Talk 1:

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Title:   Numerical simulation of fluidized beds with Geldart D particles
Speaker: Naval Koralkar
Time:    16:30

Talk 2:
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Title  : Numerical simulation of drops in a disc and doughnut pulsed column
Speaker: Raj Kumar Saini
Time   : 17:00

Abstracts:

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Talk 1:

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Gas solid fluidized beds are encountered in various industries such as chemical, energy sector and process industries. The physics of fluidized bed is modelled using two commonly used numerical approaches, two-fluid model (TFM) which treats both the carrier and disperse phase as continuum and the other one couple discrete element method to computational fluid dynamics (CFD-DEM) method. The most recent method of simulating flow of mixture, couples the macroscopic governing equations for gas phase to the second law of motions for individual particles in the system. This method is more accurate but is computationally intensive as it traces individual particle. One of the ways to decrease the computation time is to simulate the scaled down geometry of the actual bed; however, scaling of fluidized bed is non-trivial. The other challenge in modelling gas-solid flow is the selection of appropriate correlations to account for the drag between the fluid and the solid phases. The objectives of the present work are first, to investigate the scalability of the numerical simulations and secondly, to compare the performance of different drag models to predict the experimental observations.

To that end, coupled CFD-DEM simulations of two and three dimensional model and prototype bubbling fluidized bed are carried out using the open source code MFIX (Multiphase Fluid with Interphase eXchange). The experimental studies is carried at Department of Energy's National Energy Technology Laboratory. Experiments are carried out using Geldart group D nylon particles for three different superficial gas velocities.  Six different drag models as implemented in MFIX are tested. The average gas and solid phase properties such as voidage, bed pressure drop, air velocity, and different moments of the particle velocity distributions, are compared with the experimental results. A good qualitative agreement between the simulated and experimental result is observed. Also the effect of sampling window on the average particle phase properties is studied.

Talk 2:
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Solvent extraction is one of the key unit operations in the process industries. The disc and doughnut pulsed column is emerging as one of the best choices because of its much smaller footprints compared to the most commonly used mixer-settler type extraction units among various types of solvent extraction units. Hydrodynamics of single and multiphase flow (two phase) in a disc and doughnut pulsed column is studied in literature using modelling, experimental and simulation techniques.

The objective of the this work is to investigate the pulsatile flow of single and multiphase fluids in a disc and doughnut column using the techniques of CFD, in order to understand the effect of the operating conditions on the drop dynamics on the deformation, coalescence and breakage of the droplets and the distribution of the drop size of the dispersed phase. Single-phase simulations are carried out by considering with three stages of a pulsed column, which is found to be the minimum number of stages to be simulated in order to ensure the periodic nature in the central unit. The results for velocity profiles and contours of the fluid in the central stage are compared with reported results in the literature and it is found to be in good agreement. The flow of two immiscible liquids is also simulated. Simulation based on the volume of fluid method show that stable drop is observed to form at the doughnut surface in the column when the flow achieves a stationary state. The stability of the drops is found to be sensitive to the flow intensity of the continuous phase. The fluctuation of the droplet surface increases with the flow intensity of continuous phase. The simulation result also indicates that probability of coalescence and breakage increases with the number density of the droplets.