Thermodynamics HW Solutions 828

Thermodynamics HW Solutions 828 - Chapter 10 Boiling and...

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Chapter 10 Boiling and Condensation 10-47E Saturated steam at a saturation temperature of T sat = 95 ° F condenses on the outer surfaces of horizontal pipes which are maintained at 85 ° F by circulating cooling water. The rate of heat transfer to the cooling water and the rate of condensation per unit length of a single horizontal pipe are to be determined. Assumptions 1 Steady operating conditions exist. 2 The pipe is isothermal. 3 There is no interference between the pipes (no drip of the condensate from one tube to another). Properties The properties of water at the saturation temperature of 95 ° F are h fg = 1040 Btu/lbm and ρ v = 0.0025 lbm/ft 3 . The properties of liquid water at the film temperature of TT T fs = + = () / sat 2 (95 + 85)/2 = 90 ° F are (Table A-9E), ρ μ νμ l l ll l pl l k = =⋅ == ° ° 6212 1842 0 02965 0999 0358 3 . . /. . . lbm / ft lbm / ft h ft / h C B t u / l b m F Btu / h ft F 2 Steam 95 ° F ................... 85 ° F Condensate flow Analysis The modified latent heat of vaporization is Btu/lbm 1047 = F ) 85 F)(95 Btu/lbm 999 . 0 ( 0.68 + Btu/lbm 1040 ) ( 68 . 0 sat * ° ° × = + = s pl fg fg T T C h h Noting that we have condensation on a horizontal tube, the heat transfer coefficient is determined from
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