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faryuki
15-05-2007, 02:37 AM
Hello guys

How r u?

I have question for the ammonia liquid with low temp. and pumping with the ammonia pump. It is possible if the velocity of liquid ammonia with low temp we increase will be build up the gas?

many thanks

US Iceman
15-05-2007, 02:43 AM
When you pump liquid ammonia the pressure increase generates subcooling. You can see this on a pressure-enthalpy diagram.

The extent of pressure increase created by the pump means you can increase the friciton losses or static head losses equal to the pressure added by the pump, before the liquid will flash off into a vapor.

faryuki
15-05-2007, 08:21 AM
Now I have a problem with ammonia liquid pump is sometimes cavitation (at low pressure receiver -40degC). I have check the pump is over capacity so they have make adjusment and decrease the pipe suction and discharge sizing. My suspect is if they make sizing down for that pipe the velocity become increase and flash in to the vapor like u said, its correct?

thanks for your help

smpsmp45
15-05-2007, 09:58 AM
Dear US Iceman,

By any chance can you put up the PH diagram for this pump pressure increase & the Superheat increase point.

Peter_1
15-05-2007, 10:24 AM
Smpsmap, this is a normal log/p for NH3 where you have to plot the real cycle on it.

US Iceman
15-05-2007, 02:50 PM
Now I have a problem with ammonia liquid pump is sometimes cavitation (at low pressure Receiver (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=88) -40degC). I have check the pump is over capacity so they have make adjusment and decrease the pipe suction and discharge sizing.


Reducing the pipe size will not help. If the pump is a centrifugal pump, you can decrease the flow rate of the ppump by partially closing the pump discharge valve. This forces the pump to operate at a lower flow rate by increasing the pump discharge pressure.

If the pump is trying to pump too much liquid, the NPSHR (net positive suciton head required by the pump) can increase dramatically, which causes the pump to cavitate.

That's only one possible explanation. but it is the most likely.