The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Yutaka Abe - One of the best experts on this subject based on the ideXlab platform.
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Numerical Simulation of Liquid Jet Behavior in Shallow Pool by Interface Tracking Method
Volume 1: Beyond Design Basis; Codes and Standards; Computational Fluid Dynamics (CFD); Decontamination and Decommissioning; Nuclear Fuel and Engineer, 2020Co-Authors: Takayuki Suzuki, Hiroyuki Yoshida, Naoki Horiguchi, Sota Yamamura, Yutaka AbeAbstract:Abstract In the severe accident (SA) of nuclear reactors, fuel and components melt, and melted Materials fall to a lower part of a reactor vessel. In the lower part of a reactor vessel, in some sections of the SAs, it is considered that there is a water pool. Then, the melted core Materials fall into a water pool in the lower plenum as a jet. The Molten Material jet is broken up, and heat transfer between Molten Material and coolant may occur. This process is called a fuel-coolant interaction (FCI). FCI is one of the important phenomena to consider the coolability and distribution of core Materials. In this study, the numerical simulation of jet breakup phenomena with a shallow pool was performed by using the developed method (TPFIT). We try to understand the hydrodynamic interaction under various, such as penetration, reach to the bottom, spread, accumulation of the Molten Material jet. Also, we evaluated a detailed jet spread behavior and examined the influence of lattice resolution and the contact angle. Furthermore, the diameters of atomized droplets were evaluated by using numerical simulation data.
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Penetration Behavior of Liquid Jet Falling Into a Shallow Pool
Volume 9: Student Paper Competition, 2018Co-Authors: Fumihito Kimura, Hiroyuki Yoshida, Akiko Kaneko, Yutaka AbeAbstract:Mitigation measures against severe accidents (SAs) are important from the viewpoint of safety of nuclear reactors. In some scenarios of the SAs, the core Materials melt and fall into a water pool in the lower plenum as a jet. The Molten Material jet is broken up, and heat transfer between Molten Material and coolant is occurred. This process is called a fuel-coolant interaction (FCI). The aim of the present study is to clarify the liquid jet behavior falling into a shallow pool. Our focus is on the atomization conditions of a liquid jet injected into the pool with insufficient depth. In order to understand the jet behavior in a shallow pool, we performed observation of visualization with several methods and mapped observed flow regimes of jet against dimensionless numbers. As a results of observation, we succeeded visualization of internal flow.
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Breakup and fragmentation behavior of Molten Material jet in multi-channel of BWR lower plenum
Journal of Nuclear Science and Technology, 2015Co-Authors: Ryusuke Saito, Yutaka Abe, Hiroyuki YoshidaAbstract:To estimate the current status of reactor pressure vessel of Fukushima Daiichi nuclear power plant, it is important to clarify the breakup and the fragmentation behavior of Molten Material jet in boiling water reactor (BWR) lower plenum by a numerical simulation. To clarify the effects of complicated structures on jet breakup and fragmentation behavior, we conducted visualized experiments simulating the severe accident in the BWR by using the multi-channel experimental apparatus. In this study, the jet falling behavior, the jet breakup length, the fragmentation behavior and internal/external velocity profiles of the jet are observed by the backlight method and the particle image velocimetry. It is clarified that the complicated structures prolong the jet breakup length or make the fragments fall together to the lower plenum similar to the bulk state. In addition, it is clarified that strong shearing stress occurs at the crest of interfacial waves at the side of the jet. Finally, the fragment diameters mea...
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Effect of Solidification on Molten Material Jet Behavior in Coolant
Volume 6: Nuclear Education Public Acceptance and Related Issues; Instrumentation and Controls (I&C); Fusion Engineering; Beyond Design Basis Events, 2014Co-Authors: Yuzuru Iwasawa, Yutaka Abe, Eiji Matsuo, Hideki Nariai, Kazuya Koyama, Akiko Kaneko, Shimpei Saito, Hiroshi Sakaba, Ken-ichi Ebihara, Kazuhiro ItohAbstract:For the safety design of a Fast Breeder Reactor (FBR), if a Core Disruptive Accident (CDA) occurred hypothetically, it is required to suppress the rapid energy release due to a prompt criticality. Even if the rapid energy release does not occur, there is a possibility that a large amount of fuel melts. Therefore it is important to achieve Post Accident Heat Removal (PAHR). In order to achieve PAHR, it is strongly required that the Molten Material which is released from a core region gets cool and solidifies in the sodium coolant in a reactor vessel by breaking up. It is considered that the Molten fuel is injected into the coolant like a jet. Furthermore, in the actual FBR, the interfacial temperature between the Molten fuel jet and the coolant is considered to be lower than the melting point of the Molten Material. Thus for PAHR in CDA, it is important to understand the interaction between the jet and the coolant in such a condition and to estimate the Molten jet behavior quantitatively. In order to estimate quantitatively the effects of the solidification on the Molten jet behavior, we carried out the experiment in which a simulant Material was injected into a simulant coolant. In the experiment, we used low melting point alloy (Bi -Sn) and water as the simulant Molten Material and the simulant coolant respectively. In the experiments, we chose the temperature range including the condition that the interfacial temperature was lower than the melting point of the Molten Material. The jet breakup and the fragmentation behavior of the Molten Material jet were observed with a high speed video camera. Then the jet breakup length is estimated form the results. We changed the initial interfacial temperature condition by adjusting temperature of the Molten Material and the coolant. We also changed the jet velocity by adjusting the height of the nozzle tip from the water surface. From the experiment, we found that the jet breakup behavior depends greatly on the interfacial temperature and the injection velocity and that the solidification of a Molten Material jet and the growth of unstable jet surface, which results from the relative velocity of the jet to the coolant, are in a competitive relation for the jet breakup. We also found that when the Molten Material jet breaks up into fragments, the breakup length is independent of the initial interfacial temperature and the initial injection velocity.
