Abstract
The strict regulations on traditional synthetic refrigerants prompted a strong focus on eco-friendly working fluids including carbon dioxide. Nevertheless, a large throttling loss in CO2 refrigeration leads to an inefficient operation. The introduce of ejector allows for recovering part of expansion work and has positive effect on system efficiency, whereas performance deterioration may be found at off-design conditions. In this study, the design of multi-ejector with three controllable ejectors was proposed to improve the system off-design performance. A detailed experimental analysis on the CO2 multi-ejector refrigeration system was investigated. The impact of various operating conditions on multi-ejector performances including pressure lift, entrainment ratio and multi-ejector efficiency was evaluated. In addition, a comparative study was carried out taking the single-stage compression system with an expansion valve as the baseline. A maximum pressure lift of 656 kPa could be provided. An optimum pressure control (OPC) strategy was proposed and could be used to instruct the practical application in order to maximize the cooling coefficient of performance (COP) at different operating conditions. The cooling COP of multi-ejector system could be improved by 30.69 % by adopting the OPC strategy compared with the baseline.
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