Extra Exam.pdf

# Extra Exam.pdf - UNIVERSITY OF ARIZONA DEPARTMENT OF...

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UNIVERSITY OF ARIZONA DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL ENGINEERING CHEE 305 TRANSPORT PHENOMENA SPRING 2017 Test 2 Friday, March 10 Problem 1 (50 %) A very thin electric heater is sandwiched between two walls of the same material (thermal conductivity k = 5 W/m K) with the same width (L = 10 cm) (see figure). Heat is transferred at steady state by convection from the surface of the two walls to moving fluids with convective heat transfer coefficients h 1 = 75 W/m 2 K and h 2 = 120 W/m 2 K and temperatures far from the walls T ∞1 = 20 ºC and T 2 = 15 ºC. The thermal energy liberated by the heater is 950 W/m 2 of surface area. Assume that the temperature of the electric heater (T 0 ) is uniform. 1. Find T 0 . 2. Determine the heat flux through each of the two walls. h 1 h 2 T ∞1 T ∞2 L L Electric heater k k

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Problem 2 (50 %) A nuclear waste cylinder of radius R 1 , length L and conductivity k w is covered with a layer of insulation of radius R 2 and conductivity k i (see figure). The composite cylinder is placed in a large volume of liquid where it will be cooled by convection with a heat transfer coefficient h. The liquid temperature far from the cylinder is kept constant (T ). The nuclear waste liberates thermal energy at a rate E r per unit volume. Assume that heat conduction in the composite cylinder is in the radial direction only.
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