Larger Particle Diameter Research Articles

Filtration efficiency of particle-laden flows for thermal plug and abandonment of oil wells using turbulence modeling in porous media

In this work, the process of filtration of particles carried out by turbulent flows is investigated. The applied mathematical framework considers turbulent flow regime in the clear region and within the filter. The motivation for this work is to get insight on possible use of filters to separate thermite mixtures from a carrier phase and their use in thermal plug and abandonment of oil wells. Axisymmetric simulations are performed using the finite volume method. A macroscopic k-ε model is applied to handle turbulence. Pressure drop, stream function and turbulence field are computed. Using correlations in the literature, filter efficiencies are estimated based on calculated flow and pressure fields. Reynolds numbers varied from 2.3 × 103 to 4.6 × 104 for different permeabilities K ranging from 3.47 × 10−9 m2 to 8.89 × 10−9 m2, corresponding to filter particle diameters dp = 1.0 × 10−2 m and 1.0 × 10−3 m and different porosities (0.5 to 0.8). The results showed that pressure drop is strongly affected by porosity, permeability and Reynolds number; the stream function maps indicated wider stagnant zones for filters with larger particle diameters (higher permeabilities); turbulence fields showed slight generation of turbulence inside the filtration zone. The results for efficiency illustrated that, in case of filtrating thermite, higher inlet velocities, filters with particles of size 1.0 × 10−3 m and lower porosity filters favor the collection mechanism.

Computational characterization of the behavior of a saliva droplet in a social environment

The conduct of respiratory droplets is the basis of the study to reduce the spread of a virus in society. The pandemic suffered in early 2020 due to COVID-19 shows the lack of research on the evaporation and fate of droplets exhaled in the environment. The current study, attempts to provide solution through computational fluid dynamics techniques based on a multiphase state with the help of Eulerian–Lagrangian techniques to the activity of respiratory droplets. A numerical study has shown how the behavior of droplets of pure water exhaled in the environment after a sneeze or cough have a dynamic equal to the experimental curve of Wells. The droplets of saliva have been introduced as a saline solution. Considering the mass transferred and the turbulence created, the results has showed that the ambient temperature and relative humidity are parameters that significantly affect the evaporation process, and therefore to the fate. Evaporation time tends to be of a higher value when the temperature affecting the environment is lower. With constant parameters of particle diameter and ambient temperature, an increase in relative humidity increases the evaporation time. A larger particle diameter is consequently transported at a greater distance, since the opposite force it affects is the weight. Finally, a neural network-based model is presented to predict particle evaporation time.

Hydrodynamic Analysis of Tidal Current Turbine under Water-Sediment Conditions

The rivers connecting oceans generally carry sediment due to water and soil losses in China. Additionally, the maximum sediment concentration is 300 g/L, which is much higher than that of other countries. It is unknown whether seawater with sand particles will affect the power of tidal current turbine blades. It is therefore necessary to study the capture power of tidal current turbines in the water-sediment environment. In this study, the blade was divided into a number of transversal airfoil elements based on the blade element theory. The CFD-DPM model was employed to study the lift and drag coefficients of airfoil under multiphase flow, and the fluid–particle interaction was considered. The accuracy of this presented model was assessed using the experimental data of a 120 kW tidal current turbine in a water-sediment environment. Good agreement between the predictions and experimental data was observed. The effect of particle properties on the lift coefficient and the drag coefficient of airfoil were investigated in detail. Furthermore, the 120 kW tidal current turbine power was calculated based on the Blade Element Momentum theory under different particle concentrations. The results show that small diameter particles can improve the tidal current turbine power and the large diameter particle can reduce the power.

Synthesis and Properties of α-Mangostin and Vadimezan Conjugates with Glucoheptoamidated and Biotinylated 3rd Generation Poly(amidoamine) Dendrimer, and Conjugation Effect on Their Anticancer and Anti-Nematode Activities.

