Takehiko Yokomine

Unsteady three-dimensional simulation of interactions between flow and two particles

Abstract Unsteady three-dimensional simulation of interactions between uniform flow and fixed identical two particles is performed for particle Reynolds number 30, 100, 200 and 250. The drag force of interactive particles depends on Reynolds number as well as the inter-particle distance. They are attenuated when particles are aligned streamwise, augmented when they are held side by side against the mean flow. These are compared with available experimental data. Existence of periodical double-sided vortex shedding at relatively low Reynolds number is observed when particles are almost touching. The method adopted in this paper is not only simple and easy, but also accurate with a proper resolution.

The accomplishment of the Engineering Design Activities of IFMIF/EVEDA: The European-Japanese project towards a Li(d,xn) fusion relevant neutron source

The International Fusion Materials Irradiation Facility (IFMIF), presently in its Engineering Validation and Engineering Design Activities (EVEDA) phase under the frame of the Broader Approach Agreement between Europe and Japan, accomplished in summer 2013, on schedule, its EDA phase with the release of the engineering design report of the IFMIF plant, which is here described. Many improvements of the design from former phases are implemented, particularly a reduction of beam losses and operational costs thanks to the superconducting accelerator concept, the re-location of the quench tank outside the test cell (TC) with a reduction of tritium inventory and a simplification on its replacement in case of failure, the separation of the irradiation modules from the shielding block gaining irradiation flexibility and enhancement of the remote handling equipment reliability and cost reduction, and the water cooling of the liner and biological shielding of the TC, enhancing the efficiency and economy of the related sub-systems. In addition, the maintenance strategy has been modified to allow a shorter yearly stop of the irradiation operations and a more careful management of the irradiated samples. The design of the IFMIF plant is intimately linked with the EVA phase carried out since the entry into force of IFMIF/EVEDA in June 2007. These last activities and their on-going accomplishment have been thoroughly described elsewhere (Knaster J et al [19]), which, combined with the present paper, allows a clear understanding of the maturity of the European–Japanese international efforts. This released IFMIF Intermediate Engineering Design Report (IIEDR), which could be complemented if required concurrently with the outcome of the on-going EVA, will allow decision making on its construction and/or serve as the basis for the definition of the next step, aligned with the evolving needs of our fusion community.

Numerical prediction of erosion for suspension flow duct

An attempt was made to predict numerically the erosion rate of wall surfaces of a gas-solid suspension flow duct in order to establish a prediction method with wide applicability. First, the erosion rate due to a single particle collision was quantified using equations by Finnie and Bitter. The empirical constants for these equations were determined experimentally. Then, the expressions obtained were incorporated into a mathematical model based on the Eulerian description for the continuous phase as well as on the Lagrangian description for the particulate phase. In order to demonstrate the prediction accuracy, an attempt was made to reproduce the actual erosion rate observed on the surfaces of a square cross-sectioned L-type suspension flow duct. Fairy good agreement was obtained between the prediction and the measurement.

Experimental investigation of turbulent heat transfer of high Prandtl number fluid flow under strong magnetic field

Abstract An investigation of MHD effects on Flibe simulant fluid (aqueous potassium hydroxide solution) flows has been conducted under the U.S.-Japan JUPITER-II collaboration program using “FLIHY” pipe flow facility at UCLA. Mean and fluctuating temperature profiles in a conducting wall pipe were measured for low Reynolds number turbulent flows using a thermocouples probe at constant heat flux condition. It is suggested that the temperature profiles are characterized by interaction between turbulence production, turbulence suppression due to magnetic field and thermal stratification occurred even under the situation where quite small temperature difference exists in the pipe cross-section.

Numerical analysis of ultrafast heat transfer with phase change in a material irradiated by an ultrashort pulsed laser

This study is concerned with problems of ultrafast and high heat flux heat transfer with phase change. We employ the cubic interpolated propagation (CIP) method coupled with a thermoconvective model to examine the history of large-scale phase change, that is, melting and evaporation, and the mechanisms of heat transfer as a wave. It is found that wave-type heat transfer as a shock wave with phase change can be simulated without a hyperbolic heat conduction equation by means of the CIP method. Melting and evaporation occur in the energy deposition region, and energy is transferred by a shock wave beyond an energy penetration depth. The propagation velocity is hardly damped outside the energy deposition region inside aluminum thin foil, but the peak value in density, pressure, and temperature is damped rapidly. For one of the dissipation process mechanisms, generation of thermal stress can be considered. Further, it is found that the initial velocity of shock wave generated inside the energy deposition region is different for each initial incident laser intensities, though the propagation velocity is constant beyond the energy penetration depth in spite of an initial incident laser intensity.

