BACKGROUND: The bubble size distribution in gas-liquid reactors influences gas holdup, residence time distribution, and gas-liquid interfacial area for mass transfer. This work reports on the effects of independently varied gas and liquid flow rates on steady-state bubble size distributions in a new design of forced circulation loop reactor operated with an air-water system. The reactor consisted of a cylindrical vessel (∼26 L nominal volume, gas-free aspect ratio ≈6, downcomer-to-riser cross-sectional area ratio of 0.493) with a concentric draft tube and an annular riser zone. Both gas and liquid were in forced flow through a sparger that had been designed for minimizing the bubble size.
analysis of ALRs, the superfi cial gas and liquid velocities, along with the gas holdup in the riser, are taken to be the principal parameters. The gas velocity is the only independently controllable parameter, with the other two variables depending upon it. Most of the previously published works have been directed towards the prediction of one or both of these variables for a given range of gas fl ow rates in a particular reactor confi guration (Glennon et al., 1993). Joshi et al. (1990) reported that the operating conditions prevalent at the lower velocities in most ALRs are likely to be within a homogenous bubbly fl ow regime, which characterized A new model for the liquid circulation rates in airlift reactor (ALR) is presented. The model is based on the energy balance for the fl ow loop (riser, turn riser-downcomer, downcomer, and turn downcomer-riser) coupled with a drift fl ux theory of two-phase fl ow gas-liquid system, considering a bubbly fl ow regime. The predicted values of the liquid circulation rates by the developed model are compared with experimental results performed in a 22 dm 3 internal loop airlift reactor and with the results obtained in the literatures. The proposed model predicted the experimental results very well. Slip velocity relationship based on the drift fl ux model was proposed; including the gas holdup, bubble size and the liquid physical properties. The predicted slip velocity was similar to that obtained from the literature. The study revealed that appropriate arrangements of internal bioreactor parts can positively infl uence the liquid circulation velocity at the same energy consumption. The proposed models are useful in the design; scale up and characterization of the internal loop airlift reactors, and provides a direct method of predicting hydrodynamic behaviour in gas-liquid airlift reactors.On présente un nouveau modèle de vitesses de circulation des liquides dans un réacteur à air ascendant (ALR). Le modèle repose sur le bilan énergétique pour la boucle d'écoulement (colonne montante, colonne montante-colonne descendante avec coude, colonne descendante, et colonne descendante-colonne montante avec coude) couplée à une théorie de fl ux de dérive d'un système gaz-liquide d'écoulement diphasique, considérant un régime d'écoulement bullant. Les valeurs prédites des vitesses de circulation du liquide par le modèle développé sont comparées aux résultats expérimentaux obtenus dans un réacteur à air ascendant à boucle interne de 22 dm 3 et aux résultats obtenus dans la littérature scientifi que. Le modèle prédit très bien les résultats expérimentaux. On propose une relation de vitesse de glissement basée sur le modèle de fl ux de dérive, incluant la rétention de gaz, la taille de bulles et les propriétés physiques de liquide. La vitesse de glissement prédite est semblable à celle obtenue dans la littérature scientifi que. L'étude montre que la disposition appropriée des différentes parties de bioréacteur interne peut infl uencer positivement la vitesse de circulation de liquide p...
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