材料工学

Multiphase flows are very popular in ironmaking and steelmaking processes and are characterized as follows:(1) The temperature of fluids in metallurgical reactors is higher than about 1500°C, hence measurements of transport phenomena (fluid motion, heat and mass transfer) are very difficult.(2) The flow in the reactors is highly turbulent (turbulence components are usually larger than mean flow values) and chemical reactions take place at the same time. Many “cold model” experiments have been carried out due to the difficulty in doing measurements under realistic conditions. Water, oil (silicone oil, pentane, liquid paraffin, etc.) and metals with low melting temperatures (mercury, Wood's metal, etc.) are Used as working fluids. Transport phenomena encountered in ironmaking and steelmaking processes (hot metal pretreatment, converter, second refining processes, etc.) are covered here and previous experimental and theoretical results on this subject are reviewed

This paper presents a state-of-the art review on utilization of artificial intelligence in functional modification of multiphase fluids. The basic concept of such intelligent functional multiphase mixtures has been proposed and several related background technologies have been presented for R & D. Some historical backgrounds behind this topic was also documented.

The processing mechanism, structure and property of multiple filament interlaced yarns with alternate tangling and opening parts are described on the basis of experimental data. The most important factor in the interlacing process is an air flow in a yarn duct of an interlacer. The high speed turbulent air jetting into the yarn duct from an air jet nozzle opens multiple filaments of running yarns separately and changes their relative positions. An opening part is formed at the position subjected to the air jet directly and tangling parts are formed at its both ends. The tangling parts keep their forms by the friction among filaments although the tangling part formed before the air jet nozzle is directly subjected to the air jet. Filaments in the tangling parts contact with each another and the number of tangles depends on the processing conditions of the working air pressure and feed ratio.

For the purpose of developing microactuators driven by liquid crystals, transient behaviors of a nematic liquid crystal between two parallel plates under an electric field are investigated on the basis of continuum mechanics and molecular dynamics. Imposition of an electric field on the liquid crystal induces flow, called backflow, whose profile and magnitude depend strongly on the twist angle of the director; that is, the velocity profile between plates is S-shaped when the twist angle is 0 deg, and unidirectional flow is generated when the twist angle is 180 deg. It is confirmed from the molecular dynamics simulation that the rotation and rearrangement of molecules during the reorientation process generate a local bulk velocity gradient. Furthermore, we have visualized the backflow induced between parallel plates to confirm qualitatively the predictions obtained numerically. As an example of liquid crystalline microactuators, we have manufactured micromotors and examined the revolution speed as a function of the frequency of an electric field.

Electrowetting is a technique to modify wettability and meniscus shapes on electrodes by applying voltage to the electrodes. In the present article, we introduce principles of electrowetting deriving the equation connecting voltage and contact angle. Then we reviews related articles on optical devices using electrowetting including our previous works; a liquid prism controlling optic-axis using electrowetting. Numerical simulation solved meniscus shapes between each liquid to predict the relation between applied voltage and optic angle. Results in experiments and simulations are briefly reported.

In the blast furnace, there is a packed bed consists of coke and iron ore, and there is a counter flow of the condensed and gas phases. Controlling the liquid and solid flow and preventing accumulation of the liquid and the powder are important issues for the productivity and the stability of the blast furnace process. The flow of the packed bed of burden, and liquid and gas flows in the cohesive zone had been investigated. Here, studies on the permeability of the cohesive and dripping zone of the blast furnace are introduced, and how to control the physical properties of the liquid and powder are discussed for increasing the gas permeability in the packed bed. In addition, progress of numerical simulation with installing influence of the physical properties of liquid, gas and powder is introduced.

Studies on the carburization rate of metallic iron through CaO-SiO2-Al2O3 slag phase and its mechanism have been introduced as a fundamental of slag-design for the low-temperature and high-speed of iron carburization. The carbon solubility in slag increases with an increase of slag basicity, and the rate of iron carburization through slag is faster when the slag basicity is higher. From these facts, it is concluded that the iron carburization proceeds faster when the slag basicity is higher, the carbon solubility is higher, and the partial pressure of oxygen is lower. On the other hand, the carburization rate is much slower than the rate of direct carburization or carburization through slag including iron oxide (FeO). That is to say, when iron ore agglomerates including carbon source are used as a raw material, in order to enhance the carburization reaction, it is important to proceed ‘melting and carburization’ according to the following mechanism: slag component is melted not after the reduction of iron oxide (formation of metallic iron) by the carbon source, but before iron oxide is perfectly reduced to metallic iron so that iron oxide can dissolve into slag.

Ironmaking process is currently focused on the decreased reducing agent operation of a blast furnace in order to decrease CO2 emissions. Because the coke ratio is reduced in this operation, causing a huge pressure drop, it has become increasingly important to understand the in-furnace phenomena using the non-empirical method. The discrete element method (DEM), Euler-Lagrange coupling method (DEM-CFD), and fully-Lagrangian method (e.g. SPH, MPS) simulation were carried out to analyze the momentum, heat and mass transfer between the fluid and the particles in a packed bed. These developed numerical methods are using discrete element type model, which can track the movement of the solid or the fluid phase directly. The optimum bed structure for decreased reducing agent operation can be clarified by application of these methods. Moreover, three-dimensional information for understanding in-furnace local flow structure can be also obtained with high spatial resolution. This paper explains the outline of the latest numerical model of blast furnace.

