Hydrodynamics of two‐phase cocurrent downflow through packed beds. Part I. Macroscopic model

Abstract

cocurrent gas-liquid downflow through packed beds. A macroscopic model based on momentum balance is formulated for the condition of no radial pressure gradients. The model includes the effect of bubble formation on the pressure drop and holdup and is compared with the experimental data of the earlier investigators and of the present study. The model provides a functional form for correlating pressure drop and liquid saturation but some parameters have to be determined by fitting the experimental data. SCOPESeveral studies have been reported on the hydrodynamics of two-phase cocurrent downflow in packed beds which is of extensive use in industrial practice ranging from synthesis of chemicals to waste water treatment. The approach for the prediction of pressure drop and liquid saturation in those studies has been mostly empirical and the first mechanical model due to Sweeney (1967) used the momentum balance and the absence of radial pressure gradients; the model, neglects all dynamic interactions between the phases.A macroscopic model is formulated in the present study within the framework of the momentum balance using the experimentally observed condition of no radial pressure gradients. This formulation contains three parameters: two of them account for the effect of reduction in cross-sectional area available for flow of each phase due to the presence of the other, while the third accounts for the effect of bubble formation, breakage and reformation. Three well-defined regions of flow are identified and the model is satisfactorily applied to each of the regions separately. CONCLUSIONS AND SIGNIFICANCEThe measurement of pressure drop and liquid saturation in gas-liquid cocurrent downflow through packed beds has been reported in literature and correlations that are presented to predict the aforementioned parameters are empirical and cannot be extrapolated. Although distinct flow regions have been identified, none of the earlier approaches have taken into account the fact that the contacting mechanism between the phases is different in the different regions of flaw.In the present treatment, the formulation is generalized, the assumptions are explicitly stated and an attempt has been made to take into account the interaction between the phases though bubble formation, breakage and reformation. The model also presents a logical framework for the inclusion of other dynamic interactions such as friction at the interface and entrainment and is thus more comprehensive in its presentation than the model due to Sweeney (1967). The model parameters are determined independently for each of the identified regions of flow. However, a priori values are provided for five parameters out of nine on physical grounds, as well as order of magnitude values for the remaining four. Actual values for these four have to be determined by fitting experimental data to the theory. MATHEMATICAL FORMULATIONThe hydrodynamics of two-phase flow-through packed beds has been theoretically considered by Sweeney (1967) taking geometric interaction bet...

Liquid saturation in concurrent gas-liquid downflow through packed beds

“…It may be noted that Midoux et al [6] did not consider the specific surface area as variable in correlating their data. Likewise, the experimental data of the present study when compared with the correlation due to Rao et al [7] (Fig. 6) shows that the equation due to Rao et al [7] predicts higher liquid saturation than the experiment for Raschig rings.…”

“…Likewise, the experimental data of the present study when compared with the correlation due to Rao et al [7] (Fig. 6) shows that the equation due to Rao et al [7] predicts higher liquid saturation than the experiment for Raschig rings. The present correlation (Eq.…”

“…The experimental dynamic and total liquid saturation is correlated in terms of Lockhart-Martinelli parameter originally proposed for two phase flow in horizontal pipes [3] and subsequently adopted by Larkins et al [4], Sato et al [5], Midoux et al [6] and Rao et al [7] in correlating their data, defining as:…”

“…Figs. 1 and 2 compare the experimental and predicted dynamic and total liquid saturation for the experimental data of the present study and that due to Larkins [10], Speechia and Baldi [11], Sato et al [5] and Rao et al [7]. Newtonian foaming systems: The constants in Eqs.…”

Investigation of Downflow Bubble Columns: Experiments and Modeling

“…These studies can be classified either as sparger type (Rao et al, 1983;Kulkarni and Shah, 1984;Ohkawa et al, 1985), or as plunging jet type systems (Burgess et al, 1972;Van de Sande and Smith, 1976). In recent years, researchers have been attracted to a system which simultaneously gives the effect of a plunging jet as well as a sparged type system.…”