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Diamond crystals are successfully synthesized by irradiating DC arc plasma jet to the substrate set in a methanol solution. It is the important procedure to preheat the substrate by inert Ar plasma jet before introducing the methanol solution gas to the plasma jet gun. The effects of two experimental conditions, the incident power and the substrates, are investigated. In the case of the Si substrate, cubic crystalline diamond grains of same size are synthesized at the plasma power of 470W. High speed hetero epitaxy is expected by using this method. In the case of the tungsten carbide substrate, diamond crystals and carbon nanotubes are simultaneously synthesized at the plasma power of 260W. The catalytic effect of Co binder in the substrate may cause the chemical reaction of the nanotube synthesis.

This study was performed to improve the adhesiveness of a diamond-like carbon (DLC, a-C:H) layer film with an a-SiC interlayer. In previous studies, an a-SiC/DLC layer film was formed and changes in the DLC film structure and hardness caused by the thickness of the a-SiC layer were examined. After the a-SiC interlayer thickness increased and the G-peak position shifted to a lower frequency, the peak began shifting to higher frequencies. The G-peak position reached a minimum frequency at a film thickness of approximately 0.3 μm. In contrast, as the thickness of the a-SiC interlayer increased, the FWHM of the G-peak position increased almost monotonically and the number of sp3 bonds also increased. As the interlayer thickness increased, the hydrogen content in the DLC film increased, and then began decreasing, with the interlayer film thickness exhibiting a local maximum at approximately 0.3 μm. As for the DLC film hardness, a correlation between the hydrogen content and half width of the G-peak position was observed. When the hydrogen content was ≤40 at%, a positive correlation with the FWHM (G) was observed, and when the hydrogen content was 40 at% or above, a negative correlation with FWHM (G) was found. The adhesiveness of the DLC film and substrate was improved by forming an a-SiC thin film as an interlayer. The effects of the a-SiC thin film on DLC film quality were determined.

A relationship between diamond synthesis and hydrogen production in in-liquid plasma method have been investigated. Approximately 60 % energy can be recovered by collecting hydrogen gas made by ingredient solution decomposition. The relationship is trade-off. When higher energy is used to maintain the substrate temperature, the hydrogen production rate gets faster, but the diamond synthesis rate gets slower. To increase diamond synthesis rate, a method should be established which maintains the substrate temperature by lower energy and generates less hydrogen gas.

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.

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.

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.

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.

The purpose of this study is to synthesize diamond onto Si, Cu, and Fe (SUS632J2) substrates and to analyze the effect of carbon diffusion on their surfaces. Diamond was synthesized using the in-liquid microwave plasma chemical vapor deposition (IL-MPCVD) as a novel method for synthesizing diamond on various base materials. The IL-MPCVD method is superior one due to its efficiency in terms of cost, space and speed as compared to a conventional gas phase microwave plasma CVD (MPCVD). Microwaves of 2.45 GHz generated plasma in a solution which was comprised of methanol: ethanol (M:E = 97:3). Evaluation of deposited diamond films was done by a Scanning Electron Microscope (SEM) and Raman spectroscopy. Results shows that the IL-MPCVD method can form diamond films on Cu, Si and Fe substrates. The minimum time of film formation of Cu, Si and Fe are 2.5, 3.5 and 5 min, respectively. The material that forms carbide layers such as Si is a better substrate to form diamond film by the IL-MPCVD than other metal substrates such as Cu and Fe. Synthesizing diamond directly on the Fe substrate results in poor quality layers. The effect of carbon diffusion influences diamond film nucleation and diamond growth. In order to alleviate the carbon diffusion and improve the quality of the diamond film on the Fe substrate, Si has been sputtered on the Fe substrate as an interlayer. It is found that the diamond film can be formed on a Fe substrate using a Si interlayer and that heat treatment and thickening the interlayer improve its quality.

