Experimental study on the distribution characteristics of condensation frosting and defrosting on a single vertical straight fin under constrained airflow conditions

Frost accumulation on heat exchanger surfaces remains a critical challenge for air-source heat pumps operating in cold climates. While extensive research has investigated the frost mechanisms of conventional finned tube heat exchangers, localized features of condensation frosting and defrosting kinetics on individual fin structures, especially vertical straight fins subjected to non-uniform airflows, remain under-explored. This study proposes a new experimental structure that uses transparent acrylic shielding instead of parallel fin to create a constrained airflow environment, making it easier to observe the condensation and frosting characteristics on the surface of the fin. The research results indicate that the condensation droplets on the surface of the fin along the direction of constrained airflow exhibit significant spatial distribution differences. At 20 min, the non-uniformity of the equivalent droplet size and coverage rate of the condensate droplets were 0.25 mm and 16.6%, respectively. Due to the lower temperature in the central area of the fin, a significant condensation aggregation effect is formed at this location. Due to the coupling effect of edge effects and changes in air humidity, the distribution of frost layer on the fin is W-shaped. The average thickness of the frost layer at the windward reinforcement rib decreased by 38.5% compared to the edge. The reduction rate of the coverage area of the fin frost layer during defrosting shows a trend of first increasing and then decreasing, with a maximum value of 10.21 mm²/s. The research results can provide theoretical basis for optimizing the fin structure and achieving uniform frosting.