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[subhra]

I am confused if the yield from an irreversible first order heterogeneous (on the wall) reaction within a given time in a flow-through reactor will increase/decrease with fluid flow rate. It would be great if some one can clarify. The source of my confusion is as follows. On one hand, Sherwood numbers normally increase with fluid flow rate. On the other hand, residence time decrease with flow rate. I am especially interested in very fast irreversible reactions.

[chenblue]

Subhra:

For a very fast irreversible reaction, you can assume that the surface concentration of reactant (for a rxn A=> on the wall is zero. Therefore, when the flow rate increases, the concentration gradient of reactant near the wall must increase. Then you know, the yield will also increase because the reaction rate is equal to the diffusion rate (from the bulk to the wall).