Experimental investigation on the concentration distribution behaviors of mixture in an ejector enhanced auto-cascade refrigeration system

In this paper, the concentration distribution behaviors of the mixture R134a/R23 in an ejector enhanced auto-cascade refrigeration cycle (EARC) were experimentally investigated. Relationships between circulating concentration and charged concentration were explored, and the effects of the heat load and ambient temperature on the composition shift characteristics were analyzed. The results indicated that large composition shift occurred at the operation conditions, and the circulating concentration of the low boiling temperature component R23 at the condenser inlet was 25.9-38.1% higher than that in charge due to the differential hold-up of individual refrigerant components in two-phase region. The concentrations of the component in charge and circulation had a linear relationship in EARC, which was similar to those in conventional auto-cascade refrigeration cycle and Joule-Thomson refrigerator, even though these cycles were different in cycle configurations, mixture and operation conditions. R23 showed higher circulation concentration at higher ambient temperature. As the increasing heat load, the circulating concentration of R23 at the condenser inlet first increased and then decreased. In addition, different preferential solubility of individual components in the lubricating oil led to 15.4% richer R23 before the system start-up than that charged. The circulating concentration varied drastically at the early stage of the pull-down process and then tended to be stable over time. The largest shift of the circulation concentration from the charged concentration in the pull-down process reached 32.6%. This work could provide an in-depth understanding of the behaviors of the mixture concentration in the ejector enhanced auto-cascade refrigeration system. (C) 2018 Elsevier Ltd and IIR. All rights reserved.