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Experimental study on breakup and fragmentation behavior of Molten Material jet in complicated structure of BWR lower plenum
Journal of Nuclear Science and Technology, 2013Co-Authors: Ryusuke Saito, Yutaka Abe, Hiroyuki YoshidaAbstract:To estimate the state of reactor pressure vessel of Fukushima Daiichi nuclear power plant, it is important to clarify the breakup and fragmentation of Molten Material jet in the lower plenum of boiling water reactor (BWR) by a numerical simulation. To clarify the effects of complicated structures on the jet behavior experimentally and validate the simulation code, we conduct the visualized experiments simulating the severe accident in the BWR lower plenum. In this study, jet breakup, fragmentation and surrounding velocity profiles of the jet were observed by the backlight method and the particle image velocimetry (PIV) method. From experimental results using the backlight method, it was clarified that jet tip velocity depends on the conditions whether complicated structures exist or not and also clarified that the structures prevent the core of the jet from expanding. From measurements by the PIV method, the surrounding velocity profiles of the jet in the complicated structures were relatively larger than...
Ashish K. Nath - One of the best experts on this subject based on the ideXlab platform.
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development and parametric study of a water jet assisted underwater laser cutting process
International Journal of Machine Tools & Manufacture, 2013Co-Authors: Suvradip Mullick, Yuvraj K. Madhukar, Subhransu Roy, Shailesh Kumar, Dinesh K Shukla, Ashish K. NathAbstract:Abstract The conventional underwater laser cutting process usually utilizes a high pressure gas jet along with the laser beam to create a dry condition in the cutting zone and eject out the Molten Material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere, while cutting the radioactive components. In order to minimize this effect, a water-jet assisted underwater laser cutting technique has been developed using a high power fiber laser. A high velocity coaxial water-jet has been employed in place of gas-jet to remove the Molten Material through the kerf. Some amount of water vapour bubbles is formed at the laser–metal–water interface; however, they tend to condense as they rise up through the surrounding water. AISI 304 stainless steel sheet of maximum 1.5 mm thickness was cut at 1.4 m/min cutting speed with the present setup at 1800 W CW laser power, and the resulting average kerf-width was about 0.75 mm. The heat convection by water jet and the scattering of laser beam by vapour were found to influence significantly the energy efficiency of the cutting process. The effects of various processing parameters on the cutting performance were investigated. The energy efficiency improved at higher cutting speeds. An energy balance model with various loss mechanisms included has been also developed.
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Development of a Water-Jet Assisted Underwater Laser Cutting Process
2013Co-Authors: Suvradip Mullick, Yuvraj K. Madhukar, Subhranshu Roy, Ashish K. NathAbstract:We present the development of a new underwater laser cutting process in which a water-jet has been used along with the laser beam to remove the Molten Material through kerf. The conventional underwater laser cutting usually utilizes a high pressure gas jet along with laser beam to create a dry condition in the cutting zone and also to eject out the Molten Material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere while cutting radioactive components like burnt nuclear fuel. The water-jet assisted underwater laser cutting process produces much less turbulence and aerosols in the atmosphere. Some amount of water vapor bubbles is formed at the laser-metal-water interface; however, they tend to condense as they rise up through the surrounding water. We present the design and development of a water-jet assisted underwater laser cutting head and the parametric study of the cutting of AISI 304 stainless steel sheets with a 2 kW CW fiber laser. The cutting performance is similar to that of the gas assist laser cutting; however, the process efficiency is reduced due to heat convection by water-jet and laser beam scattering by vapor. This process may be attractive for underwater cutting of nuclear reactor components
Suvradip Mullick - One of the best experts on this subject based on the ideXlab platform.
