Chapter 12 Radiation Heat Transfer12-59 A coaxial radiation shield is placed between two coaxial cylinders which are maintained at uniform temperatures. The net rate of radiation heat transfer between the two cylinders is to be determined and compared with that 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= 0.7, ε2= 0.4. and ε3= 0.2. AnalysisThe surface areas of the cylinders and the shield per unit length are 233shield222outerpipe,211innerpipe,m942.0)m1)(m3.0(m314.0)m1)(m1.0(m628.0)m1)(m2.0(============ππLDAALDAALDAAThe net rate of radiation heat transfer between the two cylinders with a shield per unit length is W703=−++−++−−⋅×=−++−+−++−−=−)4.0)(942.0(4.01)1)(628.0(1)2.0)(628.0(2.012)1)(314.0(1)
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