論文発表
K. Kuwagi, T. Fukui, A. Kogane and H. Hirano, Relationship between dimensionless buoyancy and pressure drop fluctuation under fluidization conditions, Proc. The 29th International Symposium on Transport Phenomena (ISTP29), pp.1-4 (USB), Paper No.62, 30 October - 2 November, 2018, Honolulu, USA
西山真由，平井貴大，平野博之, 凹凸型マイクロ流路内における交互流の数値解析, 岡山理科大学紀要，第54号A, pp.59-65, (2019)
Tomohiko Kihara, Hideaki Obata , Hiroyuki Hirano, Quantitative visualization of fluid mixing in slug flow for arbitrary wall-shaped microchannel using Shannon entropy, Chemical Engineering Science, 200, pp.225-235, (2019)
Micro-reactors based on slug flow are among the most promising developments for improving the efficiencies of chemical reactions and unit operations in chemical engineering. Quantitative understanding of the local and global fluid dynamics and their effects on fluid mixing is required for designing effective slug flow micro-reactors. This paper proposes a new method for quantitative two-dimensional assessment of fluid mixing in slug flow. Pixel-wise calculation of local entropy inside a slug is discussed. The proposed method is based on two-phase simulation using the volume of fraction (VOF) algorithm and is thus applicable to the flow pattern in arbitrary wall-shaped micro-reactors. The method consists of three steps. (1) Flow analysis using two-phase VOF algorithm: A series of two-dimensional velocity fields inside the slug along time is obtained for a certain duration. (2) Backward particle tracking from the target image to the initial image: The slug in the initial image is divided into small regions, and each region is assigned a different label. Accumulation of backward particle tracking results reveals a two-dimensional distribution of labels in the target image. (3) Pixel-wise calculation of entropy on the obtained distribution of labels: The resulting image is a quantitative two-dimensional mixing pattern inside the slug. The proposed method was applied to three types of microchannels with different bumps on the walls. The results could quantitatively distinguish the differences in fluid mixing capability among the systems.
Atsuto Kogane, Kenya Kuwagi and Hiroyuki Hirano, Dimensionless parameter for distinction between homogeneous and bubbling fluidization regimes, Advances and Applications in Fluid Mechanics, 23(1), pp.69 – 96, (2019)
When the particle phase is dense, two fluidization regimes can be defined, i.e., homogeneous and bubbling fluidization. In this study, two approaches, i.e., the particle-scale flow analysis and dimensional analysis, were applied to study the mechanism of transition between homogeneous and bubbling fluidization regimes. The fluidization behaviors were simulated using the discrete element method and the computational fluid dynamics (DEM-CFD) coupling model. The findings reveal that the bubbling and homogeneous regimes were almost divided into two separate regions when the lateral force was plotted against the Archimedes number (Ar) and Reynolds number (Re). The boundary plane that separated the homogenous and bubbling regions was expressed as a function of (Re/Ar). Within the Stokes flow region, (Re/Ar) can be expressed by the dimensionless drag force and buoyancy. The results of plotting the dimensionless gravity term against Re revealed that the dimensionless gravity term: distinguishes between the two states of fluidization.
K. Kuwagi, A. Kogane and H. Hirano, Comparison of estimation equation obtained from dimensionless gravity term with prior equations to distinguish between homogeneous and bubbling fluidizations, Proc. of The 30th International Symposium on Transport Phenomena (ISTP30), pp.578-584, 1-3 November, 2019, Halong, Vietnam.
西山真由，平野博之, 菱形マイクロ流路内における交互流を利用した物質移動, 岡山理科大学紀要，第55号A, pp.55-59, (2019)
Kenya Kuwagi, Atsuto Kogane, Yui Sasaki, Hiroyuki Hirano, Validation of Dimensionless Parameters for Distinguishing between Homogeneous and Bubbling Fluidizations, Open Journal of Fluid Dynamics, 11, 81-97, (2021)
The difference between homogeneous and bubbling fluidization behaviors has been studied for the past 70 years, where several researchers have reported on the influence of interparticle forces in fluidization. Although inter-
particle forces such as van der Waals forces are evident in a real system, these forces are not the determinant in homogeneous fluidization, which can be simulated without any interparticle forces. In our previous study, the difference in fundamental mechanisms of the two fluidization states was analytically determined with a dimensionless gravity term, comprising the Reynolds number, Archimedes number, and density ratio. Nevertheless, some researchers insist that interparticle forces are dominant and a hydrodynamic force is not dominant. In this study, a dimensional analysis was applied to obtain a dominant parameter for distinguishing two fluidizations. Furthermore, some parameters were examined by comparing the experimental data in previous studies. The results indicated that hydrodynamic force is the dominant factor and the dimensionless gravity term is the dominant parameter in differentiating the two fluidized states.