Wall pressure measurements and flow visualization were conducted for a 90 degree elbow with an axis curvature radius the same as its inner diameter (125 mm, Rc/D = 1). Reynolds numbers 320,000 and 500,000, based on the inner diameter and bulk velocity, were examined. A deflected inflow, having an almost constant velocity slope, was introduced in the present study. The velocity at the inside was 20% faster than the bulk velocity in the plane one diameter upstream of the elbow inlet.Ensemble averaged pressure distributions showed that no difference of normalized pressure could be found in cases of Reynolds numbers of 320,000 and 500,000. Comparisons with a uniform inlet flow case [1] proved that a low-pressure region at the intrados of the elbow was weakened and that a high-pressure region outside strengthened in the deflected inflow case. The present case had a characteristic pressure distribution that the pressure downstream of the elbow increased at the inside until two diameters downstream from the elbow exit. Flow visualization concluded that the corresponding pressure increase was caused by a collision of a strengthened secondary flow convected from the extrados.The unsteady pressure distribution in the present case showed that a circumferential extent of a strongly fluctuating region in the inside and downstream of the elbow decreased, comparing with the uniform inlet flow case.[1] Power spectral density functions of pressures exhibited that the fluctuation having the Strouhal number (based on the inner diameter and bulk velocity) of 0.6 existed in the downstream region of the elbow, which is 0.1 larger than that of the uniform inflow case.Copyright © 2015 by JSME

Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Y. Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in support of the recently suggested concept of impact ignition in ICF [H. Azechi et al., Phys. Rev. Lett. 102, 235002 (2009); M. Murakami et al., Nucl. Fusion 54, 054007 (2014)]. Some experimental evidence indicates that stagnation via an expanding shock wave is stable, but its stability has never been studied theoretically. We present such analysis for the stagnation that does not involve a rarefaction wave behind the expanding shock front and is described by the classic ideal-gas Noh solution in spherical and cylindrical geometry. In either case the stagnated flow has been demonstrated to be stable, initial perturbations exhibiting a power-law, oscillatory or monotonic, decay with time for all the eigenmodes. This conclusion has been supported by our simulations done both on a Cartesian grid and on a curvilinear grid in spherical coordinates. Dispersion equation determining the eigenvalues of the problem and explicit formulas for the eigenfunction profiles corresponding to these eigenvalues are presented, making it possible to use the theory for hydro code verification in two and three dimensions., 49 pages, 10 figures, 1 table

Laser Doppler Velocimetry (LDV) measurements in a 90 degree elbow of which the curvature radius coincides with its inner diameter were examined for the cases of inflow from a long pipe, short pipe and swirl generator. Ensemble averaged flow distribution at the Reynolds number of 320000 based on the inner pipe diameter and bulk velocity shows that shortening the upstream pipe length to 4.9D from 10D induces the flow separation downstream of the elbow. Detailed observation suggests that shortening upstream pipe weakens the Prandtl's secondary flow of the first kind. Our swirl generator induced a swirling inflow with the non-dimensional angular momentum of 0.12 based on the inner pipe diameter and bulk velocity. The circumferential velocity distribution formed a shape like a Rankine combined vortex at the elbow inlet, and the accelerated axial velocity was observed at the vortex center. The axial velocity distribution however was found to be almost the same as that of the non-swirl inflow case in the latter half of the elbow. Frequency analyses showed that the Strouhal number by vortex shedding from the boundary layer occurring at the inner side of the elbow become 0.5, except for 0.6 in the case of the long pipe. The change of the Strouhal number is probably related with the boundary layer width and the local flow velocity.

LDV measurements in a 90 degree elbow, of which curvature radius coincides with the diameter have been conducted for cases of developed inflow, undeveloped inflow, swirling inflow, and deflected inflow that became faster at the inside. This paper especially focuses on a result of the deflected inflow, comparing with a result of the undeveloped inflow. The result shows that the deflected inflow reinforces a convex velocity distribution occurring near the curvature inside in the downstream region, concluding that the deflected inflow promotes the secondary flow of Prandtl's first kind in the elbow. Frequency analyses of axial flow fluctuations show that the dominant frequency can be seen in the downstream of the elbow even in the deflected inflow case. However its Strouhal number increases to 0.6 from 0.5, that is for the short pipe case. Results of frequency analyses are also shown for other cases that we have been examined. Dominant Strouhal numbers in most of the cases become 0.5, except for 0.6 in cases of the developed and deflected inflow. This frequency shift might be related with the boundary layer size and the local flow velocity, since the corresponding fluctuation is caused by vortex shedding from the boundary layer at the elbow inside.

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 ...

