Comparison of experimental performance of absorption refrigeration cycle using NH3/LiNO3+H2O working fluids with different water component proportions

Abstract

Regarding the working fluids of absorption refrigeration systems, compared with the binary ammonia/water or ammonia/salt solution, the ternary ammonia/lithium nitrate+water solution has some advantages including small viscosities, good heat-transfer efficiency and low crystallization risk. In this paper, four kinds of NH3/LiNO3+H2O solutions with different water component proportions are selected as working fluids, which is No.1(9.6%) < No.2(18.6%) < No.3(27.6%) < No.4(36.9%), and the experimental performance evaluation was conducted on a prototype of absorption refrigeration system driven by exhaust heat. First, experimental tests were carried out with varying operating conditions to evaluate their influences on performance parameters; the detailed experimental parameters operating with No.2 and No.4 working fluids are presented, and the reasons of the experimental results are explained. Then, the experimental results of four ternary working fluids and binary working fluid were compared and analyzed to evaluate the influences of water mass fraction. Compared with NH3/LiNO3, the cooling capacities of No.1, No.2, No.3, No.4 increased by 10.6%, 17.8%, 24.8%, 26.4%, respectively; the logarithmic mean temperature difference of the solution heat exchanger decreased by 1.2 K, 2.0 K, 2.6 K, 3.9 K, respectively. The comparison results indicate that, for the working fluid with larger water mass fraction, it has better heat and mass transfer characteristics, the system can produce larger cooling capacities and has lower required driven temperatures of heat sources, but the overall coefficients of performance hardly changed with the water mass fraction. The experiments and comparison results provide significant references in practical applications for the selection of working fluids of the absorption refrigeration systems.