Hiroyuki Hirano, ShogoTsuzaki, HideakiObata, Tomohiko Kihara, A colorimetric method for quantitative visualization of diffusion and internal circulation in liquid-liquid two-phase flow, Chemical Engineering Science, Chem. Eng. Sci., 249, (2022).
Herein, we propose a new method for the quantitative evaluation of mass-transfer characteristics in liquid–liquid two-phase flow during the formation of slug and its progression in a microchannel. The experimental setup included a 0.3-mm square microchannel with a Y junction. Distilled water with pH indicator and cyclohexane containing acetic acid were selected as the probe fluids. The acetic-acid concentrations were 0.05 and 0.1 vol%, while the volumetric velocity of the aqueous and organic phases was 0.03 mL/min. Acetic-acid diffusion and its internal circulation in the aqueous slug were visualized by color changes and recorded as microscopically magnified video images. By adopting a deep-learning algorithm, the aqueous slugs were segmented, and a calibration method converted color information to acetic-acid concentration values. The experimental results were comparable with those of previous studies. The presented method also revealed several new features that could not have been observed quantitatively by established experimental methods.
受賞
論文審査貢献賞，公益社団法人化学工学会，2014年，2015年
学会発表
井上 啓, 加藤暢恵, 平野博之, カオス尺度を用いた気液二相流モデルの解析, 日本応用数理学会2017年度年会講演予稿集, pp.209-210, 6-8 Sep., 2017, 東京.
熊本翔乃, 山本萌絵, 平野博之, OpenFOAMによる減圧下における立方体容器内の自然対流の数値計算, オープンCAEシンポジウム2017@名古屋 講演会 講演概要集, C13, 8-9 Dec., 2017, 名古屋.
西山真由, 平井貴大, 平野博之, 木原朝彦, 野村悦治, OpenFOAMによる壁面に凹凸を有するマイクロ流路内の液々二相交互流の数値解析, オープンCAEシンポジウム2017@名古屋 講演会 講演概要集, C16, 8-9 Dec., 2017, 名古屋.
井上 啓, 加藤暢恵, 平野博之, 水槽内に生じる気液二相流シミュレーションデータのカオス尺度による解析, 日本応用数理学会 環瀬戸内応用数理研究部会 第21回シンポジウム講演予稿集, pp.28-31, 6-7 Jan., 2018, 松江.
西山真由，平井貴大，平野博之，木原朝彦，小畑秀明, 壁面に凹凸を有するマイクロ流路内の液々二相交互流の可視化と数値解析, 第55回化学関連支部合同九州大会講演予稿集, p.89, 30 Jun. 2018, 北九州.
西山真由，平野博之，木原朝彦，小畑秀明，桑木賢也, マイクロ流路内における液々二相交互流を利用した物質移動, 第56回化学関連支部合同九州大会講演予稿集, p.53, 13 Jul. 2019, 北九州.
桑木賢也，小金篤人，平野博之, 流動化現象に対する次元解析の適用性の検討, 第57回粉体に関する討論会講演論文集, pp.134-138, 25-27 Nov. 2019, 広島.
桑木賢也, 小金篤人, 平野博之, 振動粉体層内の平均粒子速度に及ぼす容器サイズの影響, 第24回日本流体力学会 中四国・九州支部講演会演要旨集, USB pp.1-2, 30 Nov. - 1 Dec., 2019, 松山.
桑木賢也, 福岡誠也，平野博之, 車輪下の砂粒子の運動の数値シミュレーション, オープンCAE・FrontISTR合同シンポジウム2020 梗概集, A-9, 4-5 Dec., 2020, オンライン.
