Numerical investigation of thermal and hydraulic performance of fin and flat tube heat exchanger with various aspect ratios

Abstract

Thermal and hydraulic performance for laminar flow over a fin and flat tube heat exchanger with various aspect ratios studied numerically. The parameters studied were inlet air velocity and flat-tube aspect ratio. The inlet air velocity was changed within the range of 0.5–3.5 m/s, and the aspect ratio of the flat-tubes has been changed in the range of 0.33–1. To do this study, a three-dimensional numerical model was implemented to investigate the airside performance using the commercial CFD software ANSYS FLUENT 17.2. The numerical model consists of 4 tubes in a staggered arrangement, to simulate a dry cooling process in a heat exchanger. The numerical model has been validated by comparing the pressure drop and the heat transfer coefficient with the experimental published data. A good agreement was observed between the present and experimental published data. In the current study, pressure drop (ΔP), heat transfer coefficient (h), area goodness factor (j/f), and heat transfer per unit fan power (Q/Pf) were determined and illustrated graphically. The results indicated that the flat-tube aspect ratio has a significant effect on the pressure drop and the heat transfer per unit fan power. Decreasing the flat tube aspect ratio from 1 (circular tube) to 0.33 the pressure drop reduced by 33.7% and 57.3% with an air inlet velocity of 0.5 and 3.5 m/s respectively. Also, decreasing the flat tube aspect ratio from 1 to 0.33, the Q/Pf is enhanced by 52.9% and 111.5% with an air inlet velocity of 0.5 and 3.5 m/s respectively. Finally, it is concluded that the flat-tube with the lowest aspect ratio has the highest overall performance of the heat exchanger, and thus it is recommended to reduce the energy consumption.