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A concise and clear introduction to the basics of fluidization, with a view to its applications in the process and energy industries.

In this PhD thesis, the flow stability in a laboratory three-dimensional prismatic spouted bed is investigated both experimentally and in CFD-DEM simulations. Liquid is injected in bottom-spray configuration with the aim of a homogeneous distribution of the coating suspension on the whole particle bed. The range of stable spouting is increased by the installation of two parallel draft plates. Nevertheless, the instable spouting regime is found to be advantageous for obtaining a homogeneous coating as the draft plates prevent the mixing in the depth of the apparatus. In addition to the investigations on laboratory scale, the residence time behavior in a continuous pilot scale spouted bed is characterized using a novel tracer method with magnetizable particles. The back-mixing in the apparatus is reduced by the insertion of separation plates with defined transfer geometries.

This research delves into the promising domain of CO2 capture through fine solid activated carbon adsorbent, offering a more energy-efficient alternative to traditional adsorption methods. The central challenge addressed here is the utility of cheaper CO2 adsorbent, fine powder materials whose properties can be precisely tailored via molecular-level fictionalization. Equally vital is selecting an optimal fluidizing column configuration that maximizes CO2 interaction with adsorption particles and enhances adsorption efficiency. The proposed solution is a fluidized bed column uniquely equipped with integrated acoustic vibrations to counteract interparticle forces common in fine powders. For adsorption evaluations, sound-assisted fluidized-bed experimentation on a laboratory size was set up. Adsorbent material activated carbon made up of coal underwent rigorous testing between a range of 20 Hz-200 Hz and 20 dB-135 dB. Results reveal the beneficial effects of acoustic enhancement of fluidization quality and adsorption efficiency, increased adsorption capacity, enhanced bed utilization, and accelerated adsorption rates. Extensive research has been conducted on the detailed effects of major operational variables on adsorption performance, notably frequency, sound intensity, and minimum fluidization velocity. The findings highlight the pivotal role of particle size with mean size 75 microns range as a determinant of adsorption capacity at 100 Hz and 125 dB. At the end of experimentation, the adsorbent considered for the experiment is compared to the study adsorption capacity at operating conditions. The research concludes with a discussion on the effects of influencing parameters for adsorption on employing sound vibrations using fluidization technique adsorption for CO2 capture.

Large meteorite impact structures on the terrestrial bodies of the Solar System contain pronounced topographic rings, which emerged from uplifted target (crustal) rocks within minutes of impact. To flow rapidly over large distances, these target rocks must have weakened drastically, but they subsequently regained sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades. Recent drilling of the approximately 200-km-diameter Chicxulub impact structure in Mexico has produced a record of brittle and viscous deformation within its peak-ring rocks. Here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering. The observations point to quasi-continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering, followed by increasingly localized faulting. Catastrophic rock weakening upon impact of a meteorite, and hence flow, is shown to be followed by regained rock strength that enabled the formation of the peak ring during cratering.

The physical state of embryonic tissues emerges from non-equilibrium, collective interactions among constituent cells. Cellular jamming, rigidity transitions and characteristics of glassy dynamics have all been observed in multicellular systems, but it is unclear how cells control these emergent tissue states and transitions, including tissue fluidization. Combining computational and experimental methods, here we show that tissue fluidization in posterior zebrafish tissues is controlled by the stochastic dynamics of tensions at cell–cell contacts. We develop a computational framework that connects cell behaviour to embryonic tissue dynamics, accounting for the presence of extracellular spaces, complex cell shapes and cortical tension dynamics. We predict that tissues are maximally rigid at the structural transition between confluent and non-confluent states, with actively generated tension fluctuations controlling stress relaxation and tissue fluidization. By directly measuring strain and stress relaxation, as well as the dynamics of cell rearrangements, in elongating posterior zebrafish tissues, we show that tension fluctuations drive active cell rearrangements that fluidize the tissue. These results highlight a key role of non-equilibrium tension dynamics in developmental processes.A computational framework draws analogy with foams to offer a comprehensive picture of how cell behaviours influence fluidization in embryonic tissues, highlighting the role of tension fluctuations in regulating tissue rigidity.

