hw8 - assume that there is no conduction from the grass to...

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ME 322 HW #8 06.05.2008 1. Consider two black infinite parallel plates separated by a transparent medium of thickness 1 cm and thermal conductivity 0.02 W/m degC. Plate 2 is at temperature 300 K, and a known amount of energy 1000 W/m 2 is added per unit area to plate 1 and removed at plate 2. Find the temperature 1 T of plate 1. (A few iterations may be necessary.) (ANSWER: 388 K) 2. On a clear night the effective radiation temperature of the sky may be taken as -70ºC. (Note: If there were no atmosphere on the earth, the radiation temperature of the night sky would be taken as 0 K.) Assuming that there is no wind and the convection heat-transfer coefficient from the air to the dew which has collected on the grass is 28 W/m 2 ºC, estimate the minimum air temperature which the air must have to prevent formation of frost. Neglect evaporation of the dew, and
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Unformatted text preview: assume that there is no conduction from the grass to the dew or from the ground to the grass. Take the emissivity as unity for the water. (ANSWERS: 280.8 K) 3. It is not uncommon for the night sky temperature in desert regions to drop to -40ºC. If the ambient air temperature is 20ºC and the convection coefficient for still air condition is approximately 5 W/m 2 K, can a shallow pan of water freeze? The emissivity of water at 300 K is 0.96. (ANSWER: 268.5K) 4. Show that the view factor of the inclined parallel plates of equal width, w , and a common edge with angle α is ) 2 / sin( 1 12 − = F 1 w 2 w 5. Find F 12 and F 21 for the sphere lying on infinite plane. (ANSWER: 0.5 and 0) A 1 A 2...
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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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