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development and parametric study of a water jet assisted underwater laser cutting process
International Journal of Machine Tools & Manufacture, 2013Co-Authors: Suvradip Mullick, Yuvraj K. Madhukar, Subhransu Roy, Shailesh Kumar, Dinesh K Shukla, Ashish K. NathAbstract:Abstract The conventional underwater laser cutting process usually utilizes a high pressure gas jet along with the laser beam to create a dry condition in the cutting zone and eject out the Molten Material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere, while cutting the radioactive components. In order to minimize this effect, a water-jet assisted underwater laser cutting technique has been developed using a high power fiber laser. A high velocity coaxial water-jet has been employed in place of gas-jet to remove the Molten Material through the kerf. Some amount of water vapour bubbles is formed at the laser–metal–water interface; however, they tend to condense as they rise up through the surrounding water. AISI 304 stainless steel sheet of maximum 1.5 mm thickness was cut at 1.4 m/min cutting speed with the present setup at 1800 W CW laser power, and the resulting average kerf-width was about 0.75 mm. The heat convection by water jet and the scattering of laser beam by vapour were found to influence significantly the energy efficiency of the cutting process. The effects of various processing parameters on the cutting performance were investigated. The energy efficiency improved at higher cutting speeds. An energy balance model with various loss mechanisms included has been also developed.
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Development of a Water-Jet Assisted Underwater Laser Cutting Process
2013Co-Authors: Suvradip Mullick, Yuvraj K. Madhukar, Subhranshu Roy, Ashish K. NathAbstract:We present the development of a new underwater laser cutting process in which a water-jet has been used along with the laser beam to remove the Molten Material through kerf. The conventional underwater laser cutting usually utilizes a high pressure gas jet along with laser beam to create a dry condition in the cutting zone and also to eject out the Molten Material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere while cutting radioactive components like burnt nuclear fuel. The water-jet assisted underwater laser cutting process produces much less turbulence and aerosols in the atmosphere. Some amount of water vapor bubbles is formed at the laser-metal-water interface; however, they tend to condense as they rise up through the surrounding water. We present the design and development of a water-jet assisted underwater laser cutting head and the parametric study of the cutting of AISI 304 stainless steel sheets with a 2 kW CW fiber laser. The cutting performance is similar to that of the gas assist laser cutting; however, the process efficiency is reduced due to heat convection by water-jet and laser beam scattering by vapor. This process may be attractive for underwater cutting of nuclear reactor components
Juan Pou - One of the best experts on this subject based on the ideXlab platform.
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Laser cutting using off-axial supersonic rectangular nozzles
Precision Engineering, 2018Co-Authors: Antonio Riveiro, Rafael Comesaña, Félix Quintero, Fernando Lusquiños, J. Del Val, Mohamed Boutinguiza, Juan PouAbstract:Abstract Laser cutting is a well-established process in the industry, mainly for cutting metallic Materials such as steels. However, the utilization of this laser technique to process advanced Materials, such as ceramics or some aluminium alloys, is restricted due to the formation of a large heat affected zone (HAZ), rough cut edges, presence of dross, or thermal cracks. These defects are closely related to the performance of the assist gas during the removal of Molten Material. Previous works have demonstrated the impressive improvement in cut quality with the utilization of off-axial supersonic axisymmetric nozzles to inject the assist gas. This is due to the higher removal of Molten Material. However, these results can be even improved if the geometry of the gas jet is tailored to the cut kerf. In the present work, a cutting head with an off-axial supersonic rectangular nozzle was developed to improve the efficiency of the current assist gas injection systems. The performance of this system was compared with that of a converging (coaxial) nozzle, and an off-axial supersonic axisymmetric nozzle during the processing of Al2024-T3 sheets. Results demonstrated the superior performance of the new assist gas injection system in terms of cut quality and productivity (cut edge roughness was 6.5 times lower, and the cutting speed is 1.98 times higher as compared to the results found for a converging coaxial nozzle).
