The behavior of droplets collision in a flash evaporation ambient widely exists in various fields. In this work, the deformation analysis and thermal analysis models were established under the condition of flash via a computational fluid dynamics (CFD) method. First, the effects of initial temperature and collision velocity on heat and mass transfer during evaporation were considered. Then, the morphology change of the liquid phase, the mass change, and their influencing factors during the droplet evaporation process were analyzed. A very good agreement is observed between the results of this paper and the published literature. The results show that the interaction between the initial collision velocity and the initial temperature affects the heat and mass transfer performance. The initial collision velocity influences the heat and mass transfer process of the evaporating droplet by affecting the deformation characteristics of the droplet. The collision velocity and the liquid temperature have a competitive relationship with the evaporation process. Under a low-initial temperature, the collision velocity played a leading role in the evaporation of the liquid phase and the mass transfer of steam.

Cavitation effect is the most common phenomenon in the process of jet. In this work, the method of CFD numerical simulation is used to study the cavitation behaviour in the process of single hole jet. In order to obtain the mixing situation and change process of gaseous water and liquid water produced in the nozzle, the Euler multiphase flow model and the realizable k-epsilon model in the turbulence model are used. The simulation results show that the degree and frequency of liquid column breakage of cavitation water jet are far higher than those of ordinary water jet. And the structure of the nozzle also has the most ideal situation. When the nozzle inlet size is 20 mm, the nozzle diameter is 1 mm, and the nozzle length is 5 mm, which is most conducive to the growth and diffusion of cavitation bubbles. The cavitation effect increases with the increase of the inlet jet velocity, but the promotion effect does not increase significantly when the inlet velocity is greater than 2.5 m/s. From the perspective of energy consumption, the optimum velocity at this time is 2.5 m/s. And the pressure environment at the nozzle outlet also affects the cavitation phenomenon, mainly as follows: positive pressure can inhibit the cavitation effect, negative pressure can promote the cavitation effect, but the negative pressure has a limited effect on the degree of cavitation.