L18 - interparticle diffusion mixing Model for...

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CHEE 3462 Unit Operations Lecture 18 Rate of Mass Transfer = K y (y A * -y A ) Overall coefficient y A = composition of vapor y A * = composition of vapor that would be in equilibrium with x A 1 m 1 + = y x y k k K Mass transfer coefficient in liquid phase Mass transfer coefficient in gas phase curve m equilibriu the of slope x x y y m Ai A Ai * A = =
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• Local Efficiency for Distillation ' 1 n ' en ' 1 n ' n ' y y y y η + + dz Material balance over thickness dz: ( ) Adz a y y K dy ρ V A * A y A M = Gas flow rate Molar density Change in vapor mole fraction Liquid layer volume unit area bubble a ( ) area Sieve area sectional Cross A () = + z 0 M y y y A * A A V/A ρ dz a K y y dy ' A n, ' A 1, n
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s M y ' A n, * A ' A 1, n * A v ρ aZ K y y y y ln = + Superficial velocity of vapor + = s M y v ρ aZ K ' A 1, n * A ' A n, * A e y y y y ' ' A 1, n * A ' A 1, n ' A n, ' A 1, n * A ' A n, * A η y y y y y y y y 1 = = + + + = s M y v ρ aZ K ' e 1 η oy N e 1 = N oy = Number of overall gas phase transfer units o M ' η η η
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Example of Leaching Porous Solids solutes & solvent Intraparticle diffusion controls over
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Unformatted text preview: interparticle diffusion / mixing. Model for intraparticle diffusion 1-dimensional problem 2 2 ' v b x D t x ∂ ∂ = ∂ ∂ Initial condition: x = x @ t = o, -r p <b<r p Boundary conditions: x = x 1 @ b = ±r p + + + = − − − − − L β 25a β 9a β a 1 1 1 1 1 e 25 1 e 9 1 e 2 π 8 x x x x 4 π a , r t D β 2 1 2 p ' v = = Where and, average concentration in the solid = x ( ) β Φ 1 x x x x 1 x x x x η 1 1 1 M − = − − − = − − = − = 2 ' D Φ 1 p v r t As r p ↓ , β ↑ , Φ ↓ , η M ↑ If intraparticle diffusion controls, decrease the particle size. Making r p half is equivalent to making t 4 times....
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L18 - interparticle diffusion mixing Model for...

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