平野博之，木原朝彦，パク ボソン（朴 報聖），津崎翔悟，串田尚樹，小畑秀明，桑木賢也, マイクロ流路内で生じる液－液二相交互流の数値解析とシャノン・エントロピーによる物質移動評価, 環瀬戸内応用数理研究部会第24回シンポジウム講演予稿集（研究会資料）, pp.1-4, 12-13 Dec. 2020, 岡山市 岡山理科大学.
佐々木友惟, 桑木賢也, 平野博之, DEMシミュレーションで麺生地を表現するための粒子間付着力の検討, 第23回化学工学会学生発表会要旨集, B14, 6 Mar., 2021, オンライン.
佐々木友惟, 桑木賢也, 平野博之, 麺生地混練過程の粉体のDEMシミュレーョン, オープンCAEシンポジウム2021 梗概集, A-16, 2-4 Dec., 2021, オンライン.
佐々木友惟, 桑木賢也, 平野博之, LIGGGHTS 較を用いた麺生地混錬過程の粉体数値シミュレーション, 2022 年度第 29 回日本流体力学会中四国・九州支部総会講演会 論文集, 1-2, 28 May, 2022, 福岡大学.
論文発表
Jun Oshitani, Toshiki Sasaki, Takuya Tsuji, Kyohei Higashida and Derek Y. C. Chan, Anomalous sinking of spheres due to local fluidization of apparently fixed powder beds, Physical Review Letters, 116(6), 068001, (2016)
The sinking of an intruder sphere into a powder bed in the apparently fixed bed regime exhibits complex behavior in the sinking rate and the final depth when the sphere density is close to the powder bed density. Evidence is adduced that the intruder sphere locally fluidizes the apparently fixed powder bed, allowing the formation of voids and percolation bubbles that facilitates spheres to sink slower but deeper than expected. By adjusting the air injection rate and the sphere-to-powder bed density ratio, this phenomenon provides the basis of a sensitive large particle separation mechanism.
Kyohei Higashida, Kenta Rai, Wataru Yoshimori, Tomoki Ikegai, Takuya Tsuji, Shusaku Harada, Jun Oshitani, Toshitsugu Tanaka, Dynamic vertical forces working on a large object floating in gas-fluidized bed: discrete particle simulation and Lagrangian measurement, Chemical Engineering Science, 151, 105-115, (2016)
In a number of practical applications of fluidized bed, large solid objects coexist with small bed materials and the prediction of large objects' motion in fluidized is quite important. In the present study, we investigate the dynamic vertical forces working on a large sphere floating in a three-dimensional bubbling gas-fluidized bed. Numerical results obtained by using Fictitious particle method (FPM) are directly compared in detail with experimental results obtained by a non-invasive Lagrangian sensor system which can directly measure forces working on a free-moving object. In the present condition, the sphere keeps on floating near the free surface of the bed during fluidization and it shows characteristic upward and downward motions. Time-series data of the dynamic vertical forces agrees reasonably well between the simulation and the experiment and its quasi-periodicity and intermittent occurrence of characteristic peaks are confirmed. The mean and standard deviation of the dynamic vertical forces show good agreements between the simulation and the experiment with some differences in distributions of the relative frequency. From the numerical results, we confirm that the fluctuation of forces is strongly related to the bubble motions and fluid force is more dominant for the floating and sinking motions of a sphere in a fluidized bed comparing to contact force. Dependency on the superficial gas velocity is also investigated and both the numerical and experimental results show the fluctuation intensity of the dynamic vertical forces becomes larger with the increase of superficial gas velocity.
吉田幹生, 横山達也, 押谷潤, 後藤邦彰, 粒子層内に挿入した棒の引抜きによるせん断応力を利用した粒子付着性評価, 粉体工学会誌, 53(6), 386-390, (2016)
A new apparatus was developed for the evaluation of particle adhesiveness. This apparatus uses shear stress that is induced by pulling a rod across a compressed particle bed. The tested samples were spherical silica particles with number based median diameters of 0.4 and 2.8μm.
