基本情報

所属

• 工学研究院　環境循環システム部門　地圏循環工学分野

職名

• 准教授

学位

• 博士（工学）（大阪大学）

ホームページURL

https://www.eng.hokudai.ac.jp/labo/trans/

科研費研究者番号

• 80315168

J-Global ID

• 200901052121013779

研究キーワード

• 微粒子分散系   粒子流   混相流   Granular flow   Multiphase Flow   

研究分野

• ものづくり技術（機械・電気電子・化学工学） / 流体工学
• エネルギー / 地球資源工学、エネルギー学
• ものづくり技術（機械・電気電子・化学工学） / 移動現象、単位操作

担当教育組織

•  学士課程　工学部
•  修士課程　工学院
•  博士課程　工学院

職歴

• 2010年04月 - 現在 北海道大学大学院工学研究院 環境循環システム部門 准教授
• 2008年04月 - 2010年03月 北海道大学大学院工学研究科 環境フィールド工学専攻 准教授
• 2007年04月 - 2008年03月 北海道大学大学院工学研究科 環境フィールド工学専攻 助教
• 2005年04月 - 2007年03月 北海道大学大学院工学研究科 環境フィールド工学専攻 助手
• 2004年04月 - 2005年03月 北海道大学大学院工学研究科 環境資源工学専攻 助手
• 2002年04月 - 2004年03月 琉球大学工学部 機械システム工学科 助手
• 2001年04月 - 2002年03月 東京大学IML 研究員
• 1999年04月 - 2001年03月 九州工業大学SVBL 研究員

学歴

• 1996年04月 - 1999年03月   大阪大学大学院   工学研究科   産業機械工学専攻
• 1994年04月 - 1996年03月   北海道大学大学院   工学研究科   資源開発工学専攻
• 1990年04月 - 1994年03月   北海道大学   工学部   資源開発工学科

所属学協会

• 化学工学会   粉体工学会   日本混相流学会   日本機械学会   資源・素材学会   

研究活動情報

論文

• Numerical Investigation of Pore Characteristics in Compacted Sand Layers, –Physical Interpretation of Applicability of Kozeny-Carman Equation–

  Miura, O, Oishi, R, Harada, S, Yagi, T

  Geophysics (submitted) 2024年 [査読有り][通常論文]
  
• Three-dimensional Wireless Measurement of Float–Sink Object Motions in a Gas–Solid Fluidized Bed

  Katayama, T, Otsuka, Y, Saito, S, Harada, S, Tsuji, T, Oshitani, J

  International Journal of Multiphase Flow 176 104817  2024年 [査読有り][通常論文]
  
• Visualization of Mixing Upper and Lower Stratified Suspensions Using Red and Blue Fluorescent Particles

  Tanaka, Y, Iwaguchi, T, Yamamoto, Y, Otomo, R, Harada, S

  Multiphase Science and Technology 27 2 43 - 44 2024年 [査読有り][通常論文]
  
• Fabrication of Realistic Transparent Porous Media for 3D Observation of Internal Mass Transport

  Gyotoku, T, Iwaguchi, T. Hanya, Harada, S, Tanaka, Y, Yamamoto, Y

  Journal of Porous Media 27 2 43 - 55 2024年 [査読有り]
  
• Variation in the Settling Behavior of Particulate Suspension in Saturated Porous Media

  Gyotoku, T, Masuda, G, Nishimura, K, Harada, S, Tanaka, Y, Yamamoto, Y

  Journal of Porous Media 27 1 35 - 47 2024年 [査読有り]
  
• Quantitative Evaluation of the Pore Characteristics in Platelet Particle Beds by Pore Network Modeling

  Yamamoto, K, Ishiyama, K, Harada, S

  Transport in Porous Media 150 89 - 103 2023年 [査読有り]
  
• Influence of Air Velocity and Powder Bed Height on Local Density in a Gas–Solid Fluidized Bed and Float–Sink of Spheres

  Oshitani, J, Kato, S, Tsuji, T, Washino, K, Harada, S, Sakamoto, Y, Kajiwara, H, Matsuoka, K, Franks, G

  Advanced Powder Technology 34 104146  2023年 [査読有り][通常論文]
  
• Wireless Measurement of Float--Sink Motion of Variously-shaped Objects in Gas--Solid Fluidized Bed

  Uemoto, K, Narita, S, Harada, S, Sakamoto, Y, Tsuji, T, Oshitani, J, Kajiwara, H, Matsuoka, K

  Advanced Powder Technology 34 9 104111  2023年 [査読有り]
  
• Tortuosity in Platelet Particles with Various Structures

  Ishiyama, K, Harada, S, Yagi, T

  Transport in Porous Media 148 3 1 - 23 2023年 [査読有り]
  
• Diffusive Behavior of Fine Particle Assemblage Passing through Nonuniform Granular Porous Media

  Otomo, R, Nakano, Y, Harada, S

  Particulate Science and Technology 41 7 940 - 952 2023年 [査読有り][通常論文]
  
• Mass Transfer from Mobile to Immobile Regions in Irregularly-Shaped Micro-Channels at Low Reynolds Number

  Toyama, K, Togi, F, Harada, S

  Groundwater 61 5 639 - 647 2023年 [査読有り]
  
• Experimental Verification of the Brinkman Equation around Objects with Various Shapes in Gas-Solid Stationary and Fluidized Beds

  Honda, Y, Saito, S, Anzai, T, Harada, S, Tsuji, T, Washino, K, Oshitani, J, Kajiwara, H, Matsuoka, K

  International Journal of Multiphase Flow 160 104359  2023年 [査読有り]
   

  Experimental verification of Brinkman's theory, i.e., the permeation flow near an object immersed in a particle bed was conducted in this study. In order to examine the permeation flow and the fluidized state of media particles around an object in both stationary and fluidized beds, the air pressure near the object was measured by pressure sensors built in capsules with various shapes. The sensor system was fixed in the particle bed with various fluidization states and the pressure field around the object was measured. The effect of object shape was also examined by using the variously-shaped capsules, such as spherical, disk-like and cylindrical ones. The experimental results showed that the pressure around the object varies greatly with object shape. The permeation flow around the object in the particle bed was estimated by comparison with theoretical solutions. The pressure near the object in the stationary particle bed was quantitatively in agreement with the Brinkman theory, while the pressure in the fluidized bed fluctuated periodically. The experimental results suggested that the floating–sinking motion of objects in a gas–solid fluidized bed depends on the object shape and is greatly influenced by the instantaneous pressure variance near the object, rather than the averaged pressure gradient.
• Effects of Terminal Velocities on Macroscopic and Microscopic Hydrodynamic Mixing of Stratified Suspensions

