Vertical-finned microchannel heat exchangers: Fin geometry effects on thermal–hydraulic performance under dry and frosting conditions

Abstract

Optimizing fin geometry is crucial for mitigating frost-related degradation of vertical-finned microchannel heat exchangers (VMHXs) in air-source heat pumps, yet trade-offs between dry, frosting, and drainage performance remain unclear. This study experimentally compares wavy/louvered fins (1.3 mm/1.5 mm spacings) under standard dry (35/24 °C) and frosting (2/1 °C) conditions. At Re$\approx$568 (dry), louvered fins enhance Colburn $j$-factor by 54.9% but double the friction factor, with 1.5 mm spacing showing higher thermo-hydraulic efficiency (PEC) than 1.3 mm. Under frosting (484 m³ h⁻¹), louvered fins achieve higher peak heat transfer (520.5 W vs. 500.7 W) but accumulate twice the total frost mass by cycle end, leading to faster performance decay. Wavy fins (1.3 mm) exhibit superior frost resilience, 45% shorter drainage time (107.4 s vs. 195.9 s), and 24% lower water retention. All tested configurations feature a hydrophilic coating and identical core dimensions. A climate-adaptive guideline is proposed: wavy fins (1.3 mm) for high-humidity/frost-prone regions, louvered fins (1.5 mm) for dry climates, and hybrid fins for mixed conditions. This work provides practical insights for optimizing VMHX energy efficiency and operational stability in next-generation HVAC systems.