When the height of the particle bed ≥ 17.0mm and the length of the rod in the bed ≥ 11.5mm, the shear stresses obtained by this apparatus were independent of either values of the bed height or the length of the rod. Using the values of stress, the inter-particle shear forces were calculated. The calculated forces increased with packing fraction and reached asymptotic values. The order of the asymptotic values agreed with that of the theoretical values of van der Waals force. This would be because frictional forces are based on adhesive forces in the real contact area （not the apparent contact area） of the 2 bodies. Thus, the new apparatus could be used to evaluate particle adhesiveness reflecting van der Waals force.
Jun Oshitani, Kazuhiro Teramoto, Mikio Yoshida, Yasuo Kubo, Shingo Nakatsukasa, George V. Franks, Dry beneficiation of fine coal using density-segregation in a gas-solid fluidized bed, Advanced Powder Technology, 27(4), 1689-1693, (2016)
Dry beneficiation of fine coal of +150–500 μm in size was conducted using density-segregation in a gas–solid fluidized bed without any separation media. The coal particles in a cylindrical column (inner diameter = 100 mm and bed height = 100 mm) were fluidized at a given air velocity u0/umf = 1.3–3.0 for thirty minutes where u0 and umf are the superficial air velocity and the minimum fluidization air velocity, respectively. The bulk density of the coal particles in each layer 10 mm in height (ten layers in total) was measured after the fluidization to investigate the segregation. It was found that the maximum segregation is produced at u0/umf = 2.0; the segregation is less pronounced at smaller and larger air velocities investigated. The origin of the dependence of the segregation on the air velocity is related to the velocity relative to the minimum fluidization velocity, the size of the air bubbles moving up through the fluidized bed, particle movement and vertical mixing. The calorific value and ash content of the ten layers before and after the segregation were estimated by fitting the dependence of calorific value and ash content on the bulk density. If the top 7 layers after segregation are regarded as the product (70% yield), the calorific value is increased from 5063 kcal/kg to 6067 kcal/kg and the ash content is decreased from 34.0 wt% to 22.4 wt% at u0/umf = 2.0, indicating that fine coal can be upgraded by the dry separation. The combustible recovery and ash reduction resulting from the segregation indicate that the upgrade is mainly caused by rejecting ash into the lower 8th to 10th layers.
Mikio Yoshida, Ryota Takatsuki, Genta Sakamoto, Jun Oshitani, Kuniaki Gotoh, DEM simulation and analysis of the effects of adhesive forces and rotations of admixed particles on improving main particle flowability, Advanced Powder Technology, 27(5), 2084-2093, (2016)
One technique for improving particle flowability is the admixture of nano-particles to the main particles. However, the mechanisms by which this technique improves flowability are not yet fully understood. In this study we examined compressed packing, which is affected by particle flowability. In order to investigate the mechanism of improvement, discrete element method (DEM) simulation was used to investigate the effects of adhesion forces and rotations of admixed particles on packing fraction.
We conducted two types of calculations: (1) compressed packing behavior of a particle bed, and (2) particle behavior in a simple model of the relative motion of two of the main particles. The main and admixed particles were given diameters of 400 and 20 nm, respectively. The physical properties of the particles were set based on silica and glass materials. The Hamaker constant of the main particles was kept constant while that of the admixed particle was varied from 2 × 10−27 to 1 × 10−20 J. Simulations were also conducted both allowing and not allowing rotation of admixed particles.
In the packing behavior calculations, the results for the packing fraction of the main particles and the compression velocity exhibited peaks at a Hamaker constant of approximately 10−23 J for the admixed particles under 43.8 Pa compression pressure, regardless of the degree of rotation of the admixed particles. This showed that rotation of the admixed particles was not the main reason for the improvement in main particle flowability, and this peak tendency was determined by the Hamaker constant of the admixed particles. In addition, an improvement in the particle flowability via different numbers of layers of admixed particles was explained using a linked rigid-3-bodies model. This implies that the improvement in the flowability is due to a decrease in the resistance of particle movement by changing the configuration to a linked rigid-3-bodies model.
