Thermodynamics HW Solutions 651

Thermodynamics HW Solutions 651 - Chapter 8 Internal Forced...

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Chapter 8 Internal Forced Convection 8-41 Flow of hot air through uninsulated square ducts of a heating system in the attic is considered. The exit temperature and the rate of heat loss are to be determined. Assumptions 1 Steady operating conditions exist. 2 The inner surfaces of the duct are smooth. 3 Air is an ideal gas with constant properties. 4 The pressure of air is 1 atm. Properties We assume the bulk mean temperature for air to be 80 ° C since the mean temperature of air at the inlet will drop somewhat as a result of heat loss through the duct whose surface is at a lower temperature. The properties of air at 1 atm and this temperature are (Table A-15) 7154 . 0 Pr C J/kg. 1008 /s m 10 097 . 2 C W/m. 02953 . 0 kg/m 9994 . 0 2 5 - 3 = ° = × = ° = = p C k υ ρ Air 85 ° C 0.1 m 3 /min 10 m 70 ° C T e Analysis The characteristic length that is the hydraulic diameter, the mean velocity of air, and the Reynolds number are D A P a a a h c === = 4 4 4 015 2 . m m/s 444 . 4 m) 15 . 0 ( /s m 10 . 0
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This note was uploaded on 01/22/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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