hw7 - (2) How does this compare with the forced convection...

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ME 322 HW #7 22.04.2008 1. An aluminum cylinder 2 cm in diameter and 1 m in length at a constant surface temperature of 127ºC is horizontally placed in an atmospheric environment at 27ºC. As a first approximation, the radiation effect is assumed to be negligible since the emissivity of the aluminum surface is low. (1) If air blows across the cylinder at 3 m/s, what will be the rate of heat loss from the cylinder? (2) If there is no air flow across the cylinder, what will be the rate of heat loss from the cylinder? (ANSWERS: 233.7 W; 62.3 W) 2. A spherical balloon gondola 2.4 m in diameter rises to an altitude where the ambient pressure is 1.4 kPa and the ambient temperature is -50ºC. The outside surface of the sphere is at approximately 0ºC. (1) Estimate the free convection heat loss from the outside of the sphere.
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Unformatted text preview: (2) How does this compare with the forced convection heat loss from such a sphere with a low free-stream velocity of approximately 30 cm/s? (ANSWERS: 310 W; 191 W) 3. A household oven door of 0.5-m height and 0.7-m width reaches an average surface temperature of 32ºC during operation. (1) Estimate the heat loss to the room with ambient air at 22ºC. (2) If the door has an emissivity of 1.0 and the surroundings are also at 22ºC, comment on the heat loss by free convection relative to that by radiation. (ANSWER: 11.7 W; 21.4 W) 4. A circular grill of diameter 0.25 m and emissivity 0.9 is maintained at a constant surface temperature of 130ºC. What electrical power is required when the room air and surroundings are at 24ºC? (ANSWER: 90.2 W)...
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This note was uploaded on 07/30/2011 for the course ME 324 taught by Professor Nezihtopaloglu during the Spring '11 term at Yeditepe Üniversitesi.

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