How to determine pressure in tank with stable fluid

[zamakaze]

I have a pump that is pumping stable product to a tank. There is no blanketing on the tank and it is not vented to the atmosphere. What will be the pressure in the tank? Will it be due to vapor pressure of the liquid. Since vapor pressure is below atmospheric..will there be vapor in the tank at all? Will the pressure in tank increase as liquid level rises?

 

[jari001]

Unless this system is airtight, I think air will come in and bring the total pressure upto 1 atmosphere. There will be vapor since there is enough liquid to establish VLE. The pressure in the tank will increase due to increasing liquid height (hydrostatic pressure) if you measure the pressure where there is liquid (e.g. at the bottom of the tank). That increase in hydrostatic pressure will not impact your pump until the liquid level starts to approach the height of the discharge point.

 

[LittleInch]

Zamakaze.

You're asking a series of similar questions which show that you have very limited understanding of the process.

If you have no way out for the vapour then the pressure will increase as you fill the tank. So yes the pressure will increase as you fill the tank. However most "tanks" have very low max design pressure and will burst if you do this, so it is not realistic.

11 psia is quite a volatile liquid and the will be a vapour mix in the gas above the liquid. If the gas space was less than 11psia, the liquid would boil, but more than that the value will still mix with the air space. Think of gasoline in a tank.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Snickster]

This all depends on the how ideal the situation is and appears more of a hypothetical textbook problem. If before the fluid is pumped and the tank is at equillibrium then the vapor above the liquid will be at equillibrium vapor pressure considering that no other vapors are in the tank other than that of the liquid in the tank

If then the liquid is pumped into the tank at a very slow rate so that the vapor space can maintain equillibrium vapor pressure with the liquid in the tank then the vapor space pressure will not change. This considers that as the added liquid in the tank compresses the vapor, the vapor condenses fast enough to so that the pressure does not increase.

If the liquid is pumped in very fast where vapor cannot condense fast enough then the pressure will rise due compression of the vapor space. However if stopped pumping and given enough time then enough vapor will eventually condense so that ultimately the vapor space will again lower to the vapor pressure of the liquid.

 

[zamakaze]

@little inch -
thanks for your answer

 

[LittleInch]

Snickster,

You may or may not be correct in theory, but in any level of practicality the vapour will not condense sufficiently to make any appreciable difference in pressure. It is very dangerous to say "the vapour space pressure will not change" without giving any idea of how much pressure is required to force condensation and how long it takes.

I really don't think this is a practical and workable idea and could lead to inexperienced engineers doing things which cause the tank to burst or the roof to come off....

But this is all very hypothetical and smacks of some student posting to me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Snickster]

LittleInch

It appeared to me to be a hypothetical theoretical question of purely academic nature. So I answered accordingly in a purely academic theoretical response to what might happen sticking to what question was actually asked. I assumed that the person was at least familiar with rules of limits of pressure in vessels and tanks and how to mitigate high pressure situations by installing vents or relief valves.

of course you would need to consider that the pumping rate would be such that a quasi static process of just enough vapor condensing to counter balance the input of new liquid will never occur and the pressure will rise.

 

[zamakaze]

Thank you for your answers @little inch @snickster