Theoretical and experimental study of departure duration of condensate droplets from radiant cooling ceiling surfaces

In this paper, a mathematical model for predicting the departure duration of the first condensate droplet from a radiant ceiling surface was proposed on the basis of the condensation water mass. The simulation results indicate a dependence of condensation water mass on the apparent contact angle of the substrate, but almost in no relation with the surface temperature. The condensation water mass firstly increases with the increase of the apparent contact angle. It reaches a maximum weight of 522 g/m2 at an apparent contact angle of 110°, and then decreases. A visualization experiment of condensation on a radiant ceiling panel with a conventional aluminum alloy surface was performed in a climate chamber to measure the departure duration of the droplet. The measured departure duration fluctuates due to the variance of apparent contact angle and the randomness of condensation process, but it decreases sharply with the sub-cooled degree (air dew point minus surface temperature). And the average departure duration is 10 h with a sub-cooled degree of 5 °C. The theoretical model is validated as the average relative biases between the experimental and theoretical results are within 25%.