Density Mesh Research Articles

Pseudo-Transient Modeling of Li Stripping in a Li/LLZO ASSB with Interfacial Defects

Lithium (Li) secondary batteries are commonly made of two Li insertion electrodes separated and imbibed of a liquid electrolyte. This common design could benefit from two improvements: (i) using a negative electrode of Li metal (3861 mAh g-1) rather than lithiated graphite (372 mAh g-1) and (ii) choosing a dendrite-impeding solid electrolyte rather than a flammable liquid electrolyte. The all-solid-state battery (ASSB) with Li metal aims for improved safety using inorganic solid electrolytes and outstanding energy density.However, Li’s dendritic behavior and Li-electrolyte contact roughness are some of the issues slowing down the technological development of Li metal-based ASSB. The experimental approach is key to validating technological advancement. Also, it is highly demanding, considering the numerous steps and tests required, the change-of-scale limitations (e.g., from button half-cell to battery pack), and the availability of internal characterization techniques. To these considerations, numerical modeling is positioned as a support to the experimental approach for in-depth and effective technological development. It thoroughly describes multiphysics, multiscale, and multivariate phenomena of cells and batteries.Modeling studies of ASSB have been published to support experimental works. However, the research now requires transient coupled electrochemical-mechanical modeling to account for the defect's behavior inside the cell, particularly at the Li-electrolyte interface. Li7La3Zr2O12 (LLZO), a single-ion garnet solid electrolyte, is gaining traction for use in ASSB. Three types of interfacial defect at the negative electrode have been identified with this electrolyte: geometrical asperity, void, and contaminant. While other authors have published a stationary coupled electrochemical-mechanical model for interface with geometrical asperity but without void, our study presents a new transient approach. We have developed a finite elements model for the transient prediction and study of various defects at Li-electrolyte interfaces, marking a significant advancement in this field.Our research involves a detailed study of the anodic interface for an all-solid-state cell with a solid electrolyte and single-ion electrolyte. Unlike previous studies, we do not assume a perfectly flat interface or one with a filled peak or valley. Instead, we consider three cases. The first case is an interface with a lithium peak in contact with a plane electrolyte garnet. The second case is an interface with a plane lithium electrode in contact with a cracked electrolyte garnet. The third case combines the two previous cases: the interface consists of a lithium peak in contact with a cracked electrolyte garnet. To determine the defects’ initial geometry, we use a Gaussian function. The peak is connected to the electrolyte by its tip, creating a void between the electrode and the electrolyte.A numerical model is developed to simulate the potentials, stress, and strain inside the electrode-electrolyte domain. Two physics are selected: secondary current distribution and solid mechanics. The model involves charge conservation and the equation of motion, as well as transient Li stripping at the interface. These two states are coupled together using a pseudo-transient approach: steady states are computed and compiled, and time steps are calculated to fit the calculated quantity of stripped Li. An internal electrode surface is defined on all the boundaries but is applicable only to contact boundaries between the electrode and the electrolyte domains. The mesh is adapted to the new geometry at each time step to account for the defect's evolution.For each case, results are extracted for the current density vector, the geometry and mesh deformation, the pressure, and the von Mises stress. Animations and figures are presented to visualize the in-time stripping of Li. We find that the novel pseudo-transient method is consistent for all the studied cases. We also find that plastic deformation is likely to occur when touching boundaries associated with a void. We discuss the influence of interface geometry on the current and pressure distributions, which help to explain what occurs inside an ASSB.This research work highlights a contribution to the development of a novel pseudo-transient method. This method allows the coupling of the governing equations with the transient Li stripping. This generic approach to time-variable geometry provides a powerful tool for the visualization and optimization of interfaces. With this numerical method, the experimental developers of ASSB will have access to a useful tool to simulate this technology and improve it. Another highlighted novelty is the application of the developed model to the investigation of the electrostripping of Li. Different cases of time-variable interface with geometrical asperity and void are simulated. These simulations enlighten the interfacial distributions of current and pressure around defects.

