Faculty Publications
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Item Computational investigation of hydrodynamics and solid circulation in fluidized bed column(Taylor and Francis Ltd., 2021) Sriniketh, A.; Ali, A.A.Gas–solid fluidized beds are commonly used in applications where high heat and mass transfer is required, which are influenced by the quality of mixing in the bed. This largely depends on the design of gas distributor and operating conditions. Hence, in the current work, the influence of distributor design on hydrodynamics in a 3D bubbling fluidized bed column is investigated using CFD. Here, Euler-Euler model is used to predict the flow field. The predicted bed pressure drop is analyzed for various superficial gas velocities, and it has been validated with the experimental data. The solid circulation rate is calculated to quantify the flow field, and it is improved by incorporating various gas distributors such as flat, convex and concave perforated plates. The magnitude of solid circulation rate is found to be the highest for convex plate, showing that it is more advantageous than the conventional flat plate configuration. Further, the effect of operating temperature and the influence of baffle on gas–solid flow are analyzed. The rate of solid circulation is found to decrease with increase in temperature and in the presence of baffle. © 2019 Taylor & Francis Group, LLC.Item Computational modeling of hydrodynamics and mixing in a batch stirred vessel(Taylor and Francis Ltd., 2021) Falleiro, L.H.; Ali, A.A.In this work, the hydrodynamics, mixing and sedimentation is numerically investigated in the batch stirred vessel through CFD. The flow field obtained by performing transient CFD simulations using multiple reference frame (MRF) and sliding mesh approach along with standard k-? turbulence model. The velocity field is investigated spatially and temporally and liquid circulation is quantified at various impeller speeds to find an optimum impeller speed. The importance of geometry of the draft tube baffles is investigated by quantifying the vorticity, mixing time, power requirement and quality of suspension in the batch stirred vessel. It is found that suspension quantity in a batch stirred vessel is strongly dependent on the hydrodynamics. The role of the draft tube and the inner baffles is further analyzed and found that proper positioning and length of the baffles is necessary to improve the turbulence characteristics and the quality of the suspension. © 2019 Taylor & Francis Group, LLC.Item Computational investigation of flow field, mixing and reaction in a T-shaped microchannel(Taylor and Francis Ltd., 2021) Madana, V.S.T.; Ali, A.A.Microfluidics plays an essential role in process intensification, carrying out reactions safely and enhancing mass and heat transfer coefficients. In this work, hydrodynamics, mixing and reaction in the microchannel are investigated numerically and experimentally. To predict the flow field, three dimensional transient CFD simulations are performed. The irreversibility induced by the flow is used to quantify the liquid circulation. To improve the flow field, the geometry of the microchannel is modified by placing obstacles. It is found that geometric modifications have a significant effect on the hydrodynamics and hence mixing and reaction. The axial and lateral mixing are analyzed for various obstacles using Residence Time Distribution (RTD). The mixing index is calculated to characterize lateral mixing and to find an optimum configuration that supports flow field and mixing. Further, the implications of these obstacles on a fast neutralization reaction in the microchannel are studied. © 2020 Taylor & Francis Group, LLC.Item Effect of baffle configuration on hydrodynamics and solid suspension in a continuous stirred vessel(Taylor and Francis Ltd., 2022) Ali, A.A.; Bharathesh, K.Hydrodynamics of stirred vessel is difficult to predict due to complex flow conditions existing inside the reactor. Hence in this present work, hydrodynamics and solid suspension in a continuous stirred vessel are numerically investigated using Computational Fluid Dynamics (CFD). To predict the flow field, transient 3 D CFD simulations are performed using Multiple Reference Frame along with Sliding Mesh approach and realizable k-ε turbulence model. The flow field is quantified by spatial/temporal variation of liquid velocity magnitude and liquid circulation. To improve the performance of the stirred vessel, draft tube baffle configurations are proposed and these predictions are compared with the unbaffled system. Further, the suspension characteristics of solids are predicted using the Euler-Granular model and quantified by calculating cloud height in stirred vessel system. The solid concentration is found to be uniform in the baffled stirred vessel and it is concentrated at the bottom of the vessel in the unbaffled stirred vessel. Thus, the proposed draft tube configuration supports in achieving the uniform distribution of solids and overcomes sedimentation of solids in stirred vessel system. © 2021 Taylor & Francis Group, LLC.Item Experimental and computational investigation of solid suspension and gas dispersion in a stirred vessel(American Institute of Physics Inc., 2022) Ali, A.A.; Kumar, B.; Madana, V.S.T.Hydrodynamics and residence time distribution (RTD) of fluid elements are key parameters to characterize the performance of stirred vessel. They are governed by geometric and operating parameters of the stirred vessel (SV). In the present work, the performance of the stirred vessel is studied using computational fluid dynamics (CFD) with realizable k-ϵ turbulence model. The multiple reference frame and sliding mesh approach are used for impeller motion. The solid-liquid flow and associated solid suspension