  Yamamoto, Y, Otomo, R, Tanaka, Y, Harada, S

  Physical Review E 106 045109  2022年 [査読有り]
  
• FPM-SE: a Numerical Model for Dense Gas--Solid Flows with Large Non-Spherical Object

  Tsuji, T, Sakamoto, Y, Harada, S, Uemoto, K, Oshitani, J, Washino, K, Tanaka, T, Kajiwara, H, Matsuoka, K

  Chemical Engineering Science 264 118149 - 118149 2022年 [査読有り]
  
• Theoretical Consideration of the Rheological Properties of Particulate Dispersions with Aggregates

  Tanii, Y, Kamata, N, Saito, H, Harada, S, Sawada, M

  Physics of Fluids 34 093309  2022年 [査読有り]
  
• 高ポロシティを有する繊維層および粒子層中の空隙ネットワークと流体透過特性の解析 (ボロノイ分割を利用した空隙構造と動水半径の評価)

  大友涼子, 出口裕仁, 原田周作

  混相流 36 266 - 273 2022年 [査読有り]
  
• Structural Transition of Various-Sized Sphere-Platelet Mixtures

  Tani, A, Ishiyama, K, Tanii, Y, Harada, S, Satoh, H

  Physical Review E 105 044602  2022年 [査読有り]
  
• Macroscopic and Microscopic Hydrodynamic Mixing of Stratified Suspensions

  Yamamoto, Y, Yamada, K, Tanaka, Y, Harada, S

  Physical Review E 104 2 025111  2021年 [査読有り]
  
• Unstable Sinking of Spheres at Higher Air Velocity in a Gas-Solid Fluidized Bed

  Oshitani, J, Sasaki, T, Tsuji, T, Harada, S, Kajiwara, H, Matsuoka, K

  Advanced Powder Technology 32 4 1300 - 1304 2021年 [査読有り]
   

  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 u(0)/u(mf) is one of the important factors operating the fluidized bed, where u(0) and u(mf) 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 u(0)/u(mf) > 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 u(0)/u(mf) = 2-7 using glass beads of size Dgb = 425-600 lm and 600-850 lm 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 D-gb = 425-600 mu m & h(gb) = 150 mm and at D-gb = 600-850 mu m & h(gb) = 75 mm. However, the unstable sinking does occur at u(0)/u(mf) > 4 at D-gb = 600-850 mu m & h(gb) = 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. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier B.V. All rights reserved.
• Quantitative Evaluation of Solute Dispersion in Irregularly Shaped Micro-Channels

  Togi, F, Kubota, T, Toyama, K, Ishida, A, Harada, S

  Microfluidics and Nanofluidics 24:57 1 - 8 2020年 [査読有り][通常論文]
  
• Possibility of Non-Fickian Mixing at Concentration Interface between Stratified Suspensions

  Mori, M., Tai, T., Nishimura, K., Harada, S., Yamamoto, Y.

  Journal of Colloid and Interface Science 571 13 - 20 2020年 [査読有り][通常論文]
  
• Non-Invasive Measurement of Floating-Sinking Motion of a Large Object in a Gas-Solid Fluidized Bed

  Yoshimori, W, Ikegai, T, Uemoto, K, Narita, S, Harada, S, Oshitani, J, Tsuji, T, Kajiwara, H, Matsuoka, K

  Granular Matter 21 3 :42 1 - 11 2019年 [査読有り][通常論文]
   

  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.
• Scale-Independent Model of Gravitational Dispersion of Particulate Suspension in Fractal Channel

  Kurose, Y, Ishizawa, K, Soriano, M. R, Harada, S

  Chemical Engineering Science 199 231 - 239 2019年 [査読有り][通常論文]
  
• Monte Carlo Analysis of Montmorillonite Particle Structures and Modeling of Dissolution Rate Reduction

  Terada, K, Tani, A, Harada, S, Satoh, H, Hayashi, D

  Materials Research Express 6 3 035514  2018年 [査読有り][通常論文]
  
• Quantitative Evaluation of Mass Transfer near the Edge of Porous Media by Absorption Photometry

  Taiki Tanikoshi, Ryoko Otomo, Shusaku Harada

  AIChE Journal 63 2 823 - 833 2017年02月 [査読有り][通常論文]
   

  The intensive investigation of mass transfer near the entrance (edge) of porous media by quantification of the surrounding concentration field has been performed. We have adopted a noninvasive and real-time system based on light absorption photometry for measurement of the concentration field in a quasi-two dimensional cell. This system is, in principle, applicable to the measurement of various substances due to the generality of light absorption. This measurement system was applied to a simple model of the gravity-driven transport of a substance in a fluid near the edge of a porous medium in the presence of a reaction at the surface. The temporal variation of the complicated concentration field is appropriately captured with a spatial resolution of several tens of micrometers to millimeters. Quantitative analyses revealed that the geometry of the porous edge considerably affects the convection flow and invasion of substances into the medium. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 823-833, 2017
• Dynamic Vertical Forces Working on a Large Object Floating in Gas-Fluidized Bed: Discrete Particle Simulation and Lagrangian Measurement

  Kyohei Higashida, Kenta Rai, Wataru Yoshimori, Tomoki Ikegai, Takuya Tsuji, Shusaku Harada, Jun Oshitani, Toshitsugu Tanaka

  Chemical Engineering Science 151 105 - 115 2016年09月 [査読有り][通常論文]
   

  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. (C) 2016 Elsevier Ltd. All rights reserved.
• Restructuring Capability of Non-Fractal Aggregate in Simple Shear Flow

  Uyen Tu Lieu, Shusaku Harada

  Advanced Powder Technology 27 4 1037 - 1046 2016年07月 [査読有り][通常論文]
   

