About
149
Publications
4,713
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,014
Citations
Introduction
Skills and Expertise
Publications
Publications (149)
In recent years, there has been a need for cooling technology that can deal with the increasing heat generation by the miniaturized high output electronic devices. A finned heat sink with boiling cooling is considered to be a promising method that can cool those electronic devices efficiently. However, as the heat transfer increases, the void fract...
Long-term boiling experiments with long-life coolant have been made with the aim to apply a boiling cooling technology to the next generation high exothermic electronic devices. The long-life coolant commonly used for cooling electronic devices is a mixture of ethylene glycol and water with multiple antirust inhibitors as additives, which may resul...
Gas entrainment phenomena caused by a free surface vortex is a very important topic in design studies on various fluid machineries. For example, in sodium-cooled fast reactors, a free surface vortex of the sodium coolant can be generated in the reactor vessel due to the complex velocity profile/fluctuations in the coolant. With the increase in the...
Rapid cooling of reactants quenches the intermediate state of chemical reactions and enables the synthesis of novel materials that cannot be realized by thermodynamic equilibrium processes. In this study, we estimated the cooling rate of reactant solutions during the supercritical hydrothermal synthesis of metal oxide nanoparticles. Neutron radiogr...
A capacitance void fraction sensor (CVS) is applied to measure the volumetric averaged void fraction in a packed bed of spheres. The void fraction in the packed bed is one of the most important parameters to evaluate cooling characteristics in a porous debris bed during a severe accident of nuclear reactors, and the quantitative void fraction measu...
In the safety study on a sodium-cooled fast reactor, it is assumed that the high-temperature fuel debris are formed because of a core disruptive accident. During the cooling of the fuel debris, gas-liquid two-phase flow can be generated in the debris due to the coolant boiling. To improve the prediction accuracy of the flow characteristics, detaile...
Gas-liquid two-phase flow is a very complicated flow phenomenon that involves the interaction between gas and liquid phases. Recently, an accurate simulation technique of two-phase flow has been developed. However, the validation of the simulated results is insufficient due to less experimental data. It is especially difficult to measure interfacia...
This study proposes a mechanistic model-based correlation for the critical heat flux to meet the practical requirements for the design and safety analysis of light water reactors. The correlation is based on an annular film dryout mechanistic model for a single tube, which needs numerical integration from the onset of annular flow to the dryout poi...
The mixer shape in flow-type reactors plays a vital role when the reaction rate is much faster than the mixing rate. In this study, we performed neutron radiography measurements on...
In downward flow, complex two-phase flow is caused by buoyancy of bubbles. It affects not only a void fraction profile but also a point of net vapor generation (PNVG). In order to understand the fundamental characteristics of the void fraction on subcooled boiling in downward flow, the void fraction was measured by using neutron radiography. The te...
Two-phase pressure drop in the debris has been studied by many researchers concerning the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional...
To develop a lead-bismuth eutectic (LBE) cooled nuclear reactor, phase transition phenomena of the lead-bismuth are very important. In the solidification of LBE, the crystalline structure is varied with the cooling process. The volumetric expansion of LBE must be clarified for the safety of an LBE cooled nuclear reactor. The time dependence of the...
In this study, a mechanistic model-based correlation for the critical heat flux is proposed to meet the practical requirements for the design and safety analysis of pressurized water reactors. The correlation is based on a liquid sublayer dryout model for a single tube, which includes physical parameters, such as sublayer thickness and vapor blanke...
On the gas-liquid interface of a sodium-cooled fast reactor, gas (bubble) entrainment can be caused by free surface vortices, which may result in, e.g. disturbance in core power. Therefore, it is important to develop an evaluation model to predict accurately the entrained gas flow rate for the prevention of such undesirable phenomena. In the previo...
In recent years, there has been a need for cooling technology that can deal with the increase of heat generation by the miniaturization and high output of electronic devices. Fin-type heat sink with boiling cooling can be a new method that can cool the electronic devices efficiently. But, at the same time, its pressure drop will also increase. The...
