Thermodynamics HW Solutions 234

Thermodynamics HW Solutions 234 - Chapter 15 Steady Heat...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 15 Steady Heat Conduction An D L A D AA A finned fin 2 unfinned 2 total,with fins finned unfinned 2 m) m) m m m == × = =− × = =+ = + = ηπ π ππ 0 957 864 0 0025 0 02 0130 00216 864 4 0 0216 864 00025 4 0 0174 0130 0 017 0147 22 .( . ( . . .. (. ) . . R hA conv total,with fins W/m . C) m C/W ° 11 50 0147 01361 (( . ) . RR R R R total board epoxy aluminum conv =++ + ++ = ° 0 00694 0 0051 0 00039 01361 01484 . Then the temperatures on the two sides of the circuit board becomes && ) . ) ( . . . Q TT R TT Q R Q R TTQ R = ⎯→ ⎯=+ = ° + ° = ⎯= = ° ° = −≅ ° 12 21 40 32 01484 405 0 00694 405 0 02 total total board board C W C / W ) W C / W ) 40.5 C 40.5 C 3-115 A circuit board houses 80 logic chips on one side, dissipating 0.04 W each through the back side 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 864 copper pin fins on the back surface. 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 back side of the board. 4 Heat transfer from the fin tips is
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.
Ask a homework question - tutors are online