Experimental comparison on flat, wavy and louvered fins of vertical-finned microchannel heat exchangers

The drainage challenges of conventional microchannel heat exchangers under wet and frosting conditions severely limit their application in air-source heat pumps. This study introduces a vertical-finned microchannel heat exchanger (VMHX) design to facilitate the removal of condensate and melted water. An experimental comparative study is conducted to evaluate the thermal-hydraulic performance of three fin types (flat, wavy, and louvered) employed in the VMHX under dry, wet, and dynamic frosting-defrosting conditions. The results quantitatively reveal a significant tradeoff: while the louvered fin provides the highest heat transfer enhancement under dry and wet conditions (up to 13.35% and 10.71% improvement over the flat fin, respectively), it incurs a substantial pressure drop penalty (158% and 232% higher than that of the flat fin under dry and wet conditions, respectively). More critically, under frosting conditions, the louvered fin exhibits the most rapid performance decay owing to severe frost blockage, resulting in an average heat transfer rate that is 15.02% to 21.23% lower than that of the flat fin over multiple periods. In contrast, wavy and flat fins demonstrated superior and stable performance in frost-prone environments. This study concludes that the louvered fin is only recommended for applications that prioritize heat transfer under dry or high-velocity wet conditions, whereas flat or wavy fins offer a more robust and balanced solution for outdoor heat pump units where frosting is a concern. These findings provide valid data and guidelines for the fin selection and design of VMHXs.