Chapter 12 Radiation Heat Transfer12-51 A thin aluminum sheet is placed between two very large parallel plates that are maintained at uniform temperatures. The net rate of radiation heat transfer between the two plates is to be determined for the cases of with and without the shield. Assumptions1Steady operating conditions exist 2The surfaces are opaque, diffuse, and gray. 3Convection heat transfer is not considered.PropertiesThe emissivities of surfaces are given to be ε1= 0.5, ε2= 0.8, and ε3= 0.15. AnalysisThe net rate of radiation heat transfer with a thin aluminum shield per unit area of the plates is T2= 650 K ε2= 0.8 T1= 900 K ε1= 0.5 Radiation shieldε3= 0.15 2W/m1857=⎟⎠⎞⎜⎝⎛−++⎟⎠⎞⎜⎝⎛−+−⋅×=⎟⎟⎠⎞
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