Thermodynamics HW Solutions 675

Thermodynamics HW Solutions 675 - Chapter 8 Internal Forced...

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Chapter 8 Internal Forced Convection 8-56 The components of an electronic system located in a circular horizontal duct are cooled by forced air. The exit temperature of the air and the highest component surface temperature are to be determined. Assumptions 1 Steady flow conditions exist. 2 The inner surfaces of the duct are smooth. 3 The thermal resistance of the duct is negligible. 4 Air is an ideal gas with constant properties. 5 The pressure of air is 1 atm. Properties We assume the bulk mean temperature for air to be 310 K since the mean temperature of air at the inlet will rise somewhat as a result of heat gain through the duct whose surface is exposed to a constant heat flux. The properties of air at 1 atm and this temperature are (Table A-15) ρ υ = = 1143 00268 167 1006 0710 . . . Pr . kg / m W/m. C 10 m / s J/kg. C 3 -5 2 k C p Analysis (a) The mass flow rate of air and the exit temperature are determined from Air 32 ° C 0.65 m 3 /min T e Electronics, 90 W L = 1 m D = 15 cm & & (. mV == ρ 1143 kg / m )(0.65 m / min) = 0.74295 kg / min = 0.0124 kg / s
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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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