Measured and Predicted Effects of Air Flow Non-Uniformity on Thermal Performance of an R-134a Evaporator

Tests have been carried out over a wide range of operating conditions on a single circuit plate-finned tube type of refrigerant evaporator, exchanging heat between ambient air and refrigerant R134a. Uniform and non-uniform air flow distributions were applied with the objective of studying the effects of non-uniformity on heat transfer.

The experimental results revealed that, for a given total volume flow of air, heat transfer performances could be up to 15% better with a non-uniform flow where turbulence levels were also high.

Extensive comparisons were also made between these measurements and predictions from a computer model. This was designed to simulate the thermal behavior of cross-flow heat exchangers on a tube segment-by-segment basis, allowing for flow non-uniformity. Predictions were found to match measurements satisfactorily for test cases involving uniform air flows and a relatively large temperature difference between fluids. In contrast to the measured trends, the simulation results predicted a degradation in heat transfer performance for non-uniform air flow cases.