Thanks for the reply!
As shown in the image, I am getting walls 79, 80, and 81. The adjacent zones are-(1) Fluid-phase; (2) Solid-phase of porous medium, and (3) insulation respectively. So this seems physically correct.
However, I need to consider heat transferred from the wall to fluid and solid of porous medium distinctly, I am not sure how it would be done or handled by fluent!!
The heat conduction equation will be solved for the insulation zone, thus giving the wall temperature on the left side of insulation (say, T_ins_left). Now, this T_ins_left would be responsible for heat transfer at the interface of porous medium and insulation. Where the heat transfer source terms are added distinctly to the solid and fluid phases of the porous medium.

So, I need to assign different BCs to the insulation-solid_vessel and insulation-fluid_vessel.
Any help would be greatly appreciated.