Freezing characteristics of deposited water droplets on hydrophilic and hydrophobic cold surfaces

Freezing phenomena of water droplets on metal surfaces widely exist in nature and industry. While the freezing of a sessile water droplet has been extensively studied, here we report an experimental and thoeritical investigation of the freezing characteristics of a deposited water droplet on cold hydrophilic and hydrophobic aluminum surfaces and also compare them with those of the sessile droplet. The results show that the deposited droplet starts to freeze from the liquid-solid interface after the spreading contact line is arrested by the cold surface and the recalescence stage observed during the freezing of a (supercooled) sessile water droplet does not appear. Furthermore, under our experimental conditions of surface temperature and wettability, the frozen shapes of the deposited droplets on the hydrophilic and hydrophobic surfaces are only dependent on the surface temperature while those of the sessile droplets unnoticeably change with the surface temperature but significantly vary with the surface wettability. Additionally, we present a scaling analysis to describe the temporal evolution of freezing front and the relationship between freezing time and surface temperature for the deposited droplet.