Thermodynamics HW Solutions 235

Thermodynamics HW Solutions 235 - Chapter 15 Steady Heat...

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Chapter 15 Steady Heat Conduction && (. ) .( . ) ( . . . Q TT R TT Q R Q R TTQ R = ⎯→ ⎯=+ = ° + ° = ⎯= = ° ° = −≅ ° 12 21 40 32 0 93284 430 0 00694 405 0 02 total total board board C W C / W ) W C / W ) 43.0 C 43.0 C Therefore, the board is nearly isothermal. ( b ) Noting that the cross-sectional areas of the fins are constant, the efficiency of the circular fins can be determined to be a hp kA hD kD h kD c == = = ° ° = π 2 4 44 5 0 386 0 0025 14 40 / () ( . ) . W/m . C W/m. C m m 2 -1 η fin -1 -1 m m m × × = tanh tanh( . . ) .. . aL aL 14 40 0 02 14 40 0 02 0973 The fins can be assumed to be at base temperature provided that the fin area is modified by multiplying it by 0.973. Then the various thermal resistances are R L kA epoxy 2 m W/m. C) m C/W ° 0 0002 18 0 0216 0 0051 . ) . R L kA copper 2 m m ° 0002 386 0 0216 0 00024 . (( . ) . An D L A D AA A finned fin 2 unfinned 2 total,with fins finned unfinned 2 m) m) m m m × = =− × = =+ = + = ηπ ππ 0 973 864 0 0025 0 02 0132 00216 864
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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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