The axial dispersion of the liquid in a distilled water-air countercurrent flow was studied in a packed column with 10.16 cm inside diameter and 139 cm height packed with 1.27 cm-Raschig rings, squares, spheres, and half Raschig rings.
The response curves were measured at two points, which showed long 'tail's for the entire liquid flow rates investigated. And the response curves could be satisfactorily represented by the PDE medel in which the liquid divided into two parts, one dynamic region and the other stagnant, and the mass transfer took place between the two regions because of the concentration difference.
The effect of the liquid and gas flow rates and the packing shapes on the parameters of the PDE model, namely, Peclet number, mass transfer coefficient, the fraction of dynamic region, and mean residence time, were invesigated and compared with others.
The parameters were evaluated by the least squares method in the Fourier domain.
The total holdup measured was compared with that calculated by multiplying the mean residence time and the volumetic flow rate, and was in good agreements.
The fraction of dynamic region depended mainly on the liquid flow rate and the height of transfer unit calculated from NTU and the length of measuring section had the values of 0.3-1.0 m.
Finally, the Bodenstein number, i.e., the Peclet number based on the nominal packing size, was correlated with Reynolds number based on the superficial liquid velocity only, and also with Reynolds number based on the real liquid velocity, Gallileo number, and the packing shape factor, ($ad_p$).
