An explicit expression of the empirical factor in a widely used phase change model

Many boiling problems have been simulated by a phase change model (Lee model) involving an empirical mass transfer intensity factor. It is challenge to determine the value of this factor. An explicit expression of the mass transfer intensity factor is derived, and the accuracy of the expression is validated by comparing simulation results with theoretical solutions for two benchmark problems. The influences of various fluid properties (liquid phase density and thermal conductivity, latent heat, saturation temperature, vapor phase density and thermal conductivity) and mesh size on the mass transfer intensity factor are discussed. Results demonstrate that the mass transfer intensity factor depends on density and thermal conductivity of liquid phase, latent heat, saturation temperature and mesh size, but is independent of the density and thermal conductivity of vapor phase. Effects of vapor density and thermal conductivity on the phase interface movement are taken into account by the temperature of the interfacial cell. The expression reveals that a constant value of the mass transfer intensity factor throughout the computational domain is not reasonable, and which is the reason for divergence issue. In a specific computational cell, the value of the mass transfer intensity factor depends on the volume fraction of the liquid phase, and extremely large value of the factor should be consistent with extremely small volume fraction of the liquid phase. (C) 2019 Elsevier Ltd. All rights reserved.