Experimental Study on Sessile Droplet Freezing on a Cold Surface in Low Atmospheric Pressure

A visualization system is introduced to experimentally investigate the droplet freezing process under the influence of atmospheric pressure on a cold aluminum surface. The morphology and temperature evolution during droplet freezing process as well as the impact of wall temperature and droplet volume are analyzed and discussed under the low atmospheric pressure based on the current visualization system. The experiment results manifest that the droplet freezing process is significantly affected by the atmospheric pressure. The droplet freezing process undergoes five stages: the pre-cooling stage, the sub-cooling stage, the nucleation stage, the freezing and cooling stage, and the stable stage. The droplet temperature dramatically rises at the nucleation stage due to the release of latent heat and rapidly decreases at the freezing and cooling stage. The droplet freezing time decreases with the reduction of the atmospheric pressure. When the atmospheric pressure decreases to 0.1 bar, the droplet freezing temperature increases significantly. Under the low atmospheric pressure, the droplet freezing time decreases with the decrease of surface temperature and the increase of droplet volume.