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We simulate the gas-atomization process of a close-coupled annular nozzle for vacuum induction gas atomization at a three-dimensional scale. Moreover, the relationship between the simulated droplet type and experimentally metallic powder is established by comparing the morphology of droplets with powders. Herein, the primary atomization process is described by the volume-of-fluid (VOF) approach, whereas the prediction of powder diameter after secondary atomization is realized by the VOF-Lagrangian method. In addition, to completely reflect the breaking and deformation process of the metallic flow, we employ the VOF model to simulate the secondary atomization process of a single ellipsoidal droplet. The results show that the primary atomization process includes the formation of surface liquid film, appearance of serrated ligaments, and shredding of ligaments. Further, gas recirculation zone plays an important role in formation of the umbrella-shaped liquid film. The secondary atomization process is divided into droplet convergence and dispersion stages, and the predicted powder diameter is basically consistent with the experiment. In general, the four main powder shapes are formed by the interaction of five different typical droplets.

In order to investigate the energy transfer mechanism and the nonequilibrium effect during water evaporation in its own pure vapor at low pressures, a series of precise measurements are conducted to obtain the temperature profile near the liquid−vapor interface and the evaporation rates in an annular pool in a closed chamber. The results show that the interface temperature of the vapor side is higher than that of the liquid side when water evaporates in its own pure vapor at low pressures (ranging from 394 to 1467 Pa), the temperature discontinuity across the interface exists in all experimental conditions. The magnitude of the temperature discontinuity is strongly affected by the vapor pressure. A uniform temperature layer with a thickness of about 2 mm is found below the evaporating interface because of the coupling effect of evaporation cooling and thermocapillary convection. The energy required for evaporation is mainly transferred by thermocapillary convection in the uniform temperature layer. Furthermore, the numerical simulation results confirm that the evaporation flux near the cylinders is much larger than that at the middle region, which implies that most of the latent heat required for evaporation is transferred to the interface near the cylinders.

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