DESIGN AND INTEGRATION OF CO_2 GAS COOLER/CONDENSER IN A REFRIGERATION SYSTEM

摘要

As a natural working fluid, CO_2 is being used in many refrigeration and heat pump applications. Owing to its good thermophysical properties, especially its low critical temperature, heat rejection to the ambient air from the CO_2 system will take place either subcritically or supercritically, depending on the ambient air temperature and 'head' pressure control employed. The heat rejection heat exchanger will act as either a gas cooler or condenser and this should be taken into consideration in the optimal design of the heat exchanger and head pressure controls for optimal operation. Models of finned-tube CO_2 gas coolers/condensers have been developed using both the distributed (detailed model) and lumped parameter (simple model) approaches. The former has been employed to give a detailed prediction of the working fluid temperature profiles, localised heat transfer rates and effect of pipe circuitry arrangements, while the latter has been used within an overall CO_2 system model for the simulation and optimisation of the system. Both models have been validated against measurements on a specially designed gas cooler test facility. Two different gas cooler/condensers have been used for the evaluation. The validated models have been used to study the effects of CO_2 gas cooler/condenser size and controls on overall CO_2 system performance.