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A decline in natural snow due to global warming increases the reliance of ski resorts on artificial snow. To improve the formation rate and snow amount of artificial snow under any environmental conditions, it is necessary to use atomization technology that maintains the size of liquid drops of the snow-making spray field below a critical size, thus maximizing the number of freezing droplets into ice crystals. Here, we study the effects of the gas–liquid mass-mixing ratio (GLR) and the spacing (d) between two nozzles on the characteristics of the snow-making spray field produced by atomization technology for GLR of 0.05, 0.10, 0.15, and 0.2 and d of 5, 10, 15, and 20 cm. The measurement of the morphology, velocity, and particle-size distribution of the snow-making spray field is conducted by a laser particle-size measuring instrument, particle image velocimetry, and a high-speed camera. Our results show that both the spray cone and the intersection angles increase with the increase in the GLR in a two-nozzle arrangement, while the degree of interference between the nozzles increases with the decrease in spacing, d. We also find that the inward offset of the spray is the main reason for the increase in the intersection angle and the interference area and the deviation of the spray midline. In addition, we compare the characteristics of the spray field produced by the single and the two-nozzle systems. We conclude that the flow-field velocity of the single nozzle is smaller than that of the two nozzles and the velocity gradient of the liquid drops in the two-nozzle flow field varies greatly. The maximum vorticity (Max = 147) in the case of the two-nozzle arrangement is much larger than that of the single nozzle. Moreover, by analyzing the two-nozzle flow field at different spacings, we find that the particle-size distribution is most uniform for GLR = 0.10 and d = 15 cm. Thus, our study elucidates the characteristics of spray fields suitable for snow-making toward achieving higher quality and more efficient snow-making processes. [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]