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Unformatted text preview: C . W/m 17 . 10 ) 31 . 32 ( m 15 . C W/m. 04721 . 2 = = = Nu D k h The logarithmic mean temperature difference is C 2 . 148 450 180 250 180 ln 450 250 ln ln = = = i s e s i e T T T T T T T The rate of heat loss from the exhaust gases can be expressed as [ ] L L T hA Q s 25 . 710 ) C 2 . 148 ( m) 15 . ( ) C . W/m 17 . 10 ( 2 ln = = = & where L is the length of the pipe. The rate of heat loss can also be determined from [ ] kg/s 0.03603 = /4 m) (0.15 m/s) )(3.6 kg/m 5664 . ( 2 3 = = c VA m & W 7612 C ) 250 450 )( C J/kg. kg/s)(1056 03603 . ( = = = T C m Q p & & Setting this equal to rate of heat transfer expression above, the pipe length is determined to be m 10.72 = = = L L Q W 7612 25 . 710 & 857...
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Convection, Force, Mass

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