  A unique pattern interpreting the restructuring of non-fractal aggregate is established. The restructuring of an aggregate from initial structure toward a stable structure is well presented by a linear relation between the saturation degree of particle connection, and the inversed strength of aggregate. The dynamics of restructuring for different initial configuration of aggregate, from very loose to dense, in various simple shear flow condition is numerically performed. The temporal change in properties of aggregate is analyzed in terms of coordination number and volume fraction. The simulation employs Stokesian dynamics for the estimation of many-particle hydrodynamic interaction while the particle-particle interaction is calculated by van der Waals potential. Simulation results show that the aggregate restructures and exists in a stable state corresponding to the shear flow condition. The transition among the stable aggregates somewhat expresses reversible behavior. Especially in weak flow, the aggregate gradually reaches its limit structure whose properties such as coordination number and volume fraction are typically determined. Such limit aggregate plays an important role for predicting the restructuring of any non-fractal aggregate in any fluid condition. Moreover, the penetration effect of fluid flow on aggregate is discussed by means of porous sphere model. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
• Strength Deterioration of Nonfractal Particle Aggregates in Simple Shear Flow

  Kento Horii, Reiko Yamada, Shusaku Harada

  Langmuir 31 29 7909 - 7918 2015年07月 [査読有り][通常論文]
   

  The restructuring of a nonfractal particle aggregate in simple shear flow was simulated by a Stokesian dynamics approach. We studied the deformation and the resultant strength change of aggregates by the surrounding flow under the condition that the cohesive strength of an aggregate is comparable to the fluid stress. In particular, we focused on how the aggregate deteriorates because of the fluid stress exerted on it periodically. The image analysis was applied to visualized simulation results for the quantitative estimation of irreversible change in an aggregate configuration. We examined the structural change in the aggregate from various perspectives, i.e., the outer shape, the internal strength, and the fluid stress on the surface of the aggregate. The simulation results show that the aggregate gets squashed after an intricate restructuring process and it elongates along with the streamline as experimentally observed in the previous study. Regarding the internal strength, the weakest point locally develops in the aggregate by periodically varying the fluid stress. A combination of rotation and elongation effects of shear flow is complexly involved in the deterioration of the internal strength of the aggregate.
• Numerical Simulation of Concentration Interface in Stratified Suspension: Continuum–Particle Transition

  Yamamoto, Y, Hisataka, F, Harada, S

  International Journal of Multiphase Flow 73 71 - 79 2015年07月 [査読有り][通常論文]
   

  Behavior of concentration interfaces, which are apparent interfaces between a suspension and pure liquid, was studied using numerical techniques. Two types of numerical simulations were used to classify whether collective or individual behavior occurred in the ratio of the average particle separation to the wavelength of the fastest growing perturbation. The first is Lagrangian tracking of individual particles in fluid, and the second type is interface tracking of two immiscible continuum phases. These two extremely different approaches represent the dual nature of the concentration interface: immiscible with no interfacial tension and miscible with no diffusion. These results reflect the experimentally-observed behavior of particles, which is both collective and individual. Sealing of the concentration interface by particle-induced flow is crucial to collective motion of suspended particles. A proposed dimensionless parameter describes quantitatively the transition from collective to individual settling of suspended particles. (C) 2015 Elsevier Ltd. All rights reserved.
• Stability of Restructured Non-Fractal Aggregates in Simple Shear Flow

  Uyen Tu Lieu, Shusaku Harada

  Advanced Powder Technology 26 3 705 - 710 2015年05月 [査読有り][通常論文]
   

  The restructuring behavior of non-fractal aggregates in simple shear flow is numerically investigated. The change in internal structure of aggregates having different packing properties is examined by Lagrangian simulation method. The many-body hydrodynamic interaction is rigorously estimated by Stokesian dynamics approach while the adhesion of aggregate is manifested via particle-particle interaction. The simulation results show that the restructuring of aggregate originates from the superimposition of rotational and extensional component of simple shear flow. The aggregate rearranges its particles so that a stable structure corresponding to the applied shear flow is obtained. The stable structure is considered as dynamic equilibrium resulting from the balance of the forming and the disintegrating of the bonds between particles. The stable structure of aggregate is dependent strongly on shear condition but weakly on initial structure of aggregate. Despite of the significant difference in the initial packing properties, the stable structure reveals only slightly different. The dependence of stable structure on high shear tress condition is similar for all aggregates. The difference in stable structure of aggregate at low shear stress arises from the irreversible behavior of particle from quasi-stable structure to static structure. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B. V. and The Society of Powder Technology Japan. All rights reserved.
• Mass Transfer Caused by Gravitational Instability at Reactive Solid-Liquid Interfaces

  Ryoko Otomo, Nobuhiko Ishii, Keita Takahashi, Shusaku Harada

  Journal of Visualization 17 1 49 - 57 2014年02月 [査読有り][通常論文]
   

  Mass transfer in porous media has been investigated experimentally. In this paper, we present a visualization technique and discuss the behavior of a substance which transfers under the influence of gravity and reacts with the surface of porous media. Mass transfer by the reaction with porous media was demonstrated by means of electrochemical deposition experiment on particulate beds with complex structures. A copper plate (anode) and a stainless steel particulate bed (cathode) were, respectively, placed at the upper and bottom side of a thin vertical cell which was filled with copper sulfate solution. After the application of electricity, cupric ion which is provided from the copper plate to the solution transfers under the influence of gravity and it is consumed by deposition at the particulate bed. The behavior of ions between the electrodes was visualized by utilizing the infrared absorption characteristics of cupric ion. We observed gravitational instability and convection flow due to concentration gradient of ions in opposite direction to that of gravity, which is formed by reaction at solid-liquid interfaces. While downward flow caused by Rayleigh-Taylor instability was observed in the case of flat interfaces, upward flow generated from complex-shaped interfaces was greatly dependent on their geometry. The interaction of these flows resulted in the convection throughout the cell. Consequently, it is found from the results that the gravitational instability significantly varies the transport characteristics and that the reactive interface geometry greatly affects the overall mass transfer.
• Collective settling of fine particles in a narrow channel with arbitrary cross-section

  Shusaku Harada, Megumi Kondo, Kensuke Watanabe, Taiga Shiotani, Kodai Sato

  Chemical Engineering Science 93 307 - 312 2013年04月 [査読有り][通常論文]
   

  Gravitational settling of fine particles in a liquid-filled narrow channel has been studied experimentally and theoretically. Previous studies have shown that the particulate suspension with concentration interface toward gravitational direction behaves as a continuous fluid for high concentration and small particle size, and the gravity-induced instability at the interface enhances the settling motion of particles. The purpose of this study is to investigate how such a concentration interface behaves and how particles settle by gravity in various finite-sized channels. The experimental and theoretical results indicate that the aspect ratio of the channel cross-section is an important parameter for describing the settling behavior of particulate suspension. Moreover, we predict the velocity of the collective settling of particles in channels with arbitrary cross-section. (C) 2013 Elsevier Ltd. All rights reserved.
• Fluid Permeability in Stratified Unconsolidated Particulate Bed