Impacts of Urban Form on Carbon Emissions Under the Goal of Carbon Emission Peak and Carbon Neutrality: A Case Study of the Yangtze River Economic Belt

Clarifying the mechanism of influence of urban form on carbon emissions is an important prerequisite for achieving urban carbon emission reduction. Taking the Yangtze River Economic Belt as an example, this study elaborated on the general mechanism of urban form on carbon emissions, used multi-source data to quantitatively evaluate the urban form, and explored the impacts of urban form indicators on carbon emissions from 2005 to 2020 at global and sub-regional scales with the help of spatial econometric models and geodetector, respectively. The results showed that:① The carbon emissions of the Yangtze River Economic Belt increased from 2 365.31 Mt to 4 230.67 Mt, but the growth rate gradually decreased. Its spatial distribution pattern was bipolar, with high-value areas mainly distributed in core cities such as Shanghai and Chongqing and low-value areas concentrated in the western regions of Sichuan and Yunnan. ② The area of construction land in the study area expanded over the past 15 years, but the population density of construction land had been decreasing. The degree of urban fragmentation was decreasing, and the difference between cities was also progressively narrowing. The average regularity of urban shape improved, and the compactness increased significantly. ③ All indicators of urban scale had significant positive effects on carbon emissions at the global scale, urban fragmentation had a significant negative effect in 2005, and the effective mesh size (MESH) indicator of urban compactness showed a significant negative correlation with carbon emissions in the study period. ④ Total class area, patch density, and effective mesh size had the most significant impacts on carbon emissions in upstream cities. Effective mesh size, mean perimeter-area ratio, and total class area had higher influences in midstream cities. Effective mesh size, percentage of like adjacencies, and largest patch index were the key factors to promote carbon reduction in downstream cities. Cities in different regions should comprehensively consider the impacts of various urban form indicators on carbon emissions and then optimize their urban form to promote sustainable development.

Conjugate Heat Transfer Advancements and Applications in Aerospace Engine Technology

Over the past few decades, conjugate heat transfer (CHT) technology has been instrumental in predicting temperature fields within aerospace engines, guiding engine design with its predictive capabilities. This paper comprehensively surveys the foundational technologies of CHT and their applications in engine design, backed by an extensive literature review. A novel coupling iteration methodology, su-F-TFTB, was proposed. Following this, it introduced grid splicing technology tailored for heat flux conservation, which significantly enhances the adaptability of CHT grids. Ultimately, this study employed the self-developed Aerospace Engine Numerical Simulation (AENS v4.0.1) software to perform CHT analyses on NASA-C3X turbine blades equipped with ten radial cooling systems. A comparative analysis of pressure distributions across various density meshes was undertaken to affirm mesh independence. Furthermore, the impacts of the Spalart–Allmaras (SA) one-equation model and k–ω Shear Stress Transport (SST) two-equation model on the temperature distribution in conjugate heat transfer were investigated. The results indicated that the k–ω SST model exhibited superior performance, aligning closely with NASA experimental data. This validation confirmed the effectiveness of the software.

Numerical simulation of compound wings wind tunnel test for wig effect vehicle

This paper presents the comparison of numerical simulation results and wind tunnel experiment for compound WIG's wing. Numerical simulation was performed in the ANSYS Fluent software. The choice of the turbulence model and the computational mesh parameters, including the resolution of the boundary layer, are substantiated. Comparison of the results of the experiment and numerical simulation showed good convergence for middle density mesh about 7 million cells and first layer height 0.0001 m. Additional study for k-ε realizable and k-ω SST turbulence models was done. Its result founded much efficiency k-ε realizable model than k-ω SST turbulence models for compound WIG's wing. Numerical simulation takes less time and ensures the same accuracy. The results can be argued that the selected parameters of numerical simulation can be used to obtain the aerodynamic characteristics of various layout solutions for "type C" WIG craft.

Multi-resolution topology optimization using B-spline to represent the density field

This paper proposes a novel multi-resolution topology optimization method using B-spline to represent the density field, and overcomes the defects of tedious post-processing of element-based models and low computational efficiency of topology optimization for large-scale problems. The design domain embedded in the B-spline space is discretized with a coarser analysis mesh and a finer density mesh to reduce the computational cost of finite element analysis. As design variables, the coefficients of the control points control the shape of the B-spline. The optimized B-spline can be quickly and precisely converted into a CAD model. Sensitivity filtering is additionally applied to enhance B-spline's smoothness and suppress QR-patterns. Numerical examples, including 2D and 3D cases, are tested to demonstrate that the proposed method significantly saves computational time without sacrificing the performance of the optimized structure. Moreover, the post-processing procedures are streamlined, resulting in continuous, smooth, and editable models.