First Operation of the Flinak/LiPb Twin Loop Orosh2i-2 with a 3T SC Magnet for R&D of Liquid Blanket for Fusion Reactor

A Flinak/LiPb twin-loop Orosh2i-2 was constructed in the Fusion Engineering Research Project of NIFS to establish an engineering basis for the “real function” of a liquid blanket for fusion energy reactors. It was constructed with a 3 T superconducting magnet, which is the strongest in the world for these purposes. In this study, 120 litter Flinak and LiPb were successfully prepared in-situ in a purified glove-box. Designed flow velocity up to 1.5 m/sec was achieved for both. The magnetic field and velocity dependence on pressure drop agreed well with theoretical predictions. Tentative plans for phased experiments within the next few years have been presented, including operation of Supercritical-CO2 Turbine (SCOT) power generation system in the Flinak loop.

Heat transfer of multiple impinging jets with gas-solid suspensions

Abstract The heat transfer mechanism of multiple impinging jets with gas–solid suspensions has been investigated experimentally and numerically. By heat transfer experiments, the effects of nozzle Reynolds number, solid loading ratio, distance from jet exit to impingement surface, spacing between jets and solid particle characteristics on the heat transfer coefficient were cleared. In the case of using graphite particles, the heat transfer coefficient enhancement as against single phase flow are found all over the heat transfer surface. While, in the case of using glass beads particles, the heat transfer coefficient is decreased compared with single phase flow. Numerical simulation were also performed by using Yokomine et al.s model in which both turbulence augmentation and suppression due to particles can be taken into account. In the case of graphite particle, particles flow near the heat transfer surface with making belt-shaped dense region after impingement and its heat capacity and function of turbulence augmentation are used effectively. When the glass beads are used, particles are scattered after impingement and turbulent kinetic energy near the heat transfer surface is decreased.

ACOUSTIC PROPERTIES OF Pb-17Li ALLOY FOR ULTRASONIC DOPPLER VELOCIMETRY

Abstract In a lead-lithium (Pb-17Li) liquid metal blanket concept, Pb-17Li eutectic alloy circulates both as breeder and coolant under a strong plasma-confining magnetic field, experiencing magneto-hydro-dynamic (MHD) force: Lorentz force. An important aspect of the bilateral US/Japan collaboration on Tritium, Irradiations, and Thermofluid for America and Nippon (TITAN) is to investigate tritium behavior and thermal control in the Pb-17Li eutectic alloy, flow and heat transfer characterizations, and mitigation of MHD effects. The present paper focuses on Ultrasonic Doppler Velocimetry (UDV) as an effective diagnostic to measure the Pb-17Li flow in the presence of the strong magnetic field. This paper firstly describes a favorable wetting material for high-temperature transducer. Next, the acoustic property database of Pb-17Li eutectic alloy is presented. Finally, material analyses after high temperature measurements are performed to discuss the durability of titanium transducer.

Feasibly study of gas-cooled test cell for material testing in IFMIF

Temperature control performance of test pieces enclosed in IFMIF capsule by using single phase gas was estimated experimentally. The key issue of this study is to obtain the definite value of dimension of test facility and flow conditions of coolant and to clarify the temperature response of test piece to the beam-off scenario. Firstly, we have examined the cooling performance of the test cell originally proposed in IFMIF-KEP and from results of this calculation performed in three dimensional system by using brand-new turbulence model for flow and thermal fields, it is concluded that the drastical change of design of test cell is needed in order to obtain the unformity of temperatrure of test piece, to improve the responsibility of temperature measurement of test piece, and to relieve the coolant flow condition, especially for inlet pressure value. Thus, we have proposed new design of test cell and test piece arragement. A mock-up experimental facility was made based on our design and preliminary experiments for temperature control were performed. As a result, we have verified the cooling performance at the case that corresponds to two beam-off senario by using mock-up faciilty.

Development of piv technique under magnetic fields and measurement of turbulent pipe flow of flibe simulant fluid

Abstract An investigation of MHD effects on a Flibe (Li2BeF4) simulant fluid has been conducted under the US-Japan JUPITER-II collaboration program using “FLIHY” pipe flow facility at UCLA. The present paper reports a development of unique experimental techniques using aqueous solution of potassium hydroxide as a Flibe simulant. In order to apply a particle image velocimetry (PIV) technique for magnetic field condition, special optical devices were developed. The PIV measurements of MHD turbulent pipe flow at Re = 5300 were performed, and modification of the mean flow velocity as well as turbulence suppression was observed. A flat velocity profile in the pipe center and a steep velocity gradient in the near-wall region at Ha = 20 exhibits typical characteristics of Hartmann flow.