L17a - Lecture 17: Liquid Diffusion Coefficient Continued...

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Lecture 17: Liquid Diffusion Coefficient Continued • For “dilute” aqueous solution for non electrolyte: •D v = 13.26 x 10 –5 µ 1.14 *VA 0.589 µ = Viscosity of water, Cp • V=Molar volume of solute at normal boiling point, cm 3 /g-mol • Note for liquids: D AB = D BA • Because small amounts of A in B and small amounts of B in A
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Turbulent Diffusion • Moving eddies transport matter around •J A = - (Dv + ε N )*(dC A /db) ε N = eddy diffusivity ε N depends on fluid property,velocity, and also position
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Mass Transfer Coefficient P A C Ai C Ab Gas Liquid Difficult to estimate ε N and B T One describes mass transfer •k c (cm/s) = flux = J A driving force (c Ai -c Ab ) •c Ai =Concentration at boundary Ab =Concentration at bulk
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Mass Transfer Coefficient Continued •k y = J A / (y Ai -y Ab ) use gas phase y = k c * ρ M x = J A / (X Ai -X A ) use liquid phase x = k c * ρ M = k c *( ρ / M) ρ = mass density
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Models for Mass Transfer Coefficient 1. Film Theory • Suggested by Nernst (1904) Assumes entire resistance
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L17a - Lecture 17: Liquid Diffusion Coefficient Continued...

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