Faculty Publications
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Publications by NITK Faculty
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Item Numerical investigation of engulfment flow at low Reynolds numbers in a T-shaped microchannel(American Institute of Physics Inc. claims@aip.org, 2020) Madana, V.S.T.; Ali, B.Microreactors play a major role in the intensification of industrial processes. The performance of microfluidic devices depends on the flow behavior and flow regimes present in such systems. In this work, single-phase flow behavior and associated flow regimes in a T-shaped microchannel are numerically analyzed using computational fluid dynamics (CFD). To predict the single-phase flow regimes, three dimensional transient CFD simulations are performed. The critical Reynolds number (Re) at which flow regime transition and onset of engulfment occur is identified (Recritical = 300). To achieve engulfment flow at lower Re, the inlet geometry of the microchannel is modified as a convergent (C)-divergent (D) section and its effect on engulfment flow is analyzed. When the C/D ratio is 9:1, the predicted pressure drop (?p) is found to be minimum (Recritical = 75, ?p = 5.4 kPa). The understanding of the engulfment flow regime is exploited through residence time distribution (RTD). The predicted RTD profiles indicate strong recirculation among vortices. The mixing index is calculated to quantify RTD, and it is found to be minimum when the C/D ratio is 9:1. The mixing performance is further verified by introducing buoyant particles in Lagrangian manner using discrete phase modeling. The predicted dynamics are qualitatively and quantitatively analyzed through Poincaré maps and Shannon's entropy for various convergent-divergent inlets to characterize mixing. Once again, the C/D ratio of 9:1 supports in enhancing mixing in the microchannel. Hence, the proposed micromixer based on geometric modifications at the inlet helps achieve the engulfment flow regime at low Re. © 2020 Author(s).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 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).