pressure and volume changes for a liquid filled system

[jfriddell]

Engineers:

I'm working on a subsea project where I intended to de-mate a control line coupler pair. I know when I de-mate the coupler pair under pressure a very small volume of fluid (liquid) will be released from the system. The couplers have a poppet which will seat upon demate and thus trap pressure in the closed sytem. The system is 10-20 ft. of 1/2" OD SS tubing. Normal system operating pressure is 3,000 psi.

My end goal is to hopefully calculate how much the system pressure will decrease due to the small loss of fluid volume during coupler de-mating. My search on Eng-Tips.com thus far has only lead me to P and V equations related more to gas states as opposed to liquid states. Can anybody point me in the right direction of simple calculations for such a scenario?

Thanks to all.

 

[prex]

The compressibility factor of water is 4 x 10^-4 MPa^-1: this gives the relative change in volume [Δ]V/V per MPa (=145 psi) of change in pressure.
If you know the volume of water lost you can estimate directly the change in pressure.
A more complex approach would account for the reduction in volume of the tubing with the change in pressure, but I guess you don't need to go so far. Anyway this FAQ faq378-1339 can give you ideas on how to account for that.

prex

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