Thermodynamics HW Solutions 727

Thermodynamics HW Solutions 727 - Chapter 9 Natural...

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Unformatted text preview: Chapter 9 Natural Convection 9-34 A glass window is considered. The convection heat transfer coefficient on the inner side of the window, the rate of total heat transfer through the window, and the combined natural convection and radiation heat transfer coefficient on the outer surface of the window 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. Q & Outdoors -5 C Glass T s = 5 C = 0.9 L = 1.2 m Room T = 25 C Properties The properties of air at 1 atm and the film temperature of ( T s + T )/2 = (5+25)/2 = 15 C are (Table A-15) 1- 2 5 K 003472 . K ) 273 15 ( 1 1 7323 . Pr /s m 10 471 . 1 C W/m. 02476 . = + = = = = = f T k Analysis ( a ) The characteristic length in this case is the height of the window, m. 2 . 1 = = L L c Then, 9 2 2 5 3-1 2 2 3 10 986 . 3 ) 7323 . ( ) /s m 10 471 . 1 ( ) m 2 . 1 )( K 5 25 )( K 3472 . )( m/s 81 . 9 ( Pr )...
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