Exercise 1
Argon and helium diffuse through dry fine sand with a porosity n = 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 × 10−5 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:
- Compute the magnitude and direction of the total diffusive mole flux for both species. Compare with the values of flux computed from Equation 11.
- Compute the magnitude and direction of the non-equimolar flux.
- Derive an equation for xA(l) that shows how xA varies along the diffusion path.
- Compute the values for JA and JB at the midpoint of the diffusion chamber.

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