Wentan Wang

Simulation of Solid Suspension in a Stirred Tank Using CFD-DEM Coupled Approach

Abstract Computational fluid dynamics-discrete element method (CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank. Influences of operating conditions and physical properties of particles ( i.e ., particle diameter and density) on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied. The wide distribution of particle angular velocity ranging from 0 to 10 5 r·min −1 is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.

Paclitaxel loaded human serum albumin nanoparticles stabilized with intermolecular disulfide bonds

We prepared paclitaxel-loaded disulfide-crosslinked human serum albumin nanoparticles (PTX-HSA-NPs) in a microfluidic platform. The entire process includes four steps, i.e., a pretreatment step to partially reduce albumin, a mixing and co-precipitation step, a reaction step, and a dialysis step. Two important factors dominate the successful preparation of stable PTX-HSA-NPs: one is the choice of the anti-solvent in the co-precipitation step, and the other is the reaction time in the reaction step. We demonstrated that the drug-loaded nanoparticles are stable against dilution by the inter-albumin disulfide bonds, but still have a quick drug release profile in the intracellular-mimicking reduction environment. Through cell studies, we showed that the albumin nanoparticle carriers are safe and characterized the cell toxicity of the paclitaxel-loaded nanoparticles with cell lines of human breast cancer cells (MCF-7).

Visualization of In Situ Oxidation Process Between Plasma and Liquid Phase in Two Dielectric Barrier Discharge Plasma Reactors Using Planar Laser Induced Fluorescence Technique

Cold atmospheric plasma is considered to be a promising approach for decontamination purposes, e.g. dyeing water decoloration. In order to better understand the complex mechanism of the plasma physics coupled with the plasma chemistry involved in the interaction of the polluted water with the discharge plasma, a novel approach was proposed to study the in situ oxidation process between the plasma and liquid phase in two dielectric barrier discharge (DBD) plasma reactors with different bottom shape (concave vs. plane), by using the planar laser induced fluorescence technique to visualize the process dynamics. Rhodamine B was employed as the tracer dye, which was gradually decomposed by the combined effect of the chemically active radicals (OH, O, H2O2, etc.) as well as the intense UV radiation in the DBD plasma process. The results showed that the DBD plasma filaments induced certain fluctuation on the Rhodamine B liquid layer, which accordingly intensified the mass transfer to a large extent thus accelerated the oxidation process. The comparison of the measured concentration fields in the two DBD plasma reactors illustrated that the DBD reactor #1 with concave bottom showed higher oxidation efficiency than the DBD reactor #2 with plane bottom. Additionally, the experiments demonstrated that the oxidation efficiency in the DBD plasma water treatment was much better than that in the reactor with pure oxidation by ozone gas, which can be further improved by injecting the additional oxygen gas bubbles into the liquid phase in the plasma reactor.

Simulation of single-phase reacting flows in micro-channel reactors by Lattice Boltzmann method

Fluid dynamics and mixing characteristics directly influence the progress of complex reactions in micro-channel reactors. When a parallel competing reaction takes place in micro-channels, it is crucial that the time scales of mixing and reaction match with each other to reach a high selectivity. In this work, “Villermaux/Dushmann” reaction is incorporated into the modeling scheme of Lattice Boltzmann method (LBM). Using this novel model, the characteristics of mixing and reaction process are simulated in micro-channels with different geometries. The results illustrate the significant impact of the mixing performance on the reaction selectivity. The established LBM model provides a theoretical approach to understanding the interplay of mixing and reactions in micro-channel reactors, which can be applied as a tool to optimize the design of micro-channel devices.