Thermodynamics HW Solutions 184

Thermodynamics HW Solutions 184 - Chapter 15 Steady Heat...

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Chapter 15 Steady Heat Conduction 3-52 A wall consists of horizontal bricks separated by plaster layers. There are also plaster layers on each side of the wall, and a rigid foam on the inner side of the wall. The rate of heat transfer through the wall is 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 by radiation is disregarded. Properties The thermal conductivities are given to be k = 0.72 W/m °C for bricks, k = 0.22 W/m °C for plaster layers, and k = 0.026 W/m °C for the rigid foam. Analysis We consider 1 m deep and 0.33 m high portion of wall which is representative of the entire wall. The thermal resistance network and individual resistances are R 2 R 3 R 4 R 5 R 6 R 7 T 2 R R i T 1 RR hA L kA RRR L kA L ic o n v foam plaster side plaster center o == = °× = = = = = = , (( . ) . . (. ) . . ) . .
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