固液二相流・スラリー

Blood is a suspension of blood cells in a Newtonian fluid of plasma. The red blood cells (RBCs) are most numerous and behave like small deformable capsules containing a Newtonian fluid. How to treat blood flowing through vessels depends on the scale involved. The flow characteristics of blood in the microvessel with a diameter comparable with the RBC size may be determined by the behavior of individual RBCs, for which a multi-phase flow model may provide a good approximation. Some multiphase flow problems of blood flow are studied.

It is well known that the friction or the drag of the turbulent flow is reduced by adding certain additives into liquids or gas. This phenomenon is called drag reduction, and the industrial application of the phenomenon connects directly with economizing energy in the hydraulic transport process. The effect of polymers has attracted the attention of many researchers, and there are many experimental and theoretical studies about it. However, there are very few experimental studies of drag reduction in two phase flows. It is very important to understand drag reduction clearly, because it is a subject of wide interest from the points of view of studying the turbulent structure of the flow in the fluid mechanics field. In this review, some experimental results on drag reduction in two phase flows are showed, and subjects for future study on drag reduction in liquid-solid two phase flows are described.

固体粒子を水などの搬送流体と混合し、パイプラインよって輸送する水力輸送に対しても、 従来、 比較的微細な粒子を液体と混合し輸送する場合に用いられていたスラリー輸送なる用語が使用されている。このように成った背景の一つとして、 輸送対象物である固体粒子ならびに搬送流体の多様化に伴い、微粒子以上の沈降性粒子と液体との混合体を沈降性スラリーあるいは粗粒子スラリーと称するように成ったことが挙げられる。本稿では、広義に捉えられたスラリー輸送における流動を取り上げ、用語の説明を試みる。なお、 著者の独断が含まれているので、読者諸氏のご意見がいただければ幸いである。

前回はスラリーの流動を取り上げ、取り分け、スラリーの分類・流動様式関係の用語について述べた。今回は、流動の様相が変わる速度、すなわち遷移速度 (限界速度) について述べるとともに速度と命名されている用語の説明を試みる。なお、著者の独断が含まれているので、読者諸兄のご意見がいただければ幸いである。

技術革新を担う重要な研究課題の一つとして新素材開発とその応用面開発が挙げられる。近年材料科学の分野では、素形材料 (あるいは構造材料) に対して機能材料、さらには、知能材料の概念が広く認識されるに至り、その開発研究が進められてきている。流体材料に関してみても、水や空気、油といったいわば素形材料に相当するものに対して、電磁場の作用により機能性を発現させることのできる流体として、磁性流体やER流体の研究が進められてきている。さらに、より高度な機能性を付与したり、多機能化を進めることにより流体の知的の制御を行おうとする研究も開始されている。この意味からも混相流体は、重要な役割を演じるものと期待されている。本稿では、機能性流体の代表例として磁性流体を取り上げ、その基礎から応用にわたる研究の道筋を4回シリーズで解説することにする。第1回目は、混相流体的な側面から磁性流体をとらえて磁性微粒子を含む流体の特性について、第2回目では磁性流体の力学の基礎を、第3回目では磁場の作用下での各種の流れの特性について、第4回目には磁性流体の応用面について解説することにする。

流体の機能化、知能化を計る上で、混相流体の活用は重要な役割を演じるようになってきている。特に電磁場の作用下で高機能性を発揮する流体として磁性流体やER流体をベースとしてより高い付加価値を付けるための研究が活発化してきている。本講座では、機能流体の代表例として磁性流体を取り上げ、その基礎から応用にわたる研究の道筋を4回シリーズで解説するものである。前回 [1] はその1回目として、混相流体的な側面から磁性流体をとらえて磁性微粒子を含む流体の特性について解説した。今回はそれに引き続いて、磁性流体の力学を扱う場合の基礎式を中心に磁性流体力学の成り立ちについて解説することにする。

流体の機能化、知能化を計る上で、混相流体の活用は重要な役割を演じるようになってきている。特に、 電磁場の作用下で高機能性を発揮する流体である磁性流体やER流体をベースとして、より高い付加価値を付けるための研究が活発化してきている。本講座では、機能流体の代表例として磁性流体を取り上げ、その基礎から応用にわたる研究の道筋を4回シリーズで解説するものである。第1回目 [1] は、混相流体的な側面から磁性流体をとらえて磁性微粒子を含む流体の特性について、次いで前回の第2回目 [2] では、磁性流体の力学を扱う場合の基礎式を中心に磁性流体力学の成り立ちについて解説した。今回は第3回目として、磁性流体のいろいろな流れの問題を取り上げ、磁場の作用下で流動特性がどのような影響を受けるか解説することにする。