Computational Fluid Dynamics of the Right Atrium: A Comparison of Modeling Approaches in a Range of Flow Conditions

Abstract The right atrium (RA) combines flows from the inferior (IVC) and superior vena cava (SVC). Here RA mixing is simulated using computational fluid dynamics, comparing four modeling approaches. A patient-averaged model (11 M cells) was created from four volunteers. We compared: (1) unsteady k–ω Reynolds-averaged Navier–Stokes (URANS) (2) implicit large eddy simulation with second-order upwind convection scheme (iLES-SOU) (3) iLES with bounded-central difference convection scheme (iLES-BCD) and (4) LES with wall-adapting local eddy-viscosity (LES-WALE). A constant inlet flow rate of 6 L/min was applied with both IVC/SVC contributions ranging from 30–70%. A higher density mesh (37 M cells) was also simulated for models 2 and 4 (equal IVC/SVC flow) to assess the accuracy of models 1–4. Results from the 11 M cell LES-WALE model showed good agreement with the 37 M cell meshes. All four 11 M cell models captured the same large-scale flow structures. There were local differences in velocity, time-averaged wall shear stress, and IVC/SVC mixing when compared to LES-WALE, particularly at high SVC flow. Energy spectra and velocity animations from the LES-WALE model suggest the presence of transitional flow. For the general flow structures, all four methods provide similar results, though local quantities can vary greatly. On coarse meshes, the convection scheme and subgrid-scale (SGS) model have a significant impact on results. For RA flows, URANS should be avoided and iLES models are sensitive to convection scheme unless used on a highly resolved grid.

A NUMERICAL APPROACH TO THE CONTACT OF NOMINALLY FLAT SURFACES

Machined surfaces can be described by heights and wavelengths of the surface asperities that show a statistical variation. Considering that a regular wavy surface with a sinusoidal profile is the crudest model for a rough surface, studying the contact of regular wavy surfaces is a good approximation for the contact of nominally flat surfaces. Such contact problems exhibit periodicity that can be simulated with the aid of computational techniques derived for contact mechanics in the frequency domain. The displacement calculation, which is a necessary step in the resolution of the contact problem, is mathematically a convolution product that can be calculated in the frequency domain with increased computational efficiency. The displacement induced by a unit surface load can be expressed in the frequency domain by the frequency response functions, which are counterparts of the space domain solutions to half-space fundamental problems such as the Boussinesq problem. The displacement induced by a periodic pressure distribution can be computed by executing the convolution product between the frequency response function and pressure on a single period. It should be noted that the convolution calculation in the spectral domain implies that the contributions of all neighbouring pressure periods are accounted for. The need to treat numerically only a single period results in remarkable computational efficiency, allowing for high density meshes that can capture the essential features of any textured real surface. The displacement calculation promotes the solution of the contact problem by an iterative approach. The advanced method is benchmarked against existing analytical solutions for the 3D contact of surfaces possessing two-dimensional waviness. This essentially deterministic model, supported by a direct numerical solution that can be obtained for samples of real rough surfaces, presents itself as a worthy alternative to the existing statistical models for rough contact interaction.

Three-dimensional Modeling for the Transmittance of ITO/Mesh-Ag/ITO Multilayers using FDTD

In order to improve the transmittance of ITO/Ag/ITO multilayers, Ag layer was formed with mesh structure. For more accurate and practical analysis, we performed the simulations using an optical wave simulator termed the full-wave simulation program. In our simulations, the three dimensional (3D) finite-difference time-domain (FDTD) method was used to realize the high density mesh structure, and a plane wave with variable wavelengths ranging from 250 to 850 nm is incident in the z-direction at normal incidence to the ITO/Mesh- Ag/ITO film surrounded by free-air space. From the simulation results, at a higher open ratio and lower Ag thickness, the transmittance of ITO/Mesh-Ag/ITO were not influenced by other parameters. Experimental measurements were performed depending on the various Ag mesh-spaces and mesh-widths. The open ratio of about 60 % has shown the acceptable results in the points of both the optical transmittance and the electrical conductance.

