Flow-loss, efficiency, and change-of-state calculations for fluid-flow engines and heat exchangers

A theoretical analysis of the energy losses in devices transfused by fluids is presented, with a focus on the phase-change processes affecting the fluid medium inside the device. Flow losses are shown to be equivalent to the dissipative work due to friction stresses, using their relationship to heat transfer or mechanical work in order to derive equations of flow efficiency for specific types of devices (turbopump, turbocompressor, turbine, and heat exchanger). A polytropic (P) approximation of phase transformation inside the device is employed to arrive at constant P relations, dissipated-P-work values, and P efficiencies for both ideal and real fluids with actual and P efficiencies found to be almost equal for most of the devices. Standard-value ranges are given for each type of device, and sample calculations for simple and supercritical-evaporation steam-turbine and closed gas-turbine systems are presented. The applicability of mean efficiency and P-transformation calculations to discontinuous devices is demonstrated.