Thermodynamics HW Solutions 831

Thermodynamics HW Solutions 831 - Chapter 10 Boiling and...

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Chapter 10 Boiling and Condensation 10-50 Saturated steam at a saturation temperature of T sat = 55 ° C condenses on the outer surface of a horizontal tube which is maintained at 45 ° C. The required tube length to condense steam at a rate of 10 kg/h is to be determined. Assumptions 1 Steady operating conditions exist. 2 The tube is isothermal. Properties The properties of water at the saturation temperature of 55 ° C are h fg = 2371 × 10 3 J/kg and ρ v = 0.1045 kg/m 3 . The properties of liquid water at the film temperature of TT T fs = + = () / sat 2 (55 + 45)/2 = 50 ° C are (Table A-9), Steam 55 ° C Condensate 45 ° C Cooling water L tube = ? ρ μ νμ l l ll l pl l k = == × =⋅ ° ° 9881 0547 10 0554 10 4181 0644 3 3 6 . . /. . kg / m kg / m s m/ s C J / k g C W/m C 2 Analysis The modified latent heat of vaporization is hh C fg fg pl s * .( ) =+ × °− ° × 068 2371 10 45 10 33 sat J / kg + 0.68 4181 J / kg C(55 ) C = 2399 J / kg Noting that the tube is horizontal, the condensation heat transfer coefficient is determined from
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