Contribution of internal heat exchanger to transcritical R-744 cycle performance

This paper presents results of 178 experiments evaluating the effects of in ternal heat exchange (IHX) on the performance of a well-instrumented protot ype transcritical mobile air-conditioning system using R-744 (carbon dioxid e) as the refrigerant. The effect on cycle efficiency is substantial, up to 25%, because of the relatively high irreversibility at the expansion devic e in the standard transcritical cycle. Three coaxial internal hear exchange rs of various lengths, having identical cross sections, were used in the ex periments in both parallel and counterflow configurations. These data were used to develop a simulation model that predicted accurately the IHX perfor mance. Finally the model was used to develop an optimal design for a COP-ma ximizing IHX, which reduces material requirements by 50% while increasing e ffectiveness by 10%. The cycle optimization was guided by the trade-off bet ween heat exchanger effectiveness and suction pressure drop.