Using a coupled CFD – DPM approach to predict particle settling in a horizontal air stream

Preventing health and safety hazards such as dust explosions and respiratory exposure in the work force when handling and storing fine powders is a major challenge faced by plant operators [13]. Computational Fluid Dynamics (CFD) coupled with Discrete Phase Model (DPM) can be used as a tool to address this challenge by advancing the understanding of how particles deposit in a particular process. Particle settling, in air streams, is primarily dependent on the drag forces exerted on the individual particles through interactions with the suspension medium [2]. By improving the understanding of this interaction through repeatable experiments and simulations; more complex CFD – DPM simulations are possible, thus providing a significant step in reducing the risks associated with handling fine powders. To study the transport and settling of particles in air streams, an experiment was established where glass beads, alumina and iron ore dust were injected into a horizontal flow channel. The material was fed into the top of the test rig where it was then transported in a laminar air stream. Through this method particle settling, according to the particle size, can be observed by sampling different trays along the bottom of the test rig. Once the deposition of particles is analysed (using a particle size analyser) each diameter range can be tracked to determine the distance travelled. After evaluating these experiments a CFD coupled with DPM simulation was employed to predict particle deposition in the horizontal chamber. The results show a good agreement between experiments and CFD – DPM results.     

A New Approach for Calculating the Mass Flow Rate of Entrained Air in a Freefalling Material Stream

This article presents the outcomes from a series of physical experiments to measure the air entrainment rates encountered within a stream of freefalling particles. The experimental work presented spans a range of particle parameters and hopper geometries. From these results a new theory for the prediction of air entrainment is developed and presented. This new method was developed specifically to facilitate a better understanding in the area of fugitive dust control associated with material handling systems, which are driven by the air entrainment during freefalling. From the work presented in this article, a better prediction capability of freefalling bulk materials in either constrained, or unconstrained systems, will allow for the optimization of either passive or active dust control strategies. This article presents several distinct sections that detail the experimental work used to determine the freefall stream parameters that were conducted to allow the development of the entrainment equations.     

Bionic design methodology for wear reduction of bulk solids handling equipment

Large-scale handling of particulate solids can cause severe wear on bulk solids handling equipment surfaces. Wear reduces equipment life span and increases maintenance cost. Examples of traditional methods to reduce wear of bulk solids handling equipment include optimizing transport operations and utilizing resistant materials. To our knowledge, the so-called bionic design has not been utilized. Bionic design is the application of biological models, systems, or elements to modern engineering. Bionic design has promoted significant progress on the development of engineering products and systems. In order to use bionic design for wear reduction of bulk solids handling equipment surfaces, this paper introduces bionic design to bulk solids handling on the basis of analogies between biology and bulk solids handling. In addition, a bionic design methodology for the wear reduction of bulk solids handling equipment surfaces is formulated. Based on the bionic design methodology, two bionic models used for abrasive and erosive wear reduction of bulk solids handling equipment surfaces are proposed.     

From Single Particle AFM Studies of Adhesion and Friction to Bulk Flow: Forging the Links

The atomic force microscope (AFM) has been used to study inter-particle contacts in air for a range of model particles and cohesive granular materials of commercial importance. Adhesion (or pull-off force), friction and its load dependence, and particle size, morphology and roughness were measured for glass ballotini, fumed silica, alumina, limestone, titania and zeolite. Particle-wall contacts and effects of relative humidity were also studied. Most of the results, after allowing for roughness, are consistent with JKR contact mechanics and capillary bridge theory; however, the main object of the present work is to demonstrate semi-quantitative links between the AFM measurements and related bulk flow and cohesion measurements performed in parallel on the same materials. A simple model of a particle assembly will be used to compare average contact forces in typical single-particle AFM experiments and typical bulk experiments, and thus identify those regimes of powder flow where the two approaches overlap, and AFM measurements may be used with some confidence in more sophisticated modeling based on distinct element analysis (DEA). Four areas will be discussed briefly: (1) The apparent analogy between bulk yield loci and single-particle friction-load data; (2) Cohesion data and particle size effects; (3) Bulk tensile strength and single particle pull-off force; (4) Bulk wall friction and single-particle-wall friction. It is found that typical single-particle AFM experiments and bulk shear experiments converge for small particles (～ 4 μm) and low consolidation stress, when the average inter-particle contact forces are of the order 20–100nN, involve single or few asperities, and are not much larger than pull-off forces. For large particles and high consolidation loads the data do not overlap and AFM measurements may be less useful as input to simulations where sliding friction is less important, and where large normal contact forces dominate over tangential forces and are responsible for the shear strength.     

