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In metal additive manufacturing (AM), powder bed fusion technologies such as selective laser melting and binder jetting rely on the spreading of fine metal powder to build up the layers of a part. This work studies the complex interaction between metal powder particles and the recoater. We apply the Discrete Element Method (DEM) to a calibrated cohesive Ti-6Al-4V powder model, matching the particle properties to experimental measurements of size, shape and inter-particle forces. We simulate powder bed fusion recoating at varying speeds and layer thicknesses with two different recoater geometries: a toothed rake and a solid blade. Our results demonstrate that the recoating mechanism induces significant granular convection, with the recoater velocity and geometry strongly influencing the degree of particle circulation and size segregation. Notably a toothed rake recoater improved particle circulation – while the solid blade recoater increases size segregation within the heap. Furthermore the recoater was found to filter fine and coarse particles, allowing smaller particles to flow underneath the recoater, and larger particles through its teeth. Our results demonstrate the key mechanisms which drive granular convection during recoating and how the fine details of recoater geometry impacts surface layer roughness and final part quality.

The Brazil nut effect (BNE) is a counter-intuitive process of segregation of a large object inside a vibrated granular medium (GM), which has been studied widely by subjecting GMs to various kinds of shears and vibrations. In this article, we report a new kind of BNE which occurs as a consequence of granular fluctuations induced by microbe-generated gas bubbles. We call it the 'microbial Brazil nut effect'. The paper demonstrates microbial BNE for a bidisperse granular mixture as well as for intruder segregation. Furthermore, using X-ray μCT and a simple scaling argument for segregation velocity, the paper clarifies the transport mechanics of an intruder inside a bubbly granular bed. We think the reported phenomenon should be ubiquitous in the microbe-populated wet sandy floors of waterbodies and may have some implication on the distribution of material near the floors.

The Brazil nut effect (BNE) is a physical phenomenon by which large granular particles (i.e., archaeological artifacts) in a bed of small disturbed particles (i.e., soil), rise to the top surfaces. This paper examines the physical forces acting on archaeological artifacts—scattered on the surface and buried underground—to identify the major elements of site formation processes (SFPs). Combining theoretical advances in archaeology, pedology, granular physics and spectroscopy, we conducted accelerated laboratory tests on seven typical Israeli soils to form a SFP model. We suggest that the SFPs are the result of two opposing and continuous processes: soil coverage of the site started soon after human activity has ceased, and a force(s) that tends to lift buried artifacts up to exposed surfaces, acting in accordance with Brazil nut effect (BNE). The post-burial forces pressuring artifact movement upward are affected by the artifacts' density and size, soil characteristics and the local environment. As a result, some archaeological artifacts reach exposed surfaces, some are lifted to higher soil deposits but remain buried, and the rest remain in their original burial context.

We present a discrete element method study of the uprising of an intruder immersed in a granular media under vibration, also known as the Brazil Nut Effect. Besides confirming granular ratcheting and convection as leading mechanisms to this odd behavior, we evince the role of the resonance on the rising of the intruder by using periodic boundary conditions (pbc) in the horizontal direction to avoid wall-induced convection. As a result, we obtain a resonance-qualitylike curve of the intruder ascent rate as a function of the external frequency, which is verified for different values of the inverse normalized gravity Γ, as well as the system size. In addition, we introduce a large deviation function analysis which displays a remarkable difference for systems with walls or pbc.

The Moon has been the focus of several space exploration programs worldwide because it has valuable materials that could be mined and is suitable for a relay station to Mars. To realize lon...

Recently, a number of articles have reported that granular convection induced by continuous vibration is controlled by vibration velocity, in contrast with some previous studies. We have reported such an example for the Brazil nut effect when the vibration is given discontinuously, using a one-layer granular bed in a cell with down-facing side walls. Here, we report the effect of vibration phase and wall friction using the same experimental system, to confirm rising motion of an intruder induced by granular convection is again governed by vibration velocity. We compare two different cases of vibration phase for giving intermittent vibration cycles, and found one, in which granular packing is well established before grains start to lose contacts due to vibration, provides distinctly high reproducibility. We further control the side wall friction using a microfabrication technique, and found that significantly high reproducibility is attained in a cell with vertical side walls when a millimeter texture is introduced on the side walls. Our results indicate that the granular convection is universally controlled by vibration velocity. The present study opens a way to conduct highly reproducible experiments on granular dynamics, which is indispensable for deep physical understanding of granular flow and segregation.

