Thermodynamics HW Solutions 166

Thermodynamics HW Solutions 166 - bottom of the pan are to...

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Chapter 3 Steady Heat Conduction 3-26 A person is dissipating heat at a rate of 150 W by natural convection and radiation to the surrounding air and surfaces. For a given deep body temperature, the outer skin temperature is to be determined. Assumptions 1 Steady operating conditions exist. 2 The heat transfer coefficient is constant and uniform over the entire exposed surface of the person. 3 The surrounding surfaces are at the same temperature as the indoor air temperature. 4 Heat generation within the 0.5-cm thick outer layer of the tissue is negligible. Q rad T skin Q conv Properties The thermal conductivity of the tissue near the skin is given to be k = 0.3 W/m °C. Analysis The skin temperature can be determined directly from C 35.5 ° = ° ° = = = ) m C)(1.7 W/m. 3 . 0 ( m) 005 . 0 W)( 150 ( C 37 2 1 1 kA L Q T T L T T kA Q skin skin 3-27 Heat is transferred steadily to the boiling water in an aluminum pan. The inner surface temperature of the bottom of the pan is given. The boiling heat transfer coefficient and the outer surface temperature of the
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Unformatted text preview: bottom of the pan are to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer is one-dimensional since the thickness of the bottom of the pan is small relative to its diameter. 3 The thermal conductivity of the pan is constant. Properties The thermal conductivity of the aluminum pan is given to be k = 237 W/m ⋅ °C. Analysis ( a ) The boiling heat transfer coefficient is 95 ° C 108 ° C 600 W 0.5 cm 2 2 2 m 0491 . 4 m) 25 . ( 4 = = = π D A s C . W/m 1254 2 ° = ° − = − = − = ∞ ∞ C ) 95 108 )( m 0491 . ( W 800 ) ( ) ( 2 T T A Q h T T hA Q s s s s & & ( b ) The outer surface temperature of the bottom of the pan is C 108.3 ° = ° ° = + = − = ) m C)(0.0491 W/m. 237 ( m) 005 . W)( 800 ( + C 108 2 1 , , , , kA L Q T T L T T kA Q inner s outer s inner s outer s & & 3-9...
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This note was uploaded on 01/14/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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