Development of a Numerical Solver for Phase-Change and Two-Phase Flow in Porous Media
Porous media are used in several thermal management systems, such as loop-heat-pipes, to control the temperature of electronics and other components. It is important to understand the mechanisms of flow and phase-change in porous media to better control/increase the performance of those systems. In this work, we develop a CFD solver using the object-oriented OpenFOAM architecture that can simulate most of the relevant physics of flow and phase-change in porous media. The developed solver is based on an existing solver based on the IMPES (Implicit Pressure, Explicit Saturations) method, which is employed to solve the pressure and saturation equations due to the nonlinearity of the capillary and relative permeability equations. The solver is then modified to include the energy equation and phase-change models (empirical and interface equilibrium models) that can simulate temperature and phase-change, respectively. Hydrodynamic and thermal coupling of flow and phase-change in porous media is complex numerically, and, this complexity is achieved in the present study by coupling between all the governing equations and the phase-change models using the VOF (Volume of Fluid) approach. Different effective thermal conductivity models are implemented to calculate an effective thermal conductivity between the three phases (solid, liquid, and vapor) in every cell. The solver also uses temperature-dependent properties for density, thermal conductivity, and viscosity. The results obtained from this solver are compared with a one-dimension semi-analytical solution to validate the solver. An example of flow and phase-change in a section of the porous media of a loop heat pipe (LHP) is also presented.
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