A coarse grid approach for single bubble boiling simulations with the volume of fluid method

Abstract

Direct Numerical Simulation (DNS) of boiling flows requires a substantial number of grid points to precisely resolve the thermal boundary layer surrounding the phase interface. This resolution is vital for accurate calculation of the temperature gradient, which directly influences the mass transfer rate. However, the thermal boundary layer is typically three orders of magnitude smaller than the bubble's diameter, leading to an impractical number of required grid points for computational resources available on affordable PCs or workstations. To address this challenge and enable bubble-growth boiling flow simulations without relying on a supercomputer, we propose a novel numerical method within the framework of the Volume-Of-Fluid (VOF) approach. This method employs a coarse grid, where the grid size may exceed the thickness of the thermal boundary layer. By adopting this approach, we aim to achieve accurate simulation results while reducing the computational requirements associated with grid resolution. In our coarse grid approach, we model the thermal boundary layer and “artificially” maintain the interface temperature above the saturation temperature in the solution of the temperature field by incorporating a temperature-profile sharpening coefficient Ks. To validate the effectiveness of this approach, we conducted two validation cases: the Scriven bubble-growth problem and an experimental measurement of single bubble growth on a heated surface. Encouragingly, both cases showed good agreement with the simulation results. In the latter case, we introduced additional subgrid scale models, i.e., a microlayer model and a model of contact-angle hysteresis. These models enabled us to evaluate the bubble force balance accurately. The comprehensive approach described here represents an advancement in the development of sharp-interface phase-change simulation methods that can be applied to larger-scale problems and parametric investigations.