Two-phase pressure drop in the debris has been studied by many researchers in relation to the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventio...
In neutron transmission spectroscopic imaging, the transmission spectrum of each pixel on a two-dimensional detector is analyzed and the real-space distribution of microscopic information in an object is visualized with a wide field of view by mapping the obtained parameters. In the analysis of the transmission spectrum, since the spectrum can be c...
Boiling heat transfer technology is considered as a promising way to remove the large amount of heat from electronic devices whose heat generation experiences a rapid increase recently. However, by employing the boiling heat transfer, there can be one concern that the pump efficiency may be reduced due to the vapor bubbles flowing into the coolant...
In This paper, the heat transfer characteristics were evaluated using a microchannel heat exchanger that is actually in use. The microchannel heat exchanger consists of aluminum fins combined with flat perforated tubes with multiple channels made of aluminum. Although the specific heat transfer area of this heat exchanger is larger than that of the...
Water management in a polymer electrolyte fuel cell (PEFC) is a key topic for the PEFC operation. It is well known that the water accumulation in the gas diffusion layer (GDL) increases the polarization resistance, whereas the increases of the water content, λ, in the proton exchange membrane (PEM) decreases the proton conductivity. In this study,...
For visualization of flows in superfluid ⁴He, an excited helium molecule (excimer) ⁴He2* is an ideally suitable flow tracer, because it has a molecular size with a minimum influence to flow, and follows only normal-component flow around 1K but only vortices below 0.5 K. However, to visualize flow fields in 3D, small clouds (clusters) of ⁴He2* are r...
Hydrogen in materials degrades mechanical properties, which is widely recognized as hydrogen embrittlement. To understand hydrogen embrittlement, it is necessary to clarify the accumulation behavior of hydrogen under stress. The neutron radiography and neutron tomography techniques are applied to examine whether hydrogen accumulation behavior can b...
Supercritical water upgrading of heavy oil has attracted considerable attention, as the upgrading process can reduce the sulfur content and decrease the average molecular weight of the oil. Understanding the flow and mixing behavior of heavy oil in supercritical water is important to improve the process efficiency. We performed neutron radiography...
In the design study on sodium-cooled fast reactors, .it is important to investigate the gas entrainment (GE) phenomena in detail. In fact, a lot of analytical, experimental and numerical studies have been conducted to clarify the onset condition of GE and some GE onset models have been proposed. However, few studies on the modeling of entrained gas...
For the purpose of future visualization of the flow field in superfluid helium-4, clusters of the triplet state excimer ⁴He2* are generated along the micro-scale recoil tracks of the neutron-absorption reaction n + ³He → ³T + p. This reaction is induced by neutron irradiation of the ³He fraction contained in natural isotopic abundance liquid helium...
To evaluate the water-accumulation phenomena and electrochemical characteristics in an operating polymer electrolyte fuel cell (PEFC), simultaneous measurements of water distribution in the through-plane direction and the electrical impedance were carried out by using a neutron radiography and electro-chemical impedance spectroscopy. The water dist...
The lead-bismuth eutectic (LBE) is considered as a promising candidate as the coolant of the accelerator-driven system (ADS). Therefore, numerous studies have been conducted, e.g. on the corrosivity of the material exposed to the LBE flow. However, there are only a few studies on the LBE-steam two-phase flow which can be formed when the pipe raptur...
Dies ist ein Kapitel der 12. Auflage des VDI-Wärmeatlas.
Dies ist ein Kapitel der 12. Auflage des VDI-Wärmeatlas.
Solidification process of lead–bismuth eutectic (LBE) is one of the key phenomena to prevent flow channel blockage accident in an LBE-cooled accelerator-driven system. However, the solidification of liquid metal cannot be observed optically and it is difficult to detect noninvasively. In this study, the one-dimensional solidification process of the...
For flow visualization study of quantum turbulence in superfluid \(^4\)He, He\(_2^*\) excimers are unique tracers which follow only normal-fluid component flow above 1 K. To generate detectable small He\(_2^*\) clouds (clusters) required for full-space velocity field measurements, we have adopted a new method based on neutron absorption reaction of...
