PROBLEM 3.52KNOWN:Inner surface temperature of insulation blanket comprised of two semi-cylindrical shells of differentmaterials. Ambient air conditions.FIND:(a) Equivalent thermal circuit, (b) Total heat loss and material outer surface temperatures.SCHEMATIC:ASSUMPTIONS:(1) Steady-state conditions, (2) One-dimensional, radial conduction, (3) Infinite contactresistance between materials, (4) Constant properties.ANALYSIS:(a) The thermal circuit is,conv,Aconv,B2RR1/rhπʹʹ==()21cond AAln r / rRkʹ=<2icondBln r / rRkʹ=BThe conduction resistances follow from Section 3.3.1 and Eq. 3.28. Each resistance is larger by a factor of 2 thanthe result of Eq. 3.28 due to the reduced area.(b) Evaluating the thermal resistances and the heat rate ABq=qq,ʹ+( )12convR0.1m 25 W/mK 0.1273 m K/W−ʹ=××⋅=⋅cond Acond Bcond Aln 0.1m/0.05mR0.1103mK/WR8R0.8825mK/W2 W/m K
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