In the equation characterizing the mass transfer in laminar flow, the radial variation of velocity and concentration can be lumped into the axial dispersion term as below: After reading the original paper about Taylor dispersion, I know how to derive this equation. But I am still not able to understand it intuitively. How can the dispersion term make such a great difference here? Why bother ourselves with using the mean concentration rather than the concentration of single point? I hope my puzzle can be dispelled here and I will appreciate any replies.