Thermodynamics HW Solutions 275

Thermodynamics HW Solutions 275 - Chapter 3 Steady Heat...

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Chapter 3 Steady Heat Conduction Then the temperatures on both sides of the board are determined using the thermal resistance network to be R L kA R L kA aluminum epoxy m W / m. C) m m) C/W m W / m. C) m m) == ° ° 0001 237 01 015 0 00028 0 00015 18 0 00555 . (( . ) ( . . . (. ) . C 39.6 C 39.8 ° = ° ° = = ⎯→ = ° = ° + ° = ° + + ° = + + = C/W) W)(0.011 (15 C 8 . 39 C/W) W)(0.0168 (15 C 5 . 39 C/W ) 011 . 0 00555 . 0 00028 . 0 ( C ) 5 . 39 ( board 1 2 board 2 1 1 1 board epoxy aluminum base 1 R Q T T R T T Q T T R R R T T Q & & & 3-165 A circuit board houses electronic components on one side, dissipating a total of 15 W through the backside of the board to the surrounding medium. The temperatures on the two sides of the circuit board are to be determined for the cases of no fins and 20 copper fins of rectangular profile on the backside. Assumptions 1 Steady operating conditions exist. 2 The temperature in the board and along the fins varies in one direction only (normal to the board). 3 All the heat generated in the chips is conducted across the circuit board, and is dissipated from the backside of the board. 4 Heat transfer from the fin tips is negligible. 5 The heat transfer coefficient is constant and uniform over the entire fin surface.
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