A three-dimensional multiscale approach to optimal design of porous structures using adaptive geometric components

This paper presents a direct multiscale design approach for three-dimensional (3D) porous structures. The porous material modeling technique, which involves the use of the adaptive geometric components (AGCs), is employed to simultaneously describe the macrostructure and microstructure of material while the multiresolution topology optimization (MTO) is utilized to reduce the cost of finite element analysis (FEA). We use two distinct discretization levels, including a coarse mesh to perform FEA (displacement mesh) and a fine mesh to present material distribution (density mesh). The AGCs are smoothly mapped onto the density mesh to obtain an effective element density field for material interpolation and stiffness computation of displacement-mesh elements. The overall macrostructure and microstructure of the material are simultaneously optimized by straightforwardly optimizing the geometry parameters of the AGCs. The 3D porous multiscale design with non-uniform microstructure can be directly achieved with only a global volume constraint. Some numerical tests are provided to validate the applicability of the proposed approach.

Validation of Close-Range Photogrammetry for Architectural and Archaeological Heritage: Analysis of Point Density and 3D Mesh Geometry

The 3D digitization and Building Information Modeling (BIM), which is based on parametric objects, have considerably advanced by developing massive data capture techniques. Thus, reverse engineering currently plays a major role as these technologies capture accurately and efficiently the geometry, color and textures of complex architectural, archaeological and cultural heritage. This paper aims to validate close-range Structure from Motion (SfM) for heritage by analyzing the point density and the 3D mesh geometry in comparison with Terrestrial Laser Scanning (TLS). The accuracy of the results and the geometry mainly depends on the processing performed on the point set. Therefore, these two variables are significant in the 3D reconstruction of heritage buildings. This paper focuses on a 15th century case study in Seville (Spain): the main façade of Casa de Pilatos. Ten SfM surveys were carried out varying the capture method (simple and stereoscopic) and the number of shots, distances, orientation and procedure. A mathematical analysis is proposed to verify the point spatial resolution and the accuracy of the 3D model geometry by section profiles in SfM data. SfM achieved acceptable accuracy levels to generate 3D meshes despite disordered shots and the number of images. Hence, stereoscopic photography using new instruments improved the results of close-range photogrammetry while reducing the required number of photographs.

Effect of land cover and landscape fragmentation on anopheline mosquito abundance and diversity in an important Colombian malaria endemic region.

Landscape structure influences the distribution and abundance of anopheline mosquitoes and has an indirect impact on malaria transmission. This work aimed to determine the effect of land cover and landscape fragmentation on anopheline mosquito abundance and diversity in an important Colombian malaria endemic area, the Bajo Cauca region. Diversity indices were calculated for Anopheles mosquitoes collected in various localities of the region. Land cover types were characterized using orthorectified aerial photographs to estimate landscape metrics. The relationship between landscape fragmentation and species diversity was evaluated by regression analysis. The correlation between species abundance and land cover types was determined using canonical correspondence analyses. Results showed a statistically significant tendency for a lower diversity of the Anopheles community in landscapes with higher patch number, patch density and effective mesh size. For most species, there was evidence of a significant relationship between species abundance and land covers modified by anthropic activities which generate forest loss. These results indicate that activities that modify the landscape structure and land cover composition generate changes that affect the spatial distribution and composition of epidemiologically-important Anopheles species, which may impact malaria distribution in a region. This information is useful to guide control interventions that promote unfavorable landscapes for malaria vector propagation.

Stopped-Flow Dynamics Study on the Escape Behavior of Polyelectrolyte Macromolecules from Microgels: The Influence of the Path Length and Size.

