Thermodynamic Testing of Turbines and Pumps

Abstract

Hydraulic losses experienced by fluids in passing through machines effectively raise the temperature. The thermodynamic method of testing is basically a way of determining these losses by measuring temperature rise. When pressure change through a machine is measured along with temperature, the enthalpy change is known and the hydraulic efficiency can be evaluated. Knowledge is necessary of certain thermodynamic properties of the liquid which change with pressure and temperature. Heat transfer between the machine and its surroundiings is assumed to be negligible. Apparatus is described for use in several different applications of the method, but principally in the thermometric and null methods. Temperature change has usually been measured by resistance thermometers in various bridge networks. Three types of bridge are discussed, the direct current, the transformer ratio and the hydraulic bridge. Methods of sampling small quantities of the main flow are described for the null method; when the two thermometer pockets are in streams having different velocities, a differential recovery factor has to be applied. Calorimeter design details are given, with a brief review of tests in the U.K. and abroad.