Application Guidelines For Pumping Liquids That Have A Large Dissolved Gas Content
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A case history is presented pertaining to five (four operating and one spare), 150 hp sealless pumps operating in parallel in a closed loop-65° chilled liquid system. The pumping system is designed to use a liquid refrigerant as a heat transfer media, due to its desirable pumping characteristic at low temperatures. All five pumps experienced severe damage and repeated failures of the process lubricated bearings during startup of the system. Investigation and analysis of the system revealed two major problem areas in pumping liquids with dissolved gases. • The standard textbook calculation for NPSH (subscript A) may not accurately predict the effective NPSH (subscript A) for a liquid with high dissolved gas content • Two phase flow (gas and liquid) through sealless pumps may lead to product lubricated bearing failures The authors review a method for calculating the effective NPSH (subscript A) when dissolved gases are present. The authors also present appropriate system design considerations intended to assist in minimizing the amount of gas that enters, or is released within, a pump to prevent major equipment damage. Also discussed are limitations imposed on the chilling capacity of the case history pumping system due to heat rejected to the chilled liquid as it passed through the magnetic drive pumps.
Wood, Daniel W.; Hart, Robert J.; Marra, Emesto (1998). Application Guidelines For Pumping Liquids That Have A Large Dissolved Gas Content. Texas A&M University. Turbomachinery Laboratories. Available electronically from