Neutron radiography can visualize heavy oil flows in metallic reactors used to upgrade heavy oils. Thus, we visualized heavy oil flows in a packed bed using real-time neutron radiography to support its capability and to offer basic experimental data necessary for verification and validation of numerical simulations. Atmospheric residue was used as...
Two-phase flow through porous media must be well understood to develop a severe accident analysis code not only for light water reactor but also sodium-cooled fast reactor. When a core disruptive accident occurs in sodium-cooled fast reactor, the fuel inside the core become melted and interacts with the coolant. As a result, gas-liquid two-phase fl...
During the re-flooding process, the heat-transfer of inverted annular flow (IAF) plays an important role. In this investigation, to visualize the flow condition of inverted annular flow regime, thermal neutron radiography is adopted. As the neutron source, Research reactor in Institute for Integrated Radiation and Nuclear Science of Kyoto Universit...
Pulsed neutron transmission spectroscopy was applied to clarify a phase change phenomena of lead-bismuth eutectics (LBE). The melting and solidification behaviors of the LBE should be well understood to enhance the safety of an LBE-cooled accelerator driven system. In this study, the heating experiments were performed using a rectangular test secti...
Lead–bismuth two-phase flow in a cylindrical vessel and annulus was experimentally investigated by varying the surface wettability of the vessel wall. The test section used in this study was a cylindrical stainless vessel with/without inner sleeve to change the hydraulic diameter. Volume-averaged void fraction was measured by varying the surface we...
Two-phase flow through porous media should be well understood to develop a severe accident analysis code not only for light water reactor but also sodium cooled fast reactor (SFR). When a core disruptive accident occurs in SFR, the fuel inside the core may become melted and interacts with the coolant. As a result, gas-liquid two-phase flow will be...
Liquid inlet behavior to a heat surface in micro-bubble emission boiling (MEB) was investigated by flow measurement using particle image velocimetry (PIV). Subcooled pool boiling experiments under atmospheric pressure were carried out using a heat surface with a diameter of 10 mm. An upper end of a heater block made of copper was used as the heat s...
Lead-bismuth single-phase and two-phase upward flows in a round tube were measured by using an electro-magnetic probe and an electrical conductivity probe. Experiments were performed under adiabatic conditions by varying the superficial gas and liquid velocity from 0 to 0.04 m/s and 0.1 to 0.2 m/s respectively. From the experimental results, it was...
The transient behavior of nuclear fuel during loss of coolant accident (LOCA) must be evaluated not only for power reactors but also for research reactors. Kyoto University Research Reactor (KUR) is a light-water moderated tank-type reactor operated at the rated thermal power of 5 MW and has been widely utilized for a lot of scientific researches....
Liquid inlet behavior to a heat surface in micro-bubble emission boiling (MEB) was investigated by PIV measurement. Subcooled pool boiling experiments were performed using a heat surface with a diameter of 10mm. An upper end of a heater block was used as the heat surface. The subcooling was varied from 40 K to 70 K. The flow visualization around th...
It is important to investigate two-phase flow phenomena in tube bundles. In this study, difference of instantaneous and time-average void fractions in in-line and staggered tube bundles at pitch-to-diameter ratio of 1.5 were investigated. Void fraction distributions around tubes across horizontal tube bundle in liquid-gas two-phase flow were measur...
A newly developed flat heat pipe FGHPTM (Morex Kiire Co.) was experimentally investigated by using neutron radiography. The test sample of the FGHP heat spreader was 65 × 65 × 2 mm3 composed of several etched copper plates and pure water was used as the coolant. Neutron radiography was performed at the E-2 port of the Kyoto University Research Reac...
We have synthesized metal oxide nanoparticles through hydrothermal reaction at around 400°C and 25MPa by mixing the stream of metal ion solution at room temperature with another stream of supercritical water in a continuous flow-type reactor. In order to visualize the mixing behavior of the two streams, we performed neutron tomography measurements....
