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Thermodynamics HW Solutions 976

Thermodynamics HW Solutions 976 - Chapter 12 Radiation Heat...

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Unformatted text preview: Chapter 12 Radiation Heat Transfer 12-94E The circulating pump of a solar collector that consists of a horizontal tube and its glass cover fails. The equilibrium temperature of the tube is to be determined. D 2 =5 in Aluminum tube D 1 =2.5 in, T 1 ε 1 = 0.9 Air space 0.5 atm Plastic cover, ε 2 = 0.9, T 2 Water T ∞ = 75 ° F T sky = 60 ° F 30 Btu/h.ft Assumptions 1 Steady operating conditions exist. 2 The tube and its cover are isothermal. 3 Air is an ideal gas. 4 The surfaces are opaque, diffuse, and gray for infrared radiation. 5 The glass cover is transparent to solar radiation. Properties The properties of air should be evaluated at the average temperature. But we do not know the exit temperature of the air in the duct, and thus we cannot determine the bulk fluid and glass cover temperatures at this point, and thus we cannot evaluate the average temperatures. Therefore, we will assume the glass temperature to be 85 ° F, and use properties at an anticipated average temperature of (75+85)/2 =80°F (Table A-15E),...
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