Thermodynamics HW Solutions 776

Thermodynamics HW Solutions 776 - Chapter 9 Natural...

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Chapter 9 Natural Convection 9-105E The components of an electronic system located in a horizontal duct of rectangular cross section is cooled by natural convection. The heat transfer from the outer surfaces of the duct by natural convection and the average temperature of the duct 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 Radiation effects are negligible. 5 The thermal resistance of the duct is negligible. Properties The properties of air at 1 atm and the anticipated film temperature of ( T s + T )/2 = (160+80)/2 = 120 ° F are (Table A-15E) 1 - 2 3 R 001724 . 0 R) 460 120 /( 1 / 1 723 . 0 Pr /s ft 10 1923 . 0 F Btu/h.ft. 01576 . 0 = + = = = × = ° = f T k β υ Analysis (a) Noting that radiation heat transfer is negligible and no heat is removed by forced convection because of the failure of the fan, the entire 180 W heat generated must be dissipated by natural convection, 180 W L = 4 ft Air duct 6 in × 6 in Air 85 ° F 22 cfm 100 ° F Air 80 ° F && QQ
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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