林省吾, 押谷潤, 後藤邦彰, 固気流動層内での密度偏析における最下層への低密度粉体の取り込みの有無, 粉体工学会誌, 54(2), 97-103, (2017)
Four pairs of binary mixtures of glass beads and iron powder were fluidized at various air velocities. The size of iron powder was constant at 180–212 μm, while that of glass beads was varied to be 250–300 μm, 300–355 μm, 425–500 μm and 610–700 μm. It was found, in the four pairs, that glass beads (lighter particles, flotsam) move up and iron powder (heavier particles, jetsam) move down at middle ranged air velocities; density segregation appears regardless of the glass beads size. However, if the lower iron-powder-rich layers were investigated carefully for the pairs of 250–300 μm and 300–355 μm glass beads, the volume fraction of iron powder decreases with lowering the bed height, that is, the glass beads are captured in the lowest layer. On the other hand, the capturing of the glass beads does not occur in the pairs of 425–500 and 610–700 μm glass beads. The origin of the glass beads capturing, and the reason of the presence or absence at different glass beads sizes were discussed considering the particles mobility at the interface between upper and lower layers, the particles packing structure of the lower layers, and the local air velocity at the lower layers.
Mikio Yoshida, Atsushi Misumi, Jun Oshitani, Kuniaki Gotoh, Atsuko Shimosaka, Yoshiyuki Shirakawa, Effects of main particle diameter on improving particle flowability for compressed packing fraction in a smaller particle admixing system, Advanced Powder Technology, 28(10), 2542-2548, (2017)
Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the mechanisms by which this technique improves flowability are not yet fully understood. In this study, we examined compressed packing in a particle bed, which is affected by particle flowability. To estimate the mechanism of improvement, we investigated the effects of the main particle diameter on the improvement of compressed packing fractions experimentally.
The main particles were 397 and 1460 nm in diameter and the admixed particles were 8, 21, 62, and 104 nm in diameter. The main and admixed particles were mixed in various mass ratios, and the compressed packing fractions of the mixtures were measured. SEM images were used to analyze the coverage diameter and the surface coverage ratio of the admixed particles on the main particles. The main particle packing fraction was improved as the diameter ratio (=main particles/admixed particles) increased. This was explained by a linked rigid-3-bodies model with leverage. Furthermore, the actual surface coverage ratio at which the most improved packing fraction was obtained decreased with increasing main particle diameter. This was explained by the difference in the curvature of the main particle surface.
Mikio Yoshida, Tatsuki Katayama, Ryota Kikuchi, Jun Oshitani, Kuniaki Gotoh, Atsuko Shimosaka, Yoshiyuki Shirakawa, Influence of surface roughness created by admixing smaller particles on improving discharge particle flowability of main particles, Advanced Powder Technology, 30(1), 156-163, (2019)
Particle flowability can be improved by admixing with particles smaller than the main particles. However, the mechanism by which this technique improves flowability is not yet fully understood. In this study, we focused on vibrating discharge particle flowability as one type of flowability and investigated the influence of the main particle roughness created by the adhesion of the admixed particles on improving the flowability. The diameters of the main and admixed particles (MPs and APs) were 41.4 or 60.8 μm and 8 or 104 nm, respectively. The main and admixed particles were mixed in various mass ratios, and the discharge particle flow rates of the mixed particles were measured. Scanning electron microscopy images were acquired from two different angles to determine the three-dimensional surface roughness using image analysis software. We then calculated the coating structure parameters from the obtained three-dimensional surface roughness. The observed trends for improving the vibrating discharge particle flowability were found to differ from those reported for compression particle flowability. Furthermore, the main particle roughness conditions that led to the greatest improvement involved the presence of several admixed particle agglomerations between the main particles.
