# Tutorial_5 - Tutorial 5 Midterm Review(Past Midterm...

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Tutorial 5: Midterm Review (Past Midterm Questions) 1. The inner and outer surfaces of a 25-cm-thick wall in summer are at 27ºC and 44 ºC, respectively. The outer surface of the wall exchanges heat by radiation with surrounding surfaces at 40ºC, and convection with ambient air also at 40ºC with a convection heat transfer coefficient of 8 W/m 2 ·K. Solar radiation is incident on the surface at a rate of 150 W/m 2 ·K. If both the emissivity and the solar absorptivity of the outer surface are 0.8, determine the effective thermal conductivity of the wall.

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2. Starting with an energy balance on a ring-shaped volume element, derive the two- dimensional steady heat conduction equation in cylindrical coordinates for T(r,z) for the case of constant thermal conductivity and no heat generation.
3. In an experiment to measure convection heat transfer coefficients, a very thin metal foil of very low emissivity (e.g. highly polished) copper) is attached on the surface of a slab of material with very low thermal conductivity.

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