  Ryoko Otomo, Shusaku Harada

  Transport in Porous Media 96 3 439 - 456 2013年 [査読有り][通常論文]
   

  Fluid permeability of polydisperse particulate bed with finite thickness has been examined. On the assumption of creeping flow, the permeability of monodisperse particles with arbitrary arrangement is calculated by means of Stokesian dynamics approach in which the interaction between individual particles and interstitial fluid is described by multipole expansion of the Oseen tensor. We have extended such calculation method to polydisperse particulate systems which have not so dense structures (up to particle volume fraction φ ~ 0.2). The particles are located infinitely in space and their interaction has been taken into account by Ewald summation technique. For the spatial distribution of polydisperse particles, we consider locally stratified particulate beds and define stratification degree as a parameter which apparently and mathematically represents the thickness of the mixing region of different-sized particles. The permeability profiles in the particulate beds with different stratification degree show the dependence of local permeability on the spatial and size distribution of particles. Consequently, the calculation results indicate that the permeability of non-uniform polydisperse particulate bed can be predicted by integrating the local permeation resistance which is determined by the local specific surface area. © 2012 Springer Science+Business Media Dordrecht.
• Effect of different soil layers on porewater to remediate acidic surface environment at a close mine site

  Omar R. Salinas Villafane, Toshifumi Igarashi, Shusaku Harada, Mitsuru Kurosawa, Toshio Takase

  Environmental Monitoring and Assesment 184 12 7665 - 7675 2012年12月 [査読有り][通常論文]
   

  This paper describes the chemistry of porewater when constructing different soil layers on acidic weathered rock of a closed mine to remediate the surface environment. Three cases were set on a flat surface of the site, all under different layer systems. Case 1 was only composed of weathered rocks. A top neutralization layer was constructed on the weathered rocks in case 2, whereas both an upper low-permeable and middle neutralization layers were constructed on the weathered rocks in case 3. The low-permeable layer of 30 cm thick consists of clay, and the neutralization layer of 30 cm thick consists of the mixture of the weathered rock and calcium carbonate as a neutralizer. Porewater sampling systems and soil sensors to measure temperature, water content, and electrical conductivity were set at different depths. In case 1, steadily high concentrations of heavy metals were observed regardless of the depth, and the pH ranged from 2 to 4. In cases 2 and 3, a dramatic decrease in concentrations of heavy metals was observed, even below the neutralization layer. For both cases, pH values were circumneutral. There were no significant seasonable changes in heavy metals concentrations and pH of porewater by considering the temperature and precipitation. In addition, the water content of the layers in case 3 fluctuated more mildly than that in cases 1 and 2, indicating that the low-permeable layer reduced the rate of infiltration. Therefore, a significant reduction in the load of heavy metals released from the site can be achieved by both implementing neutralization and low-permeable layers.
• Particle-like and fluid-like settling of a stratified suspension

  S. Harada, T. Mitsui, K. Sato

  European Physical Journal E 35 1 1 - 6 2012年01月 [査読有り][通常論文]
   

  The gravitational settling of inhomogeneously suspended particles in a fluid has been investigated. Of particular interest is whether collective or individual motion of particles is dominant during their settlings, i.e., whether the particles settle as a continuous suspension or they settle individually relative to the surrounding fluid. We observed the settling of a stratified suspension which has the lower and upper concentration interfaces in a quasi-two-dimensional vessel. In some cases, the suspension behaves perfectly as a continuous fluid and the motion of the constituent particle is subject to bulk flow caused by the interfacial instability. In other cases, the particle behaves individually relative to the surrounding fluid. The existence of a concentration interface plays a significant role in these extreme behaviors of suspension. The transition from the collective to individual behaviors can be predicted quantitatively by a parameter which expresses the border resolution of the concentration interface.
• Direct measurement of fluid force on a particle in liquid by telemetry system

  Shusaku Harada, Yosuke Kobayashi, Takanori Sawano, Emi Noguchi

  INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 37 8 898 - 905 2011年10月 [査読有り][通常論文]
   

  For real-time measurement of the fluid force acting on a particle which moves freely in liquid, we have made a "sensor particle" with a built-in wireless sensor. The sensor particle contains a 3-axis acceleration sensor, 3-axis magnetometer, microcomputer, wireless module and cells. The MEMS acceleration sensor detects the gravitational acceleration in addition to the dynamic acceleration of particle. In order to remove the gravity from acceleration signals, we applied the external magnetic field which is oriented in the same direction as the gravity field. The 3-axis magnetometer detects the direction of external magnetic field and consequently we can remove gravitational acceleration from the sensor signals with arbitrary attitude of particle. A preliminary experiment was performed for checking the accuracy of the measurement system. Firstly we measured the force acting on a settling particle toward a solid wall in liquid. The obtained signals of acceleration (force divided by mass) agrees well with the theoretical prediction of particle motion in liquid for each instant of time. The sensor particle also detects the lubrication force which is exerted on particle for a very short time when it comes close to the wall. Moreover, we applied our system to the gravitational settling of the particle assemblage and detected the fluid force acting on a particle in multi-particle system. (C) 2011 Elsevier Ltd. All rights reserved.
• End effect on permeability of loose particulate bed having different internal structures

  R. Otomo, S. Harada

  Particulate Science and Technology 29 1 2 - 13 2011年01月 [査読有り][通常論文]
   

  Permeability through media having various structures has been studied theoretically. We consider loose porous media, like fibrous materials, and media with a localized pore network, like fractured rocks. We model complicated porous structures by using assemblage of spherical particles. The calculations of permeability are performed by the Stokesian dynamic approach, which enables us to derive fluid motion in the presence of many particles. The Ewald summation technique is employed to represent infinite and finite particulate beds. In the infinite bed where the particles exist endlessly in space, we investigate how the internal structure of the media affects permeability. The results indicate that permeability significantly depends on internal structure, particularly the void geometry. In the finite bed where the particles form a bed with finite thickness, we discuss permeability variance due to the presence of ends. It is found that permeability greatly varies in the vicinity of ends owing to the anisotropy of the flow field, which arises from the presence of ends. Copyright © Taylor & Francis Group, LLC.
• Diffusive behavior of a thin particle layer in fluid by hydrodynamic interaction

