The steam-water separator is a vital important plant in the steam generator, whose function is to remove transported small droplets in the vapor stream and provide the high quality saturated steam for the steam turbine. The performance of the steam-water separator in the steam generator has a great impact on the safety and economy of the nuclear power station. The steam-water separation mechanism is far from maturity as a result of the complexity of the separator structure and the interaction of the steam, droplets together with the liquid film. Our research team tries to build a new research route about the steam-water separation mechanism from the microcosmic behavior aspects of the droplets including the production, movement, collision, extinction as well as the phase transformation. When the droplets move during the steam-water separator, the pressure could decrease continuously due to the resistance and the structure variation, which may break the liquid-vapor equilibrium and make the droplets evaporate and then could greatly influence the steam-water separating characteristics. This paper builds a hydrodynamic-kinetic model on the static droplets phase transformation under the pressure variation condition based on the physics phenomenon description of the droplets evaporation as well as the mechanism explanation. Through different kinds of calculations by change of the time step, the model has been proved to be independent on the time step. In order to make sure that the new model is correct, this paper compares the calculation results with the experimental ones and finds that the calculation results are in wonderful accordance with the existing experimental data. The relative errors between the calculation results and the experimental ones are between ± 5%. At last, this paper conducts the detailed sensitivity analysis of different relative parameters, which are useful for the understanding of the process of the droplets evaporation as well as could deepen the comprehension of the droplets phase transformation mechanism under the condition of the pressure change. The calculation results show that the evaporation characteristics of the static droplets under the pressure variation condition are predominantly influenced by the initial pressure, the ultimate pressure of the environment, as well as the difference of the initial and ultimate pressure. In addition, the initial radius of the droplets and the environment temperature can have a great impact on the droplets evaporation characteristics This model could provide the theoretical reference for further study of the process of the droplets phase transformation during transport in the steam-water separator as well as the steam-water separating performance of the separator, which can guide the design of the steam-water separation plants.

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