Experimental study of condensation on mesh-covered surfaces

Condensation is a crucial factor affecting the thermal performance of various types of heat pipes, with the porous wick structure playing a significant role in condensation. In this study, an experimental platform was set up in a saturated atmosphere to investigate the condensation process of steam on a vertical plane surface with sintered copper screen. The effects of subcooling, mesh number, layer, and screen structure on condensation mode, droplet departure diameter, and heat transfer coefficient (HTC) were explored. The results indicate that the condensation mode of the screen is different from that of the smooth copper surface, with the screen exhibiting a rivulet mode, whereas the smooth copper surface shows a dropwise mode. Sintering pressure affects the condensation mode of a single layer of 300-mesh screen but has minimal effect on the HTC. As subcooling increases, the droplet departure diameter on the screen surface also increases. The HTC of the screen is lower than that of the smooth copper surface, with reduction varying depending on the mesh number. The effect of the layer number of screen on the HTC varies with the mesh number. The thermal resistance of condensation in the vertical orientation is not linearly related to the layer number of screen, which contrasts with the conventional thermal resistance theory. Gradient screens appear to have a minimal impact on the HTC. This study proposes an empirical formula to predict the HTC suitable for vertical mesh-covered surfaces, with an average absolute error of 13.07%, significantly improving the thermal design accuracy of heat pipes compared to conventional heat resistance theories.