Chapter 3 Steady Heat Conduction3-29 The roof of a house with a gas furnace consists of 3-cm thick concrete that is losing heat to the outdoors by radiation and convection. The rate of heat transfer through the roof and the money lost through the roof that night during a 14 hour period are to be determined. Assumptions1Steady operating conditions exist. 2 The emissivity and thermal conductivity of the roof are constant. PropertiesThe thermal conductivity of the concrete is given to be k = 2 W/m⋅°C. The emissivity of both surfaces of the roof is given to be 0.9. Q&Tsky= 100 K Tair=10°C Tin=20°C L=15 cmAnalysis When the surrounding surface temperature is different than the ambient temperature, the thermal resistances network approach becomes cumbersome in problems that involve radiation. Therefore, we will use a different but intuitive approach.In steady operation, heat transfer from the room to the roof (by convection and radiation) must be equal to the heat
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