Thermodynamics HW Solutions 746

Thermodynamics HW Solutions 746 - Chapter 9 Natural...

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Unformatted text preview: Chapter 9 Natural Convection 9-48 A room is to be heated by a cylindrical coal-burning stove. The surface temperature of the stove and the amount of coal burned during a 30-day-period 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 temperature of the outer surface of the stove is constant. 5 The heat transfer from the bottom surface is negligible. 6 The heat transfer coefficient at the top surface is the same as that on the side surface. Properties The properties of air at 1 atm and the anticipated film temperature of ( T s + T )/2 = (130+24)/2 = 77 C are (Table A-1) 1- 2 5 K 002857 . K ) 273 77 ( 1 1 7161 . Pr /s m 10 066 . 2 C W/m. 02931 . = + = = = = = f T k Analysis The characteristic length in this case is the height of the cylindir, Air T = 24 C Stove T s = 0.85 L =0.7 m D = 0.32 m m. 7 . = = L L c Then, 9 2 2 5 3-1 2 2 3 10 387 .....
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