P granules and other RNA/protein bodies are membrane-less organelles that may assemble by intracellular phase separation, similar to the condensation of water vapor into droplets. However, the molecular driving forces and the nature of the condensed phases remain poorly understood. Here, we show that the Caenorhabditis elegans protein LAF-1, a DDX3 RNA helicase found in P granules, phase separates into P granule-like droplets in vitro. We adapt a microrheology technique to precisely measure the viscoelasticity of micrometer-sized LAF-1 droplets, revealing purely viscous properties highly tunable by salt and RNA concentration. RNA decreases viscosity and increases molecular dynamics within the droplet. Single molecule FRET assays suggest that this RNA fluidization results from highly dynamic RNA–protein interactions that emerge close to the droplet phase boundary. We demonstrate than an N-terminal, arginine/glycine rich, intrinsically disordered protein (IDP) domain of LAF-1 is necessary and sufficient for both phase separation and RNA–protein interactions. In vivo, RNAi knockdown of LAF-1 results in the dissolution of P granules in the early embryo, with an apparent submicromolar phase boundary comparable to that measured in vitro. Together, these findings demonstrate that LAF-1 is important for promoting P granule assembly and provide insight into the mechanism by which IDP-driven molecular interactions give rise to liquid phase organelles with tunable properties. Significance Phase transitions have recently emerged as a key mechanism for intracellular organization. However, the underlying molecular interactions and nature of the resulting condensed phases are poorly understood. Here, we identify a role for LAF-1 in the liquid phase separation of P granules—RNA/protein assemblies implicated in germ-line maintenance. We adapt microrheology techniques to measure precise viscoelastic properties of LAF-1 liquid droplets. Our experiments reveal that electrostatic disordered protein interactions give rise to droplets with tunable material properties. RNA can fluidize protein droplets by decreasing the viscosity and increasing internal molecular dynamics. Our results provide insight into the mechanism by which molecular level interactions can give rise to liquid phase organelles with tunable material properties, potentially underlying biologically adaptable functions.

In the last decade, a few of the early attempts to bring CFD-DEM of fluidized beds beyond the limits of small, lab-scale units to larger scale systems have become popular. The simulation capabilities of the Discrete Element Method in multiphase flow and fluidized beds have largely benefitted by the improvements offered by coarse graining approaches. In fact, the number of real particles that can be simulated increases to the point that pilot-scale and some industrially relevant systems become approachable. Methodologically, coarse graining procedures have been introduced by various groups, resting on different physical backgrounds. The present review collects the most relevant contributions, critically proposing them within a unique, consistent framework for the derivations and nomenclature. Scaling for the contact forces, with the linear and Hertz-based approaches, for the hydrodynamic and cohesive forces is illustrated and discussed. The orders of magnitude computational savings are quantified as a function of the coarse graining degree. An overview of the recent applications in bubbling, spouted beds and circulating fluidized bed reactors is presented. Finally, new scaling, recent extensions and promising future directions are discussed in perspective. In addition to providing a compact compendium of the essential aspects, the review aims at stimulating further efforts in this promising field.

The collective behaviour of cells in epithelial tissues is dependent on their mechanical properties. However, the contribution of tissue mechanics to wound healing in vivo remains poorly understood. Here, we investigate the relationship between tissue mechanics and wound healing in live Drosophila wing imaginal discs and show that by tuning epithelial cell junctional tension, we can systematically alter the rate of wound healing. Coincident with the contraction of an actomyosin purse string, we observe cells flowing past each other at the wound edge by intercalating, reminiscent of molecules in a fluid, resulting in seamless wound closure. Using a cell-based physical model, we predict that a reduction in junctional tension fluidizes the tissue through an increase in intercalation rate and corresponding reduction in bulk viscosity, in the manner of an unjamming transition. The resultant fluidization of the tissue accelerates wound healing. Accordingly, when we experimentally reduce tissue tension in wing discs, the intercalation rate increases and wounds repair in less time.

This study elucidates the mechanism of fluidization instability during limestone carbonation under a 100% CO[sub.2] atmosphere and determines the influence of Al[sub.2] O[sub.3] fluidization aids (dosage and particle size) on exothermic performance. The experiments demonstrate that rapid CO[sub.2] absorption in the emulsion phase, coupled with insufficient gas replenishment from the bubble phase, disrupts the balance between drag force and buoyancy, leading to localized defluidization. This instability impedes gas exchange between the bubble and emulsion phases, resulting in bubble coalescence and channeling across the bed. The fluidization instability reduces the maximum exothermic temperature and causes significant temperature heterogeneity in the bed. With repeated thermal cycles (20 cycles), the CO[sub.2] absorption capacity of limestone diminishes (the effective conversion rate drops to 0.25), and the instability disappears. The addition of 5wt.% Al[sub.2] O[sub.3] (particle size: 0.05–0.075 mm) stabilizes the fluidization state during carbonation, significantly homogenizing the bed temperature distribution, with maximum and average temperature differentials reduced by 63% and 89%, respectively, compared to pure limestone systems.

Nanoparticles (NPs) are applied in a wide range of processes, and their use continues to increase. Fluidization is one of the best techniques available to disperse and process NPs. NPs cannot be fluidized individually; they fluidize as very porous agglomerates. The objective of this article is to review the developments in nanopowder fluidization. Often, it is needed to apply an assistance method, such as vibration or microjets, to obtain proper fluidization. These methods can greatly improve the fluidization characteristics, strongly increase the bed expansion, and lead to a better mixing of the bed material. Several approaches have been applied to model the behavior of fluidized nanopowders. The average size of fluidized NP agglomerates can be estimated using a force balance or by a modified Richardson and Zaki equation. Some first attempts have been made to apply computational fluid dynamics. Fluidization can also be used to provide individual NPs with a thin coating of another material and to mix two different species of nanopowder. The application of nanopowder fluidization in practice is still limited, but a wide range of potential applications is foreseen.