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class 27

# class 27 - Condensation Click to edit Master subtitle style...

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Click to edit Master subtitle style 8/13/11 Condensation Chapter 10 Sections 10.8 through 10.10

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8/13/11 Film Condensation on a Vertical Plate (laminar) Distinguishing Features Ø Generally, the vapor is superheated T,v∞ > Tsat and may be part of a mixture that includes noncondensibles. ( 29 , v sat T T Ø A shear stress at the liquid/vapor interface induces a velocity gradient in the vapor, as well as the liquid. Ø Thickness (δ) and flow rate ( m) of condensate increase with increasing x ( 29 m g ( 29 δ ( 29 ( 29 - - = fg v l l s sat l l h g x T T k x ρ ρ ρ μ δ 4 ) ( Can model a vertical pipe as vertical if D/2 >>> del
8/13/11 Film Condensation on a Vertical Plate Nusselt Analysis for Laminar Flow Assumptions: Ø A pure vapor at Tsat Ø Negligible shear stress at liquid/vapor interface. Obj123 0 = = y y u

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8/13/11 Flow rate per unit width: Average Nusselt Number: Total heat transfer and condensation rates: ( 29 l v l l g b m μ δ ρ ρ ρ 3 3 - = = Γ Obj126 fg s sat l p fg fg h T T c Ja Ja h h ) ( ) 68 . 0 1 ( ' , - + = fg s sat L h q m T T A h q ' ) ( = - = Properties evaluated at film temperature for liquid, Tsat for vapor
8/13/11 Effects of Turbulence : Ø Transition may occur in the film and three flow regimes may be identified and delineated in terms of a Reynolds number defined as 4 4 4 Re l m l l l u m b δ ρ δ μ μ μ Γ = = g l m l l l u b m μ δ ρ μ μ δ 4 4 4 Re = = Γ

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class 27 - Condensation Click to edit Master subtitle style...

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