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 (Δp) is found to be minimum (Recritical = 75, Δp = 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.
Hydrodynamics and residence time distribution 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. In the present work, performance of the stirred vessel is studied using computational fluid dynamics (CFD). The flow field and associated solid suspension characteristics are predicted using the Euler-Granular approach. The draft tube baffle configuration with three inner baffles and six outer baffles is introduced to enhance the performance of the stirred vessel. The chaotic mixing among fluid elements is obtained by tracking particles in the flow domain through the Lagrangian way by solving Newton's 2nd law. This is qualitatively analyzed using Poincaré map and quantitatively evaluated using Shannon entropy to characterize the extent of chaotic mixing in stirred vessel. The performance of stirred vessel is further investigated through stimulus-response tracer techniques (Residence time distribution, RTD) to detect design flaws such as by-pass and dead zones of a stirred vessel. This is analyzed for a wide range of operating parameters. The RTD data is evaluated using two-parameter model to quantify non-idealities and to find an optimum outlet location in a stirred vessel. Further, gas is dispersed into the flow domain to reduce the extent of the non-ideal parameters, accordingly an optimum gas injection point is identified that supports the design of stirred vessel.
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