α-Mangostin and vadimezan are widely studied potential anticancer agents. Their biological activities may be improved by covalent bonding by amide or ester bonds with the third generation poly(amidoamine) (PAMAM) dendrimer, substituted with α-D-glucoheptono-1,4-lactone and biotin. Thus, conjugates of either ester- (G3gh4B5V) or amide-linked (G32B12gh5V) vadimezan, and equivalents of α-mangostin (G3gh2B5M and G32B12gh5M, respectively), were synthesized, characterized and tested in vitro against cancer cells: U-118 MG glioma, SCC-15 squamous carcinoma, and BJ normal human fibroblasts growth, as well as against C. elegans development. α-Mangostin cytotoxicity, stronger than that of Vadimezan, was increased (by 2.5–9-fold) by conjugation with the PAMAM dendrimer (with the amide-linking being slightly more effective), and the strongest effect was observed with SCC-15 cells. Similar enhancement of toxicity resulting from the drug conjugation was observed with C. elegans. Vadimezan (up to 200 µM), as well as both its dendrimer conjugates, was not toxic against both the studied cells and nematodes. It showed an antiproliferative effect against cancer cells at concentrations ≥100 µM. This effect was significantly enhanced after conjugation of the drug with the dendrimer via the amide, but not the ester bond, with G32B12gh5V inhibiting the proliferation of SCC-15 and U-118 MG cells at concentrations ≥4 and ≥12 μM, respectively, without a visible effect in normal BJ cells. Thus, the drug delivery system based on the PAMAM G3 dendrimer containing amide bonds, partially-blocked amino groups on the surface, larger particle diameter and higher zeta potential can be a useful tool to improve the biological properties of transported drug molecules.

A numerical study of effects of aerosol particles on the electric activities of a thunderstorm with a 1.5D aerosol-cloud bin model

Numerical simulations are carried out to study the effects of aerosol particles acted as cloud condensation nuclei (CCN) and ice nuclei (IN) on thunderstorm properties. A two-cylinder time-dependent cloud and aerosol interaction model with the spectral bin microphysical parameterization, explicit noninductive electrification and lightning process is utilized to explore the impacts. This model not only uses the high-resolution particle size bins to describe the distributions of aerosol particles and hydrometeors, but also can be applied to study the diffusional growth of aerosol particles to cloud droplets and to track the mass of both CCN and IN in hydrometeors. The simulated cloud properties show that increased CCN concentrations result in more numerous but smaller droplets and form ice particles less efficiently, producing less numbers of graupel and less efficient conversion to raindrops. Increased IN concentrations directly enhance the heterogeneous nucleation, and then boost the subsequent microphysical processes, contributing to the production of increasingly numbers of graupel which eventually pass through the melting layer and then enhance the precipitation. As CCN concentrations increase, the charge density gained by different mass-binned ice particles and total charge density significantly decrease due to reduced large ice particles with greater diameters than 360 μm. In contrast, as IN concentrations are further increased, dramatically increased large ice particles with greater diameters than 360 μm are produced and thus, support the enhanced charge density gained by different mass-binned ice particles and total charge density. Besides, as expected, the reduced (enhanced) lightning frequency is well explained by the reduced (increased) numbers of large ice particles (diameter>360 μm).

A novel strategy for rapid development of a self-sustaining symbiotic algal-bacterial granular sludge: Applying algal-mycelial pellets as nuclei

Algal-bacterial granular sludge (ABGS) is a promising technology for wastewater treatment, benefiting from the synergetic interactions between algae and bacteria. However, the rapid start-up of the ABGS system is not trivial. Herein, a novel strategy was proposed by applying the algal-mycelial pellets (AMPs) as the primary nuclei for accelerating the development of a self-sustaining symbiotic ABGS system. The results indicated that by using this strategy complete granulation was shortened to 12 days, much shorter than the control system without AMPs dosage (28 days). The ABGS had a large particle diameter (3.3 mm), compact granular structure (1.0253 g/mL), and excellent settleability (SVI30 of 53.2 mL/g). Moreover, 98.6% of COD, 80.8% of TN and 80.0% of PO43−-P were removed by the ABGS. The nuclei of targeted algae (Chlorella) and filamentous fungi (Aspergillus niger), the enhanced production of extracellular polymeric substances (especially proteins) and the enrichment of functional bacteria (such as Neomegalonema and Flavobacterium) facilitated the granules development. The low surface free energy (-69.56 mJ/m2) and energy barrier (89.93 KT) were the inherent mechanisms for the strong surface hydrophobicity, the easy bacterial adhesion, and the short granulation period. This study provides an economically feasible approach to accelerate ABGS granulation and sustain system stability.

