Frictional and Internal Leakage Losses in Rotary-Vane Two-Phase Refrigerating Expanders

Abstract

Increasing the coefficient of performance of a vapor compression refrigeration system may be realized by utilizing work recovering expansion devices that additionally lower the enthalpy of the refrigerant at the inlet of the evaporator. Depending on the operational and geometrical parameters of the expander, laminar and viscous two-phase leakage flows within the expander may be present. Single-phase leakage models available in the literature must then be modified or rederived accordingly. A dynamic frictional model for the expander must also be developed for ideal operation (i.e., no internal leakage) and modified to account for internal leakage accordingly. This paper presents a comprehensive component-level model of inherent friction and internal leakage losses in a two-phase circular rotary-vane expander used in a vapor compression refrigeration system. The model establishes the performance of the expander as a function of geometric and fluid parameters. Accurate modeling and prediction of frictional and internal leakage losses is vital to being able to accurately estimate the efficiency, rotational speed, and the torque and power produced by the expander. Directions for future work are also discussed.