Thermodynamics HW Solutions 211

Thermodynamics HW Solutions 211 - Chapter 15 Steady Heat...

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Chapter 15 Steady Heat Conduction 3-76 Hot water is flowing through a 3-m section of a cast iron pipe. The pipe is exposed to cold air and surfaces in the basement. The rate of heat loss from the hot water and the average velocity of the water in the pipe as it passes through the basement are to be determined. Assumptions 1 Heat transfer is steady since there is no indication of any change with time. 2 Heat transfer is one-dimensional since there is thermal symmetry about the center line and no variation in the axial direction. 3 Thermal properties are constant. Properties The thermal conductivity and emissivity of cast iron are given to be k = 52 W/m °C and ε = 0.7. Analysis The individual resistances are AD L L ii oo == = = ππ (. ( . ( . 0 04 15 1885 0 046 15 2168 m) m) m m) m) m 2 2 C/W 00003 . 0 ) m 15 ( C) W/m. 52 ( 2 ) 2 / 3 . 2 ln( 2 ) / ln( C/W 0044 . 0 ) m 885 . 1 ( C) . W/m 120 ( 1 1 1 1 2 2 2 ° = ° = = ° = ° = = L k r r R A h R pipe i i i R i R pipe R o T 1 T 2 The outer surface temperature of the pipe will be somewhat below the water temperature. Assuming the
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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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