Preparation, characterization and stability of nanoliposomes loaded with peptides from defatted walnut (Juglans regia L.) meal.

This study aimed to encapsulate walnut peptides with different molecular weights (crude peptides, 5-10kDa and < 5kDa) within nanoliposomes. The peptides with molecular weight (MW) of 5-10kDa (F2) was chosen as a representative sample to indicate the formation mechanism of nanoliposomes using scanning electron microscopy (SEM) and transmission electron microscope (TEM). The storage and simulated digestion experiment were carried out to evaluate the protective effect of nanoliposomes loading walnut peptides. Our results indicated that the amino acid composition was affected by peptide MW, and F2 exhibited the highest content of hydrophobic amino acids content. The MW of peptides also affected the distribution of the peptide of nanoliposomes, resulting in changes in particle size, ζ-potential, and encapsulation efficiency. The SEM exhibited that a high concentration of nanoliposomes might result in phospholipid fusion and larger particle diameters. The TEM showed individual nanoliposomes had spherical, smooth and full vesicle structures. The nanoliposomes could improve the stability of walnut peptides during storage. The maximum peptides retention after in vitro digestion was 61.6%, indicating a better sustained release in gastric digestion. The present study suggested that nanoliposomes can offer adequate protection to the walnut peptides during storage and digestion.

Characteristics of hydrate formation, decomposition, and phase equilibrium in the transition area formed by the high-pressure jet breaking and sand filling method

Marine hydrates mainly occur in clayey silt sediments, and their occurrence environment has the characteristics of a high clay content and low permeability, which seriously inhibit an increase in the gas production rate. This study presents a new method, the high-pressure jet breaking and sand filling method, to transform the natural gas hydrate (NGH) reservoir near the production well, whereby a water jet is used to form an area of sediment with large particle diameters and high permeability. Based on indoor experiments, we report the characteristics of hydrate formation, decomposition, and phase equilibrium in the transition area formed by this method under different sand particle sizes and mass fractions. The addition of sand at a high mass fraction with a large particle diameter significantly shortened the time required for rapid hydrate formation, prolonged slow hydrate formation, and reduced the increase in temperature. With an increase in the mass fraction of large-diameter sand, the free water content of pores increased, which made it easier to form hydrates with large particles, thus delaying the hydrate decomposition rate. The phase equilibrium curves of hydrates in clayey silt sediments with sand added at mass fractions of 30% and 50% were close to that of bulk hydrate in pure water at lower temperatures. As the temperature increased, the phase equilibrium curves gradually approached those of hydrates in clayey silt sediments.

Preparation of Monodisperse Poly(Methyl Methacrylate)/Polystyrene Composite Particles by Seeded Emulsion Polymerization Using a Sequential Flow Process

We develop a sequential flow process for the production of monodisperse poly (methyl methacrylate) (PMMA)/polystyrene (PS) composite particles through a soap-free emulsion polymerization of methyl methacrylate (MMA) using the first water-in-oil (W/O) slug flow and a subsequent seeded emulsion polymerization of styrene (St) using the second W/O slug flow. In this process, monodisperse PMMA seed particles are first formed in the dispersed aqueous phase of the first W/O slug flow. Subsequently, removal of the oil phase from the slug flow is achieved through a porous hydrophobic tubing, resulting in a single flow of the aqueous phase containing the seed particles. The aqueous phase is then mixed with an oil phase containing St monomer to form the second W/O slug flow. Finally, monodisperse PMMA/PS composite particles are obtained by a seeded emulsion polymerization of St using the second W/O slug flow. We compared the reaction performance between the slug flow and the batch processes in terms of particle diameter, monomer conversion, particle size distribution, and the number of particles in the system. We found that internal circulation flow within the slugs can enhance mass transfer efficiency between them during polymerization, which results in monodisperse PMMA/PS composite particles with a large particle diameter and a high monomer conversion in a short reaction time, compared to those prepared using the batch process. We believe that this sequential microflow process can be a versatile strategy to continuously produce monodisperse composite particles or core-shell particles in a short reaction time.

