SAR - Review
The wetting of a powder or porous material by a liquid is a crucial first step in processes such as dispersion, dissolution, granulation and reconstitution, which are important in fields such as mineral processing, pharmacy and food science. It is also essential for hydrating soil in agriculture. It is important for efficient oil recovery and, in the future, it may help to store CO2 underground. The article provides a comprehensive review of the wetting of powders and granular materials, emphasizing the complexity introduced by surface heterogeneity, particle size distribution, and structural inhomogeneity. It begins by describing wetting phenomena on ideal, planar or regular surfaces. Fundamental concepts such as the Young equation and contact angle hysteresis, as well as the influence of surface roughness, heterogeneity, and dynamic effects, adaptation, and slide electrification. The review then analyzes how these theoretical frameworks extend to realistic powders, where a single contact angle is insufficient to characterize wetting behavior but whole distributions of contact angles are obtained. Several experimental methods for characterizing the wettability and surface energy of powders are discussed, including capillary rise, sessile drop and drop penetration test, X-ray tomography, inverse gas chromatography, secondary-ion mass spectrometry, sink and drop impact test. The article highlights the limitations and suitability of each method in relation to specific applications and recommends careful selection based on application needs and powder properties.
Keywords: Contact angle hysteresis, granular material, heterogeneity, porous material, surface energy, wetting
In this review, the focus will be on what the author believes are (a) the most broadly important results in of (particulate) tribocharging, (b) the most important issues to the academic community since the last IFPRI review by Matsuyama and Yamamoto in 1998, (c) the intersection of these with the issues most relevant in industry, and (d) the results that the author considers to be the most durable. In contrast to a more typical review format, where a very large number of results are discussed very briefly, this review will go into detailed summary of select results.
Section 2
Section 2 will begin with a succinct summary of essential knowledge to anyone concerned with tribocharging: namely the work-function mechanism for metal-metal contacts as developed primarily by Harper and Lowell.
Section 3
In §3, the focus will be on charging between metals and insulating particles, in particular highlighting the work of Matsuyama and Yamamoto, to illustrate the (at the very least functional) inadequacy of the work-function model for this situation and highlight the importance of dielectric breakdown.
Section 4
Section 4 will switch focus from different material (i.e., metal-insulator) charging to same-material charging—i.e., what occurs between the particles in a particulate system. Here, we will recapitulate the essential results of the groups Lacks and Jaeger, who convincingly showed that charge separation based on size occurs.
Section 5
The focus will then naturally shift in §5 to the patch models for tribocharging, including the “trapped” electron model which can be considered a special case.
Section 6
Finally, §6 will focus on the latest generation of experiments, which repeatedly measure the charge exchange between the same two objects, and which challenge the most basic tenets of the patch-model framework and force us to reconsider the underlying cause of same-material tribocharging.
Due to finite time, energy, and space, but also due to the predilections, focus, and expertise of the author, many relevant results worth mentioning will surely be missed. It is the hope, however, that this review will serve as a “good starting point” for anyone in industry who would like to know about the topic’s most durable results, as well as the most cutting edge ones, to be able to think about their particulate charging issues in a more informed way.
This review covers different key aspects of particle contacts within dense suspensions. After an introduction that motivates the necessity to account for direct surface contacts to describe the mechanical response of wet systems, we provide a general framework for contact mechanics and friction at the microscale. We then describe how friction is measured at the macroscale to introduce different methodologies developed to translate these measurements to the micro/nanoscale corresponding to interparticle contacts. The last part of the review gives a brief overview of different strategies used to modify friction and adhesion between particles. Each of the sections is accompanied by a critical discussion on perspectives and challenges for the future.
Mills and classifiers are primarily used for particle size reduction and separation across various industries, including paper, paint, plastic, pharmaceuticals, ceramics, cosmetics, foods, and fine chemicals. They are typically used to achieve a targeted particle size distribution or specific particle shape. Numerical modeling has the potential to inform equipment design to control particle transport and predicting high-wear spots. Given the substantial volume of particles processed in industrial contexts, even marginal improvements in grinding efficiency can lead to significant economic benefits. This review summarizes advancements in understanding and modeling key processes taking place at the scale of individual particles and coarse grain approaches to simulate processes at the scale of industrial units. The review concludes with a brief perspective on future research directions, including the use of machine learning for constitutive modeling and design optimization.
