Thermodynamics HW Solutions 698

Thermodynamics HW Solutions 698 - C W/m 34 40 564 5 m 02 C...

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Chapter 8 Internal Forced Convection 8-76 Oil is heated by saturated steam in a double-pipe heat exchanger. The tube length is to be determined. Assumptions 1 Steady operating conditions exist. 2 The surfaces of the tube are smooth. 3 Air is an ideal gas with constant properties. Properties The properties of oil at the average temperature of (10+30)/2=20 ° C are (Table A-13) 08 . 2 Pr C J/kg. 1880 C W/m. 145 . 0 kg/m 888 3 = ° = ° = = p C k ρ Analysis The mass flow rate and the rate of heat transfer are kg/s 5022 . 0 m/s) (0.8 4 m) 03 . 0 ( ) kg/m 888 ( 2 3 = = = π m c A m V L Oil 10 ° C 0.8 m/s 5 cm T s = 100 ° C 30 ° C 3 cm W 881 , 18 C ) 10 30 )( C J/kg. 1880 )( kg/s 5022 . 0 ( ) ( = ° ° = = i e p T T C m Q The Nusselt number is determined from Table 8-4 at D i / D o =3/5=0.6 to be Nu i = 5.564. Then the heat transfer coefficient, the hydraulic diameter of annulus, and the logarithmic mean temperature difference are
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Unformatted text preview: C . W/m 34 . 40 ) 564 . 5 ( m 02 . C W/m. 145 . 2 ° = ° = = i h i Nu D k h C 58 . 79 10 100 30 100 ln 30 10 ln m 02 . m 03 . m 05 . ln ° = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − − − = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − − − = Δ = − = − = i s e s e i i o h T T T T T T T D D D The heat transfer surface area is determined from 2 2 ln ln m 881 . 5 ) C 58 . 79 )( C . W/m 34 . 40 ( W 881 , 18 = ° ° = Δ = ⎯→ ⎯ Δ = T h Q A T hA Q s s & & Then the tube length becomes m 62.4 = = = ⎯→ ⎯ = ) m (0.03 m 5.881 2 2 i s s D A L DL A 8-77 …. 8-79 Design and Essay Problems 8-60...
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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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