New technologies for increasing the utilization of iron-scraps are strongly demanded. One of them is liquid-liquid immiscibility phenomena for metals, which can realize the separation, concentration and refining of metals. It have been reported that several alloy systems cause two immiscible liquids. In this report, the progress of researches on the following three systems for liquid-liquid immiscibility phenomena was investigated. (1) In Fe-Cu-C system, it has been reported that a uniform liquid in an Fe-Cu system separates into two immiscible phases, i.e. a Cu-rich phase and an Fe-rich phase, when C is added to the system, and in addition the minor metals contained in an Fe-Cu-C system are distributed between the Cu-rich and Fe-rich phases. In recent years, the distribution behavior of rare metals and the stability of immiscibility under cooling process etc. have been studied. (2) In Fe-Ag system, the copper removal has been tried based on the distribution of copper and the low mutual solubility for liquid Fe phase and liquid Ag phase. The oxidation removal of tramp-elements (Cu and Sn) from carbon saturated iron via silver has been proposed recently. (3) In Fe-Ca system, the refining technology of iron by using Ca and its potential has been discussed.

In steel industry, multiphase flows are observed in many processes. It is important to understand an internal state to optimize the process. However, it is difficult to measure the internal state due to high temperature and high pressure in the furnace. Therefore, it is useful to estimate these phenomena by numerical simulation. In this report, the following three contents are mainly investigated, (1) Mechanical stirring in a KR process, (2) Supersonic jets in a converter, (3) Inclusion behavior in a continuous casting. Moreover, desirable analytical methods for the converters, which will be made practical in the near future are described.

Steelmaking process consists of refining and solidification. In refining process, the impurity elements are removed by chemical reaction between slag and molten steel, mainly. To improve the reaction rate, the emulsion of fine steel droplets in slag is a useful measure. Solidification is mostly conducted by continuous casting process. In this process, lubrication between the solidification shell and mold is important and the molten oxide (mold flux) is added on the surface of molten steel. However, the entrainment of the mold flux causes the defects of the products. Many researches have been conducted in this field to clarify the multi-phase flow between molten oxide and steel. In this paper, the emulsion phenomena of molten metal in slag and entrainment of oxide in continuous casting processed are reviewed.

Surfaces of common solids are hardly wet with molten metal. When such a hardly wetted object plunges into liquid, a cavity is formed behind the object. Furthermore, a residual bubble is left on the object after the break of the cavity. In metal refining process, the residual bubble attached to desulfurizing agents such as CaO particles interferes with deep immersion and desulfurization reaction. In this report, the volume of the residual bubble was theoretically estimated for the quasi-static and quite slow (but finite speed) immersion of a sphere as a reference condition. We calculated it from a simple energy minimum principle considering the interfacial energy and liquid potential energy. The calculated volumes can approximate fairly well the measured results for two kinds of contact angles of 115° and 162°.

Three-dimensional unsteady computations by RANS model simulation and large eddy simulation (LES) of impinging gas jet on a liquid surface were carried out. Results of the simulations were compared with experiments. Time-average values of cavity depth obtained by both simulations are consistent with those of the experiments. Prediction accuracy of LES is better than that of RANS model simulations in dynamic behavior of cavity depth as well as detail of cavity shape.

The expansion and shape change behaviors of a single rising bubble in a reduced pressure vessel were observed. The main results obtained are as follows: 1) The aspect ratio, h/w, of a single rising bubble under reduced pressure is almost the same as that under atmospheric pressure. However, the width of the rising bubble expanded to 1.4 times, which is larger than the calculated expansion ratio. This may be explained by the change of the bubble shape while rising. 2) The observed single bubble shapes were ellipsoidal, spherical-cap, and breakup of spherical-cap. The upward velocity of the bubble increases with the initial volume of the bubble. The upward velocity also increases as the bubble rises.

Experiment and numerical simulation of RH circulation flow were carried out on water model. Helium gas was injected into water in up-leg and flow rate was estimated at the end of down-leg. Volume of fluid(VOF) simulation was also performed by compressible Inter Foam solver of OpenFOAM, open source CFD toolbox. Three pairs of diameter of up/down-leg,100mm/100mm, 140mm/70mm and 170mm/30mm were estimated and the circulation flow rate by numerical simulation was almost consistent with measurement. Finally the simulation with scaled up mesh and molten steel properties was carried out. The volume of injected gas became larger according to rising in the up-leg because of hydrostatic pressure distribution and the behavior of gas-liquid interface in vessel was simulated qualitatively.

This article outlines the latent heat transport properties of the metal-to-insulator phase transition materials that our research group has been conducting. The metallic solid-solid phase change materials exhibit no change in shape before and after the phase change, and therefore require no container to maintain their shape when applied to heat sink devices. This can be a fundamental solution to the problems of increased thermal resistance due to the container or capsule, and leakage of the phase change material due to their breakage, which are apparent in conventional solid-liquid type phase change thermal storage systems. In this article, we introduce the thermal behavior of vanadium dioxide for a heat sink material.

