The spectral absorptivity of aluminum coated with a thin layer of silicon dioxide may be approximated as aA,1 = 0.98 for A Ac and aA,2 = 0.05 for A > Ac where the cutoff wavelength is Ac = 0.15 µ,m under normal circumstances.
(a) Determine the equilibrium temperature of a flat piece of the coated aluminum that is exposed to solar irradiation, GS = 1368 W/m2 on its upper surface. The opposite surface is insulated.
(b) The cutoff wavelength can be modified by varying the coating thickness. Determine the value of Ac that will maximize the equilibrium tempera- ture of the surface.