfaces has been presented\nin Theme 1 and, in more detail, in the case of three geometrical shapes: a) a two-dimensional;\nb) a three-dimensional \u201ctype 1\u201d characterized by a transverse sine wave\nparallel to the wall and c) very succinctly, a three-dimensional \u201ctype 2\u201d characterized\nby two transverse sinusoidal waves, one of which being parallel and the other\northogonal to the wall.<\/p>\n\n\n\n Achieving structured surfaces on a flat surface or\ninside a cylinder (for example, a pipeline tube) can be accomplished in several\nways. In the case of structures of large dimensions (of the order of a millimetre)\nand for a limited surface, it is possible to produce them mechanically. In the\ncase of structures with a small dimension (few tens of micron) to be produced\non large surfaces, another method should be selected. The method adopted in this document comprises three stages.<\/strong><\/p>\n\n\n\n In a first step<\/em><\/strong>, structured surfaces are produced with a great accuracy\nby using a femto second laser<\/strong> on a\nrelatively rigid surface (surface erosion by laser ablation). These lasers\nallow the production of regularly shaped grooves in a periodic transverse\nmovement (3D-Type1) and with a periodically adjustable depth (3D-Type2).<\/p>\n\n\n\n In a second step<\/em><\/strong>, it is proceeded to the manufacture of a flexible mould\non the eroded (ablated) surface mentioned above. The structures of the flexible\npart are, practically, the mirror image of the structures provided by laser\nablation.<\/p>\n\n\n\n In a third step<\/em><\/strong>, the flexible part mentioned above is applied shortly\nafterwards an internal coating has been applied on the internal surface of a\ntube. After the time required for the coating to harden, the flexible part is\nremoved. The structures inside the tube are practically identical to those made\nin the first step.<\/p>\n\n\n\n _<\/p>\n\n\n\n Devices are sometimes introduced inside pipelines\nduring maintenance operations. These devices are divided into two main\ncategories: mechanical pigs<\/strong> which\nessentially aim to carry out cleaning inside a pipeline (displacement or\nremoval of paraffin deposits or liquid plugs). These pigs are strictly passive.\nThere is a second category, the purpose of which being to perform measurements\nsuch as the wall thickness of the pipeline to assess the effects of corrosion\nand adapt the flow rate and frequency of injection of anticorrosion products.\nThese pigs are equipped with electronics, batteries, transmitters and various\nsensors. They are said to be “Intelligent Monitoring Pig” or “Smart Monitoring Pig<\/strong>“.<\/p>\n\n\n\n It is proposed in this section another type of \u201cSmart Monitoring\nPig\u201d whose objective is to continuously measure the hydraulic roughness along\nthe entire length of a pipeline. The device is inspired by the operation of the\n\u201cRotating Cylinder Unit<\/strong>\u201d described\nin Theme 1 (Fluidic friction). The device operates as follows: A cylinder is\nrotated with the aid of an electric motor near the wall of the pipeline. A Pitot tube<\/strong> installed in the air gap\nbetween the cylinder and the wall measures the velocity of the intermediate gas.\nFrom this measurement it is possible to interpolate the hydraulic roughness\nfrom a calibration curve (established following a calibration phase with\ndefined roughness) which is then stored in a digital device. The measurement\ncan also be done at several transverse angles (North, South, East, West or\nintermediate).<\/p>\n\n\n\n Associated to pressure and temperature measurements,\nthe knowledge of the hydraulic roughness would provide a detailed survey of\ncorrosion and material deposit zones along the pipeline.<\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/pipeline-pig-monitoring\/<\/a><\/p>\n\n\n\n _<\/p>\n\n\n\n The cost of a pipeline depends on a very large number\nof parameters, starting with the characteristics of the fluid transported. It\nalso depends on the quality of the steel, the diameter and the design pressure\nof the pipeline as well as the compression stations (including intermediate\nstations for pipeline of several thousands of kilometres). All these parameters\nare, of course, interrelated requiring in some cases some compromise.<\/p>\n\n\n\n As the\ninvestment cost is considerable, it is important to minimize the pressure drop<\/strong>.\nFor a pipeline in a given configuration, a reduction in pressure losses can be\nobtained in different ways with sometimes high performance associated with a technological\ncomplexity.