What do we do in cases like this hypothetical mass transfer device?
Given the concentrations of species A at points 1 and 2 (��1, ��2), how do we compute the rate of mass transfer between them? We need to consider convective and diffusive mass transfer in multiple media.
Concentration profiles
The concentration profile owing purely to diffusion through a medium with constant material properties and no reaction is linear.
The concentration profile owing to convective mass transport shows a sharp change right near the surface as described for boundary layers.
Profiles with combined mechanisms usually have to match at interfaces (same concentration and slope).
Exercise: Concentrations for combined mechanisms
Sketch out the concentration profile through the device pictured above when ��,1 is greater than ��,2 and the fluid in stream 1 and stream 2 are relatively well mixed.
Matching mass transfer rates
At steady state, the amount of mass per time passing through each ‘plane’ must be equal, otherwise the system would have accumulation.
If the mass transfer area, �, is equal for all of these planes (as for the geometry above), the mass per time per area (or mass flux) must be equal. Is this true for a cylindrical geometry?
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