Diffusion in a T-Sensor

Consider next a two-dimensional case with flow coming in top and bottom on the left (see Fig. 8.16). The fluid is mainly water, but a small concentration of a second species is in the upper flow. Along the top take c = 1, and along the bottom 

If this problem is solved with a large Peclet number, oscillations appear (Ref [15] p. 217) and the mesh must be refined or some stabilization (like Petrov-Galerkin or upstream weighting) must be applied. The stabilization, of course, smoothes the solution and adds unphysical diffusion. It is up to the analyst to decide if that effect can be tolerated. 

The effect of placing a knife-edge in the device is very small it is negligible because the amount of diffusion across the line where the knife-edge would be is a very small portion of the total mass transfer, and the flow held is affected only slightly. 

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