Spring2008_midterm_statement

Spring2008_midterm_statement - Midterm Progress Assessment...

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Midterm Progress Assessment ECH 3223, Spring 2008 Wednesday, February 25 Directions: Two hours. Open book. Open notes. Calculator needed. Start each problem on a new page. Maximize your score by showing all work. Good luck to you!! Problem #1: Thermal conductivity of insulation covering sphere (30 points) A hollow aluminum sphere, with an electrical heater in the center, is used in tests to determine the thermal conductivity of insulating materials. The inner and outer radii of the sphere are R i and R o , respectively, and testing is performed under stead-state conditions with the inner surface of the aluminum maintained at T i . In a particular test, a spherical shell of insulation is cast on the outer surface of the sphere to a thickness of t . The system is in a room for which the air temperature is T and the convection coeFcient at the outer surface of the insulation is h . If the dissipation of the heater is Q (Watts) at steady state, what is the thermal conductivity of the insulation? Problem #2: Falling hailstone (30 points)
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Spring2008_midterm_statement - Midterm Progress Assessment...

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