Enhancement of Condensation Heat Transfer on Vertically Oriented Sintered Copper Powder Surfaces: an Experimental Investigation

The capillary structure within a heat pipe significantly influences the condensation heat transfer performance. In this study, an experimental setup was established under saturated atmospheric conditions to investigate the condensation behavior of water on vertically oriented sintered copper powder surfaces. The effects of subcooling, mesh count, and wick thickness on condensation mode, liquid coverage on the surface, and condensation heat transfer coefficient (HTC) were thoroughly investigated. Experimental results indicate that the surfaces of 100mesh copper powder wicks exhibit dropwise condensation, whereas those of 300-mesh wicks show filmwise condensation. On 200-mesh wick surfaces, both condensation modes are observed to coexist. As subcooling increases, the coverage ratio of liquid on the surface grows at different rates across the samples. For identical thickness and subcooling, larger mesh counts yield higher coverage ratios of liquid on the surface. Additionally, the sintered powder surfaces generally exhibit lower condensation HTC than smooth copper surfaces, with the degree of reduction varying under different subcooling conditions. Moreover, the variation in condensation HTC differs for different mesh counts as thickness changes. Droplet departure frequency also affects the condensation HTC differently for surfaces with different mesh counts. For surfaces with comparable mesh counts and thicknesses, sintered wire mesh and sintered copper powder wicks display varying HTCs under different subcooling conditions. Based on the experiments, a predictive correlation for the condensation HTC of vertically sintered copper powder porous structures is proposed, with an average MAE of 6.57 %. Compared to Nusselt's theory, the proposed correlation offers improved predictive accuracy for porous media condensation.