Collision phenomenon of lunar-soil particles under engine plume in a vacuum by numerical study

When lunar probes make a landing on the lunar surface, lunar-soil particles will be blown away by the engine plume with a significant collision phenomenon. The hard-sphere model, whose governing equations satisfy the momentum and kinetic-energy conservation equations, is used in research to study collision phenomena among particles having different diameters. The lunar-soil particles with different diameters collide 36.8–153.2 times on average, and the average speed is 50.4–426.7 m/s assuming no energy loss. When the recovery coefficient is reduced from 1.0 to 0.1, the average number of collisions increases by 16.3%–65.7%, and the average speed decreases by 24.2%–49.8%. Furthermore, the number of particle-occupied space grids increases for small-diameter lunar-soil particles as the collision process loses energy but decreases for large-diameter particles. Overall, the collision phenomenon among lunar-soil particles under engine plumes is important because it causes massive momentum and kinetic energy transfers among particles, which alters particle spatial trajectory and distribution.

Modeling Asian Dust Storms Using WRF‐Chem During the DRAGON‐Asia Field Campaign in April 2012

AbstractAsian mineral dust substantially influences air quality as well as weather and climate. It is important to forecast dust storms as a part of air quality modeling to protect public health and minimize the disruption to essential daily routines. In this study, we simulated the dust episodes during the DRAGON‐NE Asia field campaign in April 2012 utilizing the Weather Research and Forecasting model coupled with chemistry (WRF‐Chem) with 5 dust emission options and evaluated the model results with the measurements from multiple instruments including Korean geostationary satellites Geostationary Ocean Color Imager (GOCI) and Meteorological Imager (MI). The model well predicted the dust occurrences, transport, and vertically elevated structure, compared to the satellite aerosol optical depths (AOD), the Aerosol Robotic Network (AERONET) AOD and size distribution parameter Angstrom Exponent (AE), the ground‐based lidar and in‐situ observations. However, the model dust concentration varied depending on the selected dust emission option. The model also did not accurately simulate both AOD and AE. When the model AOD agreed with the AERONET AOD, AE did not agree. In general, the model concentrations were overestimated for large size particles (diameter 6–20 μm) and were underestimated for small size particles (0.5–3.6 μm), compared to the observed aerosol size distributions at surface in Korean Peninsula. Our analysis of the episode suggests that the dust is possibly mixed with the aerosols of anthropogenic origins in the Asian region. Therefore, accurate simulations of both anthropogenic aerosols and dust are helpful for evaluating models in the downwind region of the dust sources.

