The Effects of Fluid Properties on Cavitation in Centrifugal Pumps

Abstract

An analytical model of the cavitation process in a pump is developed assuming that the flow is adiabatic, frictionless, steady, and irrotational. A relationship is developed relating the volume percentage of the fluid vaporized during the cavitation process to the “thermal cavitation parameter.” Two assumptions are then introduced concerning the cavitation process in a pump pumping fluids of different cavitation characteristics. Using these assumptions, a relationship is derived indicating that the difference in net positive suction head (NPSH) of a given pump handling two fluids is a function of the difference of the reciprocals of the thermal cavitation parameter for the two fluids and of the volume percentage of the fluid vaporized. This relationship is compared with data describing the cavitation characteristics of six pumps handling four pure fluids. The change in NPSH for all of the pumps and fluids, using the cold-water NPSH as a reference, is found to correlate as a function of the reciprocal of the thermal cavitation parameter with an accuracy of ±1 ft in NPSH. Experimental and analytical methods for determining the cavitation characteristics of pumps handling petroleum-based hydrocarbon mixtures are then described. Cavitation data for two pumps handling gasoline, fuel oil, and crude oil are presented. The data correlation for pure fluids is extended to include cavitation data for petroleum-based hydrocarbon mixtures. It is found that mixtures exhibit an additional decrement in NPSH over that for pure fluids having the same value of the thermal cavitation parameter. This additional decrement is found to be temperature dependent.