<\/p>\n\n\n\n To facilitate understanding of the technical –\neconomic study, a few technical elements are recalled below. For a pipe of\ngiven diameter and a fluid of given viscosity, the thickness of the boundary\nlayer (approximately 5 times the thickness of the viscous layer) is inversely\nproportional to the density (for a gas, product of the molecular mass by the\nabsolute pressure and the inverse of the absolute temperature) and also the fluid\nvelocity. This thickness is also an inverse function of the Reynolds number.\nThe friction factor is a decreasing function of the Reynolds number up to a\nthreshold value where it is substantially determined by the relative roughness.\nPressure losses are proportional to the friction factor, the square of the fluid\nvelocity, the volumetric mass (or density), the length of the pipeline and the\ninverse of the diameter. For a given mass flow rate, the pressure drop varies with the inverse of the diameter to the power\nof 5<\/strong>.<\/p>\n\n\n\n Pipeline\nuncoated internally<\/strong>: the internal roughness of the pipeline increases\nsignificantly over time. If the Reynolds number is low (thick boundary layer),\nthe pressure drop is not significantly dependent on the roughness magnitude.\nBeyond a certain Reynolds number, the pressure drop becomes relatively large.<\/p>\n\n\n\n Internally coated\npipeline<\/strong>: By applying an internal coating with a thickness approaching\none hundred microns, it greatly reduces the internal roughness of the pipeline.\nThis value is maintained at a relatively low level for several tens of years of\noperation. This solution makes it possible to greatly reduce the pressure drop\ncompared to an uncoated pipe.<\/p>\n\n\n\n Pipeline\ncoated internally with smoothing of the coating<\/strong> before coating\nhardening (see corresponding section). This procedure allows a further\nreduction in the friction factor when the boundary layer is thin (large value\nof the velocity and pressure product that is high Reynolds number).<\/p>\n\n\n\n Pipeline\ncoated internally with 2D structuring<\/strong> (see\ncorresponding sections: 2D application and performance) of the coating before\ncuring. This procedure allows a reduction in the friction factor of around 8%\ncompared to a strictly smooth surface, regardless of the thickness of the\nboundary layer. This method is easier to implement for an average dimension of\nstructures greater than 50 microns (average thickness of the boundary layer).\nNote that for water transport, the average dimension of structures is of the\norder of 100 microns.<\/p>\n\n\n\n Pipeline\ncoated internally with 3D structuring<\/strong> (see\ncorresponding sections) of the coating before curing. This procedure allows an\nadditional reduction in the friction factor of around 16% compared to a\nstrictly smooth surface, regardless of the thickness of the boundary layer. As\nin the previous section, this method is easier to set up for an average\ndimension of structures greater than 50 microns. The realization of a\nstructured surface is slightly more expensive than that of a smooth surface\nconcerning the realization of the primary moulds.<\/p>\n\n\n\n These technical elements make it possible to choose\nthe type and method of application of an internal coating, the operating\npressure, the average diameter of the pipeline, the size and the distance\nbetween the compression stations within the framework of economic optimization.<\/p>\n\n\n\n _<\/p>\n\n\n\n –<\/p>\n\n\n\n The multiphase limits of single-phase\ncompression and pumping equipment<\/strong><\/p>\n\n\n\n Single-phase compression expression is used to mean the compression of a\ngas phase (compressible) and single-phase pumping to mean the pumping of a\nliquid phase (incompressible). Hereinafter, the term compression or pumping is\nused indifferently when it concerns a two-phase mixture.<\/p>\n\n\n\n The equipment required for single-phase compression or pumping is of the\nvolumetric type (pistons, gears, diaphragms) or of the rotodynamic part. In the\nfirst case, the energy transmitted by the pressurizing machine is directly\nconverted into pressure. These machines present many advantages including\nefficiency and the ability to compress a two-phase phase with a relatively high\n\u201cefficacy<\/strong>\u201d (this parameter measures\nthe ratio between efficiencies, respectively, in two-phase and single-phase\nflows). These machines, on the other hand, are heavy, bulky and require\nsignificant maintenance. In the second case, the energy transmitted by the pressurizing\nmachine is, firstly, converted into velocity (through a rotating wheel or\nimpeller) then into pressure (through a fixed diffuser or rectifier). These\nmachines present many advantages in terms of pressure (radial machines) and\nvolume flow (axial machines), reduced space and limited maintenance. On the\nother hand, the efficiency is largely dependent on the volume flow.