Showing papers by "Yutaka Asako published in 1998"
TL;DR: In this article, a numerical analysis and water model study of the mold region of a continuous casting apparatus are performed with a novel injection concept using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mold.
Abstract: A numerical analysis and water model study of the mold region of a continuous casting apparatus are performed with a novel injection concept using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mold. As a result, the following results were found: (1) By changing swirl strength, it is easy to control the flow pattern as well as the direction of the flow. (2) Uniform velocity distribution can be obtained within a very short distance from the outlet of the nozzle. (3) Heat and mass transfer near the meniscus can be remarkably activated compared with a conventional straight type immersion nozzle without swirl. (4) Swirl helps the superheat in the melt dissipate. (5) Penetration depth of nozzle outlet flow is decreased remarkably by the application of swirling. Those findings mentioned above are very useful to control the flow pattern in the billet and bloom continuous casters.
57 citations
TL;DR: In this paper, a bubble accumulated zone is created by swirling motion imposed on the flow in a submerged entry nozzle, which forms a bubble curtain through that all the flow pass, and the half vertical angle of the bubble curtain increases with the increasing swirl strength.
Abstract: In the steel-making processes, it is well known that suspended non-metallic inclusions can be removed by Ar gas bubbles injected in the steel baths. This study aims to remove the inclusions through a bubble accumulated zone (namely, bubble curtain) created by swirling motion imposed on the flow in a submerged entry nozzle. The results obtained through water model experiments and numerical calculations (Eulerian/Lagragian, Eulerian/Eulerian method) show as follows; the swirling motion works effectively to form a bubble curtain through that all the flow pass, and the half vertical angle of the bubble curtain increases with the increasing swirl strength. On the other hand, inclusions pass nearly parallel to the axis of the submerged entry nozzle, the trajectories of them being similar to the liquid-phase flow pattern. Therefore, a chance for a bubble and an inclusion to meet with each other would significantly increase.
23 citations
TL;DR: In this article, an enthalpy method is employed to solve the governing equations associated with melting of an unfixed solid phase-change material (PCM) in a low gravitational environment.
Abstract: This article presents a numerical method for simulating the melting process in a cavity in the presence of wall vibration. An enthalpy method is employed to solve the governing equations associated with melting of an unfixed solid phase-change material (PCM) in a low gravitational environment. In this method, the problem is solved in one domain. The PCM, initially at its melting temperature, is placed inside a rectangular enclosure. The enclosure walls are then exposed to a uniform temperature under a specified amplitude and frequency of vibration. Melting begins from all sides, and owing to natural convection, the PCM would not retain its initial shape. The governing equations are discretized by using a control-volume-based finite difference method and are solved together with the solid PCM's equation of motion. The results are presented in the form of a parametric study of the effects of aspect ratio, Stefan number, Strouhal number, and dimensionless frequency or period of vibration, on the melt thickne...
15 citations
TL;DR: In this article, a single horizontal tube has been investigated in a two-dimensional fluidized bed, and key mechanisms relating to buffeting forces on tubes have been identified, as well as pressure profiles arount it, have been measured simultaneously by strain gauges and pressure transducers.
9 citations
TL;DR: In this article, a simple one-dimensional numerical model to predict thermal response of a fire wall which is made of a nonorganic hydrate insulator, is developed for a standard fire resistance test were performed for a sand wall of five percent volume of moisture and two calcium silicate boards which contained free water, adsorbed water, and crystalline water.
Abstract: A fire wall is made of a mortar wall in which water storage materials are mixed. However, the mortar fire wall is relatively heavy. A nonorganic insulator for middle and high-temperature ranges such as a calcium silicate board is expected as a good material for the fire wall because of a light weight. Usually, a nonorganic insulator such as the calcium silicate board consists of a hydrate which contains free water, physically adsorbed water, and crystalline water. Behavior of such waters should be considered for a numerical model which is used to predict thermal responses of a fire wall. A simple one-dimensional numerical model to predict thermal response of a fire wall which is made of a nonorganic hydrate insulator, is developed. The numerical computations to simulate the thermal responses for a standard fire resistance test were performed for a sand wall of five percent volume of moisture and two calcium silicate boards which contains free water, adsorbed water, and crystalline water. The experiments for the sand wall and the calcium silicate boards were also performed. The numerical results were compared with experiments. The proposed model well predicts the thermal responses of the walls.
7 citations
TL;DR: In this article, a novel/method to prevent the suction of air from all around the contact-part between the SG and SEN during controlling the flow rate of molten steel, has been developed by giving a step to the SEN.
Abstract: With increasing requirement of steel quality in continuous casting, it is extremely important to regulate reasonably flow rate of molten steel without either biased flow or reoxidation by the suction of air from around the contact-part between sliding gate (SG) and immersion nozzle (SEN). In this study, a novel/method to prevent the suction of air from all around the contact-part between the SG and SEN during controlling the flow rate of molten steel, has been developed by giving a step to the SEN. The effects of the step in the SEN on the prevention of air suction from all around the contact-part can be summarized as follows: (1) The flow squeezed passing through the SG is turned abruptly just before the step in the SEN and, as a reverse flow, passes towards the contact-part between the SG and SEN, where its kinetic energy is converted into the pressure energy as a kind of impinging-flow-action, resulting in a positive pressure on the contact-part. (2) With increasing amount of sliding-gate-opening, the distance downstream from the gate to the step, that is necessary for the contact-pressure to be positive on the contact-part, becomes wider. Over some opening amount, the contact pressure is always positive under the condition that a dimensionless step width (ratio of step-width to inner-diameter of nozzle) is over 0.15. From the above-mentioned issues, it is found possible to prevent the air suction from all around the contact-part between the SG and SEN using the SEN with the step beneath the sliding gate.
7 citations
TL;DR: In this article, the thermal responses of a fire wall that consists of a porous material, its pores partially filled with water, are investigated numerically, and a simple one-dimensional numerical model developed in the authors' previous study is simplified to reduce the computational parameters.
Abstract: A fire wall usually contains moisture. When the wall is exposed to flame, water in the wall evaporates into vapor. The latent heat of water plays an important role in the resistance to heat propagation. A wall of high water content is therefore expected to have good fire-resistant characteristics. In this study the thermal responses of a fire wall that consists of a porous material, its pores partially filled with water, are investigated numerically. A simple one-dimensional numerical model developed in the authors’ previous study is simplified to reduce the computational parameters. The parameteric study is conducted to investigate the effects of thermal diffusivity, moisture, and density ratio on wall thicknesses of 1, 2, and 3 hours of fire resistance. The correlation between the wall thickness and fire resistance time is obtained.
5 citations
TL;DR: In this paper, the authors identified the key mechanisms relating to buffeting forces on tubes in fluidized beds by analyzing results from simultaneous measurement of force and pressure on a horizontal tube.
Abstract: Key mechanisms relating to buffeting forces on tubes in fluidized beds have been identified by analyzing results from simultaneous measurement of force and pressure on a horizontal tube. Careful experiments have been carried out in a two-dimensional fluidized bed with an accurate sensor tube for single bubble passage, bubble chains and free-bubbling. It is shown that the buffeting force in fluidized beds consists of the net pressure force, i.e., form drag and lift, and additional forces induced by particles become so large for high-velocity free-bubbling beds that it is impossible to estimate the total force only from the net pressure force, while for low velocity beds the total force is mostly accounted for by the net pressure force. The wake particles play an important role for large bubbles, and therefore the details of this component have also been investigated for single bubbles as well as for bubbles undergoing splitting and coalescence.
1 citations