Chapter 11 Fundamentals of Thermal Radiation 11-63 The absorber surface of a solar collector is exposed to solar and sky radiation. The equilibrium temperature of the absorber surface is to be determined if the backside of the plate is insulated. Insulation Air T∞= 25°C Tsky= 15°CAbsorber plate Ts= ? αs= 0.87 ε= 0.09 600 W/m2 PropertiesThe solar absorptivity and emissivity of the surface are given to αs= 0.87 and ε= 0.09. AnalysisThe backside of the absorbing plate is insulated (instead of being attached to water tubes), and thus &qnet=0αεσssolarsskysairGTThT=−+−()(44T)[ ]K346=−⋅+−⋅×=−sssTTTK)298)(KW/m10(K)288()()KW/m1067.5)(09.0()W/m600)(87.0(2444282Special Topic: Solar Heat Gain Through Windows 11-64C (a) The spectral distribution of solar radiation beyond the earth’s atmosphere resembles the energy emitted by a black body at 5982°C, with about 39 percent in the visible region (0.4 to 0.7 μm), and the 52 percent in the near infrared region (0.7 to 3.5 μm). (b) At a solar altitude of 41.8°
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