44 - PUMPS, FANS, COMPBESSORS

Abstract

This chapter presents an overview of pumps, fans, and compressors. The machines of this group are quite generally designated as “pumps.” They supply energy to the fluid, which appears as an increase either in pressure or in velocity. For compressible fluids there is a reduction in volume associated with an increase in pressure, and a part of the energy supplied is used in producing this reduction. In subsonic flow through a contracting nozzle, pressure can be converted into velocity, and in a diffuser velocity can be converted into pressure; hence, it is theoretically immaterial whether the energy supplied appears as an increase in pressure, or as an increase in the kinetic energy. The important quantity is the sum of the two, the increase in total pressure. For practical application, however, a machine that produces high pressure at a small velocity is more valuable than one that, for the same increase in total pressure, produces a small increase in pressure at a large velocity.