The thesis presents a novel, non-intrusive measurement technique based on X-ray radiography that can measure the granular temperature of tracers in steady state granular flows of arbitrary geometry. We use the technique to probe the granular convection phenomenon and investigate the effect of various material parameters and driving conditions on the granular temperature of tracer particles and their velocities. Furthermore, we attempted to infer the granular temperature of the bulk particles surrounding these tracers by comparing our technique with Positron Emission Particle Tracking (PEPT) and X-ray rheography.

Although many previous studies have focused on the Brazil nut effect, segregation in a self-gravitating circular aggregate remains relatively unexplored. In this paper, size segregation in a two-dimensional assembly of grains in a circular geometry is studied through discrete element method (DEM) numerical simulations. We show that radial segregation within an asteroid submitted to periodic perturbations is not limited to the surface but also occurs in its core. The characteristic time and the overall efficiency of the segregation mechanism are studied as the intensity of the perturbation, the frictional properties, and rotational freedom of individual grains are varied.

The direction and strength of geomagnetic field had been evolving continuously in the past. One of the few means of obtaining continuous reconstructions of this evolution relies on sedimentary records. The latter are therefore important for understanding the geodynamo and the underlying evolution of the Earth’s interior, as well as providing an important dating tool through magnetostratigraphy. Sedimentary records of geomagnetic field variations rely on two main recording mechanisms: the alignment of magnetic particles, which underlies continuous records of relative paleointensity (RPI), and the archivation of cosmogenic isotopes, in particular ¹⁰Be, whose production by cosmic ray spallation is modulated by the screening action of the dipole component of the Earth’s field. Previous studies reported similarities as well as significant differences between RPI and cosmogenic ¹⁰Be (expressed as ¹⁰Be/⁹Be) records. While a perfect match of the two records is not expected due to environmental contaminations present in both records, the similar changes during the periods characterised by significant decrease of the dipole moment are suggested owning to global field strength control of ¹⁰Be production and attenuation of non-dipolar features in RPI records measured within the sediments with the low sedimentation rates (, La direction et l’intensité du champ géomagnétique ont continuellement évolué dans le passé. L’un des rares moyens d’obtenir des reconstitutions continues de cette évolution repose sur les enregistrements sédimentaires. Ces dernières sont donc importants pour comprendre la géodynamo et l’évolution sous-jacente de l’intérieur de la Terre, ainsi que pour fournir un outil de datation important grâce à la magnétostratigraphie. Les enregistrements sédimentaires des variations du champ géomagnétique reposent sur deux mécanismes d’enregistrement principaux: l’alignement des particules magnétiques, qui sous-tend les enregistrements continus de la paléointensité relative (RPI), et l’archivage des isotopes cosmogéniques, en particulier le ¹⁰Be. Bien que l’on ne s’attende pas à une concordance parfaite des deux enregistrements, les changements similaires au cours des périodes caractérisées par une diminution significative du moment dipolaire sont suggérés grâce au contrôle global du champ de production de ¹⁰Be et à l’atténuation des caractéristiques non dipolaires dans les enregistrements RPI mesurés dans les sédiments avec les faibles taux de sédimentation. L’objectif du présent travail était d’améliorer nos connaissances actuelles sur les mécanismes d’enregistrement dans le cas des sédiments marins, en particulier :1. Les facteurs environnementaux responsables du transport et du retrait du 10Be de lacolonne d’eau et l’effet de la distribution des sources sur l’approvisionnement en ⁹Be.2. L’effet des processus post-dépôt, en particulier celui du mélange des sédiments, sur le10Be et les enregistrements RPI.3. Le mécanisme par lequel une magnétisation post-déposition est acquise près du fond dela couche mélangée en surface.4. Les causes d’un décalage systématique entre les enregistrements ¹⁰Be et RPI et lesfacteurs environnementaux affectant le RPI.Afin de démêler l’apport environnemental et magnétique dans les couches sédimentaires de ¹⁰Be/⁹Be, nous avons analysé cinq enregistrements, couvrant la dernière inversion géomagnétique. Les différentes caractéristiques d’enregistrement sur les cinq sites ont été décrites en termes de modulations climatiques additives et multiplicatives, qui dépendent essentiellement de la profondeur de l’eau, de la localisation le long des grands systèmes de courants océaniques, et de la distance à la côte. Les enregistrements RPI sont fortement affectés par les processus post-dépôt, en particulier le mélange des sédiments, qui est entièrement responsable de l’aimantation rémanente naturelle (NRM) acquise par les sédiments bioturbés, et son retard par rapport aux enregistrements ¹⁰Be. Un nouveau modèle de bioturbation a été développé pour expliquer la NRM sédimentaire dans les sédiments bioturbés. Ce modèle inclut un phénomène récemment découvert de ségrégation de taille dans la couche mélangée de surface (SML), analogue à l’effet bien connu de la noix du Brésil (Brazilian-nut). La ségrégation de taille est responsable de la plus longue permanence des grandes particules dans la SML, jusqu’au cas limite des nodules de ferromanganèse. Nous avons démontré l’effet de noix du Brésil sur les particules de microtektite, qui consiste en une ségrégation des fragments en fonction de leur taille. Le modèle de ségrégation par taille permet d’estimer la profondeur réelle du mélange sédimentaire dû à la bioturbation, une fois prise en compte la composante supplémentaire de vitesse liée à la migration des plus grosses particules vers le haut de la colonne sédimentaire.Les résultats de cette recherche ont une importance significative non seulement pour la caractérisation de la réponse au mélange des sédiments et la reconstruction des enregistrements affectés des processus de bioturbation (par exemple ¹⁰Be /⁹Be), mais aussi pour l’évaluation de la validité des modèles d’âge qui sont limités par les âges des traceurs conservateurs.