On the micro-PIV accuracy and reliability utilizing non-Gaussian particle images

Optical investigations of the dynamics of concentrated suspensions, such as in blood flows (Fitzgibbon et al. in Biophys J 108(10):2601–2608, 2015. http://doi/org/10.1016/j.bpj.2015.04.013) or slurry flows (Li et al. in Ocean Eng 163(October 2017):691–705, 2018. http://doi/org/10.1016/j.oceaneng.2018.06.046), are challenging due to reduced optical accessibility. Furthermore, the suspension particle image size can strongly deviate from the optimal particle image size for PIV measurements. Optical accessibility can be achieved by refractive index matching of surface labelled suspension particles. This results in particle images that are transparent in the particle image centre, but fluoresce at the particle image rim, resulting in ring-shaped particle images. In the present study, the influence of the particle image size on the cross-correlation result of such ring-shaped particle images is compared with Gaussian and plateau-shaped particle images. Particles of Gaussian image shape result from fully labelled particles with small image diameters and are commonly used in PIV measurements. Such particles are also utilized for the determination of the continuous phase velocities in the experimental part of the present study. With increasing image diameter, fully labelled particles are observed to assume plateau-shaped particle images. Monte Carlo simulations of synthetically generated images show that ring-shaped particle images have a superior behaviour, i.e. they assume a reduced displacement estimation error for noisy as well as for noise-free image data, compared to Gaussian and plateau-shaped particle images. This is also true for large particle image diameters when particle images are intersected at interrogation window borders or when different values of nonzero particle image displacements are considered. The detectability is similar for all three particle image shapes as long as particles do not intersect with the interrogation window border. Interestingly, for intersected particles of large image diameter, ring-shaped particle images show a slightly improved detectability compared to particle images of Gaussian and plateau shape. Furthermore, the detectability is insensitive against a nonzero particle image displacement. The usage of refractive index matched, ring-shaped particle images results in a good optical accessibility of the suspension. This allows to perform simultaneous cross-correlation evaluations on large ring-shaped particle images and fluid tracers with Gaussian particle images that are two orders of magnitude smaller compared to suspension particle images. Velocity measurements are taken on a suspension containing 5 vol% surface labelled, refractive index matched 60 upmu hbox {m} polymethylmethacrylate (PMMA) particles. Simultaneously, upmuPIV measurements of the carrier liquid flow are performed utilizing 1.19 upmu text {m} fluorescent polystyrene (PS) particles. Measurement results reveal a parabolic shape of the velocity profiles of both phases with a mean slip velocity of 7.4% at the position of maximum streamwise velocity in a 580 upmu text {m} high trapezoidal channel. An error analysis confirms the presence of these slip velocities within a 68.5% confidence interval. A measurement uncertainty in the order of magnitude of {mathcal {O}}(10^{-1} mathrm{px}) is reached for both fluid tracers and suspension particles. Overall, the present study demonstrates theoretically and experimentally that the usage of suspension particles with ring-shaped images is superior compared to Gaussian and plateau-shaped particle images of the same size. Additionally, the present study demonstrates that the usage of ring-shaped particle images allows to investigate suspension bulk dynamics by measuring velocity fields of both the suspended and the continuous phase simultaneously and with an overall uncertainty that is in the same order of magnitude as for standard upmuPIV measurements.Graphic abstract

Experimental Study on Influencing Factors of Aerosol Retention by Pool Scrubbing

During the process of containment depressurization venting, a high-temperature and high-pressure carrier gas with aerosol may be released into the spent fuel pool by a multihole injector. This aerosol in the carrier gas can be removed by pool scrubbing. A small-scale pool scrubbing facility was built to study the aerosol pool scrubbing phenomenon using a multihole injector. In this study, a gaseous mixture of nitrogen and steam is used to simulate a carrier gas, and insoluble solid particles of TiO2 are used to simulate aerosols in the carrier gas. Seven tests were performed to examine the dependence of the decontamination factor (DF) on the pool depth, particle diameter, and steam mass fraction. The results show that log(1/(1–Xm)) has a linear relationship with log(DF). DF varies exponentially with the pool depth, which has an influence on the retention of aerosols with a larger particle diameter. Particle diameters in the range of 0.2–0.52 μm have little effect on the DF. For a low-depth pool scrubbing, the steam condensation mechanism is dominant and the particle diameter does not have a significant effect on the DF. Moreover, the pool scrubbing model is discussed, and an empirical correlation is proposed to evaluate the DF of a pool.

Exploring mechanism of spout deflection in a spout fluidized bed

Spout deflection has been widely encountered in spout fluidized beds and can seriously narrow the operating range of normal spouting. However, the underlying mechanism of spout deflection phenomenon remains unknown. In this study, two hypotheses are proposed to explain the spout deflection mechanisms in spout fluidized beds, and two virtual experiments are designed to verify these two hypotheses respectively using the Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach. To verify Hypothesis I that the unsymmetrical particle fountaining, including particle spurting and particle falling, is one main reason for the spout deflection, virtual experiment I is designed where the particles are manually collected from the spurting surface and then symmetrically released to the free space above the two annulus regions to allow them to fall freely. Three symmetrical release patterns are compared, and the results confirm that the spout deflection disappears when the symmetrical particle fountaining is deployed. Moreover, two univariate tests are conducted to check the role of unsymmetrical particle falling and unsymmetrical particle spurting, respectively. The results further confirm the Hypothesis I. To verify Hypothesis II that the rheological properties of the annulus region also play a key role in determining whether the spout deflection happens, virtual experiment II is designed, in which the rheological properties of the annulus region are controlled by changing particle restitution coefficient, particle friction coefficient, background gas velocity, and particle diameter. The simulation results show that spout deflection tends to happen when the rheological properties in the annulus regions get better (i.e., larger particle restitution coefficient, smaller particle friction coefficient, larger particle diameter and larger background gas velocity). This work unveils the mechanism of spout deflection and is useful for process design and control in spout fluidized beds.

