What are the use or problems associated with air bubbles in hydrodynamic flow?

Question

In undersea and land pipelines, cavitation is a problem; should a frequency that produces tiny air bubbles be introduced to ease transmission, or a frequency that prevents air bubble production be applied to the pipeline?

Answer 1

*Cavitation is related with temperature and occurs due to collapse of bubbles in high pressure region due to low vapor pressure w.r.t. temperature.

Cavitation creates a pressure surges in the ranges of 1000 psi pressure with errosion and vibrations.

In case of centrifugal pump operating at a 2900 rpm and having air entrapped inside the casing ,you have to run the pump at a speed of 2900*800 RPM to expell the air.

So, ultimate aim is to prevent the bubbles in the pipeline.

Answer 2

Yes, as you said it's a problem of cavitation. But it can be also a problem with the increasing in vibration of the supporting structure.

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Answer 3

cavitation is where air bubbles implode, and if the collapse happens on a solid surface, the shock waves will cause rapid erosion of that part. It's rarely a good thing, especially if it happens in a location that's difficult to repair. (cavitation is really good at mixing liquids.)

However If the bubbles are introduced AFTER the pump, then it could decrease the effective viscosity of thick liquids, but only so long as the air stayed trapped in the liquid. If the air is hot then you've also got a means of warming the fluid, which could decrease viscosity.

But if the air separates out, and you get air at the top of the pipe, and the liquid at the bottom of the pipe, the benefits are lost, and you could end up with an air lock. You'd also have to watch the flow through any pipes/valves/bends to make sure the bubbles didn't collapse in them.

If the bubbles remain in suspension (and don't collapse) any pressure pulses will tend to be evened out, as the bubbles work like little springs/hydraulic accumulators. This may help in dealing with "water hammer"

Answer 4

nothing..