Thermodynamics HW Solutions 46

Thermodynamics HW Solutions 46 - ( a ) T surr = 300 K W...

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Chapter 1 Basics of Heat Transfer 1-91 A person with a specified surface temperature is subjected to radiation heat transfer in a room at specified wall temperatures. The rate of radiation heat loss from the person is to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer by convection is disregarded. 3 The emissivity of the person is constant and uniform over the exposed surface. Properties The average emissivity of the person is given to be 0.7. Analysis Noting that the person is completely enclosed by the surrounding surfaces, the net rates of radiation heat transfer from the body to the surrounding walls, ceiling, and the floor in both cases are
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Unformatted text preview: ( a ) T surr = 300 K W 37.4 = ]K K) (300 273) + )[(32 m )(1.7 .K W/m 10 67 . 5 )( 7 . ( ) ( 4 4 4 2 4 2 8 4 surr 4 rad = = T T A Q s s & ( b ) T surr = 280 K W 169 = ]K K) (280 273) + )[(32 m )(1.7 .K W/m 10 67 . 5 )( 7 . ( ) ( 4 4 4 2 4 2 8 4 surr 4 rad = = T T A Q s s & Discussion Note that the radiation heat transfer goes up by more than 4 times T surr Q rad 32 C as the temperature of the surrounding surfaces drops from 300 K to 280 K. 1-46...
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