Numerical analysis on heat transfer enhancement of wavy fin-tube heat exchangers for air-conditioning applications

Abstract

• Heat transfer enhancement at constant pumping power fits closest to real scenarios. • Larger HTC does not necessarily lead to larger heat transfer rate. • Waffle height, wave length, and fin pitch should be optimized simultaneously. • The optimized geometries yield 23% improvement of HTC and 3% of heat transfer rate. • Proper Perforation on wavy fin leads to 34% enhancement of HTC. The air-side heat transfer performance of herringbone wavy fin-tube heat exchangers can be improved by optimizing fin geometries and introducing perforations to the wavy fin. Based on a typical herringbone wavy fin-tube heat exchanger used in the outdoor unit of an air conditioner with collar outside diameter of 7.3 mm, transverse tube pitch of 22 mm, and longitudinal tube pitch of 19.05 mm, the effects of fin pitch, wave length, slits height, and geometries of slits are simulated using CFD and the outcomes are discussed in the paper. We demonstrate that constant pumping power is the ideal criterion for the performance evaluation of any new designs. The wave length has no remarkable effects on the heat transfer coefficient while the lowest pressure drop appears with the symmetric wave configuration. The heat transfer coefficient can be improved by 23.4% when the waffle height, fin pitch, and wave length are simultaneously optimized. Furthermore, punching slits on top of the windward part of wavy fins leads to a 5.5% increase in the heat transfer coefficient. In the end, 34.2% improvement of the heat transfer coefficient is yielded when combining the slit perforations to the optimum fin pitch, wave length, and waffle height.