CFD applied to heat pump system design

The effect of nonuniform airflow distribution on the thermal performance of tube-fin heat exchangers in typical outdoor units of residential air-conditioning and heat pump systems is investigated numerically. The impact of the flow nonuniformity on the pressure drop and fan-motor power requirement is also investigated. Two fin types have been investigated, smooth fins and louvered fins. A three-dimensional model was developed to predict the airflow distribution over the face of the heat exchanger. It was found that the effect of the flow maldistribution is more pronounced on the airside pressure drop and the fan power requirement than on the thermal performance of the heat exchanger. The mass-averaged pressure drop for the nonuniform flow was found to be 9% and 8% more than the pressure drop for a uniform flow distribution, using smooth fins and louvered fins, respectively. The increase in pressure drop results in a proportional increase in the fan-motor power consumption. The area-averaged heat transfer coefficient for the nonuniform flow was found to be 1.5% and 0.9% less than that predicted based on a uniform velocity distribution, using smooth fins and louvered fins, respectively. The predicted decrease in the heat transfer coefficient directly impacts the heat exchanger capacity.