Soln Conduction Heat Transf Exam Spring 2014 - 5 DLUT(cfw;tJ Midterm Exam Conduction Name ME 3345 Spring 2014 Time Allowed 55 minutes Hesketh Grade

Soln Conduction Heat Transf Exam Spring 2014 - 5...

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--------------------- --- 5 DLUT({/;tJ Midterm Exam Conduction ME 3345 Spring 2014 Hesketh Name: Time Allowed 55 minutes Grade: Question 1 (35 pts): 1cm epoxy ~...--.___________----,.. t =4.5mmt 100 A square electronic chip with dissipation of 5 W is attached to a circuit board, as shown in the figure above. Air flow provides convection heat transfer of 500 W Im2K and Tinfinity of 20°C. The thermal contact resistance between the chip and the board is R"tc 4 m2K1W. The thickness and thermal conductivity ofthe circuit board are 4.5 and 1 W/mK respectively. Convection from the back of the board is 100 W/m2K Tinfinity of20°C. Compute the following assuming radiation heat transfer can be neglected: (a) Sketch the thermal equivalent circuit and label all component values corresponding to steady-state conditions, (b) Calculate the chip temperature, (c) Ifthe maximum chip temperature allowable is 85°C, suggest how this can be achieved. ~= = 5xlO- mm and / / 1
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h" f{fc.- =- Jff~ = S-~/q:{P = 5"" If Jt7-~ ~ ~ ~F.f- h = S- jA/ /J = T& - 7;0_ Rt r£c-l-£-!c ~::::: It/ -- Z 0 + -r~ - :2 0 "- -------- 20' too+- ~S- ~S- I (.-L
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