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Exam1_S09

# Exam1_S09 - ME 315 Exam 1 Solutions 8:00-9:00 PM Tuesday...

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ME 315 Exam 1 Solutions 8:00 -9:00 PM Tuesday, February 10, 2009 1. (25 points) Consider a composite slab composed of a layer of plastic bonded to a layer of copper. The thickness of the plastic layer is 15 mm while that of the copper layer is 10 mm . The cross-sectional area of the slab is 100 cm 2 . There is contact resistance at the plastic-Cu interface due to the bonding. During testing, the plastic side is subjected to a hot fluid stream at T 1 = 400 K and a heat transfer coefficient of 200 W/m 2 K . The copper side is subjected to surrounding air at temperature T 2 = 300 K , with a heat transfer coefficient of 100 W/m 2 K . You are also given the following data: Thermal contact conductance at plastic-Cu interface = 420 W/m 2 K . k plastic = 2 W/mK ; k cu = 400 W/mK (a) Draw a thermal circuit for the composite showing all relevant thermal resistances and their numerical values. Solution 2 2 2 2 01 . 0 100 1 100 010 . 0 10 015 . 0 15 m cm m cm A m mm t L m mm t L c Cu Cu plastic plastic  2 2 1 1 , 01 . 0 200 1 1 m K m W A h R conv W K 5 . 0 2 , 01 . 0 2 015 . 0 m mK W m A k L R P P P cond W K 75 . 0

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2  2 2 01 . 0 420 1 1 m K m W A k R contact contact W K 2381 . 0 2 , 01 . 0 400 010 . 0 m mK W m A k L R Cu Cu Cu cond W K 0025 . 0  2 2 2 2 , 01 . 0 100 1 1 m K m W A h R conv W K 1 . 0
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