Wataru Yoshimori, Tomoki Ikegai, Koshi Uemoto, Shohei Narita, Shusaku Harada, Jun Oshitani, Takuya Tsuji, Hirokazu Kajiwara, Kei Matsuoka, Non-invasive measurement of floating-sinking motion of a large object in a gas-solid fluidized bed, Granular Matter, 21(3), 42, (2019)
A Lagrangian sensor system has been established to non-invasively measure both the vertical position and dynamic force acting on itself. It consists of a 3-axis acceleration sensor, a 3-axis magnetometer, a microcontroller, a wireless module, batteries, and external electromagnetic coils. In this study, we applied the system to a free-moving coarse object in a gas–solid fluidized bed. The floating and sinking motions of the object in the fluidized bed are essentially caused by differences between its density and the apparent density of the fluidized media. However, the object sometimes shows strange behavior under the influence of variance in the fluidization state. We measured the temporal change of the upward force acting on the object as well as the vertical position, which is invisible from the outside. The experimental results indicate that the force acting on the object differs significantly between the floating and sinking states and is greatly complicated by interference with rising bubbles in the fluidized bed. The probability density of the vertical position of the object shows that its motion is explained not only by hydrostatic effects, but also by inhomogeneity of the fluidization state in the bed.
Jun Oshitani, Shogo Hayashi, Derek Y.C. Chan, Order from Chaos: Dynamics of density segregation in continuously aerated granular systems, Advanced Powder Technology, 31(2), 843-847, (2020)
Under continual disturbance such as vibration, tumbling, flow or aeration, granular or powder systems can display solid or fluid like behavior. Using a well-mixed system of same size (0.2 mm) non-cohesive glass beads and iron powder, we show that gentle aeration can completely segregate the components thereby reducing the entropy of mixing to create near total order from an initially chaotic mixture. We quantify the time dependence of the segregation process and identify two dynamic pathways that dominate depending on the intensity of the aeration. Such findings can facilitate the search for energy efficient methods to process granular systems in pharmaceutical, mining and waste recovery industries.
Jun Oshitani, Ryo Sugo, Yoshihide Mawatari, Takuya Tsuji, Zhaohua Jiang, George V. Franks, Dry separation of fine particulate sand mixture based on density-segregation in a vibro-fluidized bed, Advanced Powder Technology, 31(9), 4082-4088, (2020)
Separation of fine particulate solid materials is one of most important unit operations in industry. Utilization of gas-solid fluidized beds has been considered where particulates are released from constraints due to contacts with surrounding particulates and segregation occurs according to density, size or combination of density and size. Addition of mechanical vibration to the gas-solid fluidized bed may improve dry solid separation. In this study, we investigated the dry separation characteristics of solid particulates using a vibro-fluidized bed especially focusing on the separation of fine particulate ores (≈100 μm) with small density differences. At first, we focused on the influence of fluidizing air velocity on the efficiency of segregation. Subsequently, the influence of vibration strength, vibration amplitude and frequency on segregation behavior was investigated. We found the density segregation does not occur with either gas-fluidization or vertical vibration alone. Only the combination of these effects produces density segregation. The fluidizing air velocity is an important factor to enhance the density-segregation of the particulates with small density difference.
Zhaohua Jiang, Kenta Rai, Takuya Tsuji, Kimiaki Washino, Toshitsugu Tanaka, Jun Oshitani, Upscaled DEM-CFD model for vibrated fluidized bed based on particle-scale similarities, Advanced Powder Technology, 31(12), 4598-4618, (2020)
Simulation based on discrete element method (DEM) coupled with computational fluid dynamics (CFD), coupled DEM-CFD, is a powerful tool for investigating the details of dense particle–fluid interaction problems such as in fluidized beds and pneumatic conveyers. The addition of a mechanical vibration to a system can drastically alter the particle and fluid flows; however, their detailed mechanisms are not well understood. In this study, a DEM-CFD model based on a non-inertial frame of reference is developed to achieve a better understanding of the influence of vibration in a vibrated fluidized bed. Because the high computational cost of DEM-CFD calculations is still a major problem, an upscaled coarse-graining model is also employed. To realize similar behaviors with enlarged model particles, non-dimensional parameters at the particle scale were deduced from the governing equations. The suitability and limitations of the proposed model were examined for a density segregation problem of a binary system. To reduce the computational costs, we show that the ratio between the bed width and model particle size can be reduced to a minimum value of 100; to obtain similar segregation behaviors, the ratio between the bed height and model particle size is considered unchanged.
