A Review on Flow Characteristics of Refrigerant and Oil Mixture in a Heat Pump System

This paper presents a comprehensive review of oil retention and performance of oil separator in a heat pump system. Liquid volume fraction model, viscous film model and analytical model from continuity and momentum equations for predicting the oil retention amount in a heat pump system are reviewed. In addition, weighing a test section, using an oil injection and extraction device and optical analysis for measuring the oil retention amount are introduced and experimental results are analyzed. Numerical studies which used commercial tools for computational fluid dynamics or suggested a new model by simplifying the flow in cyclone separator are reviewed. Effects of droplet size and angular velocity of gas phase flow in cyclone separator on the performance are discussed. Experimental methods for measuring the efficiency of oil separator are introduced, and theoretical analysis on the efficiency and pressure drop of cyclone separator is suggested.