\nFurthermore, these machines are totally unsuitable for two-phase compression or\npumping, whether in the presence of a small quantity of liquid associated with\na gas phase (erosion is an additional drawback) or of a small quantity of gas\nassociated with a liquid phase (gas plug at the entrance a radial wheel).\nBeyond a very low level of gas (for a pump) or liquid (for a compressor), the\ntwo-phase efficacy tends towards zero.<\/p>\n\n\n\n Helico – axial hydraulics – Poseidon type –\n1st generation hydraulic<\/strong><\/p>\n\n\n\n To overcome the inability of conventional rotodynamic machines to\ncompress or to pump two-phase effluents, IFP has developed in the eighties a\nhelico axial hydraulic system called \u201cPoseidon\u201d. The impeller (the wheel)\nincludes vanes with a very small entry angle (often less than 10 degrees) and a\nvery small curvature. These blades are therefore relatively long (overlap ratio<\/strong> between 1.5 and 2.0)\ngenerating relatively high viscous losses. According to this design, the\naccelerations in the longitudinal, transverse and radial directions are\nrelatively low. These characteristics are obtained by a small variation of the\npassage section (the area) along the flow path, a small blade curvature and the action of a Coriolis force in the\nradial direction reducing the effect of the centrifugal force<\/strong>. For a low or\nhigh gas- liquid volume flow ratio represented by the GLR parameter<\/strong> (for \u201cGas – Liquid Ratio\u201d), the two-phase efficacy is\nclose to 1. On the other hand, for an intermediate GLR (between 2 and 10\ndepending on the geometry), the efficacy decreases significantly when the GLDR parameter<\/strong> (for \u201cGas – Liquid\nDensity Ratio\u201d) is reduced.<\/p>\n\n\n\n In conclusion<\/strong><\/em> <\/strong>– Despite relatively good performance compared to single-phase machines, Poseidon hydraulics present several drawbacks: significant viscous losses and low two-phase efficacy at intermediate GLR\u2019s.<\/p>\n\n\n\n Helico – axial hydraulics with interfacial\nslip control – 2nd generation hydraulic<\/strong><\/p>\n\n\n\n The operation of the Poseidon hydraulics is satisfactory at low GLRs,\nthe low orthogonal accelerations (longitudinal, transverse and radial) limiting\nto some extend the separation of the phases in the three main directions.\nBeyond a certain GLR (for example 2 – value dependent on many parameters\nincluding pressure, viscosity and surface tension), the two phases separate,\ngenerating strong interfacial losses. In strictly helico-axial hydraulics, the\nliquid phase is projected against the surface with the larger diameter slowing\nit down in its displacement towards the outlet (relatively large viscous forces)\nwhich in turn induces a braking of the gaseous phase (high energy dissipation\nat the interface of the two phases). The difference in velocity between the two\nphases is referred to as the interfacial\nslip<\/strong>. The parietal braking of the liquid film increases with a decrease of\nthe liquid film thickness.<\/p>\n\n\n\n To remedy this situation, the external part of the impeller (larger\ndiameter) is tuned to provide it with a very slight radial shape including, at\nthe inlet, a convex curvature (centre of the curvature directed outwards)\nallowing a large acceleration of the liquid phase and, at the outlet, a concave\ncurvature (centre inward) allowing a reduction in the acceleration of the\nliquid phase. These two curvatures help to minimize the velocity difference\nbetween the two phases. This action is referred to as “interfacial slip control”.<\/strong> This action allows a relatively large increase in the two-phase efficacy\nfor any value of GLR, including, for low values of the GLDR parameter.<\/strong><\/p>\n\n\n\n The control of the interfacial slip allows a certain “relaxation” of the impeller\nblade parameters<\/strong>. In particular, the blade length may be reduced (smaller overlap\nratio) limiting viscous losses, thus, providing higher single and two phase efficiencies.\nIn addition the blade curvature may be increased, consequently, providing a\ngreater manometric head coefficient (compression ratio).<\/p>\n\n\n\n In conclusion<\/em> – This second-generation hydraulic system presents, compared to the first-generation, in single phase flow, a higher efficiency and a higher manometric head coefficient as well as a higher two-phase efficacy<\/strong>.<\/p>\n\n\n\n Radio – helico – axial hydraulics – Wet gas<\/strong><\/p>\n\n\n\n The design of hydraulics suitable for compressing wet gas derives from\nthe design of the second generation helico axial hydraulics.<\/p>\n\n\n\n The terminology \u201cwet gas\u201d<\/strong>\ndenotes a low level of liquid fraction within the gas phase corresponding to a\nsignificant braking of the liquid film along the surface with the larger\ndiameter. As a result, the external curvatures located, respectively, at the\ninlet and at the outlet of the impeller are accentuated so as to greatly\naccelerate the liquid film (small thickness) towards the outlet.