Modelling the performance of a new cooling unit for refrigerated transport using carbon dioxide as the refrigerant

Abstract

• Development of a dynamic numerical model of a CO 2 cooling unit. • 3 layouts, including a back-pressure valve, ejector and auxiliary evaporator. • The ejector can give a COP increase of +15.9% at T amb = 42 °C, T i = −5 °C. • The auxiliary evaporator can extend the operating range of the ejector to lower T amb . • The auxiliary evaporator gives a max COP increase of 21.0% for T amb = 25 °C, T i = 5 °C. This paper provides a theoretical assessment of the thermal performance of a new CO 2 vapour-compression system for refrigerated transport applications. Three different configurations are investigated: the standard back-pressure with low pressure receiver lay-out and two arrangements integrating a two-phase ejector. In particular, the use of an auxiliary evaporator in the outlet line of the ejector is considered, to extend the ejector operating range. A numerical model of the system is developed and its theoretical performance is discussed for different values of internal space temperature and external ambient temperature. Simulations’ results show that the ejector cycle configuration is convenient when the system is operating in a hot climate with a maximum COP increase (compared to the traditional configuration) equal to 15.9%, at 42 °C ambient temperature and -5 °C internal space temperature. The use of an auxiliary evaporator can extend the operating range of the ejector to lower values of ambient temperature, with a maximum COP improvement (over the traditional configuration) equal to 21.0% at 25 °C ambient temperature and 5 °C internal cargo space.