Lecture 4 - Unimolecular Diffusion

Lecture 4 - Unimolecular Diffusion - 2/24/2012 Lecture 4:...

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2/24/2012 1 Lecture 4: Diffusion of A through Stagnant Gas B • Diffusion of A through Stagnant Gas B - A physical description of the problem - Calculation of the flux, N A - Calculation of the diffusive flux and the convective flux - Calculation of x A (z), x B (z) 1 Diffusion of Benzene (Gas A) through Stagnant Air (Gas B) Pure Benzene (A) Air (B) z 1 z 2 Through the accidental opening of a valve, benzene has accumulated in an open container in an industrial plant in a remote, difficult to reach area. Your boss would like you to estimate the following quantity: The rate of evaporation of benzene as a molar flux in (mol/cm 2 •s) x A2 Stagnant Air N B =0 Stagnant = No NET movement of B. z The vapor pressure of benzene in air at 25 o C is 0.131 atm. D AB = 0.095 cm 2 /s x A2 =0 and x A1 = ? T = 25 o C (298 K) P = 1 atm R = 82.06 cm 3 •atm/mol•K A, B Ideal Gases z 1 = 0 and z 2 = 0.5 cm x A1 V-L Equilibrium at z 1 is established fast relative to the rate of diffusion. 1 131 . 0 A of pressure vapor 1 = = P p x A 2
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2/24/2012 2 At steady-state, which of the following statements is FALSE regarding this system? a. The convective flux of A is nonzero. b. The convective flux of B is nonzero. c. The magnitude of the convective flux of A is equal to that of B. d. The magnitude of the convective flux of A varies with z. Pure Benzene (A) Air (B) z 1 z 2 x A1 x A2 Stagnant Air z The vapor pressure of benzene at 25 o C is 0.131 atm. D AB = 0.095 cm 2 /s T = 25 o C (298 K) P = 1 atm R = 82.06 cm 3 •atm/mol•K A, B Ideal Gases z 1 = 0 and z 2 = 0.5 cm x A2 =0 and x A1 =0.131 3 N B =0 Stagnant = No NET movement of B. Pure Benzene (A) Air (B) z 1 z 2 x A1 x A2 N B =0 Stagnant = No NET movement of B. z
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This note was uploaded on 03/18/2012 for the course ECON 201 taught by Professor Çakmak during the Spring '10 term at Middle East Technical University.

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Lecture 4 - Unimolecular Diffusion - 2/24/2012 Lecture 4:...

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