An integrated methodology for automating the determination of layout and materials handling system

There is a severe scanty of models and solution techniques for the determination of layout and the materials handling system when neither are fixed. This is a complex problem for which this paper proposes a new integrated methodology using a knowledge-based/optimisation approach to the problem. The knowledge-base consists of facts and rules to determine the feasibility of using a materials handling equipment type for a given move. The optimisation part determines the layout of machines minimising the materials handling costs and the dead space in the layout using a multi-criteria optimisation model. The methodology aims to minimise materials handling costs, aisle space usage and dead-space in the resulting layout. It is particularly applicable to heavy manufacturing environments. The system outputs the optimum location, configuration and orientation of machines, and the material handling equipment types, their design capacities, utilisations and the assignment of moves to each item of materials handling equipment. The results of a successful application to an example problem are given.     

Mechanistic modelling of tests of unbound granular materials

Various tests are used to characterise the strength and resilience of granular materials used in the subbase of a pavement system, but there is a limited understanding of how particle properties relate to the bulk material response under various test conditions. Here, we use discrete element method (DEM) simulations with a mechanistically based contact model to explore influences of the material properties of the particle on the results of two such tests: the dynamic cone penetrometer (DCP) and the resilient modulus tests. We find that the measured resilient modulus increases linearly with the particle elastic modulus, whereas the DCP test results are relatively insensitive to particle elastic modulus. The DCP test results are also relatively insensitive to inter-particle friction coefficient but strongly dependent on the particle shape. We discuss strengths and weaknesses of our modelling approach and include suggestions for future improvements.     

Experimental Investigation of Air Entrainment in Free-Falling Particle Plumes

Powders and granulated solids are widely used in industrial bulk solids storage, handling, and transportation systems. Such bulk materials handling operations frequently involve a falling stream of material. During such a process, the surrounding air is induced to flow with the falling particle stream, forming a particle-driven plume. Herein, experimental research results are reported on this fundamental problem, focusing in particular on the velocity profile of air entrained by the free-falling particles. This investigation shows that the velocity profile of the induced air can be modeled as a Gaussian distribution. The radius of the particle plume is found to increase linearly with increasing drop height, and it also increases with increasing bulk solid mass flow rate. Comparisons are made with other entrainment flows, such as jets and plumes, and it was found that air entrainment and hence the angle of spread of the particle-driven plumes was much less than for the other entrainment flows. The angles of spread of the particle-driven plumes were found to be in the range 1.3° < θ _s  < 1.8° as compared to θ _s  ≈ 5.7° for miscible plumes arising from sources of heat, for example. In addition, the centerline velocity of the induced air in the particle plumes was found to increase significantly with increasing drop height. Results from high-speed digital video records show that the bulk material does not dilate in a uniform manner as it falls, and a series of distinct particle clouds form in the core of the particle-driven plume. These clouds eventually disperse over a sufficiently large drop height.     

Topological optimization for the design of microstructures of isotropic cellular materials

The aim of this study was to design isotropic periodic microstructures of cellular materials using the bidirectional evolutionary structural optimization (BESO) technique. The goal was to determine the optimal distribution of material phase within the periodic base cell. Maximizing bulk modulus or shear modulus was selected as the objective of the material design subject to an isotropy constraint and a volume constraint. The effective properties of the material were found using the homogenization method based on finite element analyses of the base cell. The proposed BESO procedure utilizes the gradient-based sensitivity method to impose the isotropy constraint and gradually evolve the microstructures of cellular materials to an optimum. Numerical examples show the computational efficiency of the approach. A series of new and interesting microstructures of isotropic cellular materials that maximize the bulk or shear modulus have been found and presented. The methodology can be extended to incorporate other material properties of interest such as designing isotropic cellular materials with negative Poisson's ratio.     

Improvement of stenting therapy with a silicon carbide coated tantalum stent

State of the art cardiovascular stent materials are a compromise between bulk properties and surface related properties. As a consequence, deficiencies in both characteristics lead to serious limitations of stenting therapy. Beside a dissatisfying X-ray visibility of current stent materials, which hinders precise angiographic control of the stent during implantation, insufficient hemocompatibility causes subacute vessel occlusions despite stringent anticoagulant medication. Additionally, bleeding complications result which further limit the therapeutical success. Therefore it is essential to develop a new coronary stent with improved material properties for the bulk of the stent and its surface. This is realized by a hybrid concept. The stent is manufactured from tantalum, having a high inherent radio-opacity. The stent is coated with amorphous silicon carbide, optimized for hemocompatibility. An appropriate deposition technology to maximize coating adhesion was developed. Amorphous silicon carbide was investigated in vitro and in vivo to assess its suitability for coronary stents.     