As a candidate for latent heat storage materials, a semiclathrate hydrate (SCH, a kind of clathrate hydrate) has been expected. A remaining challenge toward the practical use of SCHs is to diminish a large degree of supercooling in the SCH crystallization. One of the effective solutions is the utilization of the hysteresis called the “memory effect”. The memory effect diminishes supercooling and/or the induction period in the clathrate hydrate recrystallization. We have elucidated that the solution structures (called clusters) remaining in the aqueous solution after complete SCH decomposition is closely related to the memory effect. In this paper, we introduce the experimental results on the residual clusters in the tetra-n-butylammonium bromide (TBAB) aqueous solution resulting from TBAB SCH decomposition, which were observed by scanning electron microscopy (SEM) with the freeze-fracture replica method, a small-angle X-ray scattering (SAXS), and a high-precision differential scanning calorimetry (μDSC).

Effective handling of reusable waste heat is one of the important fundamental technologies for reducing energy consumption as well as promoting energy conservation. Among possible ways for handling waste heat, thermal energy storage is the key technology in the thermal energy management. Basically, there are two major classes of materials for achieving thermal energy storage, which are known as phase change materials (PCMs) and chemical heat storage materials. Although some of them are familiar to our daily life and are widely used in various social systems, detailed molecular mechanism of thermal energy storage remains elusive at present. In the TherMAT project, we are now investigating the basic mechanism of thermal energy storage for both material systems based on the predictive computer simulations. As for PCM, sugar alcohols are known as one of the promising candidate for achieving large amount of thermal energy storage. Based on the molecular and crystal structures of known sugar alcohols, we have computationally designed and predicted a new organic molecular material which can achieve larger amount of thermal energy storage than ever known. At first step, we carefully analyzed molecular properties of known C4, C5 and C6 sugar alcohols based on the classical MD simulations. Then we have clarified the molecular factors that control physical properties, such as melting point and latent heat. On the basis of these detailed analyses, we proposed molecular design guidelines to achieve effective thermal energy storage; 1) linear elongation of carbon backbone, 2) separated distribution of OH groups, and 3) even numbers of carbon atoms inside the carbon skeleton. Our computational results clearly demonstrated that if we carefully designed molecular structures, non-natural sugar alcohols have potential ability to achieve thermal storage density up to 450-500 kJ/kg, which is larger than the best value of the present known organic PCMs (~350 kJ/kg).

The extensional flow has attracted attention in dispersing the nanofillers and immiscible polymer blends on the nanoscale since the extensional flow enables the direct stretch of the nanofillers and polymer droplets without rotation. Based on the fundamental analysis, we have revealed the dispersion effect of extensional flow. Furthermore, we proposed a new mixing element of a twin-screw extruder, fixed Blister Disc (XBD), that enables generating a strong extensional flow field. This paper reviewed the previous studies and introduced the case studies of compounding the nanocomposites and polymer blends using a twin-screw extruder equipped with the XBD mixing element.

We investigated birefringence of suspended cellulose nanofiber (CNF) liquids with constant flow rate owing to flow-induced orientation change of the suspensions passing through a rectangular channel with a tapered contraction. For rheological properties, non-Newtonian viscosity and gel-like behavior of CNF-suspensions exhibited. Velocity in the flow direction and elongational rate increased around the inlet of contraction. The experimental results of CNF-suspensions were independence of tapered angle for the contraction. However, overshoot behavior of tapered angle = 120° alone exhibited. Moreover, the resultant birefringence was dependence of the tapered angle. For understanding the experimental results, we discussed flow behavior (flow path line) and relationship between velocity and birefringence. Possibility of existence of corner-vortex before contraction was discussed. Furthermore, the experimental results were compared with those of a polymer solution (aqueous solution of Xanthan-Gum). The difference between two test fluids was obtained.

Understanding multiphase flows with phase change is of fundamental importance for the optimal design and operation of polymer processing. However, the study of multiphase flows with phase change is challenging in practice because polymers have complex physical properties and it is difficult to obtain precise thermal-hydraulic measurements of multiphase flows with phase change due to the high temperatures involved in polymer processing. Computational simulations overcome many of these difficulties and thus provide an essential alternative to study intricate thermal-hydraulic mechanisms not easily observed in a laboratory setting. In this article, I review the current state-of-the-art as well as outstanding challenges in the study of multiphase flows with phase change in polymer processing through the author’s computational studies on the motion of bubbles and drops with phase change.

Recently, plastic problems related to global warming and ocean pollution have become serious social problems. In order to confront the plastic problems, efforts are being made world widely to develop various technologies aimed at realizing recycling-oriented society. The use of naturally derived polymer material such as CA (Cellulose Acetate) is expected to be an effective way to solve the plastic problems. In the present research, a simulation technology for predicting the morphology of CA/PVA (Polyvinyl Alcohol) polymer blend formed in a twin screw extruder is proposed. The effectiveness of the technology was verified by comparing with the experimental data collected under various operating conditions of a twin screw extruder.