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exam3_sol - ME 410 Name Spring 2008 Exam 3 Exam is open...

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ME 410 Spring 2008 Name Exam 3 Exam is open notes, open book. Problems have indicated point value. Problem 1 (50 pts) The sides of an electronics package are rectangular aluminum plates 70 cm wide and 40 cm high and act as a heat sink for the contents. The plate temperature must not exceed 340 K. If air at 300 K is blown upward over the plates at 1 m/s, estimate the power each plate dissipates by convective heat transfer. 0.7 m 0.4 m q 1 m/s T =300 K, T s =340 K, L = 0.4m Properties of Air taken at T f =320K ~ 325 K Pr = .7035, k = 28.15E-3 W/mK, ν = 18.405E-6 m 2 /s β = 1/320 K -1 Determine 2 . 21733 Re 8 31679 . 2 1 4905 . 0 Re 2 3 2 2 3 2 = = = = = = ν ν β ν ν β VD E TD g Gr mixed VD TD g Gr Since it is mixed, we need an Nu correlation for Forced and Natural to plug into the following ( ) 3 1 3 3 N F Nu Nu Nu + = The natural convection is helping the forced convection so it is additive. Classify I-A-1-I, equation 7.25 0599 . 87 Pr Re 664 . 0

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