Experimental study on feeding characteristics of conical bottom pneumatic spout feeder for biomass pyrolysis

To solve the inherent problems that bridging and agglomeration phenomena of biomass feedstock existing in the biomass pyrolysis process, and the pyrolysis by-product can not be recycled reasonably, a novel conical bottom pneumatic spout feeder was designed, which used a conical hopper, pressure chamber and inclined spout pipe and utilized the gravitational potential energy of biomass to achieve a continuous and stable feeding process. Various tests were conducted experimentally to obtain the feeding characteristics of the new feeder, where different parameters of biomass and spout pipes were included. The results showed that a high moisture content and a large particle diameter had negative impacts on the feeding. The inclined angle and inner diameter (ID) of the spout pipe at the optimal feeding effect were 30°, 20mm, respectively, and the optimal range of spout gas velocity was 5-7m/s. A physical model of gas-solid flow was established based on Ergun and Bernoulli equations, and the mathematical correlation of the feeding rate was obtained. The deviation between the calculated values and the experimental values was within ±7%, indicating that the model had a high predict accuracy.

Simulation Study on the Effect of Dielectrophoresis Force on a Separation of Platelet from Blood Cell in a 3D Mini Channel

In recent years, separation of platelet from a blood cell received growing attention due to its usages for blood disorders or any disease treatment. However, the conventional separation techniques have some constraint due to its limitation to separate the cells with similar properties, costly, requires longer processing time, and less data accuracy. Thus, under the effect of a uniform electric field, a dielectrophoretic (DEP) force was applied as its ability to separate on a similar diameter size of cells, has lower cost, and requires only a small volume of sample. In this study, a 3D mini channel model with a Y-shape was developed using AutoCAD® and the velocity profile distribution was observed using ANSYS© Fluent version 19.1. Three parameters were observed at various an electric field intensity; E=±1 to ±5 V/mm, an electric field frequency, f=1 kHz to 1 MHz and a particle diameter; d=1.3 to 2.0μm. The results show the velocity was increased as the higher of electric field intensity and larger particle diameter. Besides, the DEP force was increased as the higher electric field intensity was charged for all tested frequencies. As well, as the higher the electric field intensity charged and the larger the particle diameter, the stronger of the DEP force. It can be concluded that the DEP force at d=2.0μm and E=5 V/mm was the optimum conditions and obtained the highest result among all the tested parameters. Under these optimum conditions, it shows the DEP force can separate the platelet from the blood cells.

Inhibited radiation transmittance and enhanced thermal stability of silica aerogels under very-high temperature

Silica aerogels are applied extensively in thermal insulation due to their extra-low density and thermal conductivity. However, this can be heavily undermined under high temperature, especially beyond 700–800 °C, due to not only a high transparency for radiation heat transfer, but also an instability caused by nanoparticle collapse. The present study demonstrated a solution to this problem by two steps. Firstly, the size effect of nanoparticles is explored by experimentally preparing unconventional samples composed of large-diameter particles (larger than 20 nm). The prepared sample microstructures and radiative characteristics are investigated by SEM apparatus and FTIR measurements, respectively. Additionally, based on the fractal structures reconstructed using the Diffusion-Limited Colloid Aggregation (DLCA) method, the effects of particle size on thermal stability of silica aerogels are theoretically investigated and the light shielding performance is numerically analyzed by the Generalized Multiparticle Mie-solution (GMM) method. The simulation and experimental results indicate that the enhanced size of nanoparticles can improve the radiative inhibition and thermal stability property under high temperature significantly. However, the ideal above should be refined as it brings an increasing contribution of conduction heat transfer. Thus, a novel structure of core-mantle nanoparticle is proposed to retain the excellent resistance in radiation but avoid an increased thermal conduction. The present work may pave a new direction for developing aerogels under extreme temperature conditions, compared with the widely-used opacifier addition.