  Shusaku Harada, Ryoko Otomo

  PHYSICAL REVIEW E 80 6 066311  2009年12月 [査読有り][通常論文]
   

  The hydrodynamic effect on a thin particle layer, which moves relative to fluid by an external force, is investigated theoretically and numerically. Because of the presence of layer ends, the arrangement of particles in the layer is anisotropic and the drag force acting on them varies according to the position. The resulting relative motion of particles brings about the spreading of the layer. We have studied such a diffusive behavior of particle layers, which have various internal arrangements. We have assumed a non-Brownian system in which the particles move relatively owing to only the variance of hydrodynamic force. The hydrodynamic force on each particle was calculated by Stokesian dynamics approach. The results show that the relative motion of particles is greatly influenced by the internal arrangement of the particle layer. In consequence, the overall diffusive motion of particle layer varies with the arrangement even if the particle concentration is similar. It is in contrast to the gradient diffusion of Brownian particles.
• Structural change in non-fractal particle clusters under fluid stress

  S. Harada, R. Tanaka, H. Nogmi, M. Sawada, K. Asakura

  COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 302 1-3 396 - 402 2007年07月 [査読有り][通常論文]
   

  The restructuring of particle clusters having a dense packing structure under fluid stress is investigated numerically. The rearrangement of particles in the cluster and the breakage of their interparticle bonds in simple shear flow are examined by the Lagrangian-type simulation. The hydrodynamic force exerted on multiple particles is estimated by Stokesian dynamics approach. The interparticle force is calculated from the retarded van der Waals potential based on the Lifshitz theory. The simulation results show that the particle cluster rotates with the rotation of the surrounding flow and deforms due to the fluid stress along the principal axes of the stress tensor. These complex effects bring the irreversible change of the internal structure to the cluster. It is found that the structural change of the cluster can be explained by the initial rearrangement of primary particles and the successive crack growth that takes a long time. Such a long-term structural change is analogous to that of the fatigue crack growth of solid materials. We discuss the dynamics of the restructuring of a dense cluster from this point of view and propose a mathematical model which describes the restructuring process in a flow field. (C) 2007 Elsevier B.V. All rights reserved.
• Dependence of fragmentation behavior of colloidal aggregates on their fractal structure

  S. Harada, R. Tanaka, H. Nogami, M. Sawada

  JOURNAL OF COLLOID AND INTERFACE SCIENCE 301 1 123 - 129 2006年09月 [査読無し][通常論文]
   

  The fragmentation dynamics of aggregate of non-Brownian particles in shear flow is investigated numerically. The breakup behaviors of aggregates having the same connectivity but the different space-filling properties are examined. The Lagrangian particle simulation in a linear flow field is performed. The effect of surrounding fluid on the motion of multiple particles is estimated by Stokesian dynamics approach. The inter-particle force is calculated from the retarded van der Waals potential based on the Lifshitz theory. The results obtained in this work indicate that the fragmentation behavior of colloidal aggregates depends on their fractal structure. However, if the resultant aggregate size is smaller than the critical one, the fragmentation behavior shows the universality regardless of their original structure. Furthermore, the restructuring of aggregate in shear flow and its effect on the fragmentation process are also discussed. (c) 2006 Elsevier Inc. All rights reserved.
• Wave propagation in a dynamic system of soft granular materials

  S Harada, S Takagi, Y Matsumoto

  PHYSICAL REVIEW E 67 6 061305  2003年06月 [査読無し][通常論文]
   

  The wave propagation in a dynamic system of soft elastic granules is investigated theoretically and numerically. The perturbation theory for simple fluids is applied to the elastic granular system in order to relate the elastic properties of individual particles with the "thermodynamic" quantities of the system. The properties of a piston-driven shock are derived from the obtained thermodynamic relations and the Rankine-Hugoniot relations. The discrete particle simulation of a piston-driven shock wave in a granular system is performed by the discrete element method. From theoretical and numerical results, the effect of the elastic properties of a particle on shock properties is shown quantitatively. Owing to the finite duration of the interparticle contact, the compressibility factor of the elastic granular system decreases in comparison with that of the hard-sphere system. In addition, the relation between the internal energy and the granular temperature changes due to the energy preserved with the elastic deformation of the particle. Consequently, the shock properties in soft particles are considerably different from those in the hard-sphere system. We also show the theoretical prediction of the speed of sound in soft particles and discuss the effect of the elasticity on an acoustic wave.
• Spouting of fine powder from vertically vibrated bed

  S Harada, H Li, K Funatsu, Y Tomita

  CHEMICAL ENGINEERING SCIENCE 57 5 779 - 787 2002年03月 [査読有り][通常論文]
   

  Experimental and numerical studies of spouting of powder from vertically vibrated bed are performed. The powder flows out vigorously through a side orifice of the vertically vibrated vessel in which the powder is contained, provided that the vibration acceleration is greater than the gravitational one. The mechanism of the efflux and the relationship between the efflux rate and the vibration condition are examined. The interstitial air pressure in the bed is measured and is compared to the numerical analysis considering the relative motion of the powder bed to the vibrated vessel and percolation air flow. The outflow behavior of powder is observed by using a high-speed video camera. The experimental and the numerical results show that the powder spouts out intermittently with periodic air outflow, which is generated in response to the change of the gap between the bed and the vessel base. Furthermore, it is found that the efflux rate of powder is in proportion to the generated air pressure and in inverse proportion to the vibration frequency. (C) 2002 Elsevier Science Ltd. All rights reserved.
• Fluid force acting on a particle falling toward a wall

  Syusaku Harada, Toshitsugu Tanaka, Yutaka Tsuji

  JSME International Journal, Series B: Fluids and Thermal Engineering 44 4 520 - 525 2001年11月 [査読無し][通常論文]
   

  A direct simulation of the falling motion of an immersed solid particle toward a wall is performed to investigate the mechanics of hydrodynamic collision of particles. The time-dependent boundary-fitted coordinate system is applied to the calculation of fluid flow around solid bodies. The fluid force acting on the particle is calculated by integrating the surface stress without any models. The obtained particle motion is compared with the corresponding experiment and theoretical analysis. The results of the numerical simulation, the experiment and the analysis using theoretical models agree quantitatively with respect to the falling motion of the particle. When the particle falls toward the wall, fluid force due to the squeeze of fluid in the gap is increased and prevents the particle from approaching the wall. As a result, the particle is decelerated and the fluid force caused by the unsteady motion of the particle is significantly increased. The numerical results reveal that the total fluid force acting on the particle can be explained by the sum of steady and unsteady fluid forces.
• Granular jump in low velocity pneumatic conveying of solid particles in a horizontal pipeline

