Thermodynamics HW Solutions 742

Thermodynamics HW Solutions 742 - Chapter 9 Natural...

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Unformatted text preview: Chapter 9 Natural Convection 9-46 A rectangular container filled with cold water is gaining heat from its surroundings by natural convection and radiation. The water temperature in the container after a 3 hours and the average rate of heat transfer are to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. 4 The heat transfer coefficient at the top and bottom surfaces is the same as that on the side surfaces. Properties The properties of air at 1 atm and the anticipated film temperature of ( T s + T )/2 = (10+24)/2 = 17 C are (Table A-15) 1- 2 5 K 003448 . K ) 273 17 ( 1 1 7317 . Pr /s m 10 489 . 1 C W/m. 02491 . = + = = = = = f T k Air T = 24 C Container T s = 0.6 The properties of water at 2 C are (Table A-7) C J/kg. 4214 and kg/m 1000 3 = = p C Analysis We first evaluate the heat transfer coefficient on the side surfaces. The characteristic length in this We first evaluate the heat transfer coefficient on the side surfaces....
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