Band 21, Heft 2

Geldart classified powders into four categories and assigned each category its own unique characteristic. Geldart A particles, being easily aeratable, show a unique feature of ‘Homogenous expansion’ before bubbling. In this work, an additional feature for the Geldart chart is proposed which adds significant utility for the processing of Geldart A particles. CFD was used to characterize the entire Geldart A region of the Geldart chart based on detailed fluidization behavior. For this, Eulerian–Eulerian Two-fluid model (TFM) simulations were conducted for 25 particle systems across the entire span of the Geldart A region. The simulations (Solid volume fraction (SVF) contours) of bed evolution, taken before the appearance of multiple bubbles, were analyzed in detail. The particle systems were then sub-categorized into Red (5% average bed expansion), Orange (12.5% average bed expansion), and Green (30% average bed expansion) sub-types. The sub-types were plotted on Geldart chart, and for the first time a continuum heat map was generated, from which the ‘level of fluidizability’ of all Geldart A powders can be conveniently gaged. The map can be used for a more informed choice of powder for various industrial applications. Also, the A/B boundary proposed by Verloop was found to be a better fit for our proposed continuum when compared to the original Geldart A/B boundary. The 2D Simulation results performed in this work, found adequate validation against experimental findings in literature. Further, fine mesh 2D simulation results compared well with 3D simulations for dense bed, and were thereby deemed adequate for revealing dense bed behavior before onset of multiple bubbles.

The ion transport properties across the membrane under conditions of different membrane types, solution concentrations, flow rates and temperatures were investigated in a four-compartment reactor. By combining linear sweep voltammetry and chronopotentiometry, the limiting current density ( I lim ), the ion transition time ( τ ) and the difference between ion transport numbers in the membrane and the solution ( t m – t s ) were determined. And the diffusion boundary layer thickness ( δ ) of the membrane-solution system at steady-state conditions was measured by electrochemical impedance spectroscopy. The results show that the use of Selemion membrane and the increase of solution concentration, flow rate and temperature, I lim and τ increase, t m – t s and δ decrease. This means the concentration polarization of the system is weaker and complete concentration polarization is more difficult to occur. At the same time, I lim , τ and t m – t s are strongly related to solution concentration and temperature, while the diffusion boundary layer thickness is mainly affected by solution concentration and flow rate. Additionally, I lim of anion exchange membranes is larger than that of cation exchange membranes due to the difference in migration rates of anion and cation.

This paper evaluates the impact of a special design of non-uniform surface roughness on the operating parameters of a gas–solid cyclone numerically. The cyclone surface is divided into 32 separate rings with different roughness heights when the roughness height varies from 0.2 to 3 mm. The results show that the tangential velocity is reduced and the axial velocity is enhanced by increasing the height of non-uniform roughness. It is observed that the cyclone with smooth walls can collect 7 μm solid particles while 3.7 and 2.77 μm particles can be separated by one-inlet and two-inlet cyclones, respectively. For the cut-off size diameter of d 50 , the one-inlet cyclone with smooth walls can collect the particles with a diameter of 1.24 µm, while the cyclone with R Nu  = 0.2, 0.5, 1, 2, and 3 mm can collect 1.3, 1.6, 1.8, 0.83, and 1.88 µm particles, respectively. The results demonstrate that the erosion rate decreases with the roughness and this reduction is larger for the one-inlet cyclone.

The burden surface shape and distribution in the shaft directly affect the gas distribution, heat transfer and chemical reactions inside the blast furnace. The current study developed a three-dimensional model of bell-less top charging to investigate the influence of the “central coke charging/sub-central coke charging” (CCC/SCCC) mode on the burden surface shape, burden distribution, and mass percentage of ore-to-coke (O/C). The results showed that the burden height of the region between the middle and edge is low by applying the CCC mode, while there is a heap valley in the center and a heap top in the middle region when the SCCC mode was adopted. In radial direction, the mass percentage of bigger size coke in the middle region is largest for the CCC mode, while the largest of the mass percentage was obtained in the center region by applying the SCCC mode. In longitudinal direction, the mass percentages of bigger coke and ore at the top region are largest for both modes. Besides, the mass percentage of O/C increased and then decreased to zero at the center for both modes. And the maximum of the mass percentage of O/C were 7.63 and 7.38, respectively.

Microfluidic devices/systems, including Micro-Total-Analysis-System (µTAS), Point of Care Testing (POCT) and Lab-On-a-Chip (LOC) are used in many chemical and biological assays applications. Among the vital tasks that these microfluidic devices must achieve essentially include a high degree of mixing and accordingly, micromixers are being used for the same purpose. The design depends on the yield required in particular application. In the proposed study, the four kinds of heart-shaped micromixers with different obstacles have been studied through simulations. The influence of the shape and size of different obstacles viz., circular shape, diamond shape, teardrop shape, and heart shape obstacles on the performance characteristics has been studied. The performance characteristics namely, the mixing index and pressure drop have been used. In accordance with the study, a heart-shaped micromixer with heart shape obstacles (HSM-HSO) has come out to be the most efficient micromixer due to the significant chaotic convection effect. The heart-shaped micromixer with heart shape obstacles (HSM-HSO) of size 0.350 µm × 0.350 µm has shown better performance for a wider range of Reynolds number (Re), i.e., mixing index of Re > 0.99, for Re of 0.1 and Re in the range of 15–45.

