Exercise 1

Argon and helium diffuse through dry fine sand with a porosity = 0.3 in the diffusion chamber of Figure Exercise 1-1. The molecular weights are 39.9 g/mole for argon (species A) and 4 g/mole for helium (species B). The pressure in both headers is maintained at 1 × 105 Pa and the temperature is 25 °C. The effective molecular diffusion coefficient is 2.37 × 105 m2/s under these conditions. To a close approximation, the mole fraction of argon is xA = 1 in the left header and xA = 0 in the right header. The diffusion chamber is 0.05 m long. For the steady-state condition:

  1. Compute the magnitude and direction of the total diffusive mole flux for both species. Compare with the values of flux computed from Equation 11.
  2. Compute the magnitude and direction of the non-equimolar flux.
  3. Derive an equation for xA(l) that shows how xA varies along the diffusion path.
  4. Compute the values for JA and JB at the midpoint of the diffusion chamber.
Figure showing Isobaric diffusion of argon (species A) and helium in a sand-filled chamber.

Figure Exercise 1 Isobaric diffusion of argon (species A) and helium in a sand-filled chamber.

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Flux Equations for Gas Diffusion in Porous Media Copyright © 2021 by David B. McWhorter. All Rights Reserved.