There is no energy equation for the solid phase when porous domain is defined. The only way to simulate the energy transfer between the solid and the fluid phase of the porous media flow is to define an additional variable (AV), which will represent enthalpy or energy of the solid phase. For heat in a solid, one needs to select a 'Diffusion Transport Equation' under 'Fluid Models', and define a Kinematic diffusivity for this diffusion equation.

To calculate effective thermal conductivity, specify the following expression

K_eff=(void fraction)*(a_fluid*rho_fluid*Cp_fluid)+(1-(void fraction))*(a_solid*rho_solid*Cp_solid)

(where 'a' is a kinematic diffusivity). Usually, fluid thermal conductivity is known, therefore

K_eff=(void fraction)*k_fluid+(1-(void fraction))*(a_solid*rho_solid*Cp_solid)