Thermophysical properties and applications of CaCl2-LiBr(1.35:1)/H2O as a working pair
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摘要: 圍繞以LiBr/H2O為工質對的單級太陽能吸收式制冷循環因對太陽能集熱溫度要求高而難以實現應用的問題，提出了CaCl2-LiBr（1.35∶1）/H2O（CaCl2與LiBr的質量比為1.35∶1）新型工質對，系統地測定了其結晶溫度、飽和蒸氣壓、密度和黏度，并與LiBr/H2O進行了比較.結果表明，采用CaCl2-LiBr（1.35∶1）/H2O作為太陽能單級吸收式制冷循環的工質對，在同一制冷工況條件下，其發生溫度，即太陽能集熱溫度比采用LiBr/H2O的情況低6.2℃.另外，采用浸泡法測試了碳鋼、316L不銹鋼和紫銅在CaCl2-LiBr（1.35∶1）/H2O中的腐蝕速率，結果表明316L不銹鋼和紫銅的腐蝕性非常小，可滿足實際工程應用的要求.Abstract: 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.
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