流体の機能化、知能化を計る上で、混相流体の活用は重要な役割を演じるようになってきている。特に、電磁場の作用下で高機能性を発揮する流体として、磁性流体やER流体をベースとしてより高い付加価値を付けるための研究が活発化してきている。本講座では、機能流体の代表例として磁性流体を取り上げ、その基礎から応用にわたる研究の道筋を4回シリーズで解説するものである。第1回目 [1] は、混相流体的な側面から磁性流体をとらえて磁性微粒子を含む流体の特性について、ついで第2回目 [2] では、磁性流体の力学を扱う場合の基礎式を中心に磁性流体力学の成り立ち、そして前回の第3回目 [3] は、磁性流体のいろいろな流れの問題を取り上げ、磁場の作用下で流動特性がどのような影響を受けるかを解説した。今回は、最終回として、磁性流体の応用面について解説することにする。

Since slurry transportation systems are very useful to transport bulk materials, the systems are used in transporting ores and tailings in mining industries and in dredging harbors. This paper describes the characteristics of the slurry transportation systems, and the plan and application of the systems, written as follows, in mineral development in Japan. 1) The plan of Ishikari coal slurry tranport pipeline. 2) The hydraulic transportation system in Sunagawa coal mine. 3) The backfill slurry transportation system in cut-and-fill stoping. 4) The Oodate-Noshiro tailling slurry transport pipeline. 5) The pilot plant system of slurry transportation for sediment sand in Sakuma dam reservoir. 6) The manganese nodule mining system using airlift pump by National Research Institute for Pollution and Resources. 7) The control of gas kick and drilling mud flow in drilling well for methane hydrate production.

Flow patterns of settling slurry flow in a horizontal pipe can be represented graphically on the pressure drop-flow rate relation at a constant concentration, because the mechanism of pressure drop depends makedly on the flow regimes: stationary bed, sliding bed or moving bed, saltation flow, heterogeneous flow, and pseudo-homogeneous flow. Although it is difficult to clarify the sharp boundaries between these categories, the criterion based on concentration distributions may be one of the most effective parameters that depend on the degree of homogeneity. The main objective of this paper is, therefore, to discuss criteria for determining flow patterns and an analytical method of concentration distributions, introducing an interesting method of displaying solids flow behavior on a monitoring screen.

This paper reviews recent research on the numerical simulations of solid-liquid and three-phase flows. The numerical simulations are classified into three types, namely, non-model, half-model and model type. Typical research of each type and constitutive equations for the motion of solid in liquid are briefly introduced.

In solid-fluid two phase flows, the interaction between particles and particle-wall play important roles. They are deeply related not only to individual motions of the particle but to the formation of meso-scale structure such as particle clouds. Therefore the foundamental study on the interaction of particles has been required for modeling the solid-fluid flow. In this paper, theoretical models of short-range interaction between solids in fluid are briefly reviewed. Then we describe the direct simulation of the sedimentation of a solid particle toward a wall, and discuss the fluid force acting on the particle at finite Reynolds number. Furthermore, it is shown that the fluid effects due to the unsteady motion of the particle are significant role on short-range interaction in liquid.

To better understand the processes which occur in magma chambers and in liquefied sediments, we conduct laboratory experiments of gravitational instability of a close packed granular medium in a liquid. First we consider a case in which a granular medium overlies a liquid layer. Here the lowermost thin layer of a granular medium dilates and becomes mobile to form a rheological boundary layer (RBL), from which narrow granular plumes grow downwards. We measure the wavelength and the growth rate of the instability and constrain the thickness of the RBL to be only about twice the particle size, and its packing fraction as Φ = 0.42, indicating dilation. When the granular medium is thicker, we find that the granular plumes organize themselves into convection cells. Importantly, the ascent velocity of the boundary between the granular medium and the liquid layer is approximately constant regardless of the thickness ratio of the two layers. A scaling in which the packing fraction of the RBL governs the ascent velocity is found to explain the results well. Next we extend the first experiment and model magma chamber roof melting and subsequent particle settling. An experimental cell consists of a lower layer of a thermally convecting molten wax, and an upper layer comprising of a mixture of particles and solid wax. As the interstitial solid wax of the upper layer melts, the particles become mobile and settle downwards. From experiments with different particle sizes, we find that when the particle is smaller than 0.1 mm, cycles in which melting starts and stops, occur spontaneously. Melting stops due to the formation of a stable stratification in the melt layer which suppresses the vertical heat transfer. Melting resumes by the convective overturning because the cell is heated from below. A dimensionless Buoyancy number is found to explain the critical particle size well. As a third experiment, we consider the instability caused by liquefaction. Here an experimental cell consists of a water-immersed granular medium which is size-graded into 2 layers such that the upper layer has a smaller permeability. When the cell is shaken vertically, liquefaction occurs and the water temporarily accumulates at the 2 layer interface resulting in a gravitational instability. From experiments in which we vary the acceleration and frequency of shaking, we find that there is a critical acceleration for instability to occur, and that this acceleration is minimum at a frequency of about 100 Hz. We show that the frequency dependence can be interpreted from a combined condition of energy and jerk of shaking exceeding their respective critical values.

