CLOSE CIRCUIT PRESSURE

[roker]

Hello.

we have a close circuit chilled water system suppling the water to a heat exchanger located at 30 meters height, the pump is located at ground, the suction pressure is 4 barg and the dischrge is 8 barg.
when the pump is stopped what will be the pressure in the return line at 30 m height and at ground? will it be the same pressure?
what are the rules to calculate the pressures in close pumping circuits/

regards,
roker

 

[joerd]

Think about it & do the Bernoulli thing. If the pump is stopped, the dynamic pressure drop goes away. You have to determine the fixed pressure point (usually an expansion drum of some sort) and calculate static pressure differentials from there.
If you have high flowrates and suddenly stop a pump you can run into water hammer problems. Then a dynamic analysis is required to give you the transient pressure profile.

Cheers,
Joerd

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[quark]

4 barg at suction is a concern to me, could it be 3barg? Also, the 4 barg differential seems to be too high (just a gut feeling). Check with the designed pressure drops and it may be right time for cleaning.

 

[sshep]

Roker,
Do you have a chilled water surge and expansion drum near the suction of the pump? This would be my experience and joerd's as well I note.

The pressure at which this drum is operated at shutdown will be needed to determine the pressures at points of the system based on the elevation relative to that drum. From the info you have given, the pressure at the top of the loop (30m) could be 1 bar (i.e. holding 4bar on drum minus 30m of elevation) or vacuum (if water is allowed to slump into the drum at shutdown).
best wishes,
sshep