Chapter 8 Internal Forced Convection8-41Flow 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. Assumptions1Steady operating conditions exist. 2The inner surfaces of the duct are smooth. 3Air is an ideal gas with constant properties. 4 The pressure of air is 1 atm. PropertiesWe 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) 7154.0PrCJ/kg.1008/sm10097.2CW/m.02953.0kg/m9994.025-3=°=×=°==pCkυρAir 85°C 0.1 m3/min 10 m 70°C TeAnalysisThe characteristic length that is the hydraulic diameter, the mean velocity of air, and the Reynolds number are DAPaaahc====4440152. m m/s444.4m)15.0(/sm10.0
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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.