Performance Simulation of a R744-R717 Cascade Refrigeration System According to Operating Conditions

Abstract

The evaporating temperature range required for the low temperature freezing system is from -50℃ to -30℃. Since it is difficult to keep the required capacity in a cabinet, it is advantageous to design the system using a cascade refrigeration system. Use of carbon dioxide and ammonia would be advantageous since ammonia is an environment-friendly working fluid and has a high capacity for performance improvement. To investigate the performance characteristics of the R744-R717 cascade refrigeration system, a theoretical model was developed and performance was analyzed according to cascade heat exchanger operating temperature. The optimal cascade R744 condensing temperature was -5℃, and maximum COP was 1.13 when the temperature difference of the cascade heat exchanger was 5℃. In addition, the total system COP increased by 1.17 when the cascade temperature gap was 3℃ at the middle temperature of -7.5℃. Key wordsCascade refrigeration system(캐스케이드 냉동시스템), Carbon dioxide(이산화탄소), Ammonia(암모니아), COP(성능계수) †Corresponding author, E-mail: hhcho@chosun.ac.kr