Thermophysical properties and applications of CaCl₂-LiBr(1.35:1)/H₂O as a working pair

Absorption refrigeration is an ideal way to utilize solar energy in summer. For a single-stage solar-driven refrigeration cycle based on the typical working pair of LiBr/H₂O, the required generation temperature is up to 88.0℃, which is too high for the commonly used flat plate solar collectors or vacuum glass tube solar collectors. Thus far, this problem has been addressed via two methods:(1) using high-temperature solar collectors and (2) applying a two-stage absorption refrigeration cycle. In literature, a study pertaining to the former was conducted on the performance and economic feasibility of a 100 kW single-stage solar-driven absorption air conditioning system using heat pipe vacuum tube solar collectors, and another study pertaining to the latter was conducted on the performance and economic feasibility of a 100 kW two-stage solar energy absorption refrigeration air conditioning system using flat-plate solar collectors. Their results show that the system cost is high for the former and that the system cost is high and the coefficient of performance is low for the latter. In addition, the results show that the latter system is complicated. Thus, there are currently few commercial applications for the solar-driven absorption refrigeration system. In this study, a new method has been proposed that can address the existing problem, i.e., the required generation temperature is too high for flat plate solar collectors or vacuum glass tube solar collectors in a solar-driven single-stage refrigeration cycle, using a new working pair instead of LiBr/H₂O. In this study, it is found that CaCl₂/H₂O has an absorption characteristic benefitting refrigeration, although its absorption ability is limited owing to its relatively low solubility. Based on CaCl₂/H₂O, a new working pair of CaCl₂-LiBr(1.35:1)/H₂O has been proposed. The crystallization temperature, saturated vapor pressure, density, and viscosity of this working pair were systematically measured, and the results show that the required solar collector temperature or the generation temperature of CaCl₂-LiBr(1.35:1)/H₂O for a single-stage absorption refrigeration cycle is 6.2℃ lower than that of LiBr/H₂O under the same refrigeration conditions. In addition, the corrosion rates of the carbon steel, 316L stainless steel, and copper in CaCl₂-LiBr(1.35:1)/H₂O were measured with a weight loss method, and the results show that the corrosion rates of 316L and copper are sufficiently low for practical applications.