Heat and mass transfer performance of wet air flowing around circular and elliptic tube in plate fin heat exchangers for air cooling

Fin and tube heat exchangers are widely used in air conditioning. In this study the effect of tube shape on air-side heat and mass performance was experimentally and numerically investigated under typical operating condition, varying both dry bulb temperature and air flow velocity. The experimental results showed that the dry-bulb temperature has little impact on sensible heat transfer rate, whereas the mass transfer rate increased with the increase of dry-bulb temperature. Compared with circular tube, the heat transfer coefficient of elliptic tube is about 66% higher and the dehumidifying coefficient is around 21% higher. However, the difference of the dehumidifying coefficient between two tube shapes shrinks towards equality when the dry bulb temperature reaches to 28 °C. To further discuss the heat transfer mechanism of circular and elliptic tube heat exchangers, three-dimensional numerical simulations were conducted based on the experiments. The results showed that the heat and mass transfer performance was closely related to the tube shape. When wet air flowed around elliptic tube, the streamline shape served to make the flow and temperature field uniform. The flow boundary layer as well as temperature boundary layer was thinned, especially on the upstream and downstream of tubes, so the influence of wake was reduced and the water vapor was efficiently removed. This results in improvement of the heat and mass transfer performance in the wake region of each tube. For the same heat duty, the plate fin heat exchanger with elliptic tube is more compact than that with circular tube.