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water pressure

water pressure

water pressure

(OP)
Hi there !

This time I've got a odd question.
Seems banal, but I can't work it out.

Issue: A sealed tank is completely filled with water @ 72.5 PSI and a known outside temperature, (ex 77 F).
The tank is not insulated with respect of outside temperature

Let's suppose that, after one day, pressure changes to 50 PSI.

Question 1: Is this pressure variation physically possible ? The sole affecting variable would be outside temperature
Question 2: Should it be the case, how can I calculate new outside temperature ? It seems to me it is not possible to utilize saturation properties of water. At described pressures we got temperatures over 212 F.

Many thanks
 

RE: water pressure

AO1958,
       I think you must have your sums wrong. You say the temperature rises from 77 F to 212 F. This cannot be right. If the pressure decays then the temperature must drop not increase.

RE: water pressure

All of the tanks I'm familiar with would be scrap metal if you put 72.5 psi(g?) on them.  An API tank will generally lose its top around 5 psig.  Let's pretend you said "vessel" instead of "tank".

A liquid full vessel will change pressure about 100 psi for ever 1°F temperature change, so if it cooled of a fraction of a degree the change from 72.5 to 50 psi(g?) is very possible.

For a partially full vessel you would have go give us a lot more information, but like D5B123 says the temperature would have had to have dropped, not risen

David

RE: water pressure

AO1958,

Please take a look at this FAQ

http://www.eng-tips.com/faqs.cfm?fid=1339

Then rearrange the formula you'll find there solving to calculate the temperature reduction ΔT that will lead to a pressure reduction ΔP of 22.5 psi.

αfΔT-βΔP=αvΔT+ΔPD/tE

 
 

RE: water pressure

You would need to account for the expansion of the tank due to pressure and temperature, and the expansion of the water due to pressure and temperature.  Not necessarily a trivial problem.  Although it does sound a lot like homework.

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