Numerical investigation of the thermal-hydraulic performance of finned oblique-shaped tube heat exchanger

Plate fin and tube heat exchangers (FTHX) are widely used in HVAC applications due to the high effectiveness to cost ratio for heat transfer between two fluids. For air-cooled residential air conditioning unit applications, the overall efficiency of the unit is limited by the air-side heat transfer coefficient, which is much lower than that of the refrigerant-side. In this paper, oblique-shaped tube with the same tube area is introduced to replace the circular tube in FTHX to enhance the overall thermal-hydraulic performance of the air-side heat transfer. Numerical investigations of plain FTHX with circular tube, elliptic tube and oblique-shaped tube are conducted to analyze and compare the thermal-hydraulic performance. The results show that, although the heat transfer amount is comparable between the three finned tube designs, the pressure drop of the finned oblique-shaped tube is significantly lower by 53.6 - 58.7% than the finned circular tube at the same air inlet velocity. The oblique-shaped tubes have smaller frontal area and is streamlined, resulting in much smaller wake and lower flow velocity, thus significantly reducing the pressure loss. For a particular heat exchanger size and heat capacity, the fan power requirement for the finned oblique-shaped tube heat exchanger is the lowest.