Thermodynamics HW Solutions 613

Thermodynamics HW Solutions 613 - Chapter 7 External Forced...

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Chapter 7 External Forced Convection 7-85 A cylindrical oven is to be insulated to reduce heat losses. The optimum thickness of insulation and the amount of money saved per year are to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the insulation is one- dimensional. 3 Thermal conductivities are constant. 4 The thermal contact resistance at the interface is negligible. 5 The surface temperature of the furnace and the heat transfer coefficient remain constant. 6 The surfaces of the cylindrical oven can be treated as plain surfaces since its diameter is greater than 1 m. Properties The thermal conductivity of insulation is given to be k = 0.038 W/m °C. Analysis We treat the surfaces of this cylindrical furnace as plain surfaces since its diameter is greater than 1 m, and disregard the curvature effects. The exposed surface area of the furnace is 2 2 2 side base m 69 . 70 m) m)(6 5 . 1 ( 2 m) 5 . 1 ( 2 2 2 2 = + = + = + = π ππ rL r A A A o
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