In this study, the axial dispersion characteristics of
a fixed-bed
reactor with different packed structures were investigated via computational
fluid dynamics (CFD) simulation. The discrete element method was employed
to develop the physical model of a fixed bed. Then, CFD simulations
were performed to investigate the flow resistance coefficient under
different Reynolds numbers. The prediction values were in fair agreement
with those calculated by the Carman equation, thereby validating the
proposed CFD model. The tracer pulse method and the step method were
employed to evaluate the residence time distribution characteristics
in the fixed-bed reactors where the mean residence time and axial
dispersion coefficient were calculated. The distribution characteristics
of the tracer concentration and fluid velocity were also obtained
and used to explain the mixing performance of the fixed bed. This
simulation study can contribute to the optimization design and scaling
up of reactors with porous packed structures.
Non‐Newtonian fluids flowing in a concentric annulus have been widely observed in industrial chemical processes. In this study, the hydrodynamic characteristics of a non‐Newtonian fluid (polymer solution) in concentric annulus are investigated using computational fluid dynamics (CFD) modeling and numerical simulation methods. First, a simple grid independence analysis is carried out to select appropriate grid parameters. Then the rationality of the proposed CFD model is confirmed by the near‐wall velocity profiles. Based on the validated model, the effects of the fluid properties and radius ratio on the flow structure characteristics are studied at various inlet velocities. According to the simulated flow fields (i.e., velocity, pressure, strain rate, and wall shear stress), the flow pattern, flow resistance, and residence time distribution characteristics are analyzed in the laminar and turbulent regimes. The presented results show that non‐Newtonian fluids have unique flow behaviors in concentric annulus when compared with Newtonian fluids.
In this study, the mixing quality of high-viscosity yield stress fluid (Carbopol aqueous solution) under laminar and turbulent flow regimes was evaluated through a numerical experimental study. A three-dimensional computational fluid dynamics large-eddy simulation (CFD-LES) model was employed to capture large-scale vortex structures. The proposed CFD model was validated by the experimental data in terms of mean velocity profiles and velocity-time history. Thereafter, the CFD model was applied to simulate the residence time distribution using the tracking technique: tracer pulse method and step method. In addition, the non-ideal flow phenomena caused by molecular diffusion and eddy diffusion were evaluated. The effects of the rheological properties on the mixing performance were also investigated. The presented results can provide useful guidance to enhance mass transfer in reactors with high-viscosity fluids.
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