Contribution of internal heat exchanger to transcritical R744 cycle performance.

The paper presents results of 178 experiments evaluating the effects of internal heat exchange on the performance of a well-instrumented prototype transcritical mobile air-conditioning system using R744 (carbon dioxide) as the refrigerant. The effect on cycle efficiency is substantial, up to 25%, because of the relatively high irreversibility at the expansion device in the standard transcritical cycle. The test data were used to develop a simulation model. Finally the model was used to develop an optimal design reducing material requirements by 50% while increasing effectiveness by 10%. The cycle optimization was guided by the trade-off between heat exchanger effectiveness and suction pressure drop.