Shinji Ebara

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.

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.

Entrainment behavior of activated dusts in the fusion reactor under LOVA

The safety analysis for of loss-of-vacuum accident (LOVA) as well as ingress-of-coolant event (ICE) is among the last task left in ITER R&D. On the assumption of LOVA after occurring ICE, it is corollary that activated dusts are under the wet condition. Transport behavior of in-vessel activated dusts under wet condition is not known well in comparison with dry case. In this study, the wetted particles transport behavior is investigated experimentally by using a vacuum vessel that serves as a steam generator. The relations among the relative humidity, the entrainment of particles in the exhaust gas flow and the adhesion rate of dust particles on the confined wall have been cleared. The entrainment ratio decreases as the relative humidity increases and increases as the initial pressure difference increases.

Ice Formation and Pressurization Under Low Pressure in Cryostat

Abstract The purpose of the Experimental Vacuum Ingress Test Apparatus (EVITA) program is to obtain useful data for safety analysis of serious potential accidents for ITER. The numerical predictions for EVITA have been done by using the MELCOR, PAX, and CONSEN codes under conditions in which temperature is always kept above 273 K. In the EVITA program, high-temperature and high-pressure steam is injected into the vacuum vessel housing the cryogenic plate. Consequently, the phenomena that occur in the vicinity of the impingement surface are expected to be exceedingly transient and complex. The subject of this study is the development of a valid numerical code for the EVITA program. A key point of this study is to describe all of the phenomena, for example, shock-wave propagation and phase change under low pressure. In this study, the C-CUP method is employed, which describes these phenomena. To investigate phenomena with EVITA, numerical analysis had been done with several conditions concerned with input power. As a result, we succeeded in obtaining a fundamental code for the EVITA program as well as interesting views of EVITA.

Numerical study of heat transfer characteristics in a tube with regularly spaced twisted tape

Abstract An effective heat transfer enhancement scheme is required to compensate for the decrease in heat transfer due to MHD effects in FLiBe based blanket design of fusion reactor. In present study, a twisted tape is selected as a potential candidate for a turbulence promoter, and a thermohydraulic behavior of turbulent flow of an electrically conducting fluid in a non-conducting pipe with twisted tape insertion under a transverse magnetic field is investigated. As a result, significant decrease of heat transfer performance is not observed compared with the same flow without the tape insertion because the heat transfer is dominated by the strong helical flow which is not suppressed by the magnetic field.

Experimental Investigation on Dust Behavior in Fusion Reactor at LOVA

Abstract The safety analysis on LOVA is among the last task left in ITER R&D. On the assumption of LOVA after ICE, it is corollary that activated dusts are under wet condition. The transport behavior of dust under the wet condition is not known well in comparison with dry case even in the conventional engineering systems. Moreover, in the case of LOVA after ICE a shock wave is assumed to generate in the vacuum vessel. The purpose of this experimental study is to investigate the dust behavior under the wet condition including the interaction between shock wave and dust by supposition of LOVA. In this experiment, entrainment ratio and adhesion ratio of dust are measured and discussed. Thereby we understood the behavior of dust in the wet condition and report it.

Structural analysis with thermal effects for vessels of the gas-cooled high-flux test module of IFMIF

Abstract So as to make the most of an available irradiation test volume of the gas-cooled high-flux test module of the International Fusion Materials Irradiation Facility, the vessel of the test module is supposed to have a rectangular shape, into which specimens can be packed spatially efficiently. There is a large pressure difference of several atmospheric pressures between the inside and the outside of the vessel because gaseous helium flows inside the vessel to control the temperature of the specimens and a low-vacuum condition is kept outside the vessel for safety reasons. This pressure difference is assumed to cause readily the deformation of the vessel wall. Even a slight deformation should be taken seriously because the deformation of the vessel noticeably affects the coolant flow, that is, cooling performance. In this study, we performed elastoplastic finite element analysis for two rectangular vessels of the high-flux test module proposed by FZK and Kyushu University. In addition to the material nonlinearity, by taking into account the geometrical nonlinearity and thermal stress, we could obtain detailed results such as relations between the deformations and the pressure differences.

Thermo-Hydraulic Design of High Flux Test Module for IFMIF-EVEDA in Japan

The purpose of the High Flux Test Module (HFTM) in International Fusion Material Irradiation Facility (IFMIF) is to irradiate material specimens to a very high fluence (DEMO relevant ones) in a very few years. In IFMIF-EVEDA which is selected as one of the broader approach activities, the reference solution for the assemblies is a vertical set-up (EU); an alternative horizontal solution, H-HFTM (Japan), which could become very useful for very high temperature tests, is also part of this work. This paper presents the overview of H-HFTM and reports on the recent Japan activities for H-HFTM in the IFMIF-EVEDA framework.

Numerical analysis for thermal and mechanical properties of pebble bed

In solid breeder blanket design of fusion power plants, the ceramic breeder pebble bed plays a very important role. Its mechanical and thermal properties are necessary to design the blanket. In this study, thermomechancal properties of the bed such as effective thermal conductivity and stress-strain relation are investigated by means of numerical simulation. A discrete element manner is adopted in the simulation in order to clarify the influence of the individual particle properties upon the bulk behavior. As a result, the thermo-mechanical properties of pebble bed were well re-created in a computational space by means of the numerical model used in this study.

Numerical Simulation of Turbulent Flow and Heat Transfer in a Cooling Channel of IFMIF High Flux Test Module

Abstract In the high flux test module of the International Fusion Materials Irradiation Facility, temperature control of irradiated specimens are done by gas cooling and electric heating. The width of cooling channels is supposed to be 1 mm in the module vessel which is a rectangular duct with wall thickness of 1 mm. Since there is large pressure difference up to several atmospheric pressure between the inside and outside the vessel, it is considered that the vessel wall and the cooling channels easily deforms. In order to estimate cooling performances for the coolant flowing in the deformed channel, we conduct a finite element analysis of turbulent heat transfer in a mildly curved channel using large-eddy simulation. It is found\from the simulation that heat transfer on the concave wall drastically changes according to local change in flow aspect such as separation while that on the opposite flat wall is affected only by average flow velocity and is not largely changed by the channel deformation.