The void fraction profile in a boiling channel is essential in analyzing convective flow boiling, where several investigations have been conducted. But due to the difficulty in the treatment of the non-thermodynamic equilibrium phenomena under subcooled conditions, the issues in comprehensive void fraction profile has not been solved, yet. To impro...
Gas-liquid two-phase flow in a narrow gap has been studied to develop a solid target cooling system for an accelerator driven system. Flow measurements are important to understand two-phase flow dynamics also in such a narrow channel. Although contact methods can measure detailed structure of two-phase flow, the intrusive effect on the flow becomes...
Most mono-propellant thruster technologies were developed in the 1960s. Those basic principles and fundamental mechanisms, such as the catalyst and propellant, are still in use without major technical innovation. However, much remains to be clarified in terms of the mechanisms and quantitative limitations of the hydrazine decomposition phenomena in...
The present paper describes gas-liquid two-phase flow measurements in a packed bed of spheres using neutron radiography. Porous debris formed during a severe accident of a nuclear reactor should be cooled by a coolant and the cooling characteristics are dominated by two-phase flow behavior in the debris bed at the initial stage of the accident. The...
Adsorption refrigerator is one of the efficient tools for waste heat recovery, because the system is driven by heat at relative low temperature. However, the coefficient of performance is low due to its batch operation and the heat capacity of the adsorber. In order to improve the performance, it is important to optimize the configuration to minimi...
High frame rate neutron radiography has been utilized to investigate two-phase flow in a metallic duct. However, images obtained by high frame-rate neutron radiography suffered from severe statistical noise due to its short exposure time. In this study, a spatio-temporal filter was applied to reduce the noise in the sequence images obtained by high...
In order to clarify the water-accumulation phenomena in an operating polymer electrolyte fuel cell (PEFC), the water distribution in a small fuel cell was measured in the through-plane direction by using neutron radiography. The fuel cell had nine parallel channels for classifying the water-accumulation process in the gas diffusion layer (GDL) unde...
A polymer electrolyte fuel cell (PEFC) generates electricity by the electrochemical reaction. It is well known that the water accumulation in the gas diffusion layer (GDL) reduces the cell performances. Hence, itis important to clarify the liquid water transport phenomenon in the PEFC. In this study, visualization of water transport phenomenon in a...
Measurements of void fraction distribution around tubes across horizontal tube bundle in liquid-gas two-phase flow were carried out using X-ray radiography system. Under bubbly flow condition, it was observed that bubbles mainly passed through the vertical tube gaps and accumulated on the upstream side of the tubes. Also it was observed that void f...
In this work, CeO2 nanoparticles were synthesized hydrothermally with supercritical water using a tubular flow reactor with three different configurations and various flow rates of the feed solution and supercritical water, and the effects of the reactor configuration and the flow rates of the two streams on the size distributions of the synthesize...
In a severe accident of a lead–bismuth-cooled accelerator-driven system, a gas–liquid two-phase flow with a large liquid-to-gas density ratio might appear, such as a steam leakage into hot lead–bismuth flow. It is still difficult to predict such phenomena because there are no available flow models for two-phase flow with a large density ratio compa...
It is important for a design of an adsorber to clarify adsorbed refrigerant distribution in adsorbent bed during transient conditions with adsorption or desorption, because the adsorption and desorption process is complex phenomena with heat and mass transfer and strongly effect on the cycle performance of an adsorption refrigerating cycle. Adsorbe...
Water management in a polymer electrolyte fuel cell (PEFC) is a key topic for PEFC operation. A microporous layer (MPL) has been recently used to improve the water flooding in the gas diffusion layer (GDL) around the catalyst layer. However, the mechanisms of this MPL are not completely understood because of the difficulty of measuring the water di...
In relationship to a solid target cooling system of an accelerator-driven system (ADS), wettability effect on boiling heat transfer has been experimentally investigated by irradiation with ultraviolet and gamma rays (γ-rays). The experimental apparatus consists of a copper heater block, a rectangular container, and a thermostat bath. Two copper hea...