The 2023 IFPRI Powder Flow Workshop was attended by approximately 70 live participants and 40 online registrants. It consisted of seven academic keynote presentations and two industrial talks aimed at inspiring brainstorming discussions on the subject of solids handling, which remain one of the major industrial challenge of our time [1]. To suggest which speakers, discussion leaders and panelists to invite, and to draft questions that the audience should address, the organizers conducted a survey on the interests of IFPRI members.
This report begins with results of the survey. After summarizing keynote presentations and their significance, we provide a synopsis of discussions, and we identify knowledge gaps that should elicit future grants from IFPRI or other funding agencies. The workshop schedule and talks are attached to this document.
Discrete Element Method (DEM) consists in solving the equations of motion of a collection of rigid particles by accounting for their contact interactions [32, 137, 60, 29, 120]. Over the last 40 years, DEM has matured into a general-purpose tool for the simulation of industry-related particulate processes and for the investigation of the complex behavior of granular materials. With rising computational power and inclusion of realistic particle characteristics, both the accuracy and the computational efficiency of DEM simulations have continuously increased, but the level of expectations of DEM has considerably grown at the same time.
This report attempts to outline the horizons of granular modeling beyond the current practice of DEM. It is not meant to be a review of DEM and its recent numerous achievements or alternative methods to DEM, but to serve as an objective description of the issues and new resources that may lead to a paradigm shift in near future. The seminal report of P.W. Cleary for IFPRI, entitled “Review of DEM for Industrial Applications", in 2010 provides a clear and rich background of DEM together with the breadth of industrial applications that are possible with DEM [29]. Despite huge progress accomplished during the last decade, most themes and issues developed and exemplified in that report about discrete modeling and its applications are still relevant. The present report may be considered as a complement to that one, with the somewhat different goal of highlighting the shortcomings of the current practice of DEM and the novel trends that can allow us to identify the most promising future developments. Several examples of coupled DEM-CFD (Computational Fluid Dynamics) simulations are cited in this report, but the focus will be on the particles and their interactions in DEM.
Section 1
In section 1, we discuss the role of DEM as an original approach for gaining knowledge on particulate systems alongside theory and experiment. We argue that DEM is an inherently bottom-up approach and the adequate definition of numerical material is as much important as the mathematical algorithm used for the prediction of cooperative dynamics. We also describe the three levels of DEM with increasing complexity of the numerical material and the scope of a data-driven approach with the potential power of providing tools to improve accuracy and efficiency. We underline the interpretive use of DEM in connection with theory and the origins of its general trustworthiness in connection with experiment.
Section 2
In section 2, we highlight the role of contact interactions and their implementation in DEM. The focus will be on several ambiguities and shortcomings which need to be resolved, such as normal force positivity and memory of tangential displacements. We develop the difference between force laws and contact laws and the prospect of a shift from the hard-particle soft-contact approach to a soft particle hard-contact approach. We also consider different models of adhesion and recent models of elastoplastic contacts and discuss their applicability and consequences for granular dynamics. Finally, we focus on parametric randomness and more specifically polydisperse input parameters as a major ingredient of physics fidelity that has been so far ignored in DEM simulations.
Section 3
Section 3 is devoted to the representation and implementation of particle shape with its variants as a key input of DEM. In particular, we discuss arbitrary particle shapes and their extraction from image data as a step towards data-driven DEM and the contact detection issues. We underline the role of shape polydispersity and discuss the issue of reducing particle shape to a small number of descriptors or through its effect in connection with dissipation.
Section 4
In section 4 we describe different modeling strategies for particle breakage at the sub-particle and particle levels. The realism and efficiency of sub-particle methods are discussed, such as breakage criteria with regard to fracture mechanics, finite size effects, shapes of the generated fragments, and recently developed hybrid methods. We discuss how the higher physics-fidelity of sub-particle models can be combined with the computational efficiency of particle level models.
