I am doing a simulation on capillary driven evaporator to get its temperature profile, its a porous media so there has to be an effective thermal conductivity. Based on porosity, solid material conductivity and working fluid conductivity fluent is by default taking volume average effective thermal conductivity i.e.,

k_eff=k_s(1-porosity) + porosity(k_l)

but this is over predicting the value so I want to use some other correlation i.e.,

k-eff=k_l(k_l/k_s)^-(1-porosity)^(0.6)

but there is no option to input effective thermal conductivity so if I am making a UDF then how to implement it.

Please help me with the solution I am really struggling with the problem