Yukiharu Iwamoto

Unsteady Elbow Pipe Flow to Develop a Flow-Induced Vibration Evaluation Methodology for Japan Sodium-Cooled Fast Reactor

This paper describes the current status of flow-induced vibration evaluation methodology development for primary cooling pipes in the Japan sodium-cooled fast reactor (JSFR), with particular emphasis on recent research and development activities that investigate unsteady elbow pipe flow. Experimental efforts have been made using 1/3-scale and 1/10-scale single-elbow test sections for the hot-leg pipe. The 1/10- scale experiment simulating the hot-leg pipe indicated no effect of pipe scale in comparison with the 1/3- scale experiment under inlet-rectified-flow conditions. The next experiment using the 1/3-scale test section was performed to investigate the effect of swirl flow at the inlet. Although the flow separation region was deflected at the downstream from the elbow, the experiment clarified a less significant effect of swirl flow on pressure fluctuation onto the pipe wall. An additional experiment was intended to study the effect of elbow curvature. The experiments with water revealed no clear flow separation in a larger curvature elbow case than that of the JSFR. Since the interference of multiple elbows should be investigated to understand turbulent flow in the cold-leg pipe geometry, 1/15-scale experiments with double elbows were carried out to clarify that flow in the first elbow influenced a flow separation behavior in the second elbow. Simulation activities include Unsteady Reynolds Averaged Navier Stokes equation (URANS) approach with a Reynolds stress model using a commercial computational fluid dynamics (CFD) code and Large Eddy Simulation (LES) approach using an in-house code. A hybrid approach that combined with RANS and LES was also applied using a CFD code. Several numerical results appear in this paper, focusing on its applicability to the hot-leg pipe experiments. These simulations reasonably agreed with the experimental data using the 1/3-scale test section.

Synthesis of Single-Wall Carbon Nanotubes by In-Liquid CVD

High-speed synthesis of the carbon nanotubes in liquid is introduced. The conventional method for synthesizing carbon nanotubes is generally known as gas-phase chemical-vapor deposition (CVD). With that method, carbon nanotubes of high purity can be synthesized, but the synthesis rate is low. Even though the synthesized carbon nanotubes are excellent materials, they cannot be used in large quantities. Accordingly, in this study, single-wall carbon nanotubes (SWCNTs) are synthesized by “in-liquid” CVD. Since the molecular density of a liquid is much higher than that of a gas and the liquid has a cooling effect, performing CVD in a liquid can provide a high-speed growth rate of CNTs on substrate materials. A silicon substrate on which cobalt micro particles are deposited as the catalyst was used. Electrical-resistance heating was used for growing carbon nanotubes in pure ethanol. The synthesized nanotubes were analyzed by scanning electron microscope, transmission electron microscope, and Raman spectroscopy. The results of these analyses indicate that SWCNTs were successfully synthesized over a wide area of the substrate surface. By investigating the synthesized carbon nanotubes under varied experimental conditions (such as pressure and substrate surface roughness), it is shown that surface roughness of the substrate and the bubble behavior are related to the synthesis mechanism of the CNTs.

Basic Characteristics of In-Liquid Plasma Jet and Electrode Damage

The most progress towards a practical method of fusing municipal waste incineration ash has been in the use of a plasma jet that employs arc discharge, a form of thermal plasma. However, a remaining problem is that stable plasma generation is prevented by melting of the nozzle of the plasma-jet torch by the high-temperature plasma flow. With the objective of developing high-speed fusion treatment for waste materials using an in-liquid plasma jet, basic research was conducted on plasma stability and the durability of plasma-jet torches, including electrodes and nozzles. Basic plasma jet characteristics such as the discharge voltage, current, and power value at the time of plasma jet generation were investigated experimentally. The relationship between the temperature distribution near the tip of a plasma jet torch and electrode damage was investigated by fluid-heat coupled analysis using the finite element method.

Deposition of a Diamond-Like-Carbon Film by Ion Plating and Investigation on its Adhesiveness

Diamond-like-carbon (DLC) films are promising as coating materials. Ion plating, an excellent method in terms of adhesiveness, step coverage, and deposition rate, can form not only pure metal films but also oxide films, nitride films, and carbonized films. In this study, which aimed to form a DLC film with good adhesiveness and a diamond crystal structure, a DLC film, with a SiC interlayer formed by ion plating with introduction of tetramethylsilane (TMS), was formed. It was experimentally revealed that as the interlayer thickness increases, the crystal structure in the DLC film becomes more diamond rich, and the adhesiveness of the DLC film and substrate is thereby improved.

Epitaxial Growth of Diamond by In-Liquid Plasma CVD Method

Currently, novel method to synthesize diamond film on material substrate called as in-liquid microwave plasma CVD (IL-MPCVD) has been achieved. It has been studied and improved in addition expected as new method instead of conventional gas phase microwave plasma CVD (MPCVD). The purpose of this study is to synthesize single crystal diamond using IL-MPCVD in high speed deposition. The experimental conditions, methanol was poured in to the reactor. Each of diamond particles (100) and (111) was embedded on the stainless steel substrates (SUS632J2). It was mounted to the substrate holder of in-liquid plasma equipment and installed on the top cover. The distance between the tip of the electrode and the substrate was kept to 1.5mm. A microwave of 2.45GHz was irradiated into the quartz glass tube reactor from the rectangular cavity resonator with 4 mm diameter tungsten electrode and the plasma was generated at its tip. The microwave was adjusted in appropriate power to maintain a certain substrate temperature. Diamond films were evaluated by Raman spectroscopy, Scanning Electron Microscope (SEM) and Laser Microscope (LM). As a result, the best orientation for epitaxial growth was found to be (100) which have film growth gradually and smooth surface. Whereas (111) face has polycrystalline film with irregularity growth and rough surface. The remaining H and C after CO synthesis satisfying H/C>20 is necessary to synthesized diamond using IL-MPCVD. The deposition rate was about 32 μm/h when both single crystal and polycrystalline diamond film were synthesized.