Section 5
Section 5 is devoted to DEM models of soft particles, i.e. particles undergoing large deformations without breakage. We briefly present the surface deformation methods based on material points or nodes at the particle surface, and volume deformation methods based on continuum field description of the particle behavior.
Section 6
In section 6 we discuss several computational issues. The important role of parallel computing, specially on General-Purpose GPUs, for the applicability of new models of high physics fidelity and for speedup of simulations is underlined. The limits of particle coarsening are discussed. We also recall new developments in original multiscale hybrid models and the benefits of concurrent use of discrete and continuum simulations of granular materials. Finally, we discuss the ways Machine Learning models can be used with DEM simulations and a data-driven approach allowing expensive calculations of contacts, forces and velocities in DEM algorithms to be replaced by a Machine Learning-enabled framework.
Section 7
In section 7 we consider the issues of verification and validation and discuss the methods of uncertainty quantification as an asset to reinforce the reliability of DEM in application to real-world processes. We use examples of rigorous uncertainty quantification to illustrate the treatment of uncertainties related to the input data and model approximation. We also present the concept of validation metric for optimal use of experimental data for the evaluation of model form errors.
Section 8
Finally, we present an outlook of future directions around and beyond DEM in section 8. Recent algorithmic developments are qualified according to their contributions to physics fidelity, data fidelity, computational efficiency, and game-changing nature. We discuss the developments beyond the hard-particle approximation and the scope of a data-driven DEM.
It is well known that attractive particle-particle interactions become more decisive with decreasing particle size. Especially in dry fine grinding processes, where small particles are produced within a dry environment by different types of mechanical stress, these forces lead to a variety of challenges, such as a complicated control of the powder behavior, a decrease of grinding efficiencies and production rates as well as obtaining high product finenesses. In order to control these forces, chemical liquid or solid additives – so called grinding aids – are added to the process in many industrial dry fine grinding applications. Even though the benefits of grinding aids have already been shown in various experimental studies and industrial applications, their selection and application is still mostly based on empirical knowledge. As shown in this review article, the variety of applied substances, ground materials and target finenesses, but also available mill types, process designs, mill and process parameters as well as analysis methods complicate the development of a comprehensive understanding. Within this article, we present the basic mechanisms of action of various liquid, gaseous and solid grinding aids. Subsequently, it is shown how grinding aid molecules interact with the solid particle surface, leading to decisive changes of the particle and bulk behavior. Based on various scientific studies it is shown, how this may affect the micro- and macro-processes inside the mill as well as the whole grinding plan.
Potential Topics for a Research Brief
A method selection guide is also included.
Encouraging Commercial Development
Presented for encouraging commercial development of the technology, including workshop ideas and.
Commercialization of Methods
A few of these methods have been commercialized, but most of them have not. Recommendations are.
In-line Methods
Been increased in some applications. Several in-line methods quantify rheology and phase distribution.
Characterization Developments
Characterization have been expanded, and the resolution and dynamic range of size measurement have.
New Developments
Noteworthy new developments have been identified. The concentration ranges for size and shape.
Variants of Known Methods
And patents use variants of known characterization methods, but a dozen innovative or otherwise.
Context and References
Place them in context, 75 background references are also provided. Over 80% of the reviewed papers.
Relevant Examples
Most relevant examples from a field of over 3200 titles and abstracts published between 2014 – 2020. To.
Characterization of Suspensions
Characterization of suspensions and slurries. The 165 publications reviewed here were selected as the.
Literature Review
A comprehensive literature review was conducted on new and emerging methods for in-process.
Abstract
Abstract
The description of ‘smart’ is applied to a variety of systems that are capable of reacting to a change in environment and providing a unique response. The scope of this review is focused on environmentally responsive smart particles, with a secondary emphasis on in-situ sensor particles for in-process characterization. This review provides information on particles developed to ‘smartly’ respond to mechanical, thermal, chemical, biological, electromagnetic, magnetic, or electrical stimuli. The review covers multiple aspects of “smart” particles, including their applications, mode of action, preparation methods, and fate. Smart particles used for commercial and experimental applications are included.