<\/p>\n\n\n\n This configuration results in a diameter significantly increased at the\noutlet, compared to the inlet, providing a more radial shape of the impeller.\nThis configuration presents two advantages: less droplet erosion at the\nimpeller inlet and a higher manometric head coefficient which is required in\nthe case of the compression of a gas with a lower volumetric mass compared to a\ntwo phase flow with medium GLR.<\/p>\n\n\n\n Helico \u2013 radio – axial hydraulics – Bubbly flow and viscous liquid<\/strong><\/p>\n\n\n\n In bubbly flow (very low GLR), separation forces (accelerations acting\nin the three main orthogonal directions) have a lesser effect compared to the\ndrag forces acting on bubbles submerged in the liquid phase.<\/p>\n\n\n\n As the separation forces get smaller, it is possible to apply a certain\n“relaxation” on the design parameters defining the 1st generation\nhydraulic (Poseidon). It is, in particular, possible to design a hydraulic with\na more radial shape (Helico radio axial), to shorten the length of the blades\nand to bend them so as to increase as well the efficiency as the manometric\nhead coefficient of an impeller.<\/p>\n\n\n\n In the presence of a viscous liquid, the drag forces acting on the\nbubbles increase further compared to a situation with a non-viscous liquid. As\na result, it is possible to apply a greater “relaxation” on the\ndesign parameters of the 1st generation hydraulic.<\/p>\n\n\n\n http:\/\/yvcharron.com\/index.php\/two-phase-flow-pumps\/<\/a><\/p>\n\n\n\n _<\/p>\n\n\n\n The multiphase limits of single phase\nexpansion or turbine equipment<\/strong><\/p>\n\n\n\n By single-phase expansion it is meant here the expansion of a gaseous\nphase (compressible) through an expander and by single-phase depressurization,\nthe let-down of a liquid phase (incompressible) through a turbine. These\nexpansions or let downs result in energy supply.<\/p>\n\n\n\n It is generally easier to depressurize, with a single-phase equipment, a\nslightly two-phase mixture (low or high GLR) than to pressurize it. However,\nthese depressurizations generally take place through a single stage.<\/p>\n\n\n\n The challenge is to design a two-phase\nmulti-stage turbine so as to respond to a high expansion rate<\/strong>.<\/p>\n\n\n\n Helico – axial hydraulics – 1st generation<\/strong><\/p>\n\n\n\n According to a simplified approach, an expansion impeller (wheel) of a\ntwo-phase multistage turbine looks similar to a compression impeller of a\ntwo-phase multistage pump, the inlet section of the compression impeller acting\nas the outlet section of the expansion impeller. The same principle goes for\nthe opposite sections. The same principle goes also for the static elements (diffuser\nand inducer). However, the outlet angle of the expansion inducer is\nsignificantly reduced compared to the inlet angle of the compression diffuser.<\/p>\n\n\n\n This hydraulic expansion provides advantages similar to those of the pumping\none.<\/p>\n\n\n\n Helical – axial hydraulics – 2nd generation<\/strong><\/p>\n\n\n\n The control of the interfacial slip in the wheel of a two phase turbine\nis similarly carried out to the control described for a compression system. It provides\na significant improvement in both single and two-phase performance.<\/p>\n\n\n\n Radio – helical – axial hydraulics – Bubbly\nflow and viscous liquid<\/strong><\/p>\n\n\n\n Consideration of the interfacial slip as well as the ratio of the forces\nof separation and drag of the bubbles in the liquid leads to the same\nconclusions as those made in the context of a compression or pumping system.<\/p>\n\n\n\n1.2-Texture of a coated and an uncoated surface<\/strong><\/h3>\n\n\n\n
1.3-Measurement of hydraulic roughness – Large boundary layer range<\/strong><\/h3>\n\n\n\n
1.4-Structured surfaces for turbulent friction reduction<\/strong><\/h3>\n\n\n\n
1.5-Deformable or porous coatings and injection of materials<\/strong><\/h3>\n\n\n\n
1.6-Parietal slip<\/strong><\/h3>\n\n\n\n
Theme 2 – PIPELINES<\/strong><\/h1>\n\n\n\n
2.1-General information on pipelines<\/strong><\/h3>\n\n\n\n
2.2-Aging of pipe internal coatings<\/strong><\/h3>\n\n\n\n
2.3-Impact of welds on gas transport<\/strong><\/h3>\n\n\n\n
2.4-Realization of structured surfaces inside a long tube<\/strong><\/h3>\n\n\n\n
2.5-Measurement of hydraulic parameters inside a pipeline<\/strong><\/h3>\n\n\n\n
2.6-Technico economical studies<\/strong><\/h3>\n\n\n\n
Theme 3 – TWO PHASE FLOW<\/strong><\/h1>\n\n\n\n
3.1-Two-phase compression – pumping<\/strong><\/h3>\n\n\n\n
3.2-Two-phase expansion – turbines<\/strong><\/h3>\n\n\n\n
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