Condensation and frosting of a single fin with concave structure under inter-fin airflow

Uneven condensation and frosting buildup on heat pump fins impair thermal performance, obstruct air passage and increase defrosting power use. Relying on the novel concave structures on fin surfaces, an innovative method that induces nucleation behavior to regulate the spatial distribution of condensation and frosting was proposed. In this study, a closed-loop test rig with acrylic constrained narrow channels was constructed to create confined airflow between densely packed parallel heat exchanger fins. A visual measurement system continuously recorded the dynamic growth of condensed droplets and frost layers. The results show that concave structures effectively restrain local condensation and frosting and greatly improve the spatial distribution uniformity of droplets and frost. The maximum droplet size at the central linear concave structure is reduced by 82.8%, and the central frost thickness is decreased from 0.40 mm to 0.19 mm. Different concave geometries lead to varying degrees of condensation inhibition. In the 11th square, the linear concave structure reduces the droplet coverage rate by 74.7% relative to the plain fin, whereas the arc-shaped concave structure yields an 18.7% reduction. Meanwhile, the arc-shaped concave structure decreases the non-uniformity of droplet distribution by 41.8% compared with the linear concave structure. The above findings verify the effectiveness of the induced nucleation method based on concave features for regulating the spatial distribution of condensation and frosting. The present study offers useful implications for exploring intricate nucleation mechanisms of condensation and frosting, homogenizing the spatial distribution of surface moisture, and optimizing low-temperature heat harvesting techniques.