  Y. Tomita, K. Funatsu, S. Harada

  Handbook of Powder Technology 10 353 - 359 2001年 [査読無し][通常論文]
  
• 壁面近傍の自由沈降粒子に作用する流体力

  原田周作, 田中敏嗣, 辻 裕

  日本機械学会論文集B編 66 649 2313 - 2319 2000年 [査読有り][通常論文]
   

  Direct simulation of sedimentation of a solid particle toward a wall is performed to investigate the hydrodynamic interaction between a particle and a wall. The time-dependent body-fitted coordinate system is applied to the calculation of the fluid motion around the solid bodies. The fluid force acting on the particle is calculated by integrating the surface stress. The obtained particle motion is compared with the corresponding experiment and the theoretical models. Furthermore, it is discussed the transition of individual components of fluid force through the sedimentation.
• 流体中の壁面と円柱の衝突問題に関する数値解析

  原田周作, 田中敏嗣, 辻 裕

  日本機械学会論文集B編 65 633 1520 - 1527 一般社団法人日本機械学会 1999年 [査読有り][通常論文]
   

  A numerical analysis of incompressive flow around a solid cylinder which falls to a solid wall was performed to study the effect of fluid on the interaction between solid bodies. A time-dependent boundary-fitted coordinate system and a transformable grid which moves arbitrarily were adopted in order to express unsteady and relative motion of solid boundaries. The fluid force acting on the cylinder was calculated directly by integrating the stress and the pressure on the surface without using any models. The effect of the induced pressure on the behavier of the cylinder was studied, and the results were compared with the analytical theory of lubrication. The obtained pressure in the gap showed similar profiles to the one derived from the lubrication theory. Furthermore, it was studied about dominant effects on the motion of the cylinder in the fluid, especially about the effect of the unsteady motion of the cylinder. In addition, it was examined the effect of the inclination of the wall to the motion of the cylinder.
• Numerical analysis of dense phase liquid-solid flow in a horizontal pipe

  S Harada, T Tanaka, Y Tsuji, K Asakura

  Fluid Mechanics and Its Application: IUTAM Symp. Lubri, Trans. Viscous Mater. 43 31 - 42 1998年 [査読無し][通常論文]
   

  Numerical simulations of the liquid-solid flow in a horizontal pipe were performed by the Lagrangian/Eulerian approach. Motion of individual coarse particles was calculated by the Newton's equation of motion. The contact forces were given by DEM (Discrete Element Method)[1] model, which enables ones to estimate the forces on the moving particles in contact with their neighbors. The motion of liquid was calculated by solving the local averaged equations of continuity and motion. The calculated results showed the characteristic flow patterns of liquid-solid systems, such as flows with a moving bed or a deposit. The relation between the fluid velocity and the flow pattern agreed with the experimental results of sediment transport.
• 高濃度粗粒固液混相流の3次元シミュレーション

  朝倉國臣, 舟山高明, 原田周作, 中島 巌

  資源と素材 114 6 403 - 409 The Mining and Materials Processing Institute of Japan 1998年 [査読有り][通常論文]
   

  In this study, solid-liquid flows with coarse particles, which form a highly concentrated zone in a pipe, were simulated. In general, the cell size of the continuous phase is larger than the particle size. However, with increases in particle size, the cell size must be close to the particle size in order to maintain high resolution of the fluid velocity. Simulation using equal cell and particle sizes was carried out to investigate the effects of fluid velocity, pressure gradient and void fraction on the settling motion of a particle in rest water. For simulating a particle cloud, a conventional Lagrangian/Eulerian method using the drag coefficient of a particle cloud was employed. The results so obtained were compared with the results using the drag coefficient of a single particle under the same flow and particle conditions.
• Simulation of descending particles in water by the distinct element method

  K. Asakura, S. Harada, T. Funayama, I. Nakajima

  Powder Technology 94 3 195 - 200 1997年 [査読有り][通常論文]
   

  The motion of descending glass beads (10 mm in mean diameter) in water was simulated in an hourglass-like tube using the three dimensional distinct element method (DEM). The fluid flow is postulated to be an axisymmetric laminar flow, owing to the predominance of radial and longitudinal components. The fluid phase was solved by the SIMPLE scheme. Conventional (linear and non-linear) DEM models indicate that the elements must exert tension on one another just before separating. This is in conflict with the expected shape of a load-displacement loop for an element moving ar a slow rare and with damping energy loss depending oil its velocity. The untenability of these models has been excluded by adopting the Hunt model for simulation. The coefficients of interparticle and particle-wall friction were evaluated in water. The overall motion of the particles in water is satisfactorily simulated by the DEM. (C) 1997 Elsevier Science S.A.
• 水中落下粒子群の離散要素法によるシミュレーション

  朝倉國臣, 原田周作, 舟山高明, 中島 巌

  資源と素材 112 4 219 - 224 1996年 [査読有り][通常論文]
  

書籍

• 流体力学ハンドブック (日本流体力学会編)

  原田周作 (担当:分担執筆)
  東京大学出版会（刊行予定） 2023年
• 粉粒体の構造制御・ハンドリング技術

  原田周作 (担当:分担執筆)
  技術情報協会 2013年
• ながれの事典

  原田周作 (担当:分担執筆)
  丸善 2004年

その他活動・業績

• 重力下における液中微粒子の集団性

  原田周作 ながれ 34 (5) 321 -326 2015年 [査読無し][通常論文]
  
• 固体粒子を含む液体の流れに関する研究

  原田周作 混相流 27 (2) 183 -186 2013年 [査読無し][通常論文]
  
• 微粒子懸濁液の集団的挙動と個別的挙動

  原田周作 塗装工学 48 (6) 204 -209 2013年 [査読無し][通常論文]
  
• 流体力を測るLagrangianセンサ

  原田周作 粉体工学会誌 49 (7) 538 -545 2012年 [査読無し][通常論文]
   

  We have made a Lagrangian sensor for real-time and non-invasive measurement of fluid force acting on a particle which moves freely in liquid. The sensor particle contains an acceleration sensor, magnetometer, microcomputer, wireless signal transmitter module and cells. The acceleration sensor detects the acceleration of particle （acting force divided by mass） for each instant of time. The magnetometer detects the direction of external magnetic field, which is oriented in the same direction as the gravity, for the removal of gravitational acceleration from acceleration signals with arbitrary attitude of particle. We have performed some preliminary experiments in order to check the accuracy of the measurement system. The measured results agree well with the theoretical prediction of particle motion in liquid. Moreover, we applied the Lagrangian sensor to a multi-particle system for the measurement of fluid force under the influence of other particles.
• 濃度界面が引き起こす液中微粒子の集団運動

