Experimental evaluation on thermal performance of an air-cooled absorption refrigeration cycle with NH3–LiNO3 and NH3–NaSCN refrigerant solutions

Abstract

This paper experimentally analyzes thermal performance of an air-cooled type single effect absorption refrigeration cycle with ammonia–lithium nitrate and ammonia–sodium thiocyanate solutions as working pairs. Ammonia/salt system has simple construction, low evaporating temperature (<0°C) and high working efficiency. Ammonia is one kind of environment-friendly refrigerants. Hence, ammonia/salt absorption refrigeration cycles are considered to be the most possible ones for practical application in small capacity refrigeration units. An experimental apparatus has been designed and built in Wuhan, China, to evaluate the cycle thermal performance of air-cooled type single effect ammonia/salts absorption refrigeration system. The experimental apparatus operates steadily under different working conditions. A set of tests have been conducted and the corresponding experimental data are measured and recorded to show the variation of the system performances with different system working parameters. For the NH3–LiNO3 system, the measured lowest evaporation temperature reaches −13.1°C with corresponding average system COP of 0.15, and the average refrigerating capacity is about 670W. For the NH3–NaSCN system, with a measured evaporation temperature of −7.5°C, the corresponding average COP is 0.20, and the average refrigerating capacity was about 590W. According to the experimental results, the actual measured COP of NH3–NaSCN system are in the range of 0.20–0.35, which are a little higher than that of NH3–LiNO3 system (actual measured COP ranging from 0.15 to 0.29). Under similar working condition, NH3–LiNO3 system can reach a lower evaporation temperature than that of NH3–NaSCN system. The experimental results of the present study demonstrate the feasibility and capability of ammonia/salt absorption refrigeration cycle for freezing purpose under air cooling conditions. Although the coefficient of performance of the experimental apparatus is below expectation while comparing with the theoretical results, optimization methods are put forward by the present paper for further research.