Influence of internal heat exchanger position on the performance of ejector-enhanced auto-cascade refrigeration cycle for the low-temperature freezer

Abstract

This paper presents a thermodynamic investigation on the configuration optimization of the ejector-enhanced auto-cascade refrigeration cycles for −80 °C freezers. The performance comparisons based on the genetic algorithm are carried out among four different modified cycles with differently positioned IHX. The natural binary mixture R1150/R600a is used as the working fluid. The simulation results illustrate that adding IHX could improve the overall system performance, and adopting IHX at the evaporator outlet is more effective for performance enhancement than that at the condenser outlet. The most significant performance improvements are obtained in the optimized cycle, which simultaneously adopts the dual-IHX at the condenser and evaporator outlets. Compared to the cycle withnot IHX, the average COP and exergy efficiency improvements reach up to 55.2%, and the compressor displacement and system initial capital cost are reduced by 52.9% and 17.5%, respectively. The pressure lift ratio increases, and the entrainment ratio declines due to the application of the IHX at the condenser outlet. Theoretical results provide a guide for improving the ejector-enhanced ultra-low temperature freezer in the applications of the −80 °C freezing.