Experimental study of dew formation on metal radiant panels

•Experiments were conducted to analyze the dew formation on radiant panels.•The time from condensate nucleating to falling off radiant panels was measured.•Dew formation is an extremely slow process at low sub-cooled degrees.•Hydrophobic surfaces have a delaying effect on the dew formation on radiant panels.•The size of the droplet falling off decreases as the contact angle increases. The risk of condensation on radiant cooling panels used in hot and humid regions has limited their application and broad adoption in the market. This paper describes an experimental study of dew formation on metal radiant panels. Two metal radiant panels with hydrophobic and untreated aluminum alloy surfaces were prepared for investigation and a constant temperature and humidity environmental chamber was employed to simulate the various indoor thermal environments. The results indicate that sub-cooled degrees had a significant effect on the elapsed time from the condensate nucleating to falling off the horizontal radiant panels, which was over 10h at a sub-cooled degree less than 3°C. In addition, the hydrophobic surface demonstrated a delaying effect on the dew formation on the radiant panels. The feature size of the critical pendant droplet falling off the hydrophobic surface (with a contact angle of 96.7°) was 5.6mm, while that of the untreated aluminum alloy surface (with a contact angle of 66.1°) was 7.3mm. Furthermore, simulation results show that the feather size of the critical pendant droplet falling off the horizontal surface decreases as the contact angle increases. Based on these results, hydrophobic surfaces represent a promising new method for limiting condensation on radiant panels.