Chapter 8 Internal Forced ConvectionAssumptions1Steady flow conditions exist. 2 Heat generated is uniformly distributed over the two surfaces of the PCB. 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 310 K since the mean temperature of air at the inlet will rise somewhat as a result of heat gain through the hollow core whose surface is exposed to a constant heat flux. The properties of air at 1 atm and this temperature are (Table A-15) ρυμμ==°=×=−−11430 026816710060710189 10208 1053505...Pr...,@kg / mW/m. C10 m / sJ/kg. Ckg / m.skg / m.s3-52KkCpbsAir 32°C 0.8 L/s TeElectronic components, 35 W L= 18 cmAir channel 0.25 cm ×12 cm Analysis(a) The mass flow rate of air and the exit temperature are determined from &&(.mV==××ρ1143 kg / m )(0.8 10 m / s) = 9.14 10 kg / s3-33-4&&()&&QmCT TT TQmCpe ie ip=−→=+=°×°−32914 104C+35 Wkg / s)(1006 J / kg. C)70.1 C(b) The mean fluid velocity and hydraulic diameter are VVADAPmchc×
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