Keywords: parietal sliding increase reduction change wall velocity material hydrophobia fluid dynamics experiment results
Fluid dynamics background
It has been shown experimentally, at several occasions, that the nature of the channel wall and of the fluid in contact with it, intervenes in the degree of hydraulic or aerodynamic drag: acceleration or braking calling into question the condition of zero velocity at the wall.
Example of fluid velocity change
A relatively well-known example is hydrophobia. An agent is mixed with water in order to create a hydrophobic situation between the liquid and the wall. It follows that the water molecules slightly move away from the wall, parallel to it, generating less contact and less shock between these two elements and, consequently, causing a reduction in viscous and turbulent losses as well as an increase in flow velocity. Conversely, if a hydrophilic situation is created, the molecules are attracted to the wall, generating an increase in energy losses and a reduction in the flow rate.
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