The influence of NH3-H2O-LiBr ternary working fluid on the performance and solution circulation in ammonia absorption refrigeration system

Abstract

The ammonia absorption refrigeration system(AARS) has been widely applied in the recovery of industrial waste heat. Using NH3-H2O-LiBr ternary working fluid is an effective way to promote the performance of AARS. While previous studies mainly focused on the vapor–liquid equilibrium of the NH3-H2O-LiBr solution and the performance variation of the ternary system under specific working conditions, this paper aims to experimentally investigate the influence of LiBr on performance and solution circulation under various operation conditions. Experiment results indicated that 15%(w/w) was the optimum LiBr concentration across all working conditions. The COP of the ternary system was 7.55% higher than the binary system at most and the heat source temperature of the ternary system can be reduced by 25 °C to reach the same COP of the binary system. The COP was promoted because the rectifier cooling duty decreased by 53% at most, resulting in a reduction of its proportion in the heating capacity from 28.6% to 17.0%. Although the circulation ratio increased by 52% when the LiBr concentration increased from 5% to 15%, the absorber cooling duty experienced an average increase of 6.19%. The effectiveness of the solution heat exchanger was improved from 66.8% to 76.3% when the LiBr concentration increased from 5% to 20%. As the rise of the circulation ratio leads to higher pump power, the viscosities of the NH3-H2O, H2O-LiBr, and NH3-H2O-LiBr solutions were measured. The results demonstrated that solution temperature and NH3 concentration had more influence on solution viscosity than LiBr concentration. The viscosity increased by 6.2%, 17.1%, and 7.1% when the LiBr concentration increased by 11.26%, NH3 concentration increased by 9.5%, and solution temperature dropped by 2 °C, respectively.