We reported the fabrication of several monodispersed poly(2-vinyl pyridine)-poly(N-isopropylacrylamide) (P2VP-PNIPAM) microgels including the P2VP core (non-cross-linked) and PNIPAM (cross-linked) shell by mature emulsion polymerization. The fast escape behavior (diffusion process) of linear P2VP chains through a porous PNIPAM layer was investigated by a pH jump stopped-flow apparatus. The time-dependent dynamic traces (corresponding to the scattered light intensity) decreased at the initial timescale of several seconds and then reached an apparent equilibrium, confirming the efficient escape of P2VP chains from microgels. Compared with the previously reported literature, such an accelerated escape process resulted from the sharply increased internal charge repulsive force caused by the protonation of P2VP moieties under acidic conditions. The obtained characteristic relaxation times by single exponential fitting of these kinetic traces were dependent on the final pH values, equilibrium temperatures, shell thickness (path length), and cross-linking density (mesh size). We believe that this work can provide an efficient way to investigate hindered diffusion, especially the initial rapid diffusion stage. Not only that, the proposed model can also provide theoretical guidance to some practical applications, such as membrane separation and the exocytosis phenomenon of intracellular proteins or macromolecular substances.

Effect of XFEM mesh density (mesh size) on stress intensity factors (K), strain gradient ([formula omitted]) and stress corrosion cracking (SCC) growth rate

The extended finite element method (XFEM) is now widely used for crack simulations. The researchers have performed the crack simulations using the XFEM without re-meshing. Due to recent problems of discrepancies in the experimental and computational results, the mesh density (numbers of elements/unit area) or mesh size of the XFEM is a questionable field. In this research, the effect of the XFEM mesh density (mesh size) on stress intensity factors (K), strain gradient (dεdr) and stress corrosion cracking (SCC) growth rate has been investigated using the XFEM method provided by the ABAQUS. Two specimens with embedded cracks in a flat plate of Inconel-600, under the same load and environment (340 °C), are used. The embedded cracks are of different lengths with localized circles of randomly chosen radius. The stress intensity factors, K, strain gradient with respect to the propagated crack, dεdr, and the stress corrosion cracking (SCC) growth rate are estimated. In order to check the trend, the process is repeated on three different applied loads. It has been noticed, well studied and proposed that when “local mesh size (MS)” to “embedded crack length (Le)” ratio (MS/Le) ≤ 0.0005 in two of the specimen used, the K and dεdr become smooth and the simulated SCC crack growth results are nearest to the experimental values of the SCC crack growth rate.

Assessment of Road-Induced Landscape Fragmentation and Implications for Landscape Planning: the case of İzmir Province

Yollar, buyuk bir cevre sorunu ve biyolojik cesitlilik kaybi ile peyzaj parcalanmasinin ana nedenlerinden biri olarak kabul edilmektedir. Yapilan arastirmalar, yollarin genellikle artan peyzaj parcalanmasina yol actigini; ayrica araclarin neden oldugu kirlilik ve yol aglari etrafindaki yerlesimlerin hizla artmasi yoluyla peyzajlarin yapisi ve isleyisini de etkilediklerini ortaya koymaktadir. Bu calisma, Izmir ili merkez ilcelerinde yollarin varligi ile peyzaj parcalanmasi arasindaki iliskiyi sinif ve peyzaj duzeyinde peyzaj metriklerini kullanarak incelemektedir. Calismada, CORINE arazi ortusu haritasi (CLC2012) ve Urban Atlas2012 (Kent Atlasi2012) (UA2012) ile birlikte kullanilarak, calisma alanina iliskin detayli yol verisinin icerildigi ve icerilmedigi arazi ortusu haritalari kullanilmistir. Analizler FRAGSTATS 4.2 ve ArcGIS 10.5.1 yazilimlarinda gerceklestirilmistir. Sonuclar artan yol varliginin kent peyzajinda artan parcalanmaya sebep oldugunu gostermektedir. Ancak, yollarin neden oldugu parcalanmanin degerlendirilmesinde bazi peyzaj metriklerinin etkinliklerinin olasi kisitliliklarini goz onunde bulundurmak gerekmektedir. Diger yandan, bu calismanin sonuclari, peyzaj parcalanmasini degerlendirirken yama sayisi (NP), alan agirlikli ortalama yama alani (AREA_AM), kenar yogunlugu (ED) ve etkin ag boyutunun (MESH) peyzaj parcalanmasina iliskin daha saglikli degerler sundugunu vurgulamaktadir. Calisma, biyolojik cesitliligin desteklenmesi ve insanlarin yasam kalitesinin iyilestirilmesi bakimindan yollar ve yol aglari cevresinde firsatlar yaratmak icin peyzaj planlama uygulamalarina isik tutabilecek bazi onemli onerilerle sonlandirilmistir. Ornegin, pratik anlamda, yol aglari cevresinde yol kenari bitki ortusu ve bitkilendirilmis banketler, yol aglarinin parcalanma etkisini azaltabilir ve peyzaj baglantililigini arttirilabilir. Ayrica, bu alanlarin korunmasi ve duzenli bakimi peyzaj kalitesinin arttirilmasinda ve biyolojik cesitliligin desteklenmesinde de onemli rol oynayacaktir.

