CFD Analysis Of A Double Suction Cooling Water Pump

Abstract

In 1991, four large double suction cooling pumps were installed at a chemical plant in Texas. Although these pumps met performance specifications on the test stand, they proved to be noisy when installed. Sound power levels greater than 93 dbA were observed. Pumping applications involving cooling water have been especially difficult to solve over the tears, due to the presence of dissolved air inherent in a cooling tower sump. Water that contains large amounts of dissolved air changes the apparent required net positive suction head (NPSH). In such applications, traditional correction techniques failed because the entire system was not analyzed, and the source of the noise generation could not be pinpointed. This paper deals with the steps involved with obtaining a solution to this problem. A computational fluid dynamics (CFD) analysis was performed on the pump and impeller. Initial investigation revealed that the impeller was not the source of the problem. The casing inlet was then analyzed. The model indicated the presence of separation in the suction nozzle, causing a flow distortion at the impeller eye. A unique guide ring was developed to minimize the flow separation. The CFD analysis was revised to reflect the new geometry, and a significant improvement in the flow was predicted. A prototype guide ring was manufactured and installed in one of the four pumps. Pressure profiles were obtained by experiment to validate the analyses. The results are discussed.