Systematic design optimization of grabs considering bulk cargo variability

Ship unloader grabs are usually designed using the manufacturer’s in-house knowledge based on a traditional physical prototyping approach. The grab performance depends greatly on the properties of the bulk material being handled. By considering the bulk cargo variability in the design process, the grab performance can be improved significantly. A multi-objective simulation-based optimization framework is therefore established to include bulk cargo variability in the design process of grabs. The primary objective is to reach a maximized and consistent performance in handling a variety of iron ore cargoes. First, a range of bulk materials is created by varying levels of cohesive forces and plasticity in the elasto-plastic adhesive DEM contact model. The sensitivity analysis of the grabbing process to the bulk variability allowed three classes of iron ore materials to be selected that have significant influence on the product performance. Second, 25 different grab designs are generated using a random sampling method, Latin Hypercube Design, to be assessed as to their handling of the three classes of iron ore materials. Of this range of grab designs, optimal solutions are found using surrogate modelling-based optimization and the NSGA-II genetic algorithm. The optimization outcome is verified by comparing predictions of the optimization algorithm and results of DEM-MBD co-simulation. The established optimization framework offers a straightforward and reliable tool for designing grabs and other similar equipment.     

Predicting whether a material is ductile or brittle

In this paper we discuss the various models that have been used to predict whether a material will tend to be ductile or brittle. The most widely used is the Pugh ratio, $G/K$, but we also examine the Cauchy pressure as defined by Pettifor, a combined criterion proposed by Niu, the Rice and Thomson model, the Rice model, and the Zhou-Carlsson-Thomson model. We argue that no simple model that works on the basis of simple relations of bulk polycrystalline properties can represent the failure mode of different materials, particularly where geometric effects occur, such as small sample sizes. Instead the processes of flow and fracture must be considered in detail for each material structure, in particular the effects of crystal structure on these processes.     

Effect of hyaluronic acid incorporation method on the stability and biological properties of polyurethane–hyaluronic acid biomaterials

The high failure rate of small diameter vascular grafts continues to drive the development of new materials and modification strategies that address this clinical problem, with biomolecule incorporation typically achieved via surface-based modification of various biomaterials. In this work, we examined whether the method of biomolecule incorporation (i.e., bulk versus surface modification) into a polyurethane (PU) polymer impacted biomaterial performance in the context of vascular applications. Specifically, hyaluronic acid (HA) was incorporated into a poly(ether urethane) via bulk copolymerization or covalent surface tethering, and the resulting PU–HA materials characterized with respect to both physical and biological properties. Modification of PU with HA by either surface or bulk methods yielded materials that, when tested under static conditions, possessed no significant differences in their ability to resist protein adsorption, platelet adhesion, and bacterial adhesion, while supporting endothelial cell culture. However, only bulk-modified PU–HA materials were able to fully retain these characteristics following material exposure to flow, demonstrating a superior ability to retain the incorporated HA and minimize enzymatic degradation, protein adsorption, platelet adhesion, and bacterial adhesion. Thus, despite bulk methods rarely being implemented in the context of biomolecule attachment, these results demonstrate improved performance of PU–HA upon bulk, rather than surface, incorporation of HA. Although explored only in the context of PU–HA, the findings revealed by these experiments have broader implications for the design and evaluation of vascular graft modification strategies.     

Novel Approach for Assessing Cyclic Thermomechanical Behavior of Multilayered Structures

Microelectronic devices require material systems combining multiple layers of material for proper operation. These inevitably have different properties, for example, the elastic modulus or the coefficient of thermal expansion. Permanently reoccurring Joule heating and successive cooling during the operation of such devices lead to high thermal stresses within the materials and even failure due to thermomechanical fatigue or delamination of layers. This is dependent on the internal stress state and the amount of plastic strain accumulated. Here, in situ thermomechanical cantilever bending experiments on a Si–WTi–Cu material system to investigate these internal stress states and their influence on deformation behavior using a novel experimental methodology are shown. During heating to $T_{\text{max}}=400°\mathrm{C}$, the Cu layer undergoes partial plastic deformation, which may lead to the failure of a potential device using this material combination. To assess the internal stress and strain states based on the in situ observation, a model incorporating plastic deformation and known residual stresses of layers is proposed and verified by Finite Element Analysis.     

Scalable TriDAS for the NEMO project

The data acquisition for the NEMO km³ detector is based on the all data to shore approach. The continuous data stream, coming from more than 8000 PMTs, will be greater than 32 GBps, and therefore it requires a fast on-line filtering for an appropriate noise suppression. An on-shore multi-system Trigger Infrastructure has been studied to handle and real-time analyze such an amount of data. In order to accomplish the data acquisition of the NEMO prototype tower, expandable algorithms and services for data handling, system control and monitoring have been prepared.     