Domain decomposition based parallel computing for multi-scale coronary blood flow simulations

In the present study, we demonstrated a parallel P2P1 finite element scheme with a four-step fractional splitting approach to conduct a multiscale coronary flow simulation. The three-dimensional (3D) computational fluid dynamics (CFD) for patient-specific coronary artery flow and zero-dimensional (0D) lumped-parameter network (LPN) modeling for distal coronary beds was fully coupled, and an MPI parallel algorithm based on domain decomposition was applied. A parallel conjugate gradient (CG)-LPN subroutine for the 3D-0D coupled system with a monolithic scheme was derived, and it provides a correct pressure solution that may not be obtained by the conventional CG solver, particularly when the subdomain division intersects the 3D-0D coupling outlet. The overall computing time for parallel CG-LPN does not show a noticeable difference from the conventional CG solver, despite the extra MPI calls for data transfer at the interfaces of subdomains.For the BiCGSTAB solver, the block ILU(0) preconditioner showed favorable performance for a high density mesh compared with the simple Jacobi preconditioner. MPI_COMM is a major bottleneck that saturates the overall parallel performance at high core count, but a computing time of less than 10 min per cardiac cycle on a medium density mesh could be attained for a patient-specific coronary flow simulation using 60 CPU cores run in parallel, which is in an acceptable range for clinical practice. Further tests of accuracy are needed with a large set of patients to enable wide use of the proposed technique in helping to make interventional decisions in routine clinical practice for coronary stenotic lesions.

Removal of Manganese Ions (Mn2+) from a Simulated Wastewater by Electrocoagulation/ Electroflotation Technologies with Stainless Steel Mesh Electrodes: Process Optimization Based on Taguchi Approach

This study depicts the removal of Manganese ions (Mn2+) from simulated wastewater by combined electrocoagulation/ electroflotation technologies. The effects of initial Mn concentration, current density (C.D.), electrolysis time, and different mesh numbers of stainless steel screen electrodes were investigated in a batch cell by adopting Taguchi experimental design to explore the optimum conditions for maximum removal efficiency of Mn. The results of multiple regression and signal to noise ratio (S/N) showed that the optimum conditions were Mn initial concentration of 100 ppm, C.D. of 4 mA/cm2, time of 120 min, and mesh no. of 30 (wire/inch). Also, the relative significance of each factor was attained by the analysis of variance (ANOVA) which indicates that the percentage of contribution followed the order: time (47.42%), C.D. (37.13%), Mesh number (5.73%), and Mn initial Conc. (0.05%). The electrolysis time and C.D. were the most effective operating parameters and mesh no. had a fair influence on Mn removal efficiency, while the initial conc. of Mn. had no significant effect in the studied ranges of control factors. Regression analysis (R2= 90.16%) showed an acceptable agreement between the experimental and the predicted values, and confirmation test results revealed that the removal efficiency of Mn at optimum conditions was higher than 99%.

A combined experimental and numerical investigation of flow dynamic in a methane reformer filled with [formula omitted]-Al2O3-supported catalyst

In this study, the combination of numerical simulations and experiments have been carried out to investigate a flow dynamics in a methane reformer that filled with the porous nickel-based catalyst. CFD-modeling was performed in commercial software ANSYS Fluent. The high density meshes were generated for numerical investigation. The numerical simulation is performed for the wide range of the Reynolds numbers. The experimental investigation allowed obtaining an array of experimental data for verification of a numerical model. The comparison of the pressure drops between experimental and simulation results show a good correlation with divergence of results less than 7–8%. To determine the effect of porosity properties of the medium on numerical results, two cases of CFD modeling were realized (with taking into account the porous medium properties and without it). The discrepancy between results is increasing with an increase of the gas flow rate, while for the low flow rates the results are almost similar. The local resistance coefficient of a packed-bed as a function of inlet velocity were obtained. It was found that the local resistance coefficient in the velocity range from 0.5 m/s to 3 m/s varies more than twice.

