Applying high-emissivity paints to radiating surfaces is a common technique used to enhance heat transfer by radiation.

(a) For large parallel plates, determine the radiation heat flux across the gap when the surfaces are at T1 = 350 K, T2 = 300 K, s1 = s2 = ss = 0.85.

(b) Determine the radiation heat flux when a very thin layer of high-emissivity paint, sp = 0.98, is applied to both surfaces.

Determine the radiation heat flux when the paint layers are each L = 2 mm thick and the thermal conductivity of the paint is k = 0.21 W/m · K.

(d) Plot the heat flux across the gap for the bare sur- face as a function of ss, with 0.05 ss 0.95. Show on the same plot the heat flux for the painted surface with very thin paint layers and the painted surface with L = 2-mm-thick paint layers.