Chapter 3 Steady Heat Conduction(b) The total thermal resistance with the fiberglass insulation is C)W.m/6048.0(C/W02253.0)mC)(16.8W/m.036.0(C/W02253.0424conv,2glassfiber 321total°+°=°+°=++++=LLRRRRRRThe thickness of insulation is determined from cm7.7m0.077==⎯→⎯°+°°−=⎯→⎯−=∞44total21insCW.m/6048.0(C/W02253.0C)823(W9.99LLRTTQ&The outer surface temperature of the wall is determined from C8.3°=⎯→⎯°°−=⎯→⎯−=∞22conv22insC/W00350.0C)8(9.99TTRTTQ&DiscussionThe outer surface temperature is same for both cases since the rate of heat transfer does not change. 3-170Cold conditioned air is flowing inside a duct of square cross-section. The maximum length of the duct for a specified temperature increase in the duct is to be determined. Assumptions1Heat transfer is steady. 2 Heat transfer is one-dimensional. 3 Thermal conductivities are constant. 4Steady one-dimensional heat conduction relations can be used due to small thickness of the duct wall.
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