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# Depth of boiling liquid and measurement of void fraction in tank

## Depth of boiling liquid and measurement of void fraction in tank

(OP)
Dear all,

A couple of simple questions which I'd welcome your opinion on... I have a process vessel which is partially filled with a single component saturated liquid. Above the saturated liquid is vapour. Occasionally, due to an upset, the pressure in the vapour space is rapidly decreased. The liquid then proceeds to boil violently.

1) Given that the vessel is reasonably tall, is it sensible to assume that when the depth of liquid is great enough such that the head of liquid exceeds the saturation pressure of the liquid at the liquid temperature, boiling is suppressed. Or, as the boiling is vigorous, will advection caused by bulk flow in the vessel carry vapour bubbles to a depth below the depth where you would expect the boiling to be suppressed by the head of liquid?

2) Can anyone suggest a method of calculating the void fraction at a given depth?

3) If the tank has visual access, can anyone suggest a method of measuring the void fraction at a given depth?

### RE: Depth of boiling liquid and measurement of void fraction in tank

1) I don't think so but you need to provide some data. Even at say 5m high liquid head the difference in pressure is circa 0.5 bar. How much does the pressure decrease by??

In a perfect non moving liquid then maybe you might see some effect if very carefully controlled, but in reality no - the liquid will be moving around. As the liquid vaporizes it will loose heat due to the latent heat of vaporization so will fall and create a circulation

2) Do you mean the amount of space the vapour bubbles take up?

3) See above

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