Modification and extension of a standard volume-of-fluid solver for simulating boiling heat transfer

TLDR: In this article, the modifications and extensions of the Volume-of-Fluid solver in the OpenFOAM CFD package for the simulation of boiling flows are presented.

Abstract: In the present paper the modifications and extensions of the Volume-of-Fluid solver in the OpenFOAM CFD package for the simulation of boiling flows are presented. The main difficulties in the simulation of boiling flows are high temperature gradients at the liquid- vapor interface and microscopic heat and mass transfer at the 3-phase contact line. As the smeared interface in a pure Volume-of-Fluid method does not allow a precise reconstruction of the interface and thus hinders the accurate determination of the local temperature gradient, the solver is extended by a Level-Set method and a geometric reconstruction method. This facilitates an exact determination of the temperature gradient and of the local evaporation rate. In addition, the solver is extended by a sub-model for the microscale evaporation at the contact line which cannot be resolved on a CFD mesh. The sub-model is coupled to the simulation by adapting the thermal coupling between the solid heating wall and fluid domain. The modifications and the resulting model are validated by simulating phase change in a simple geometry and by simulating the heat and mass transfer during single bubble boiling. Further, the model is applied to perform a 3D simulation with adaptive mesh refinement of a lateral bubble merger. Very good qualitative and quantitative agreement with analytical approaches and experimental observations can be found.