Exact Analysis Of Radiative And Conductive Heat Transfer Through Radiative Grey Films

A new method is introduced to calculate radiative heat transfer between two grey end plates with an arbitrary number of thin grey films in between. With this method it is also possible to do an almost exact analysis for coupled radiative and conductive heat transfer through one film between two grey end plates. It is almost exact for an arbitrary position of the film because the maximum deviation from the true heat flux can be evaluated exactly. There is one position of the film between the plates where the new method for coupled heat transfer is absolutely exact. This is where the heat flux is a minimum. This is a most interesting result for all heat insulating applications. The position for the minimum heat flow through more than one film can be determined exactly as well as the value of the heat flow itself. It has been shown by experiment that the method for radiative heat transfer can be applied not only to multifilm layers but also to PMMA foam or capillary structures. First experiments were in excellent agreement with theory.