This paper is intended to validate the numerical simulation tool, which is Unsteady Reynolds Averaged Navier-Stokes equation (U-RANS) approach with the Reynolds Stress Model using a commercial computational fluid dynamics code, by applying to the flow through a single short-elbow in the 1/10 and 1/3 scale water experiments simulating the Japan Sodium-Cooled Fast Reactor (JSFR) hot-leg piping. An additional objective of this paper is to investigate the effect of outlet condition at which the coolant overflows a partition wall in the upper part of an intermediate heat exchanger in the JSFR design. The numerical results were in good agreement with the 1/10 and 1/3 scale experimental data indicating time-averaged velocity distributions, flow field visualization, and power spectral densities of pressure fluctuation. These comparisons can conclude that the U-RANS numerical simulation tool was validated with its applicability to a single short elbow flow. The numerical simulation has also shown that the unsteady flow fields in the short elbow flow, which was characterized by a cyclic secondary flow and the subsequent horseshoe vortex. In this study, the effect of the outlet condition was also examined through the numerical simulation. At the outlet of the pipe, the simulation modeled the partition wall in the upper part of the intermediate heat exchanger, which has never been simulated in the experiments. The numerical simulation results were compared between with and without the intermediate heat exchanger at the pipe outlet in terms of the time-averaged velocity distribution, pressure fluctuation power spectral density, and so on. In the result, no significant difference between them was observed, so that it can be said that the effect of the outlet condition is negligibly small.

Wall pressure measurements and flow visualization were conducted for a 90 degree elbow with an axis curvature radius the same as its inner diameter (125 mm, Rc/D = 1). Reynolds numbers 320,000 and 500,000, based on the inner diameter and bulk velocity, were examined. A deflected inflow, having an almost constant velocity slope, was introduced in the present study. The velocity at the inside was 20% faster than the bulk velocity in the plane one diameter upstream of the elbow inlet. Ensemble averaged pressure distributions showed that no difference of normalized pressure could be found in cases of Reynolds numbers of 320,000 and 500,000. Comparisons with a uniform inlet flow case [1] proved that a low-pressure region at the intrados of the elbow was weakened and that a high-pressure region outside strengthened in the deflected inflow case. The present case had a characteristic pressure distribution that the pressure downstream of the elbow increased at the inside until two diameters downstream from the elbow exit. Flow visualization concluded that the corresponding pressure increase was caused by a collision of a strengthened secondary flow convected from the extrados. The unsteady pressure distribution in the present case showed that a circumferential extent of a strongly fluctuating region in the inside and downstream of the elbow decreased, comparing with the uniform inlet flow case.[1] Power spectral density functions of pressures exhibited that the fluctuation having the Strouhal number (based on the inner diameter and bulk velocity) of 0.6 existed in the downstream region of the elbow, which is 0.1 larger than that of the uniform inflow case.

Recently in nuclear plants, it has occurred thermal fatigue failure accidents because of thermal fluctuations that called Thermal Striping in T-junction where mixed a higher temperature sodium and a colder temperature sodium into each other. Then, we set up turbulence promoter in T-junction piping system, effects of turbulence promoter on flow characteristics have been investigated experimentally using flow visualization techniques (the dye injection method) and velocity measurement by LDV. As a result, it is clarified that secondary streams in pipe sections becomes stronger and diffusion of momentum is promoted in case with turbulent promoter.

In recent years, the rotational speed of gas turbines is increasing more and more to increase the pressure ratio per one stage and hence to reduce the total number of stages. Accordingly, it is becoming more common that the relative inflow is supersonic near the tip of the fan and the first stage compressor cascades. At higher speeds, it is well-known that stable operating range becomes extremely narrow due to surge and choke. In this circumstances, it is important to understand the characteristics of the supersonic compressor in the off-design region as well as at the design point.

A novel compression scheme is proposed, in which hollow targets with specifically curved structures initially filled with uniform matter, are driven by converging shock waves. The self-similar dynamics is analyzed for converging and diverging shock waves. The shock-compressed densities and pressures are much higher than those achieved using spherical shocks due to the geometric accumulation. Dynamic behavior is demonstrated using two-dimensional hydrodynamic simulations. The linear stability analysis for the spherical geometry reveals a new dispersion relation with cut-off mode numbers as a function of the specific heat ratio, above which eigenmode perturbations are smeared out in the converging phase.

Based on Guderley's self-similar solution, stability of spherical converging shock wave is studied. A rigorous linear perturbation theory is developed, in which the growth rate of perturbation is given as a function of the spherical harmonic number l and the specific heats ratio γ. Numerical calculation reveals the existence of a γ-dependent cut-off mode number lc, such that all the eigenmode perturbations for l > lc are smeared out as the shock wave converges at the center. The analysis is applied to partially spherical geometries to give significant implication for different ignition schemes of inertial confinement fusion. Two-dimensional hydrodynamic simulations are performed to verify the theory.