The hydrodynamics and the pulse properties in the pulse flow regime of gas‐liquid downflow through a packed column were studied using 6 mm Raschig rings and 3 mm spheres as packings. The pulse flow regime is considered to be gas‐continuous flow outside the pulses and more like dispersed bubble flow inside the pulses and the pressure drop is viewed as being contributed to by the gas continuous part outside the pulses and by the pulses themselves. Correlations for the total pressure drop, the pressure drop across the pulse and for the pulse velocity are obtained. The experimental data of the average holdup, the pulse holdup, the base holdup and the transition from gas continuous to pulse flow regime are compared with the literature values.

Local instantaneous solid-liquid mass transfer coefficients were measured in two-phase gas-liquid downflow through packed columns for 3 X 3 mm and 6 X 6 mm cylinders. An electrochemical technique was used. Liquid flow rates from 3.0 to 26.6 kg/m2.s and gas flow rates from 0.07 to 1.16 kg/m2*s covered the gascontinuous, ripple, and pulse flow regimes. Timeaveraged mass transfer coefficients in trickle flow and in pulse flow for the pulse proper and the base (outside the pulse) were found to increase with increasing gas and liquid rates. Correlations are presented in terms of liquid phase Reynolds numbers and in terms of Kolmogoroff numbers. The mass transfer coefficients in the pulse were found to correspond closely to the coefficients that would be attained in the dispersed bubble flow regime. V. G. RAO and A. A. H. DRINKENBURG Department of Chemical EnglneerlngRljksunlversltelt Gronlngen 9747 AG Gronlngen, The Netherlands SCOPE Trickle-bed reactors, when operated in the gas-continuous trickle flow regime, are generally restricted to relatively slow reactions since the rate is often controlled by the mass transfer resistance. Operation of the reactor at higher gas and liquid rates produces pulse flow in which high transfer rates can be realized (Hirose et al., 1976). The pulse flow regime is better suited for fast reactions than the trickle flow regime. For design, the resistance to absorption of gaseous components into the liquid and the transfer of the reacting species through the liquid film to the catalyst surface must be known, which necessitates the study of solid-liquid mass transfer. The many reported studies on solid-liquid mass transfer generally have utilized one of two methods: measuring the dissolution rate of some soluble packing or packing coated with a soluble dye, or measuring the electrical current in water under diffusion-limited transport conditions.The electrochemical method has certain advantages over the other. It facilitates direct and instantaneous measurements of solid-liquid mass transfer and is thus very useful to measure mass transfer fluctuations, especially under pulsing flow conditions. Chou et al. (1979) first measured such fluctuations in pulse flow. The pulses were found to play an important role in enhancing mass transfer coefficients, Not much is known about the mass transfer coefficients in the pulses, their dependence on flow rate of the phases, and the packing properties. No study other than Chou's has been reported in this direction. All earlier studies employed the dissolution method, from which only time-averaged values were found.The present study was conducted to understand the fundamental nature of the pulses with respect to mass transfer, the extent of mass transfer fluctuations, and their qualitative and quantitative influence on mass transfer. The instantaneous mass transfer from a single active particle (brass cylinder electrochemically coated with nickel) in the bed was measured. Beds with particles of 3 X 3 mm and 6 X 6 mm cylinders were used. The active particl...

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...

Two‐phase pressure drop and dynamic and total liquid saturation are experimentally determined for air‐water system under cocurrent downflow through packed beds using packing differing widely in geometry. The experimental data of the present study as well as that available in literature is satisfactorily correlated in terms of: (a) Lockhart‐Martinelli parameters; and (b) the Reynolds numbers defined for the respective phases and the bed porosity, taking into account the flow behavior of the phases through the packed bed.

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