We herein report the design of a two-dimensional cold moving bed with a wedge-shaped insert to investigate the effect of flow corrective insert on the flow characteristics of solid-solid mixture and further, to characterize the flow mechanism. The geometric dimensions and locations of the five types of wedge inserts used in this study were obtained using a reported method. Quartz sand and silica gel were selected as the solid experimental materials. The flow pattern, downward speed, and variation in local mixing ratios following complete mixing were explored. Six experimental conditions were established, and the mixing degrees along both the vertical and horizontal directions in the moving bed were measured. Fluctuation of the mixing degree was minimized when the insert half-angle θ2 was 50°, while at θ2=20°, the mixed materials above the insert shifted downward uniformly. The mixing ratio of quartz sand gradually decreased in the core flow region and increased in the transition region with increasing bed depth. In addition, as θ2 decreased, the stagnant region within the insert became smaller, and the mixing ratio increased. These results demonstrate that the flow corrective insert can enhance the funnel flow as well as influence the flow separation of the solid–solid mixture.
The impingement of fly ashes may lead to erosion of monolithic SCR De-NOx catalysts. In the present study, DPM (Discrete Particle Model) and CFD (Computational Fluid Dynamics) models were coupled to investigate the erosion behavior in honeycombed SCR De-NOx catalysts. The effects of particle diameter, particle density, gas velocity, turbulent diffusion, chemical reaction and channel size on catalyst erosion were analyzed in detail. Increasing particle Stokes number and equivalent diameter of channel can mitigate catalyst erosion, while the rise of gas velocity results in the increase of catalyst erosion rate. Turbulent diffusion promotes catalyst erosion caused by particles with low Stokes number, but the effect of turbulence on erosion by particles with high Stokes number is inactive. De-NOx chemical reaction leads to the increase of gas temperature on the wall region, which slightly prevents catalyst erosion. The simulation results show that inertial impact in the inlet section and turbulent diffusion in middle and outlet sections are the dominant mechanisms for catalyst erosion.
The dispersion and aggregation behavior of surface-modified nanoparticles in organic solvents is investigated by numerical simulations based on the discrete element method. In the simulation model, the van der Waals attractive force, the force based on the mixing energy between the surface modifier and solvent, and the elastic repulsion force by surface modifiers are considered as the interactions between two nanoparticles, in addition to the contact force, hydrodynamic drag force, and Brownian random force. The effects of the surface modifier, the solvent, and the volume fraction of nanoparticles on the dispersion and aggregation behavior are investigated. Decanoic acid-modified nanoparticles are well dispersed in cyclohexane because of the high affinity of decanoic acid with cyclohexane, but aggregate in toluene because of their low affinity with toluene. Oleic acid-modified nanoparticles are dispersed in toluene because of their high affinity with toluene. Furthermore, a phase diagram indicating the dispersion and aggregation behavior of surface-modified nanoparticles in toluene is projected onto the plane of the volume fraction of nanoparticles versus the interaction parameter between the surface modifier and solvent.
The present study presents a kind of novel ultrafiltration membrane which can be applied to purify water containing hexavalent chromium (Cr(VI)) ions and was prepared via the immersion phase inversion method. 2-Amino-4-thiazoleacetic acid was used as the additive of the novel ultrafiltration (UF) membrane and the membrane material was polyvinylidene fluoride (PVDF). The effects of technical parameters on the performance of the novel UF membranes were investigated. The prepared polymer blend membrane was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and contact angle measurements. The experimental results showed that the pure water flux of the membrane was 318.11 L/m2·h, the contact angle was 81.2° and the adsorption capacity of chromium ion was 165 µg/cm2. The modified PVDF membrane presented better adsorption abilities for chromium ion than that of the traditional membrane.
A simplified method was proposed for separately evaluating a fouling mechanism and a fouling degree in constant pressure dead-end microfiltration from limited flux decline data in reference to the conventional indices such as the silt density index (SDI) and the modified fouling index (MFI). Two indices were proposed: one is the fouling mechanism index (FMI) estimating the fouling mechanism; the other is the fouling degree index (FDI) evaluating the fouling degree. Both indices were calculated from the measurements of filtrate volumes collected during a given time interval at two different filtration times and analyzed based on the blocking filtration law involving the cake filtration mechanism. Moreover, these indices well evaluated the variation over time of the flux decline throughout the course of filtration in dead-end microfiltration. The usefulness and validity of the indices were verified from microfiltration experiments of a variety of colloids ranging from nanometer- to micrometer-size.
The thermal characteristic of a plate evaporator for boiling water have been experimentally investigated. Stainless-steel plates with five kinds of surface roughness (a mirror-polished surface and four kinds of polished plate surface, F2, F0, F-1, and F-2 polishing) were used for the investigation. The roughness order is F-2>F-1>F0>F2>mirror. The local boiling heat transfers were measured on the evaporator surface using ten thermocouples inside the evaporator. For a comparison of the heat transfer characteristic of the evaporator, the local boiling heat transfer coefficient was measured when the polishing direction was perpendicular or parallel to the water flow at a range of pressures (0.3–0.4 MPa) and flow rates (20–60 mL/min). The results indicate that the local heat transfer coefficient increased with increasing vapor quality at all surface conditions. For F0 polishing, the heat transfer coefficient on the surface with perpendicular polishing was much larger than that on the surfaces with parallel and mirror polishing. In particular, the heat transfer coefficient of the perpendicularly polished surface (F2 and F0 polishing) was increased six-fold in comparison with that of the mirror surface at a vapor quality of 0.35. However, for the F-1 and F-2 perpendicularly polishing plates, the heat transfer coefficients were smaller than those of the F0 and F2 perpendicularly polishing plates. For the F2 perpendicularly polished plate, heat transfer enhancement was confirmed, along with an increase in the number of bubbling points, on increasing the system pressure. For the polished surface, the heat transfer coefficient increased with increasing flow rate. This indicates that the bubble formation cycle was promoted by an increased flow rate.
BaTNR (barium trinitroresorcinate) particles were first synthesized through a segmented flow synthesis method. The optimal synthesis conditions of barium trinitroresorcinate (BaTNR) were obtained by orthogonal experimental design using segmented flow technology. The optimal synthesis conditions are composed of barium nitrate solution with a pH value of 5.5 and molar concentration of 0.20 mol·L−1, magnesium styphnate solution with a pH value of 4.5 and molar concentration of 0.15 mol·L−1, and reaction temperature of 65°C. The optimized batch conditions were compared with segmented flow arrangements through a reproducibility experiment, which indicates that BaTNR synthesized by segmented flow is superior to a conventional technique in terms of crystal morphology, uniformity and yield. In addition, the possibility of continuous and safe synthesis of BaTNR using micro-segmented flow technology is introduced.