Axial dispersion in channel flow. Consider the pressure-driven laminar flow in a channel of height \(2 h\). Derive the following formula for the axial dispersion coefficient:

\[D_{\mathrm{E}}=\frac{2 h^{2}\langle vangle^{2}}{105 D}\]

Here \(\langle vangle\) is the averaged velocity and \(D\) is the diffusivity of the species under consideration.