Hello John,nThank you for the reply.n Regarding the point 1B in your reply, if I specify heat flux/temperature at the bottom wall, then the effect is not because of external radiation, but now thermal energy will be involved, which is not the case. So for eg. IR radiation through the wall because of an external thermal source is different from defining heater temperature at the wall itself, because then the temperature of the wall will also change, and not just the emitted radiation. nI came across External Radiation Temperature under radiation section of thermal boundary conditions. According to some discussions like this, I believe I can define External emissivity and External radiation temperature corresponding to the IR source (i.e. heater in my case), directly at the bottom wall to replicate the effect of the radiation through the wall. What do you think?nRegarding the second point, I figured out I can define the absorption and relaxation as the function of the source term. For eg. I can have a sinusoid or a square wave form of the source term, which will correspond to the absorption and relaxation time in the system.nBest Regards,nAnanyann