Why Does Air-Lock Reduce Fluid Flow in Tubes?

[sarmin]

Hi,

I have come across "air-lock," as a concept to explain decreased flow of fluid in a tube as a result of air bubbles introduced into the system. I'd really appreciate an explanation for why this happnes? is it because air is compressible? is there a text that would recommend as a reference? Thank you.

 

[abercrombiems02]

Yes, you are correct about air being compressible. Imagine a tube with a constant cross sectional area. If an air bubble is introduced into a system that previously had steady flow, then what happens is the pressure in the bubble and the water need to balance. In order to achieve this some of the kinetic energy in the stream is used to compress the air bubble. The fluid does work on the bubble by changing its volume so that the pressures are equal. (Remember E = P*V). So some of the kinetic energy in the stream is lost as result of doing work on the bubble. This increases the entropy of the system. Same result of the prescence of friction. So we can think of the bubble as being a source of friction in the flow. As for the text's I really don't know of one that addresses this problem specifically, but I do recommend "Fundamentals Of Aerodynamics" By John D. Anderson. After talking about some aspects of compressible flow there is a section on Poiselle (spelling) Flow, which is the case of viscous flow in a pipe