Thermodynamics HW Solutions 30

# Thermodynamics HW Solutions 30 - radiation heat transfer...

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Chapter 1 Basics of Heat Transfer 1-71 The rate of radiation heat transfer between a person and the surrounding surfaces at specified temperatur es is to be determined in summer and in winter. Assumptions 1 Steady operating conditions exist. 2 Heat transfer by convection is not considered. 3 The person is completely surrounded by the interior surfaces of the room. 4 The surrounding surfaces are at a uniform temperature. Properties The emissivity of a person is given to be ε = 0.95 Analysis Noting that the person is completely enclosed by the surrounding surfaces, the net rates of
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Unformatted text preview: radiation heat transfer from the body to the surrounding walls, ceiling, and the floor in both cases are: ( a ) Summer: T surr = 23+273=296 W 84.2 = ]K K) (296 273) + )[(32 m )(1.6 .K W/m 10 67 . 5 )( 95 . ( ) ( 4 4 4 2 4 2 8 4 surr 4 rad − × = − = − T T A Q s s εσ & T surr Q rad ( b ) Winter: T surr = 12+273= 285 K W 177.2 = ]K K) (285 273) + )[(32 m )(1.6 .K W/m 10 67 . 5 )( 95 . ( ) ( 4 4 4 2 4 2 8 4 surr 4 rad − × = − = − T T A Q s s & Discussion Note that the radiation heat transfer from the person more than doubles in winter. 1-30...
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