Carbon dioxide, refrigerated container, COP, ejector, microchannel heat exchanger
This paper describes the design and performance evaluation of a transcritical R744 (CO2) multi-temperature, mobile refrigerated container system. The efficient and widespread use of R744 in both large-scale supermarket refrigeration systems and small-scale glass-door merchandisers has been shown through numerous studies and field demonstrations in recent years, indicating the suitability of this refrigerant to almost any refrigeration application. However, the extreme operating conditions of this refrigeration application intended for use in ambient temperatures up to 57°C while still maintaining a frozen temperature of -20°C make using R744 as a refrigerant a unique challenge here. The targeted use of the refrigerated container is for military applications, but a successfully developed system will show that R744 is a suitable refrigerant for a range of container applications. In order to achieve reasonable efficiency at the extreme conditions of this application, several improvements have been implemented: Improved gas cooler performance with a microchannel heat exchanger, internal heat exchange, and expansion work recovery with an ejector. The benefits of each of these improvements are discussed, and preliminary results are presented to show the realistic performance enhancement that can be achieved with each of these improvements. The results presented in this paper show that while the very high ambient temperature of this system presents a unique challenge, it also allows for very significant COP improvement using each of the above improvements methods.