Comparison of the experimental evaluation of a solar intermittent refrigeration system for ice production operating with the mixtures NH_3/LiNO_3 and NH_3/LiNO_3/H_2O

摘要

A solar powered intermittent absorption refrigeration system has been developed and evaluated with the ammonia/lithium nitrate (NH_3/LiNO_3) and ammonia/lithium nitrate/water (LiNO_3/H_2O) mixtures. The system, designed to produce up to 8 kg/day of ice, was developed in the Centra de Investigacion en Energia of the Universidad Nacional Autdnoma de Mexico. It consists of a Compound Parabolic Concentrator (CPC) with a cylindrical receiver acting as the generator/absorber during the generation and evaporation stages respectively, a condenser, an evaporator and an expansion device. The system operates solely with solar energy and no moving parts are required. Several test runs were carried out at different solution concentrations for both mixtures under study. Evaporator temperatures as low as -8 ℃ were obtained for a time period of 8 h. Comparing the performance of the system operating with the two mixtures, it was found that with the ternary mixture the solar coefficients of performance can be up to 24% higher than those obtained with the binary mixture, varying from 0.066 to 0.093. In addition, with the ternary mixture the initial generation temperatures resulted to be up to 5.5 ℃ lower than those obtained with the ammonia/lithium nitrate mixture, at the same time the maximum operating pressures were around 1.5 bar higher.