Porous biodegradable scaffolds have many applications in bioengineering, ranging from cell culture and transplantation, to support structures, to induce blood vessel and tissue formation in vivo. While numerous strategies have been developed for the manufacture of porous scaffolds, it remains challenging to control the spatial organization of the pores. In this study, we introduce the use of the granular convection effect, also known as the muesli or brazil nut effect, to rapidly engineer particulate templates with a vertical size gradient. These templates can then be used to prepare scaffolds with pore size gradients. To demonstrate this approach, we prepared templates with particle size gradients, which were then infused with a prepolymer solution consisting of the pentaerythritol ethoxylate (polyol), sebacoyl chloride (acid chloride), and poly(caprolactone). Following curing, the template was dissolved to yield biodegradable polyester‐ether scaffolds with pore size gradients that could be tuned depending on the size range of the particulates used. The application of these scaffolds was demonstrated using pancreatic islets, which were loaded via centrifugation and retained within the scaffold's pores without a decrease in viability. The proposed strategy provides a facile approach to prepare templates with spatially organized pores that could potentially be used for cell transplantation, or guided tissue formation. Refereed/Peer-reviewed

If one wishes to gain a deep understanding of segregation in vibrofluidized systems, it is vital to first have a strong understanding of vibrofluidized systems in general, and the various phenomena exhibited thereby. This chapter aims to provide the reader with a solid grounding concerning the key concepts and terms relating to these systems, and an understanding of the processes – such as fluidization, convection, and the nonequipartition of energy – within these systems which underpin their segregative behaviors. The chapter begins by introducing the key parameters associated with vibrated granular systems and their role in the fluidization process, before revisiting the granular temperature and the process of granular convection, and finally giving an overview of the various phase states in which a vibrated granular system may exist.

Local three-dimensional radiation-hydrodynamics simulations of patches of the surfaces of solar-type stars, that are governed by small-scale granular convection, have helped analyzing and interpreting observations for decades. These models contributed considerably to the understanding of the atmospheres and indirectly also of the interiors and the active layers above the surface of these stars. Of great help was of course the availability of a close-by prototype of these stars – the sun.In the case of an asymptotic-giant-branch (AGB) star, the convective cells have sizes comparable to the radius of the giant. Therefore, the extensions of the solar-type-star simulations to AGB stars have to be global and cover the entire object, including a large part of the convection zone, the molecule-formation layers in the inner atmosphere, and the dust-formation region in the outer atmosphere. Three-dimensional radiation-hydrodynamics simulations with CO5BOLD show how the interplay of large and small convection cells, waves, pulsations, and shocks, but also molecular and dust opacities of AGB stars create conditions very different from those in the solar atmosphere.Recent CO5BOLD models account for frequency-dependent radiation transport and the formation of two independent dust species for an oxygen-rich composition. The drop of the comparably smooth temperature distribution below a threshold determines to onset of dust formation, further in, at higher temperatures, for aluminium oxides (Al2O3) than for silicates (Mg2SiO4). An uneven dust distribution is mostly caused by inhomogeneities in the density of the shocked gas.

