Chemical Engineering Research & Design, Vol.79, No.1, 71-80, 2001
Improved liquid hold-up correlation for randomly packed towers
The state-of-the-art tools for the evaluation of the total liquid holdup in gas-liquid counter-current randomly dumped packed beds are critically evaluated by thoroughly interrogating a wide hydrodynamic database. This database, consisting of ca. 1,500 experiments on liquid hold-up below the flooding point, represents an important portion of the non-proprietary information released in the literature since the 1930s. Providing access to diversified information, it is dedicated to embracing wide-ranging temperature and gas density levels, and packing shapes extending from classical ones to modern third generation packings. Furthermore, a total of eleven correlations on the total liquid hold-up extracted from the literature are cross-examined using the database. Many limitations regarding the level of accuracy and generalization come to light with this investigation. Artificial neural network modelling and dimensional analysis are then proposed to improve the accuracy in predicting the total liquid hold-up in the pre-loading and the loading regions of packed beds. A combination of five dimensionless groups, comprising the liquid Reynolds (Re,), Froude (Fr,), and Ohnesorge (Oh,) numbers as well as the gas Froude (Fr,) and Stokes (Sr,) numbers are used as the basis of the correlation. The correlation yields an absolute average relative error of ca. 14% for the whole database and remains in accordance with trends reported in the Literature.