1. The problem statement, all variables and given/known data I am doing an assignment with multiple heat transfers, and have to investigate the effects of including thermal radiation vs saying that thermal radiation is negligible. I know that the equation for thermal radiation is q = A*σ*(T14 - T24) (*) In my case the equation is slightly more complicated since I am looking at concentric cylinders, but the equation itself is not what I am hung up on. 2. Relevant equations I know that radiation will occur between two black/grey bodies. If there are two metal plates near each others, and one is hot, the heat will radiate to the cold plate using the relationship above. What I am unsure of is whether thermal radiation occurs within a material itself. As in, should one apply eqn (*) in a scenario where there is only one metal plate, and one wants to look at the temperature difference across that individual plate. 3. The attempt at a solution I currently think that one does not account for radiation within a single material, as most of the literature/textbooks I have looked at describe thermal radiation between two black/grey bodies. I have not learned about thermal radiation in my classes though before, so I am not confident in making this assumption.