water pressure

[AO1958]

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

 

[DSB123]

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.

 

[zdas04]

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

 

[ione]

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 ?T that will lead to a pressure reduction ?P of 22.5 psi.

?f?T-??P=?v?T+?PD/tE

 

[JStephen]

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.