Thermodynamics HW Solutions 188

Thermodynamics HW Solutions 188 - Chapter 15 Steady Heat...

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Chapter 15 Steady Heat Conduction 3-55 A wall is constructed of two layers of sheetrock spaced by 5 cm × 12 cm wood studs. The space between the studs is filled with fiberglass insulation. The thermal resistance of the wall and the rate of heat transfer through the wall are to be determined. Assumptions 1 Heat transfer is steady since there is no indication of change with time. 2 Heat transfer through the wall is one-dimensional. 3 Thermal conductivities are constant. 4 Heat transfer coefficients account for the radiation heat transfer. Properties The thermal conductivities are given to be k = 0.17 W/m °C for sheetrock, k = 0.11 W/m °C for wood studs, and k = 0.034 W/m °C for fiberglass insulation. Analysis ( a ) The representative surface area is A = × = 10 6 5 0 6 5 .. m 2 . The thermal resistance network and the individual thermal resistances are T 1 R 1 R i R 2 R 3 R 5 R 4 T 2 W 15 . 5 C/W 858 . 4
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