characteristics are predicted using the two-fluid model (Euler-Granular). The performance of the stirred vessel is characterized by analyzing predicted velocity magnitude, solid concentration (suspension quality), and solid sedimentation. This is compared with the stirred vessel with draft tube baffle configuration (three inner baffles and six outer baffles). The recirculatory flow in draft tube SV helps to achieve uniform suspension and less sedimentation. Further, CFD simulations are carried out in Lagrangian way to analyze chaotic mixing among fluid elements. This is qualitatively analyzed using Poincaré map and quantitatively evaluated using Shannon entropy. The extent of chaotic mixing in draft tube SV is found to be high. The performance of the stirred vessel is further investigated through stimulus-response tracer techniques (RTD) to detect design flaws such as bypass and dead zones. This is analyzed for a wide range of operating parameters and identified optimum conditions (flow rate, impeller speed) for the operation of SV. The four different outlet pipe locations are chosen in SV. The bypass and dead volume are analyzed accordingly, and an optimum outlet pipe location is found. To reduce the extent of non-ideal parameters, three different gas source locations are considered and gases are dispersed in the form of bubbles. The gas dispersion at optimum gas injection point is found to reduce non-ideal parameters and improve the design of stirred vessel. © 2022 Author(s).Item Computational investigation of hydrodynamics, flow regimes and bubble size distribution in an airlift reactor(Taylor and Francis Ltd., 2023) Ali, A.A.; Bhasme, M.Airlift reactors (ALRs) are widely used in the chemical, petrochemical biological industry. A fundamental understanding of the flow field in these airlift reactors are necessary for efficient design and scaling up. In this work, the behavior of the flow field is investigated using the Euler–Eulerian approach. The liquid phase is modeled as continuous and the gas phase is dispersed in the form of bubbles. Three dimensional (3 D) transient computational fluid dynamics (CFD) simulations are performed to characterize flow behavior in ALR. The spatio-temporal variations in the flow field are quantified and an optimum liquid level in the ALR is determined. Various gas source locations are chosen and their effects on bubble plume motion are analyzed to find an optimum gas injection point that supports plume oscillation. Further, CFD simulations are performed to identify the prevailing flow regime in ALR for various gas source locations, and it is compared with experimental observations. The homogeneous and heterogeneous flow regimes are observed at lower and higher flow rates, respectively. The bubble size distribution is predicted using population balance equations through bubble coalescence and breakage models with interphase force formulations. This is computed through the discrete method of moments. The bubble size distribution is found to be narrow at lower gas flow rates and wider at higher gas flow rates. These predictions provide a unified description to characterize flow regimes in ALR. © 2022 Taylor & Francis Group, LLC.Item EFFECT OF NOZZLE CONFIGURATION ON PERFORMANCE OF A SPRAY DRYER(University of Chemical Technology and Metallurgy, 2024) Ali, A.A.; Kumar, S.S.In this work, hydrodynamics and drying characteristics of spray dryer is numerically investigated using computational fluid dynamics (CFD) using Euler-Lagrangian (EL) approach. The gas phase is modelled as the continuous phase and solid particle as the dispersed phase. The turbulence in the gas phase is predicted using RNG version of k-ε model. As airflow pattern influences the time spent by particle in drying chamber, the spatial variation of air velocity and its circulation rate is quantified. Accordingly, optimum conditions for drying the feed slurry are determined. Further, five different outlet pipe locations are chosen and the optimum location is identified which supports the highest evaporation rate. To improve the product quality, conventional nozzle is modified and particle impact positions are analyzed. The particles impact positions on the dryer’s surface are found to be minimum for the proposed nozzle configuration and it improves the final product quality. © (2024), (University of Chemical Technology and Metallurgy). All Rights Reserved.Item CFD MODELLING OF NON-ISOTHERMAL PROTON EXCHANGE MEMBRANE FUEL CELL (PEMFC): ROLE OF BAFFLES(University of Chemical Technology and Metallurgy, 2024) Ali, A.A.; Ganta, N.Through oxidation (H2 ) and reduction (O2 ) reactions, the chemical energy of the fuel is converted by proton exchange membrane fuel cell (PEMFC) into electricity and is therefore considered an energy converter. In this work, performance of a PEMFC is numerically investigated using computational fluid dynamics (CFD). To characterize the non-isothermal behavior of PEMFC, 3D transient CFD simulations are performed. The distribution of H2 and O2 mass fractions, temperature, and current density profiles are analyzed for various operational conditions. The optimum condition (voltage = 0.1 V; thickness of gas diffusion layer (GDL) = 0.0127mm; thickness of catalyst layer (CL) = 0.014mm) for an operation of PEMFC is identified Trapezoidal and rectangular baffles are proposed into the flow channels to enhance the performance of PEMFC. The rectangular baffle configuration supports maximum conversion of reactant gases (H2 = 24.16 %, O2 = 41.72 %) in comparison with the trapezoidal baffle. A significant increase in conversion is reported when the number of baffles in the gas flow channel is increases. Thus, PEMFC performance is enhanced with baffle configuration. © (2024), (University of Chemical Technology and Metallurgy). All Rights Reserved.