Coagulation of particles in the fluid is often observed in nature and it is a multiphase phenomenon utilized in various processes. Coagulation phenomenon is also observed in molten metal system in the same as water and air system. Until now, coagulation of particles such as oxide inclusions, have been focused on because large inclusions raise harmful defects in final products. Therefore, many researches have been performed in the both side of theory and experiment. In this paper, kinetics of coagulation behaviors is summarized for information to analyze the growth rate of aggregates, particle size distribution and so on. In addition, recent researches and issues for coagulation mechanism are introduced briefly in the view point of multiphase phenomenon.

A progress of slurry transport is described in this report. In around 1980, slurry transport was extensively studied. Papers on pressure losses of slurry flows, transition velocity, measurement of in-situ concentration, snow/ice-water slurry flows were published by several researchers. Recently, the study on slurry transport is not so active, but solid-liquid flows can be seen in many fields. It is anticipated that studies on solid-liquid flows in the fields of disaster site restoration and next-generation resources and energy development will be progressed.

The turbulence modulation, that means influences of dispersed particles to the fluid turbulence, is one of the challenging subjects in the multiphase flow research. In recent decades, experimental and numerical researches have been conducted extensively. Especially the direct numerical simulation (DNS) became a powerful means to reveal the multiphase turbulence phenomena. But DNS cannot become a practical tool for multiphase flows in industry or in nature. In this review article, an example of particle-laden flow by the immersed solid method and our recent progress for the application to the two-phase heat transfer are shown. Then, considering the current status, it is pointed out that some moderately-averaged equation, which includes momentum exchange and residual stress terms, is essential for semi-DNS including finite-sized particles (e.g., Kolmogorov scale particle) to deal with large-scale multiphase flow fields.

We investigate lateral migration of particles dispersed in Stokes fluid. Arbitrary shaped and non-uniform charge distributed particles are discussed in this paper. Translation-rotation coupling of the particle sometimes produces the complex motions. The motions of the particles are not always parallel to external fields, such as gravity, electric field and shear flow. The migration direction and the trajectories of the particles are dependent on their shapes etc. Especially chiral particles, which cannot be superimposed to their mirror images, migrate to opposite direction of their mirror images isomer. The topics here can be applied to the separation method of the particles.

In recent years, self-assembly of complex fluids has received considerable attention in the fields of nanoscience and nanotechnology. Self-assembly is involved in various functional materials that are widely used in industry and there is a strong relationship between self-assembled structures and specific functions. Hence, the understanding and controlling of the self-assembly controlling of complex fluids is important and a useful process in materials chemistry and engineering. In this paper, the recent developments on studies of the structure formation and flow properties of amphiphilic molecules and Janus colloids in solution, using coarse-grained simulation that takes into account hydrodynamic interactions are reviewed. We first briefly introduce the dissipative particle dynamics method and discuss in detail the self-assembly behavior and viscosity properties of surfactant aqueous solution in nanotubes. Following this, we describe another simulation method in which solvent particles are modeled explicitly as point particles, which is the so-called “the multi-particle collision dynamics (MPCD)". The relation between the structural and rheological properties of Janus colloids in solution, using molecular dynamics simulations coupled to MPCD is reported. In general, the shear viscosity of the dispersion correlates strongly with the size of the aggregates not aggregates shape. These results allow us to determine the dynamic properties solely based on structural information.

In this study, the effects of polymer flexibility and entanglement on elastic instability were investigated by observing sodium hyaluronate (Hyaluronic Acid Sodium salt, Na-HA) solution in planar abrupt contraction-expansion microchannels. The rigidity of Na-HA in a solution is affected by ion concentration in the solution. Therefore, we prepared Na-HA water solution and Na-HA PBS solution with concentrations from 0.15 wt% to 0.45 wt%. The rheological properties were measured and analyzed to detect the Na-HA overlap and entanglement concentrations. The flow regimes of the Na-HA solutions in several planar abrupt contraction-expansion channels were characterized in terms of rheological properties, polymer flexibility and polymer entanglement.

Dense suspension of non-Brownian particles such as potato starch often shows counter-intuitive behaviors due to its discontinuous rheological property. Using this particular rheological property, people can run on a dense suspension. However, once the motion of leg becomes too slow, the leg is arrested, namely, it is difficult to walk on the surface. To explain this peculiar behavior, propagation of jamming front caused by an impact onto a dense suspension has been considered recently. The effectively solidified zone is developed by the jamming-front propagation. This solidified zone effectively increases viscosity of the suspension. In addition, when the jamming front reaches the bottom of the container, a solidified pillar which causes effective elasticity is developed. Because the lifetime of the solidified zone is short, the suspension recovers usual viscosity after a while. To characterize the viscoelastic properties of the impacted dense suspension, a set of simple impact experiments was performed. A solid sphere was dropped from a certain height onto a suspension. The impact and rebound dynamics were recorded by a high-speed camera. Using the kinematic data, viscoelasticity of the impacted suspension was measured. The obtained data are consistent with the idea of jamming-front propagation. In addition to the impact onto a static target, impact experiments onto a dense suspension under the influence of mechanical vibration were also performed. Although the mechanical vibration can significantly deform the free surface of suspension, the impact response was hardly affected. In this article, a brief review of the impact-induced jamming-front propagation and the resultant effective viscoelasticity is presented.