Yes, you can use the Richards equation in combination with Darcy's law to model the mold fill phase in COMSOL Multi-physics simulator. The Richards equation is a commonly used equation for simulating flow in porous media, and it accounts for the effects of capillary pressure and unsaturated flow.

To incorporate the Richards equation into your simulation, you can utilize the Subsurface Flow Module in COMSOL, which provides functionality for modeling flow in porous media. This module includes the Richards equation as one of the available physics interfaces.

By incorporating the Richards equation, you will be able to analyze flow and void formation at the mesoscopic and microscopic scales, in addition to the macroscopic voids detected using Darcy's law and the level set module. The Richards equation allows for the consideration of capillary effects and the movement of liquid within the porous structure, which can be important for capturing the behavior of fluid flow at finer scales.

In addition to the Richards equation, you may also consider incorporating other physics modules or features in COMSOL to study dual-scale flow phenomena. Some possible suggestions include:

Remember to carefully set up the simulation parameters, define appropriate material properties, and validate your model against experimental data or known results to ensure accurate and reliable simulation results.

Thank you for your response Ali Behrad Vakylabad .