Jun Oshitani, Toshiki Sasaki, Takuya Tsuji, Shusaku Harada, Hirokazu Kajiwara and Kei Matsuoka, Unstable sinking of spheres at higher air velocity in a gas–solid fluidized bed, Advanced Powder Technology, 32(4), 1300-1304, (2021)
Float-sink of large objects (on order of cm) in a gas-solid fluidized bed of powder (on order of 100 s of microns) based on density difference has been utilized for dry density separation in industry. The air velocity u0/umf is one of the important factors operating the fluidized bed, where u0 and umf are the superficial air velocity and the minimum fluidization air velocity, respectively. It is empirically known that the sinking of heavy objects is “occasionally” unstable in the fluidized bed combustor, for which the higher air velocity u0/umf > 4 is used. Unstable sinking means heavy objects that are expected to sink but sometimes do not. However, the precise conditions at which the unstable sinking occurs are not clear. In this study, we investigated the float-sink characteristics at a given air velocity u0/umf = 2–7 using glass beads of size Dgb = 425–600 μm and 600–850 μm as the fluidized powder bed media. The float-sink experiments were carried out at the bed height hgb = 150 mm and 75 mm using density adjusted spheres (diameter = 30 mm). We found that the spheres stably float or sink based on density difference at Dgb = 425–600 μm & hgb = 150 mm and at Dgb = 600–850 μm & hgb = 75 mm. However, the unstable sinking does occur at u0/umf > 4 at Dgb = 600–850 μm & hgb = 150 mm. These results indicate that the powder size and the bed height are key factors to induce the unstable sinking at the higher air velocity.
Takuya Tsuji, Alexander Penn, Taisuke Hattori, Klaas P. Pruessmann, Christoph R. Müller, Jun Oshitani, Kimiaki Washino, and Toshitsugu Tanaka, Mechanism of anomalous sinking of an intruder in a granular packing close to incipient fluidization, Physical Review Fluids, 6(6), 064305, (2021)
Objects released into a granular packing close to incipient fluidization may float or sink depending on their density. Contrary to intuition, Oshitani et al. [Phys. Rev. Lett. 116, 068001 (2016)] reported that under certain conditions, a lighter sphere can sink further and slower than a heavier one. While this phenomenon has been attributed to a local fluidization around the sinking sphere, its physical mechanisms have not yet been understood. Here, we studied this intriguing phenomenon using both magnetic resonance imaging and discrete particle simulation. Our findings suggest that local fluidization around the sinking sphere and the formation and detachment of gas bubbles play a critical role in driving this anomaly. An analysis of forces acting on the intruder revealed that the upward-directed fluid force acting on a sphere is almost fully counterbalanced by the sum of the net contact forces and the gravitational force acting downward, when the sphere density is close to the bulk density of the granular packing (ρsphere/ρbulk≈1). At the time when bubbles detach from the sphere, the gas pressure gradient experienced by the sphere is slightly attenuated and the sphere is pushed downward by the particle cap located on top of the sphere. Because the deviations from the force equilibrium are small, the sphere sinks slowly. Even after the sphere has reached its final stable depth, local fluidization in combination with bubble formation remains in the proximity of the sphere.
Jun Oshitani, Masaki Hino, Shinichiro Oshiro, Yoshihide Mawatari, Takuya Tsuji, Zhaohua Jiang, George V. Franks, Conversion air velocity at which reverse density segregation converts to normal density segregation in a vibrated fluidized bed of binary particulate mixtures, Advanced Powder Technology, 33(5), 103583, (2022)
It is well known, when binary mixtures of different-density particles of the same size are vertically vibrated or fluidized by airflow through the bottom, the particles segregate by density. Reverse density segregation occurs in the vibrated bed; heavier particles move upward and lighter ones move downward, and normal density segregation occurs in the fluidized bed; lighter particles move upward and the heavier ones move downward. In this study, we investigated the particles’ behavior in a vertically vibrated fluidized bed at various air velocity using two types of particulate mixtures of glass beads (GB) and stainless steel powder (SP) or iron powder (IP) of same size. We found that reverse segregation converts to normal segregation at a certain air velocity; here we call it “conversion air velocity”. Then, we investigated the likely origin of the conversion air velocity considering the minimum fluidization air velocity umf determined for the three monocomponent particles (GB, SP and IP) with and without vibration. We found that the conversion air velocity is close to the umf of the lower density particles (GB) with vibration, indicating that the conversion from reverse segregation to normal segregation occurs around umf of lighter particles with vibration.