A lot of research has been conducted on swarm and modular robots and their reconfiguration. For this kind of robot system, it is best to simplify each individual module in order to avoid making the swarm system too complex in the interest of reducing the computing power necessary for a task.This paper proposes a swarm robot system capable of self-segregation by changing the size of each agent, utilising the Brazil Nut Effect. The self-segregation allowed by this effect lead to the simplification of the control protocol necessary for the swarm.We simulated a swarm robot system consisting of circular modules capable of changing their radius and, with the aid of externally supplied vibrations, utilising the Brazil Nut Effect to achieve segregation of the swarm. The effect also allowed for the migration of individual modules through the swarm. Additionally, we harnessed this segregation effect in simulation to create a flow of modules within the swarm, whilst the swarm was confined within a vibrating container.Lastly, we took the first steps toward physical verification of the experimental results by designing and building a prototype for a circular robot module capable of changing its radius in a manner inspired by a spiral torsion spring.

Rayleigh-Benard convection in normal fluids shows interesting variation when a boundary is temperature modulated. As granular fluids show quite good resemblance to normal fluids, it is expected that they exhibit similar variation in convective dynamics under such a condition. A study of convection in granular fluids by injecting spatially non-uniform energy through a boundary is done in this paper. Emphasis is made on the dependence of onset and strength of granular convection on the relevant dimensionless parameters characterizing the convective state. The non-uniform energy injection is modelled by spatially periodic modulation of the lower boundary. It is seen that the amplitude and the wavelength of the periodic modulation are two new important parameters characterizing the dynamics.

Particles separation and patterning in fluidic environment is fundamental for many mechanical, biomedical, and chemical applications. There still remain challenges for manipulation the external forces to separate different kinds of particles. Chladni patterns have raised great interest in the field of self-assembly for particles of different materials. The particles bounce randomly on the vibrating plate, and gradually accumulate to nodal lines or anti-node. However, existing utilization of the Chladni effect mainly focuses on patterns and trajectories manipulation. The mechanism for simultaneous manipulation of multiple kinds of particles is still unclear. In this work, the separation of multiple kinds of particles is investigated using the inverse Chladni pattern. The particles accumulate to different positions in the annulus or circular region, forming ordered pattern at the anti-node. Besides, the acoustic streaming vortex is achieved, which serves as the local virtual container for particles separation. Additionally, the local horizontal Brazil nut effect occurs due to the combined effects of acoustic streaming, collision with the vibrating plate, buoyancy, and gravity. Separation of particles with different sizes and densities can be realized horizontally by the acoustic streaming vortex. We realize the simultaneous separation of as many as four kinds of particles. This work investigates the manipulation mechanism for multiple kinds of particles by the inverse Chladni pattern, thereby potentially providing an effective platform for particles patterning and simultaneous separation of multiple kinds of particles.

Accepted: 2017-11-25, 資料番号: SA1170256000

The structure of mono-sized sphere packings (diameter d) in cylindrical containers (diameter D and height H) both with and without inner cylinders (diameter Di) has been investigated in detail by means of advanced X-ray computed tomography. The geometrical parameters were varied in a wide range; in all experiments 1d vertical vibration was applied. Five experiments were selected with characteristically differing local packing structures. The influence of container geometry, filling and vibration procedures on the formation of regular packings is discussed and a simple correlation is presented to assess whether structured packings occupy a significant fraction of the total packed volume. For a packing with moderate densification, the regular structures are restricted to small wall zones and a random packing exists in the largest part of the packing volume. By selecting appropriate vibration parameters, the zones with regular structures can increase considerably and can persist in the total packed volume. The increasing crystallisation causes an increase of the container packing fraction. For cylinders with H/D ≫ 1 and moderate D/d, regular structures develop preferentially in radial direction from a hexagonal layer at the concave wall. For H/D < 1 and D/d ≫ 1, hexagonal dense structures grow preferentially above the flat bottom plate and can occupy a great portion of the total volume. The role of granular convection on these crystallisation processes has been addressed. Previous statements that the thickness of wall zones is ≈(4–5)d are not generally valid for mono-sized sphere packings; the development of a comprehensive correlation is the task of a future work. Structural details of the packings close to concave, plane and convex walls are analysed via void fraction distributions, sphere centre positions, contact angle distributions, coordination numbers, radial distribution function and Voronoi tessellation. The combination of these methods provides a comprehensive understanding of structural details. Only a few characteristic results are presented; special topics will be the subject of forthcoming publications.