Measurement and analysis of H2 and O2 bubbles diameter produced by electroflotation processes in a modified Partridge-Smith cell

Diameter and distribution of the bubbles generated by water electrolysis are of vital importance in the electroflotation process of fine particles. It is well known that these parameters influence the efficiency of the flotation process because they affect the collision, adhesion, and transport mechanisms. Moreover, the smaller the bubble diameter, the better the recovery of fines due to the larger surface area of the bubble. Thus, the aim of this work was to evaluate the influence of some of these parameters on the diameter and distribution of hydrogen and oxygen bubbles, produced by electroflotation. A modified Partridge–Smith binary cell with platinum electrodes was used. The system pH, current density, electrolyte concentration, and electrode mesh spacing were evaluated. The results showed that the increase in the pH of the system produced two opposite behaviours in the diameters of hydrogen and oxygen bubbles. The diameter of the hydrogen bubbles decreased, whilst that of the oxygen bubbles increased. The increase in current density and electrolyte concentration caused a decrease in the diameter of the hydrogen and oxygen bubbles. Finally, the increase in the wire diameter and electrode mesh spacing caused an increase in the diameter of hydrogen and oxygen bubbles.

Gelation studies on acrylic acid‐based hydrogels via in situ photo‐crosslinking and rheology

ABSTRACTThe gelation characteristics of acrylic acid (AA)‐based hydrogels were investigated using real time in situ photocrosslinking and rheological measurements. The gel point and gelation times were established using Winter–Chambon criteria. Frequency independence of tan δ was observed in all cases, such that G′ and G″ scaled as ∼ωn. The Flory–Stockmayer theory was used alongside other indices in order to probe the gelation and the post‐gelation characteristics of the critical gels and the fully formed hydrogels. Network relaxation exponents (n) were influenced by the concentrations of AA and methylene bis‐acrylamide. The gel stiffness (S) decreased with an increase in the concentration of the monomer and of the concentration of the crosslinker, while network branching decreased (lower fractal dimensions) at the gel point. The conversion at the gel point was found to be iso‐conversion with respect to the intensity of the UV irradiance used in the photocrosslinking reactions (1–20 mW/cm2). Thus, network clusters and the crosslinking reaction mechanism were the same irrespective of radiation intensity, although the rates of the reactions were affected. Having sufficient amounts of reactive species at the time of cure drive the crosslinking reactions beyond the gel point to greater crosslink density and smaller mesh sizes. The effects of auto‐acceleration and free‐volume were observed and shown to have key effects on the gelation mechanisms and the branching topographies of the network, when the concentration of the known polyacrylamide medium were not controlled. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46691.

Finite element analysis and improved design of large-scale belt-conveyor drums

Purpose Large-scale belt-conveyor systems are extensively used in open mines to continuously transport bulk material. Conveyor pulleys are critical components and failures have significant financial consequences due to extended downtime. Aiming at increasing their durability, two critical spots are identified: the drum and the welds between end-plates and drum. Alternative designs have been evaluated. The paper aims to discuss these issues. Design/methodology/approach Loads on the driving drum are determined from measurements of the bearing force and the motor power. The friction interaction between belt and drum is described by the creep model and its impact is evaluated by comparing the results obtained for low and typical values of friction coefficient. Alternative designs are analysed using finite element method with optimised variable density mesh. The stress field and the deformations are calculated and evaluated. Findings Friction affects the torque transmission capacity and force distribution, but it is shown that in this case it has almost no impact on the maximum von Mises stress which occurs on the inside surface of the drum; therefore fatigue cracks initiated there, cannot be visually detected. A reinforcing diaphragm is added at the mid-plane to reduce the stress. A new, improved design is proposed to eliminate welds between the end-plates and the drum. Research limitations/implications The new proposed design has to be tested in the field to ultimately validate its higher durability. Originality/value The impact of the friction of the belt on the drum is demonstrated. The reinforcement resulting from a mid-plane diaphragm is quantitatively evaluated and assessed. A new improved pulley design is proposed aiming at significantly increased operational life compared to the one of the current design.