Pump Cavitation: Various NPSHR Criteria, NPSHA Margins, Impeller Life Expectancy

Abstract

This tutorial deals with pump cavitation, discussing various net positive suction head required (NPSHR) criteria, net positive suction head available (NPSHA) margins and impeller life expectancy. It gives an introduction to the subject matter and provides insights on particulars like cavitation inception, 3 percent head drop, and 40,000 hours impeller life, as well as NPSH scaling laws. It further devotes attention to the effect of dissolved gases and thermal suppression (i.e., thermodynamic effect). With regard to numerical prediction capabilities the use of computational fluid dynamics (CFD) shall be discussed. Furthermore, guidance for cavitation damage diagnosis shall be given, including the peculiar aspects of various cavitation modes, the prediction of cavitation erosion rate, and assessment of impeller life expectancy. The tutorial will further address NPSHR criteria and NPSHA margin factors.