Improvements of Heat Transfer and Refrigerant Distribution in Plate-type Evaporator by Vapor Re-circulation Using an Ejector

Abstract

We proposed a new method to enhance the average evaporating heat transfer coefficient ( α_r) in the refrigeration cycle. This new method is to re-circulate the vapor refrigerant from the evaporator outlet to the inlet by using an ejector. The α_r is improved by increasing the vapor quality and the mass flow rate of refrigerant at the evaporator inlet. In this study, experiments were performed to evaluate the effectiveness of the proposed method utilizing plate-type evaporators and refrigerant R404A. The α_r in evaporators with 10 and 50 plates was measured under different mass velocity (m₀) conditions. The coefficient of performance (COP) was also measured. The α_r in the vapor refrigerant re-circulated evaporator improves 1.5 times or more compared with the conventional evaporator and is improved by increasing the m₀. The refrigerant distribution in an evaporator with 50 plates is improved compared with that the α_r in the evaporator with 10 plates. It is also found that the COP in the refrigeration cycle with the vapor refrigerant re-circulated evaporator improves as compared with the conventional cycle by the fact that the effect of improved α_r was larger than the influence of increased pressure loss.