A polymer electrolyte fuel cell (PEFC) generates electricity from an electrochemical reaction. However, water accumulation in the gas diffusion layer (GDL) reduces the cell performance. Therefore, the membrane must be kept at the appropriate humidity level for proton conduction. Hence, water management in a PEFC is essential for operation, and it i...
The experimental studies on the accelerator-driven system (ADS) are being conducted for the basic research of nuclear transmutation analyses with the combined use of the core at the Kyoto University Critical Assembly (KUCA) and the fixed-field alternating gradient (FFAG; 100 MeV protons) accelerator, in the Kyoto University Research Reactor Institu...
For developing an accelerator-driven system (ADS), many studies, such as those on accelerator development, subcritical system neutronics, materials irradiation effects, and thermal hydraulics, are required. In the Research Reactor Institute at Kyoto University (KURRI), ADS is planned as a future neutron source. Recent activities of relevant ADS stu...
In order to evaluate the local pressure drop in the gas channel of a polymer electrolyte fuel cell (PEFC), liquid droplet were modeled as two shapes by using neutron radiography. Based on the models, local pressure drop caused by a droplet were evaluated by CFD as a function of the water saturation, and it was applied to a network model calculating...
We have visualized the distributions of temperature and water density in a tubular flow reactor for supercritical hydrothermal synthesis of nanoparticles by neutron radiography, and investigated the effect of reactor configuration on the mixing behavior in the reactor. Here, three types of reactors were used, and the mixing behaviors of supercritic...
Supercritical water is used in various chemical reaction processes including hydrothermal synthesis of metal oxide nano-particles, oxidation, chemical conversion of biomass and plastics. Density of the super critical water is much less than that of the sub-critical water. By using neutron radiography, Peterson et al. have studied salt precipitation...
Kyoto University research Reactor (KUR) restarted in Spring 2010 with low enriched fuel (20%) after 4 years tentative interruption for fuel conversion. There are two facilities for neutron imaging: 1) B4 port at supermirror neutron guide tube (5x10(7) n/cm(2)/s at 5 MW, 1 cmx7.5 cm), 2) E2 port (3x10(5) n/cm(2)/s at 5 MW, 15 cm dia.). As we have la...
Water distributions of a polymer electrolyte fuel cell (PEFC) with 9-parallel channels during operation were visualized using a neutron radiography facility at 84 port in KUR (Kyoto University Research Reactor). An imaging system with a neutron image intensifier (I.I.) was employed for reducing the exposure time, and the water distributions in the...
Although the flow oscillation strongly affects the characteristic of the critical heat flux, the detailed feature of these phenomena had not been fully understood, so far. One of the reasons of the lack of the reports is owing to the characteristics of the flow oscillation, i.e. the flow oscillation is strongly influenced by the operating condition...
In the pottery sample which is the replica of the archeological sample, we attempted to get simultaneously not only the image by neutron radiography but also the information about elemental components by prompt gamma-ray analysis (PGA) at the B-4 beam hole that is usually used for the neutron radiography facility in Kyoto University Research Reacto...
Effect of surface wettability on boiling heat transfer was studied by applying radiation induced surface activation. Oxidized metal surfaces were irradiated by ultraviolet light, gamma ray, and proton beam, to investigate the radiation effect on the surface wettability. Proton irradiation experiments were performed at the FFAG accelerator complex o...
The void fraction in a forced convective flow boiling is very important information for understanding the characteristics of the boiling two-phase flow. Consequently, many experimental investigations have been carried out to obtain the local void fraction so far, but the detail data among the whole of the test-section has not been enough. Especiall...
Critical Heat Flux (CHF) is a very important designing factor of boiling systems, such as boiler and so on. Under flow instabilities condition, such as density wave oscillation, the CHF value is drastically decreased with an increase of oscillatory amplitude and oscillatory period, and the wall heat capacity becomes a very important parameter. In o...