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°.
Solute control in boundary layer under a high temperature environment is important from the industrial viewpoint, because mass transfer in boundary layer is often rate-determining step of chemical reactions and chemical composition of solidified alloy is determined by solute concentration in the vicinity of solid-liquid interface. An alternating electromagnetic force is one of candidates to control the mass transfer in the boundary layer of molten metals and alloys since it can directly excite a flow in it. The alternating electromagnetic force also has a potential to enhance the removal of inclusions in molten metal because increase in their collision efficiency is expected. This paper reviews the recent investigations on possibility of the alternating electromagnetic force as a tool of solute concentration control and inclusion removal. A model experiment using an electrolyte aqueous solution and electrodes having a shape with triangles aligning in line was carried out to clarify the effect of the alternating electromagnetic force on solute concentration distribution in the vicinity of the boundary between the electrode and the electrolyte aqueous solution. The alternating electromagnetic force imposition changed the solute concentration distribution because of the flow excitation. Then, it was applied to solidification of an alloy. Local eutectic area ratio of a Sn-10mass% alloy was dependent on the imposing period of the alternating electromagnetic force during its solidification. This suggests that the alternating electromagnetic force might control the solute distribution. Theoretical investigation on collision frequency among the inclusions using the alternating electromagnetic force suggests that this method is suitable for small inclusions collision and the collision frequency increases as frequency of the alternating electromagnetic force becomes low.
The removal technology of single-wafer processing using ozone is proposed on photoresist removal in the semiconductor manufacturing. Ozone is friendly for the environment and no harm to the product. Before now, the authors indicated that disk-shaped nozzle forms a vortex structure between the disks which is considered to cause the reduction of photoresist removal rate. This study proposes a disk-shaped convex nozzle to suppress the vortex. In order to investigate the effects of the presence or absence of the convex, the removal experiments were conducted. As a result, disk-shaped convex nozzle had the higher removal ability than disk-shaped nozzle in the convex part. Next, as a new removal method, we suggest the ozone microbubble with a Venturi tube. To investigate the performance of the photoresist removal with it, first, the generation of ozone microbubbles is observed in the Venturi tube via a high speed video camera. Next, to clarify the effect of the superficial liquid and gas velocities, the ozone microbubble, and presence or absence of convex, ozone water concentration measurement and photoresist removal experiments were conducted. As a result, the ozone water concentration increased with increasing superficial velocity and the remaining photoresist thickness reduced. Also, ozone microbubble had the higher removal ability than ozone water single-phase. Compared presence and absence of convex, convex influenced photoresist removal efficiently. In addition, compared with the existing study, it is suggested that the superficial liquid and gas velocities and ozone water concentration affect the photoresist removal rate.
An experimental investigation was performed for the pulp-suspension flow in a channel with a partition plate, which is an extremely simplified model of the dispersion part of the hydraulic headbox of papermaking machines. This study was tried to make the papermaking system most suitable and was conducted to obtain the fundamental findings. To do it, flow visualization and optical measurements of the fiber concentration were made in the wake region of a flat plate. Characteristics of the pulp-suspension flow were examined for five flow cases based on the flow patterns found in the authors' previous report (2010) for a channel. The behavior of the pulp fibers and flow in the wake is strongly related to the flow states in the passages of the partition plate and also depends on the shear layer generated at the trailing edge of the plate. The partition plate is slightly effective for obtaining a uniform time-averaged fiber concentration distribution and for making the fluctuating fiber concentration lower.