DEVELOPMENT OF MASS-CONSERVATIVE PHASE-CHANGE MODEL FOR CONVECTIVE BOILING SIMULATIONS

A numerical method based on Computational Fluid Dynamics (CFD) has been developed to simulate convective nucleate boiling flows in laminar and turbulent flow regimes. A single set of Navier-Stokes equations is solved based on a staggered finite-volume algorithm on Cartesian grids using Smagorinsky model for sub-grid scale turbulence. A color function is used for the two-phase flow model with a local sharpening scheme [1] to prevent the smearing of the color function, and Brackbill's Continuum Surface Force (CSF) model [2] is used for the surface tension and the wall adhesion force. A sharp-interface mass-conservative phase change model [3], which can capture the velocity jump accurately, is used for the mass transfer model. A micro-region model developed by Stephan [4] is used to model the mass transfer at the vapor-liquid-solid triple point, and the mass transfer rate and the surface tension force in the micro-region is introduced to the Navier-Stokes solver. The developed scheme is validated against the experiments of convective boiling flows in the horizontal and vertical flow directions [5]. The validation cases considered in this paper are based on a single nucleation site and single bubble growth, in the same approach as Li and Dhir [6], and several assumptions are used for the initial and boundary conditions to complement the limited measured data. Thus, the comparison between the simulation and the experiment may not have the true meaning of validation, but the computed bubble liftoff diameter and time show agreement with experiments under the given conditions, and the applicability of the developed method to the simulation of convective boiling flows is demonstrated.