Effect of the Ni/Al Ratio on the Performance of NiAl2O4 Spinel-Based Catalysts for Supercritical Methylcyclohexane Catalytic Cracking

Supercritical methylcyclohexane cracking of NiAl2O4 spinel-based catalysts with varying Ni/Al deficiencies was investigated. Thus, catalysts with Ni content of 10–50 wt.% were prepared by typical co-precipitation methods. The calcined, reduced, and spent catalysts were characterized by X-ray diffraction, O2 temperature-programmed oxidation, NH3 temperature-programmed desorption, N2 physisorption, O2 chemisorption, scanning and transmission electron microscopy, and X-ray fluorescence. The performance and physicochemical properties of the reference stoichiometric Ni3Al7 catalyst differed significantly from those of the other catalysts. Indeed, the Ni-deficient Ni1Al9 catalyst led to the formation of large Ni particles (diameter: 20 nm) and abundant strong acid sites, without spinel structure formation, owing to the excess Al. These acted with sufficient environment and structure to form the coke precursor nickel carbide, resulting in a pressure drop within 17 min. On the other hand, the additional NiO linked to the NiAl2O4 spinel structure of the Al-deficient Ni5Al5 catalyst formed small crystals (10 nm), owing to the excess Ni, and displayed improved Ni dispersion. Thus, dehydrogenation proceeded effectively, thereby improving the resistance to coke formation. This catalytic behavior further demonstrated the remarkable activity and stability of this catalyst under mild conditions (450 °C and 4 Mpa).

Numerical Simulation of the Mixing and Hydrodynamics of Asphalt and Rubber in a Stirred Tank

Computational fluid dynamics (CFD) has been used to analyze the mixing process of Asphalt and Rubber (AR) in a stirred tank with a six flat-blade disc turbine (Rushton), a down-pumping 45° pitched-blade turbine (PBTD-6) and a down-pumping propeller (TXL). The two-phase (solid-liquid) flow in the considered stirred tank has been modelled in the framework of an Eulerian-Eulerian approach, a laminar-flow assumption and a multi-reference frame strategy. The following effects have been investigated: The influence of the impeller speed, impeller type, crumb rubber (CR) particle diameter and initial CR particle loading on the quality of the CR particle’s suspension. The outcomes of the numerical simulations have been found to be in good agreement with the experimental results. The most important findings can be summarized as follows. The flow velocity on the lower part of the stirred tank, induced by the Rushton impeller, is the highest for the three considered mixing systems at the same impeller speed. The suspension quality of CR particles increases with the impeller speed. A larger particle diameter and a higher initial CR particle loading lead to an uneven distribution of particles. The degree of homogeneity in the Rushton impeller system is better than that of the PBTD-6 impeller system and the TXL impeller system at the same impeller speed, while the suspension uniformity of the TXL impeller system is the best possible one for the same power consumption.

Erosion Mechanism and Sensitivity Parameter Analysis of an innovative shaped Curved Pipeline

In the process of natural gas transportation, it is unavoidable for particles to collide with the wall, which will cause erosion of curved pipeline. Reasonable curved pipeline structure can effectively avoid the erosion failure. In this paper, an innovative shaped curved pipeline formed by extrusion of cylindrical indenter is presented. The erosion mechanism and sensitivity parameter analysis of the innovative shaped curved pipeline is studied by numerical simulation and compared with that of ordinary elbow. In addition, the effects of extrusion parameters and particle parameters on erosion of innovative shaped curved pipeline were also studied. The results show that the dent can effectively reduce the maximum erosion rate of elbow. With the increase of dent depth, the maximum erosion rate of elbow is decreasing. With the increase of indenter diameter, the ability to reduce the maximum erosion rate decreases. Under the harsh conditions of large particle diameter and high particle velocity, the dent has a better ability to reduce the maximum erosion wear rate, and the maximum erosion rate can be reduced by 26.8%.