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• A heat and mass transfer model of droplet for artificial snow-making was established. • The critical droplet size for artificial snow-making under different environments was obtained. • The relationship between gas-liquid mass mixing ratio and snow-making density was studied, and the optimal gas-liquid mass mixing ratio suitable for artificial snow-making was obtained. This study investigates the heat and mass transfer of liquid droplets freezing in the process of artificial snow-making, and emphatically analyses the effects of droplet size, ambient temperature and relative humidity on the evaporative cooling and freezing of liquid droplets by establishing a theoretical model. On this basis, the critical droplet size for snow-making under different environmental conditions is obtained, and the accuracy of the droplet freezing model was verified by artificial snow-making experiments. Finally, by analyzing the density of artificial snow under different environmental conditions, the optimum gas-liquid mixing mass ratio (GLR) suitable for snow-making is obtained. The results show that the liquid droplets could be frozen under the action of self-evaporation and convection heat transfer with ambient. The time required for the droplet to be frozen completely shows a positive correlation with ambient temperature, relative humidity and droplet size. In the evaporation cooling stage, the droplet cooling rate increases with the decrease of ambient temperature, and in the phase transition stage, the time for the droplet resists the latent heat of phase transition increases with the increase of the droplet size. When the droplet size is smaller than the critical size for snow-making, the artificial snow can be achieved at a maximum temperature of 3 °C. The snow density decreases with the increase of GLR. And when the GLR is greater than 0.15, the snow density tends to be stable. [ABSTRACT FROM AUTHOR]

Droplet evaporation on rough substrates is ubiquitous in nature and has numerous technological applications, such as coating. To study the evaporation characteristics of nanodroplets on substrates with different rough structures, molecular dynamics simulations have been performed. Based on the Wenzel wetting model, three systems with different rough structures were constructed, in which the ratios of contact area (RCA) between substrates and nanodroplets were 33.3%, 50%, and 66.6%, respectively. The results indicate that the evaporation pattern of the nanodroplet in the system with RCA = 33.3% is the mixed mode, the evaporation pattern of the nanodroplet in the system with RCA = 50% is the constant-contact-radius mode, and the evaporation pattern of the nanodroplet in the system with RCA = 66.6% is the constant-contact-angle mode. Meanwhile, when the temperature of substrates (T) is suddenly raised from 0.67 to 0.83 ε/kB, followed by a corresponding rise in the temperature of nanodroplets, we find that temperature and evaporation rates of the nanodroplets increase with the increase in RCA in this period. Changes in RCA that lead to the changes in substrate wettability affect the heat transfer between nanodroplets and substrates. In particular, the more the substrate wettability, the higher the heat transfer efficiency. Moreover, the wettability of the substrate in the systems with RCA = 50% and 66.6% promotes the heat and mass transfer in the three-phase contact line region of the nanodroplets during the evaporation process, while the non-wettability of the substrate in the system with RCA = 33.3% suppresses the local heat and mass transfer. This work offers further knowledge of droplet evaporation on rough substrates, which, in turn, provides a reference for the process optimization of its technological applications. [ABSTRACT FROM AUTHOR]