Vibration has been employed in various engineering processes for material handling. The famous Brazil nut effect, large particles tend to rise to the top under vibration, initiates various research about vibration induced particle segregation. Particle size and density are two determining factors for their behaviour under vibration. Previous research in University of Nottingham proves vertical vibratory separation to be a promising environmental friendly mechanical separation method for recycling metallic fraction from shredded Waste Electric and Electronic Equipment (WEEE) stream. A pilot scale thin cell vibratory separator has been developed to investigate the potential for WEEE recycling applications. Shredded copper and polypropylene particles have been chosen to mimic metallic and non-metallic fractions in WEEE. Vibratory separation experiment with controlled environment and addition of solid lubricant are presented in this paper. The result demonstrates the effect of relative humidity and solid lubricant on improving flowability of granular system hence successful vibratory separation. The proposed mechanisms for the presence of moisture and solid lubricant are lubricant effect and elimination of static electricity.

We numerically and experimentally study the segregation dynamics in a binary mixture of microswimmers which move on a two-dimensional substrate in a static periodic triangular-like light intensity field. The motility of the active particles is proportional to the imposed light intensity and they possess a motility contrast, i.e., the prefactor depends on the species. In addition, the active particles also experience a torque aligning their motion towards the direction of the negative intensity gradient. We find a segregation of active particles near the intensity minima where typically one species is localized close to the minimum and the other one is centered around in an outer shell. For a very strong aligning torque, there is an exact mapping onto an equilibrium system in an effective external potential that is minimal at the intensity minima. This external potential is similar to (height-dependent) gravity, such that one can define effective `heaviness' of the self-propelled particles. In analogy to shaken granular matter in gravity, we define a `colloidal Brazil nut effect' if the heavier particles are floating on top of the lighter ones. Using extensive Brownian dynamics simulations, we identify system parameters for the active colloidal Brazil nut effect to occur and explain it based on a generalized Archimedes' principle within the effective equilibrium model: heavy particles are levitated in a dense fluid of lighter particles if their effective mass density is lower than that of the surrounding fluid. We also perform real-space experiments on light-activated self-propelled colloidal mixtures which confirm the theoretical predictions., 10 pages, 5 figures, JCP Special Topic on Chemical Physics of Active Matter

In this paper, we present a study on object transportation by swarm robots based on granular convection. We especially focused on the segregation phenomenon observed in a mixture of different size particles and applied its characteristics to design a system for carrying an object to its destination. The robot in this system is driven only by a combination of random force, a constant force exerted by the destination, and a spring force exerted by fixed points that operates as a constraint. The object is passive and driven only by the collision of the robots. Although none of the robots has a special device that detects the target object and other robots, the object is delivered to the destination. In this paper, we first explain the fundamental characteristics of the behavior of a system based on a robotic swarm without constraint. Then, we explain the behavior of the same system with constraint. The results are as follows. (1) The robotic swarm without constraint transports the object appropriately when a constant repulsive force exerted by the destination is added; in contrast, the swarm with constraint transports the object when a constant attractive force exerted by the destination is added. (2) The traveling speed of the object is related to its size, especially in the system with constraint. (3) The higher the density of the robots, the faster the object is moved to the destination, especially in the system without constraint.

Segregation of granular materials under vibration or flow conditions such as the Brazil nut effect has been well known, however, there is yet no consensus mechanisms to explain this phenomenon. This study attempts to investigate particle buoyant forces in the segregation process. To explain the difference of the segregation behavior for the large particle with different size, a modified calculation method of particle buoyant force is suggested for considering the effect of particle size ratio. A simple verification illustrates its validity.

The vibration-induced segregation (e.g., rising of one large intruder - so called Brazil Nut Effect (BNE)) is studied by discrete element method. Vibration frequency and amplitude are two dominating factors in the occurrence of BNE and a phase diagram is constructed. For fixed vibration amplitude, segregation only occurs when vibration frequency is within a certain range. Larger vibration amplitude can expand the range of vibration frequency for BNE. Size ratio and the intruder shape are studied under certain vibration conditions. Larger size ratio can enlarge the segregation intensity. The shape of the intruder influences the segregation process by the intruder′s orientation. Standing-like initial orientation can increase the time required for the intruder to reach the top while lying-like initial orientation cannot significantly affect the vertical segregation.

