Thermodynamics HW Solutions 829

Thermodynamics HW Solutions 829 - Chapter 10 Boiling and...

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Chapter 10 Boiling and Condensation 10-48E Saturated steam at a saturation temperature of T sat = 95 ° F condenses on the outer surfaces of 20 horizontal pipes which are maintained at 85 ° F by circulating cooling water and arranged in a rectangular array of 4 pipes high and 5 pipes wide. The rate of heat transfer to the cooling water and the rate of condensation per unit length of the pipes are to be determined. Assumptions 1 Steady operating conditions exist. 2 The pipes are isothermal. 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 4 tubes × 8 tubes Analysis The modified latent heat of vaporization is hh C fg fg pl s * .( ) (. =+ ° ° 068 1040 0 999 85 sat Btu / lbm + 0.68 Btu / lbm F)(95 ) F = 1047 Btu / lbm The heat transfer coefficient for condensation on a single horizontal pipe is F ft Btu/h 1942 ft) F(1/12
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