Skylab Diffusion Demonstration Experiments

The helium molecules will move to the bottom, and the carbon dioxide molecules will move to the top. If the two species are denoted by A and B, and the total fluxes as and Ag, then the net flux N can be written as 

FIGURE 9.1 Container with a partition separating helium and carbon dioxide.  

The movement of A comprises two components, one due to the bulk motion N and the fraction of N which is A, and the second component resulting from the diffusion of A, J.  

A mass balance over an incremental volume of height Az at steady state across a constant cross-sectional area, A is shown by  

Combining the previous two equations and integrating the resulting second-order 

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