  原田周作 可視化情報学会誌 32 (126) 14 -18 2012年 [査読無し][通常論文]
  
• 微粒子分散系の動的特性

  原田周作 物性研究 88 (2) 281 -288 2007年 [査読無し][通常論文]
  
• マイクロスケールの流体力学的拡散

  原田周作 粉体工学会誌 42 (11) 799 -803 2005年 [査読無し][通常論文]
   

  Sedimentation of solid particles is an important phenomenon in various engineering processes related to coating, accumulation, separation, filtration and so on. It is well-known that the sedimentation velocity in a stationary fluid is influenced by hydrodynamic interactions between particles and is a function of volumetric concentration of particles. In addition, the hydrodynamic interactions induce complex effects, such as the large-scale fluctuations in the sedimentation velocity, the self-diffusion of particles and the instability at the interface of sedimenting suspension. In this paper, the hydrodynamic diffusion, which is one of the hydrodynamic effects, of particle layer with a finite height is discussed. Researches on the hydrodynamic diffusion are reviewed and our recent numerical studies on the diffusivity of particles in microscale are reported.
• 外力により発生する粒子噴流

  原田周作 噴流工学 21 (1) 13 -18 2004年 [査読無し][通常論文]
  
• 固液二相流における固体間の近接相互作用

  原田周作 混相流 15 (3) 252 -257 2001年 [査読無し][通常論文]
  
• 固気二相流の流動様式と可視化

  富田侑嗣, 原田周作 14 (2) 158 -165 2000年 [査読無し][通常論文]
  

特許

• 特開2002-19967:粉粒体供給用フィーダおよびその供給システム  

共同研究・競争的資金等の研究課題

• 「混合」の流体力学的体系化 －液中微粒子の集団性と個別性－

  日本学術振興会：科学研究費助成事業

  研究期間 : 2023年04月 -2026年03月 

  代表者 : 原田 周作, 田中 洋介, 山本 恭史
• 混合廃棄物の乾式素材分離技術の高度化に向けた流動層内での物体浮沈メカニズムの解明

  日本学術振興会：科学研究費助成事業

  研究期間 : 2021年04月 -2025年03月 

  代表者 : 押谷 潤, 原田 周作, 辻 拓也

   

  流動化させる粉体として粒子径の異なるガラスビーズを用い、流動層の風速と層高を変化させて様々な密度の球の浮沈実験を行った。いずれの粒子径においても層高が低く風速が小さい場合において浮力と重力を基本とするアルキメデスの原理に基づくような浮沈挙動が確認され、粉体の質量／(流動層の断面積×高さ)で求まる流動層の見掛け密度よりも小さな密度の球が浮揚し、大きな球が沈降した。一方、層高が高く風速が大きい場合は密度差から沈降すると予想された球が沈降せず層内を漂うという興味深い結果が得られ、流動層内での物体浮沈が条件によってはアルキメデスの原理に基づかないことが明らかとなった。そこで、流動層内の球に対して浮力と重力以外に働く力の存在を検討するために、無線式センサシステムを構築した。磁気センサと加速度センサおよびそれらの信号を無線発信する機器を内蔵した球を作成して実験を行った結果、アルキメデスの原理に基づく浮力よりも大きな鉛直上向きの力が定常的ではないがごく稀に急に働くことが明らかとなった。さらに、流動層内での物体浮沈について数値シミュレーションを行った結果、上記の実験と同様に低風速では安定した物体浮沈が再現されたのに対し、風速が大きい場合ではアルキメデスの原理から沈降すると予想された球が沈降せずにある瞬間に大きな鉛直上向きの力を受けて浮揚するという興味深い結果を得た。以上の結果は、研究課題名に挙げた混合廃棄物の乾式素材分離技術の高度化に向け、粉体の粒子径や層高、風速の大小が安定した物体浮沈を阻害する可能性を示唆するものであり有意義であると思われる。
• 不混和界面と混和界面の動力学に関する統一的解釈－メゾスケールでの物質混合機構－

  日本学術振興会：科学研究費助成事業

  研究期間 : 2019年04月 -2022年03月 

  代表者 : 原田 周作, 田中 洋介, 山本 恭史

   

  液体中に分散した固体微粒子が形成する見かけ上の界面（濃度界面）の動力学的性質，および界面近傍における微粒子の混合現象の解明を目的とした研究を行った．濃度界面の3次元形状測定システムを開発し，重力沈降する微粒子分散系の濃度界面挙動を調べた．その結果，濃度界面の混和性・不混和性が変化することにより種々のモードの沈降形態が出現することが確認された． さらに濃度界面近傍の微粒子の混合現象に関する実験および数値解析を行った．その結果，上下粒子の集団性および沈降速度比の違いにより，粒子スケールの混合（ミクロ混合）と密度不安定に起因した巨視的な混合（マクロ混合）が条件に応じて出現することがわかった．
• 濃度界面の微視的解釈および固液流動系の能動的制御への応用

  日本学術振興会：科学研究費助成事業

  研究期間 : 2014年04月 -2017年03月 

  代表者 : 原田 周作, 山本 恭史

   

  本研究では，液体中に不均一に分散した固体微粒子の重力沈降挙動について，その集団性を理解するとともに，沈降速度や分散挙動を能動的に制御するための技術を確立した．純粋な液体との間に濃度界面を有するような微粒子分散系の沈降挙動に関して,濃度界面における流体との相対運動を微視的に観察することにより，集団性の形成メカニズムについて明らかにした．さらに分岐や断面積変化を有するような複雑流路中での集団的な粒子沈降挙動について調べ，流路の幾何学的特性量から沈降速度を予測・制御可能な物理モデルを構築した．
• 岩石の亀裂自己修復機能とその強度・破壊制御への応用

  日本学術振興会：科学研究費助成事業

  研究期間 : 2010年04月 -2014年03月 

  代表者 : 金子 勝比古, 川崎 了, 奈良 禎太, 伊藤 真由美, 椋木 俊文, 広吉 直樹, 坂口 清敏, 原田 周作

   

