Thermodynamics HW Solutions 690

Thermodynamics HW Solutions 690 - Chapter 8 Internal Forced...

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Chapter 8 Internal Forced Convection 8-68E The exhaust gases of an automotive engine enter a steel exhaust pipe. The velocity of exhaust gases at the inlet and the temperature of exhaust gases at the exit are to be determined. Assumptions 1 Steady flow conditions exist. 2 The inner surfaces of the pipe are smooth. 3 The thermal resistance of the pipe is negligible. 4 Exhaust gases have the properties of air, which is an ideal gas with constant properties. Properties We take the bulk mean temperature for exhaust gases to be 700 ° C since the mean temperature of gases at the inlet will drop somewhat as a result of heat loss through the exhaust pipe whose surface is at a lower temperature. The properties of air at this temperature and 1 atm pressure are (Table A-15) /s ft 10 5902 . 0 F Btu/h.ft. 0280 . 0 lbm/ft 03422 . 0 2 3 - 3 × = ° = = υ ρ k 694 . 0 Pr F Btu/lbm. 2535 . 0 = ° = p C Noting that 1 atm = 14.7 psia, the pressure in atm is P = (15.5 psia)/(14.7 psia) = 1.054 atm. Then, /s ft 10 0.5598 = ) /s)/(1.054 ft 10 5902 . 0 ( lbm/ft 03608 . 0 ) 054 . 1 )( lbm/ft 03422 . 0 ( 2 3 - 2 3 - 3 3 × × = = = Exhaust 800 ° F 0.2 lbm/s 80 °
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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