Abstract: A one-dimensional evaporation model for simulating water evaporation under vacuum condition is proposed by using Fick's diffusion law. Based on the correspondence between saturated water temperature and pressure, a method for determining the thickness of diffusion boundary layer is developed. An experimental system of water film low pressure heating and evaporation is set up. The vaporization and temperature variations of water film under different conditions are studied. By comparing the predicted results and experimental data for evaporation mass and temperature changes, it is found that the model accurately predicts the evaporation characteristics of water film under low pressure and heating conditions. Based on the current mathematical model, the effects of vacuum pressure, heating heat flux, and chamber volume on water evaporation rate and vapor pressure are further studied. The results indicate that the lower the pressure, the higher the heat flux, and the larger the chamber volume are, the higher evaporation rate is and the shorter time is needed to reach saturation.

Key words: Fick's law, evaporation model, film evaporation, evaporation rate, diffusion boundary