  本研究では，亀裂自己修復現象に関する一連の実験的研究を実施し，その工学的応用を試みた。具体的には，まず，岩石の低速亀裂伸長現象に及ぼす環境条件の影響を実験的に分析し，低速亀裂進展の機構を解明した。次に，亀裂自己修復現象に関して実験的検討を行い，その機構と活性化条件などを明らかにした。また，亀裂伸長プロセスを数値解析的に検討し，亀裂方向制御など高度制御破砕の設計法を提案した。これらの成果に基づいて，岩質材料の長期強度を予測する方法を提案し，環境条件の制御により長期強度を制御できることを明らかにした。
• 濃度界面を有する微粒子分散系の集団的挙動と個別的挙動

  日本学術振興会：科学研究費助成事業

  研究期間 : 2011年 -2013年 

  代表者 : 原田 周作, 山本 恭史

   

  液体中における濃度差によって生じる微粒子の集団性を利用して，沈降速度や分散挙動を制御する技術を確立した．本研究では，液体中に不均一に分散した粒子の沈降形態は，粒子懸濁部が周囲の流体と不混和にふるまい，界面不安定が沈降挙動を支配する「液体的沈降」，および懸濁粒子が個別的に干渉沈降を行う「粒子的沈降」が沈降形態の極限として現れることを示し，その推移のメカニズムを明らかにした．本現象を能動的に利用することにより，沈降促進や分散制御など微粒子に関連する工学プロセスの技術向上が期待される．
• 海洋バイオマス利用による CO2 削減およびバイオ燃料化に関する研究

  日本学術振興会：科学研究費助成事業

  研究期間 : 2010年 -2012年 

  代表者 : 瀬名波 出, 小西 照子, 平良 東紀, 玉城 史郎, 藤村 弘行, 石川 正明, 若井 謙介, 大城 尚紀, 小田 拓也, 平岡 雅規, 原田 周作

   

  本研究では火力発電所や下水処理施設などから排出される二酸化炭素(CO2)を海藻を育てるための資源として再利用した。高濃度の CO2を海水に人工的に溶かし、それを海藻に与えることで藻類の光合成(成長速度)を飛躍的に高めた。通常の海水に比べて約 1.9 倍以上に成長が高まる結果を得た。また海藻を原料としたバイオエタノールの試作を成功させた。このようにCO2を減らし,また CO2を新たな資源として再利用する「炭素回生システム」研究開発を行った。
• テレメトリシステムを用いた液中粒子のダイナミクスに関する研究

  日本学術振興会：科学研究費助成事業

  研究期間 : 2003年 -2004年 

  代表者 : 原田 周作

   

  近年、ナノ・マイクロテクノロジーの発展に伴い,特定の波長の光を吸収する半導体粒子などの機能性微粒子の研究が盛んに行われており,溶媒中における微粒子挙動の解明が求められている.しかしながら低Reynolds数条件における粒子間の流体力学的相互作用は長距離性を有すること,また近接極限において連続体近似が破綻することなど複雑な因子を多く含むため,溶媒中における微粒子の分散・凝集のダイナミクスはほとんど明らかにされていない.本研究では,このような粘性流体中における固体粒子のダイナミクスに関連する研究として,粒子の自由運動にともなう位置および加速度変化を同時測定し,さまざまな条件における固体間の流体力学的相互作用の詳細を調べた.3種類の液中粒子の加速度計測用センサ粒子(以下,センサ粒子)を製作した.ピエゾ抵抗型微小加速度センサ,信号増幅部および電源部からなる小型回路をアクリル製中空粒子に内蔵し,データ取得のために,テレメトリ回路による無線送信,内蔵マイクロロガーによるデータ蓄積,微細エナメル線による有線通信の3手法を用いた回路を製作した.また外部からLED変位計,レーザ変位計を併用した粒子変位の非接触測定を行った.外部からの粒子変位測定により,低Reynolds数条件における粒子-固体壁面の接近時の粒子挙動が明らかとなった.固体壁面への接近時に潤滑効果による過大な流体力が作用し,壁面近傍で急激な減速運動を行う粒子の加速-減速過程は,低Reynolds数条件の定常流体力および非定常流体力の線形和により得られる粒子軌跡と定量的に一致した.またセンサ粒子による加速度測定により,定性的な流体力変化の傾向が得られた.本実験結果から,流体中の固体衝突に伴う流体力学的効果の詳細が明らかとなった.
• 付着性微粉末の機械的流動化現象の研究

  日本学術振興会：科学研究費助成事業

  研究期間 : 1999年 -2000年 

  代表者 : 富田 侑嗣, 原田 周作

   

  鉛直振動下における容器内粉体層の内部圧力変動と容器からの粒子噴出現象に対して,実験的,数値的研究を行った.側壁にオリフィスを有する円筒容器に付着性粉体を充填して鉛直振動を付加すると,粒子はオリフィスを介して外部に勢い良く噴出する.本噴出現象の発生機構の解明および付着性粉体操作技術への応用を目的として,層内部の圧力変動と噴出挙動との関連性,付加振動に対する噴出流量の変化を調べた.粉体層内部の流体圧の経時変化を測定すると同時に,圧力測定と同期させた噴出挙動の高速度ビデオ撮影を行い,それらの関連性を検証した.また粉体層と内部透過流体の連成運動に対する数値解析を行い,圧力変動機構の考察を行った.その結果,粉体層内部の流体圧は付加振動に対応して周期的に変動し,その内部圧力変動に対応して充填粒子が間欠的に噴出することが分かった.さらに圧力変動は,数値解析結果から得られた流体透過に起因する圧力変動と,付加振動との位相差や変動の大きさに関して概ね一致した.以上より,鉛直振動下の粉体の噴出現象は,容器と粉体層の相対運動により発生した間隙流体の透過流動が外部との周期的な流体運動を誘起し,その運動に充填粒子が追従した現象であることが分かった. さらにさまざまな振動条件における噴出特性を調べた結果,本実験条件では質量流量は層内部の発生圧力に比例し,付加振動数に反比例することが分かった.これは流路に周期的な圧力差を与えた場合の気流の流量変化と同じ傾向であり,すなわち粒子は周期的な流体の流出入に追従して噴出することが明らかになった.また付加振動条件と噴出流量との関係に一定の傾向が見られたことから,鉛直振動を利用した付着性粉体の新しい供給技術への応用の可能性が確認された.
• 微粒子分散系の動的特性
• Dynamics of colloids and suspensions

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