Surface modification of organic powders for enhanced rheology via atomic layer deposition

Some organic additive manufacturing feedstocks can be cohesive and tend to agglomerate in suspensions, which can lead to significant challenges in formulating solids-loaded fluids, like those used in many additive manufacturing processes. By depositing an ultra-thin, layer of a second material conformally with the surface of the feedstock powder, Atomic Layer Deposition (ALD) can be used to uniquely modify the surface and, thereby, cohesion of the powder material without changing the properties of the bulk material. This paper demonstrates low temperature (<115 °C), ALD of aluminum oxide on temperature-sensitive materials: first, on polyimide thin film flats, then, on melamine and nylon organic powder feedstocks with the goal of improving their powder rheology. The process produced amorphous aluminum oxide-hydroxide coatings that are both uniform and conformal to the powder’s surface. Aluminum oxide coatings on the nylon powders did not show a significant change in the flow properties of the powder, given the already low cohesivity of nylon. In contrast, the highly cohesive melamine powders exhibited significant improvements in flowability after being coated with a layer as thin as 20 nm, due to a reduction in inter-particle cohesivity. The basic flowability decreased from 199 to 185 mJ and the specific energy increased from 4.95 to 6.39 mJ/g.     

Nanoparticles: biosynthesis,translocation and role in plant metabolism

Nanotechnology is an emerging field of science that applies particles between 1 and 100 nm in size for a range of practical uses. Nano‐technological discoveries have opened novel applications in biotechnology and agriculture. Many reactions involving nanoparticles (NPs) are more efficient compared to those of their respective bulk materials. NPs obtained from plant material, denoted as biogenic or phytosynthesised NPs, are preferred over chemically synthesised NPs due to their low toxicity, rapid reactions and cost‐effective production. NPs impart both positive and negative impacts on plant growth and development. NPs exhibit their unique actions as a function of their size, reactivity, surface area and concentration. An insight into NP biosynthesis and translocation within the plant system will shed some light on the roles and mechanisms of NP‐mediated regulation of plant metabolism. This review is a step towards that goal.Inspec keywords: nanofabrication, nanoparticles, nanobiotechnology, particle size, reviews, botany, biochemistryOther keywords: chemically synthesised NPs, low toxicity, rapid reactions, cost‐effective production, positive impacts, plant growth, translocation, plant system, plant metabolism, nanotechnological discoveries, biotechnology, agriculture, plant material, biogenic NPs, phytosynthesised NPs, bulk materials, nanoparticles, biosynthesis, surface area, review, size 1.0 nm to 100.0 nm     

Assessment of Mechanical Properties of Cohesive Particulate Solids. Part 2: Powder Flow Criteria

The fundamentals of cohesive particulate solids' consolidation and flow properties using a reasonable combination of particle and continuum mechanics by means of micro/macrotransition of the "characteristic particle contact" are explained. The adhesion force models of Tomas (2001a) are used to derive the stationary, instantaneous T S1 time yield loci and consolidation loci. Next, the uniaxial compressive strength σ c ( σ 1 ), effective angle of internal friction } e ( σ 1 ), and bulk density 𝜌 b ( σ 1 ) are obtained as powder constitutive functions. The approach has been shown to be effective for the data evaluation of cohesive powder flow properties, like a very cohesive titania nanopowder (surface diameter d s = 200 nm, solid density 𝜌 s = 3870kg/m 3 ) with the fit r 2 xy > 0.95. Finally, these models in combination with accurate shear cell test results are used as constitutive functions for computer-aided silo design for reliable flow.     

A RHEOMETER FOR MEASURING THE PROPERTIES OF GRANULAR MATERIALS

ABSTRACT

A great many technological applications such as pneumatic handling of grains and minerals, drying of particles, gasification of solid fuels, require an understanding of the properties of granular solids. Material parameters which can describe the common phenomena exhibited by these granular materials, such as dilatancy, cohesion, adhesion, frictional resistance, etc. need to be incorporated in the model and methods devised for measuring and quantifying them. Reliable experiments are required to measure the properties of these materials. However, this branch of rheology has not been as well studied as the rheology of fluids due to the difficulties inherent to grannular materials in that they exhibit both solid-like and fluid-like properties. Here, we discuss the development of an instrument which can evaluate the material properties of grannular solids. Experimental investigations verify the commonly exhibited phenomena by these materials and estimate the various forces which are generated due to the flow of these materials, thereby enabling their characterization.