Thermodynamics HW Solutions 840

Thermodynamics HW Solutions 840 - Chapter 10 Boiling and...

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Chapter 10 Boiling and Condensation 10-56 Saturated steam at a saturation temperature of T sat = 50 ° C condenses on the outer surfaces of a tube bank with 20 tubes in each column maintained at 20 ° C. The average heat transfer coefficient and the rate of condensation of steam on the tubes are to be determined. Assumptions 1 Steady operating conditions exist. 2 The tubes are isothermal. Properties The properties of water at the saturation temperature of 50 ° C are h fg = 2383 × 10 3 J/kg and ρ v = 0.0831 kg/m 3 . The properties of liquid water at the film temperature of TT T fs = + = () / sat 2 (50 + 20)/2 = 35 ° C are (Table A-9), Steam 50 ° C 20 ° C Condensate flow 20 tubes in a column ρ μ νμ l l ll l pl l k = == × =⋅ ° ° 994 0 0 720 10 0724 10 4178 0623 3 3 6 . . /. . kg / m kg / m s m/ s C J / k g C W/m C 2 Analysis ( a ) The modified latent heat of vaporization is J/kg 10 2468 = C 0) 2 C(50 J/kg 4178 0.68 + J/kg 10 2383 ) ( 68 . 0 3 3 sat * × ° ° × × = + = s pl fg fg T T C h h The heat transfer coefficient for condensation on a single horizontal tube is C W/m 8425 m) C(0.015 ) 20 50 ( s) kg/m 10 720 . 0 ( ) C W/m 623 . 0 )( J/kg 10 2468 )(
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