The drag coefficient plays a vital role in the modeling of gas-solid flows. Its knowledge is essential for understanding the momentum exchange between the gas and solid phases of a fluidization system, and correctly predicting the related hydrodynamics. There exists a number of models for predicting the magnitude of the drag coefficient. However, their major limitation is that they predict widely differing drag coefficient values over same parameter ranges. The parameter ranges over which models possess a good drag prediction accuracy are also not specified explicitly. Accordingly, the present investigation employs Geldart’s group B particles fluidization data from various studies covering wide ranges of Re and εs to propose a new unified drag coefficient model. A novel artificial intelligence based formalism namely genetic programming (GP) has been used to obtain this model. It is developed using the pressure drop approach, and its performance has been assessed rigorously for predicting the bed height, pressure drop, and solid volume fraction at different magnitudes of Reynolds number, by simulating a 3D bubbling fluidized bed. The new drag model has been found to possess better prediction accuracy and applicability over a much wider range of Re and εs than a number of existing models. Owing to the superior performance of the new drag model, it has a potential to gainfully replace the existing drag models in predicting the hydrodynamic behavior of fluidized beds.

Experimental investigations have been carried out in Reversed Flow Jet Loop Reactor (RFJLR) to study the influence of liquid flow rate, gas flow rate, immersion height of two-fluid nozzle in reactor and nozzle diameter on gas holdup without circulation, that is, gas-liquid mixture in draft tube only (E gd ) and gas holdup with circulation loop (E g ). Also critical liquid flow rate required for transition from draft tube to circulation loop has been determined. Gas holdup was measured by isolation valve technique. Gas holdup in draft tube and circulation loop increased with increase in liquid flow rate and gas flow rate. It is observed that the increased flow rate is required for achieving a particular value of gas holdup with larger nozzle diameter. Nozzle at the top edge of draft tube have higher gas holdup as compared to other positions. It has been noted that, no significant recirculation of gas bubbles into the top of draft tube from annulus section has been observed till a particular liquid flow rate is reached. A plot of gas holdup with no circulation and with circulation mode determines minimum liquid flow rate required to achieve complete circulation loop. Critical liquid flow rate required to achieve complete circulation loop increases with increase in gas flow rate and is minimum at lowest immersion height of two-fluid nozzle.Des investigations expérimentales ontété effectuées dans un réacteurà jet età boucle de circulationàécoulement inversé pourétudier l'influence du taux d'écoulement du liquide, du taux d'écoulement de gaz, de la hauteur d'immersion de deux busesà fluides dans le réacteur et du diamètre de la buse sur la retenue de gaz sans circulation c.-à-d. le mélange gaz-liquide dans le tube d'aspiration seulement (Egd) et sur la retenue de gaz avec boucle de circulation (Eg). Le taux d'écoulement critique du liquide exigé pour la transition du tube d'aspiration jusqu'à la boucle de circulation aégalementété déterminé. La retenue de gaz aété mesurée en utilisant la technique de vanne d'isolement. La retenue de gaz dans le tube d'aspiration et la boucle de circulation a augmenté avec l'accroissement des taux d'écoulement du liquide et de gaz. Une augmentation substantielle du taux d'écoulement du liquide aété observée pour un même Eg en fonction de l'augmentation du diamètre des buses et la buse se trouvant au bord supérieur du tube d'aspiration a une retenue de gaz plusélevée. Il aété noté qu'aucune recirculation significative de bulles de gaz dans la goulotte de descente de l'espace annulaire n'aété observée jusqu'à ce qu'un taux d'écoulement particulier du liquide ne soit atteint. Un tracé de retenue de gaz avec et sans circulation et détermine le taux minimum d'écoulement de liquide requis pour réaliser une boucle complète de circulation. Le taux minimum d'écoulement requis pour réaliser la boucle complète de circulation augmente avec l'accroissement du taux d'écoulement de gaz et est au minimumà la hauteur minimum d'immersion des deux busesà fluides (Hn = 50 mm).

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The hydrodynamics of a gas-solid fluidized bed (FB) is affected by the bubble diameter, which in turn strongly influences the performance of a fluidized bed reactor (FBR). Thus, determining the bubble diameter accurately is of crucial importance in the design and operation of an FBR. Various equations are available for calculating the bubble diameter in an FBR. It has been found in this study that these models show a large variation while predicting the experimentally measured bubble diameters. Accordingly, the present study proposes a new equation for computing the bubble diameter in a fluidized bed. This equation has been developed using an efficient, yet infrequently employed computational intelligence (CI)-based datadriven modelling method termed genetic programming (GP). The prediction and generalization performance of the GP-based equation has been compared with that of a number of currently available equations for computing the bubble diameter in a fluidized bed and the results obtained show a good performance by the newly developed equation.