受賞
樋野将貴, 優秀プレゼンテーション賞, 第26回流動化・粒子プロセッシングシンポジウム, 2020年11月26日
学会発表
Takamasa Yokouchi, Jun Oshitani, Akinori Hirata, Takuya Okamoto, Dry Separation of Particulate Construction Waste Residue Using Density-Segregation in a Vibro-Fluidized Bed, Asian Particle Technology Symposium (APT 2017), 2017年7月31日（台湾）
Shunsuke Kato,Jun Oshitani, Kyohei Higashida, Takuya Tsuji, Shusaku Harada, Hirokazu Kajiwara, Kei Matsuoka, Stability of Float-Sink of Spheres in a Fluidized Bed at Higher Air Velocity, Asian Particle Technology Symposium (APT 2017), 2017年7月31日（台湾）
Ryo Sugo, Jun Oshitani, Dry Separation of Particulate Ore Using Density-Segregation in a Vibro-Fluidized Bed, Asian Particle Technology Symposium (APT 2017), 2017年7月31日（台湾）
加藤駿介, 石井眞, 押谷潤, 辻拓也, 原田周作, 梶原洋和, 松岡慶, 高風速固気流動層内の物体浮沈の検討, 粉体工学会秋季研究発表会, 2017年10月11日（大阪）
横内貴正, 川元貴皓, 押谷順, 平田晃則, 岡本拓也, 振動流動層を用いた建設廃棄物残渣の適正処理に向けた基礎的検討, 粉体工学会秋季研究発表会, 2017年10月11日（大阪）
須郷涼, 日髙央喬, 押谷潤, 振動流動層を用いた密度差の小さな粒状混合物の乾式比重分離技術の開発, 粉体工学会秋季研究発表会, 2017年10月11日（大阪）
須郷涼, 押谷潤, 振動流動層を用いた粒状鉱物の乾式高品位化, 2018年9月18日（鹿児島）
横内貴正, 押谷潤, 平田晃則, 岡本拓也, 振動流動層を用いた建設廃棄物残渣の乾式比重分離, 化学工学会第50回秋季大会, 2018年9月18日（鹿児島）
須郷涼, 押谷潤, 馬渡佳秀, 振動流動層による粒状鉱物の乾式高品位化技術の開発, 第24回流動化・粒子プロセッシングシンポジウム, 2018年12月5日（東京）
加藤駿介, 押谷潤, 辻拓也, 原田周作, 梶原洋和, 松岡慶, 高風速からなる固気流動層内での物体沈降の不安定化に関する実験的検証, 第24回流動化・粒子プロセッシングシンポジウム, 2018年12月5日（東京）
横内貴正, 押谷潤, 平田晃則, 岡本卓也, 馬渡佳秀, 振動流動層による建設廃棄物残渣の乾式比重分離技術の開発, 第24回流動化・粒子プロセッシングシンポジウム, 2018年12月5日（東京）
Tetsuaki Matsuoka, Takamasa Yokouchi, Jun Oshitani, Yoshihide Mawatari, Vibro-fluidized bed separation of particulate construction waste residue based on density-segregation, 18th Asian Pacific Confederation of Chemical Engineering Congress (APCChE 2019), 2019年9月25日（北海道）
樋野将貴, 押谷潤, 辻拓也, 振動流動層内での粉体密度偏析に及ぼす風速の影響, 第26回流動化・粒子プロセッシングシンポジウム, 2020年11月26日（オンライン）
松岡哲明, 横内貴正, 押谷潤, 馬渡佳秀, 振動流動層を用いた建設廃棄物残渣からの木片などの有機物の分離, 第26回流動化・粒子プロセッシングシンポジウム, 2020年11月26日（オンライン）
樋野将貴, 押谷潤, 振動層内での粉体密度偏析に及ぼす振動強度の影響, 第27回流動化・粒子プロセッシングシンポジウム, 2021年12月16日（オンライン）