Chapter 8 Internal Forced Convection 8-51 Air enters a rectangular duct. The exit temperature of the air, the rate of heat transfer, and the fan power 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 in the duct is 1 atm. Properties We assume the bulk mean temperature for air to be 40 ° 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 this temperature and 1 atm are (Table A-15) /s m 10 702 . 1 C W/m. 02662 .0 kg/m 127 . 1 2 5-3 × = υ ° = = ρ k 7255 .0 Pr C J/kg. 1007 = ° = p C T s = 10 ° C L = 7 m Air duct 15 cm × 20 cm Analysis ( a ) The hydraulic diameter, the mean velocity of air, and the Reynolds number are D A P h c == = 4 4015 20 1 5 01714 (. (. .
This is the end of the preview. Sign up
access the rest of the document.
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.