We investigate the dynamics of regolith on rubble-pile asteroids to explain granular processes observed in reality. In particular, we explain how the appearance of boulders on the surface of asteroid Itokawa could have resulted from a size sorting process in granular media called the Brazil Nut Effect (BNE). The Discrete Element Method (DEM) is implemented to perform numerical simulations of the BNE in a micro-gravity environment caused by inter-particle collisions during seismic vibrations. Firstly, we present the results of how the BNE depends on the magnitude of surface gravity. It is estimated that segregation processes on Itokawa occur over much longer time-scales (in the order of a few hundred years) than the same processes would require in the presence of a strong gravitational field, like on Earth. Secondly, we also find that the size sorting could also result from kinetic sieving encountered during granular avalanches. Finally, we discuss how the void-filling mechanism becomes more efficient when there is a higher relative size difference between the boulders and the surrounding grains. Our model has important implications in understanding the resurfacing of Itokawa by trying to explain one of the many complex geophysical processes that occur in such unique conditions.

Modeling conductive heat transfer from rotary drum walls to a particle bed via discrete element method simulations, three time scales were determined: 1) the characteristic heating time of the bed, τ; 2) the particle thermal time constant, τp; and 3) the contact time between a particle and the wall, τc. Results fall onto a monotonic curve of τ/τc vs. ϕ (τp/τc), with three heating regimes. At low ϕ, conduction dominates, and the system heats quickly as a solid body. At high ϕ, granular convection dominates, and the bed heats slowly at a nearly uniform temperature. At intermediate ϕ, the system heats as a cool core with warmer outer layers. The results of this work have important implications for improving the design and operation of rotary drums (e.g., energy-intensive calcination processes). By calculating τp and τc from material and operating parameters, the characteristic heating time, τ, can be predicted a priori.

To study the energy dissipation mechanism of nonobstructive particle dampers (NOPDs) and provide guidance to the application of NOPDs, the dense granular flow theory was introduced to establish a quantitative energy dissipation model for NOPDs. The convection movement of the particles under vibrational excitations was studied using the discrete element method, and the Prandtl mixing length theory was adopted to modify the constitution law of dense granular flows. The pressure of the granular flow was obtained by equivalenting the vibrational excitation to a body force acted on particles. Theoretical results showed that the energy dissipation rate of the NOPD was increased with the vibration intensity and decreased with the granular diameter. It also indicated that particles near the side wall and the bottom of the damper dissipated more energy than those particles in other regions. The theoretical model was verified by simulation and experimental result. The results may provide a new approach to studying the energy dissipation mechanism of NOPD and give some guidance to enhancing the damping performance of NOPD in engineering practices.

In this study, the Brazil nut segregation problem was experimentally investigated in a 3D vertically vibrating granular bed. A high-speed camera was used to record the rise time of larger particles (i.e., intruders). The results showed that the rise time decreased with an increase in the size ratio of monosized immersed granular materials. The percolation effect is the dominant mechanism that influences the Brazil nut segregation behavior of monosized immersed granular materials. The percolation effect is stronger when the size ratio is higher, leading to a stronger Brazil nut effect. In addition, the results indicated that the rise times of the intruder are shorter with multisized immersed granular materials than those with monosized immersed granular materials. The rise velocity does not increase monotonically with an increase in the filling bed height. In addition, the base roughness significantly influences granular segregation. The Brazil nut effect is mitigated, resulting in longer rise times with the bumpy base.

By coupling the heat transfer and chemical reactions, biomass-steam gasification in a lab-scale spouted gasifier is numerically simulated via the multiphase particle-in-cell approach. The proposed model is firstly validated with the experimental results. Then, the spatial distributions of biomass particles, spout-annulus boundary, the gas species, the gas-solid flux, together with the influences of operating parameters are discussed. The results demonstrate that: (i) similar to the well-known Brazil nut effect, density-induced segregation of biomass and sand species results in the accumulation of large-diameter biomass species near the bed surface. High temperature does not change the general distribution of the spout-annulus boundary; (ii) the gaseous products mainly concentrate in the fountain; enlarging the bed height and biomass diameter reduces but increases the mole fraction of CO and H2, respectively. The steam-biomass ratio has a promoting effect on the production of H2, while higher gasification temperature reduces the H2 yield; (iii) enlarging the bed height and steam-biomass ratio decreases and increases the vertical flux of both the gas and solid phase in the dense region, respectively. The increase of bed height and steam-biomass ratio reduces and enlarges the gas voidage, respectively. The results obtained in this work provide meaningful insights regarding the presence of Brazil nut effect induced by the density difference and the complicated multiphase flow in the spouting apparatus, which will be beneficial to the design and optimization of this kind of gasifier.