Figure 2

Schematic diagram of mass transfer in a percolation column. (a) Diagram of percolation device; (b) Schematic diagram of percolation. (h is the height of the percolation column, u₀ is the flow rate, D_ax is axial diffusivity, K_x is the mass transfer coefficient, \({C}_{w}^{*}\) is concentration of ingredients on the outer surface of medicinal material particles).