Thermodynamics HW Solutions 642

Thermodynamics HW Solutions 642 - = i e p T T C m Q &...

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Chapter 8 Internal Forced Convection 8-22 Steam is condensed by cooling water flowing inside copper tubes. The average heat transfer coefficient and the number of tubes needed are to be determined. Assumptions 1 Steady operating conditions exist. 2 The surface temperature of the pipe is constant. 3 The thermal resistance of the pipe is negligible. Properties The properties of water at the average temperature of (10+24)/2=17 ° C are (Table A-9) C J/kg. 5 . 4184 kg/m 7 . 998 3 ° = = ρ p C Also, the heat of vaporization of water at 30 ° C is kJ/kg 2431 = fg h . Analysis The mass flow rate of water and the surface area are Steam, 30 ° C L = 5 m D = 1.2 cm Water 10 ° C 4 m/s 24 ° C kg/s 0.4518 = m/s) (4 4 m) (0.012 ) kg/m 7 . 998 ( 4 2 3 2 π = π ρ = ρ = m m c D A m V V The rate of heat transfer for one tube is W 468 , 26 ) C 10 24 )( C J/kg. 5 . 4184 )( kg/s 4518 . 0 ( ) ( = ° ° =
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Unformatted text preview: = i e p T T C m Q & & The logarithmic mean temperature difference and the surface area are C 63 . 11 10 30 24 30 ln 10 24 ln ln ° = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − − − = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − − − = Δ i s e s i e T T T T T T T 2 m 0.1885 = m) m)(5 012 . ( ππ = = DL A s The average heat transfer coefficient is determined from C . kW/m 12.1 2 ° = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ° = Δ = ⎯→ ⎯ Δ = W 1000 kW 1 ) C 63 . 11 )( m 1885 . ( W 468 , 26 2 ln ln T A Q h T hA Q s s & & The total rate of heat transfer is determined from kW 65 . 364 kJ/kg) 2431 )( kg/s 15 . ( = = = fg cond total h m Q & & Then the number of tubes becomes 13.8 = = = W 468 , 26 W 650 , 364 Q Q N total tube & & 8-4...
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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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