Microfluidics is thought to have a high development potential and a wide range of applications in biomedical research. The design of micromixers has gotten a lot of attention because they are such a crucial aspect of microfluidic devices. The passive micromixer has the advantages of simple construction and steady performance over the active micromixer. In this paper, a fractal wall micromixer is proposed, and the flow characteristics and mixing process of the secondary fractal double wall micromixer are studied using intuitive flow patterns and quantitative calculation methods. The results show that the mixing efficiency of secondary fractal wall is higher than that of primary fractal wall, and with the increase of h , the mixing efficiency and pressure drop begin to decrease gradually. When there is a secondary fractal wall structure on both sides, when Reynolds number (Re) = 0.1, the mixing efficiency of the outlet can reach 95%, and when Re = 100, the mixing efficiency of the outlet can reach 99%, almost complete mixing. The fractal wall micromixer has good mixing effect and shows great application potential in chemical engineering and biological engineering.

Among the pharmaceutical compounds, tetracycline is the second most common group of antibiotics in terms of production and consumption worldwide, which their entrance in to hospital, domestic and industrial wastewaters pollute water sources and environment and finally leads to antibiotic resistance. The aim of this study was to determine the efficiency of electrochemical processes, Fenton, electro-Fenton (EF) and sono-electro-Fenton (SEF) separately and using Graphite (G)/β-PbO 2 anode to remove tetracycline from aqueous solutions. First, experiments for the electrochemical process by the response-surface methodology (RSM) using variables including pH (3–9), initial tetracycline concentration (20–100 mg/L), electrolysis time (4–45 min) and current density (0.5–4.5 mA/cm 2 ) was designed and the optimal conditions of these variables were 3.5, 25.6 mg/L, 42.6 min, and 1.98 mA/cm2, respectively. Under the optimal conditions of the electrochemical process, the effect of FeSO 4 with values of 0.02-0.08 g/250 mL in the Fenton process and the effect of H 2 O 2 of 0.05–0.5 mg/L in the EF process were investigated, and the optimal values of 0.06 g/250 mL and 0.2 mg/L was obtained for FeSO 4 and H 2 O 2 , respectively. Under optimal conditions, the removal efficiencies of SEF, EF, sono-electrochemical (SEC), electrochemical, Fenton and ultrasonic processes were 98.8%, 93.6%, 87.9%, 81.3%, 71.6%, and 11.5%, respectively. G/β-PbO 2 anode had only 37.5% higher removal efficiency than graphite anode. Under the optimal conditions of SEF process, changes in toxicity reduction by bioassay with E. coli and Staphylococcus aureus bacteria were 86% and 58.4%, respectively, and the kinetic study showed that the removal of tetracycline by SEF process with R 2 =0.9975 followed the pseudo-first-order kinetics. Finally, intermediate compounds obtained from tetracycline analysis were identified using LC-MS analysis.

The one-dimensional premixed laminar freely propagating flame was used to numerically simulate the laminar combustion characteristics of primary reference fuel (PRF). The equivalence ratios are set as 0.7–1.5 at initial temperatures of 298, 358, and 403 K, initial pressures of 1, 2, and 5 atm. Laminar burning velocity (LBV), adiabatic flame temperature (AFT) and mole fractions of H, CO, CO 2 , C 2 H 4 at Φ = 1.0 are investigated. Meanwhile, temperature sensitivity, rate of production (ROP) and reaction pathway are analyzed. The results show that LBV and AFT decrease with n-heptane doping ratios increasing. With the increase of initial temperatures, the LBV and AFT increase. With the increase of initial pressures, the LBV decreases, while AFT increases slightly. Through temperature sensitivity analysis, it can be found that R1 H + O 2 ⇔ O + OH and R97 OH + CO⇔ H + CO 2 are main exothermic reactions. R12 H + OH + M ⇔ H 2 O + M and R56 H + CH 3 (+M) ⇔ CH 4 (+M) are major endothermic reactions. n-Heptane is decomposed into C 2 H 4 and C 2 H 3 , and iso-octane is decomposed into CH 3 , CH 3 O, and CH 2 O. These small molecule species are further oxidized to generate HCO, which is finally changed into CO 2 .

The initial liquid film is the basis of material evaporation during distillation, so it is of great significance to study the distribution of the initial liquid film of distributor in the process of scraping film molecular distillation. In this paper, CFD is used to study the distribution of distributor liquid film, and the mathematical model of the triangular tooth distributor and its peripheral cylinder is established, and the effects of the triangular tooth distributor’s speed, feed rate, and feed position on initial liquid film uniformity are investigated. And the reliability of the numerical simulation model is verified by experiments. In this paper, a new feed structure that includes an intermediate feed device and inclined tooth distributor is proposed and researched by numerical simulation. And compared with the previous structure, the liquid film distribution is more uniform. This has important guiding significance to the optimization of equipment in production.