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Effects of processing parameters on laser cutting of aluminium–copper alloys using off-axial supersonic nozzles
Applied Surface Science, 2011Co-Authors: Antonio Riveiro, Rafael Comesaña, Félix Quintero, Fernando Lusquiños, Juan PouAbstract:Abstract Conventional laser cutting involves the utilization of converging coaxial nozzles to inject the assist gas used to remove the Molten Material. This processing system prevents the utilization of this technique to cut aluminium alloys for aerospace applications. The inefficient removal of Molten Material by the assist gas produces cuts with poor quality; very rough cuts, with a large amount of dross, and a large heat affected zone (HAZ) are obtained. An alternative to increase the assist gas performance is the utilization of off-axial supersonic nozzles. Removal of Molten Material is substantially increased and cuts with high quality are obtained. On the other hand, pulsed laser cutting offers superior results during the processing of high reflectivity Materials as aluminium alloys. However, there are no experimental studies which explore the pulsed laser cutting of aluminium alloys by means of a cutting head assisted by an off-axis supersonic nozzle. The present work constitutes a quantitative experimental study to determine the influence of processing parameters on the cutting speed and quality criteria during processing by means of off-axial supersonic nozzles. Cutting experiments were performed in pulsed mode and the results explained under the basis of the Molten Material removal mechanisms. Performed experiments indicate a reduction in cutting speed as compared to continuous wave (CW) mode processing and the existence of two processing regimes as a function of the pulse frequency. Best results are obtained under the high pulse frequency one (f > 100 Hz) because the superior capabilities of Molten Material removal of the supersonic jets are completely exploited in this processing regime.
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A model of Material removal mechanisms in pulsed laser cutting of ceramics
International Congress on Applications of Lasers & Electro-Optics, 2004Co-Authors: Félix Quintero, Fernando Lusquiños, Mohamed Boutinguiza, Juan Pou, R. Soto, F. Varas, Mariano Perez-amorAbstract:A theoretical model of the pulsed laser cutting of ceramics is presented. The ejection mechanisms of the processed Material from the cutting front are modeled under the assumption that the ceramic Material may be both melted and evaporated by the laser radiation. Therefore, three ejection mechanisms are investigated simultaneously: ejection of Molten Material by the assist gas, evaporation of the liquid, and ejection of Molten Material due to the recoil pressure generated by the evaporation from the cutting front.The temporal evolution of the ejection mechanisms is solved for several laser pulse modes. Theoretical results are compared with experimental observations to validate the conclusions regarding the influence of frequency and pulse length on the cutting process.A theoretical model of the pulsed laser cutting of ceramics is presented. The ejection mechanisms of the processed Material from the cutting front are modeled under the assumption that the ceramic Material may be both melted and evaporated by the laser radiation. Therefore, three ejection mechanisms are investigated simultaneously: ejection of Molten Material by the assist gas, evaporation of the liquid, and ejection of Molten Material due to the recoil pressure generated by the evaporation from the cutting front.The temporal evolution of the ejection mechanisms is solved for several laser pulse modes. Theoretical results are compared with experimental observations to validate the conclusions regarding the influence of frequency and pulse length on the cutting process.
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Comparative study of the influence of the gas injection system on the Nd:yttrium-aluminum-garnet laser cutting of advanced oxide ceramics
Review of Scientific Instruments, 2003Co-Authors: Félix Quintero, Fernando Lusquiños, Mohamed Boutinguiza, Juan Pou, R. Soto, Mariano Perez-amorAbstract:Cutting of advanced oxide ceramics is still a difficult task. In this work, the possibility to effectively cut them using a Nd:YAG laser guided by an optical fiber is demonstrated. The key points are the aerodynamic interactions of the assist gas jet in the fusion laser cutting of ceramics. A comprehensive study of the influence of these aerodynamic interactions on the laser cutting of advanced oxide ceramics has been carried out. The characteristics of the heat affected zone (HAZ) were studied related to the efficiency of the assist gas to eject the Molten Material. It has been demonstrated that the HAZ can be avoided with a suitable design of the gas injection system combined with an appropriate selection of the values of the processing parameters. With the aim of improving the efficiency of the assist gas injection system, a new cutting head with an off-axis supersonic nozzle was developed. Furthermore, a comparison between the utilization of a conventional coaxial conical nozzle to inject the assist gas and the new system is presented. The results obtained give clear proof that the use of the new gas injection system leads to a great improvement on the cut quality by means of a more efficient removing of the Molten Material out of the cutting front. This result is of special interest in the laser fusion cutting of thick ceramic plates at high processing rates.
Reinhart Poprawe - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation on a new hybrid laser process for surface structuring by vapor pressure on ti6al4v
Journal of Materials Processing Technology, 2020Co-Authors: André Temmler, S Drinck, Reinhart PopraweAbstract:Abstract Besides conventional structuring processes such as turning, milling or photo-chemical etching, laser processes are increasingly being used for surface structuring of metals. These laser processes differ fundamentally in that structuring is carried out either by Material removal or by Material redistribution. In this study, a new hybrid process of Material ablation by means of pulsed laser radiation and Material redistribution based on a remelting process by means of cw laser radiation is experimentally investigated. Besides an introduction to this new hybrid process, we give a detailed description of the equipment and methods used as well as surface structures produced on Ti6Al4V. A melt pool was generated on a prepared Ti6Al4V surface using cw laser radiation with a laser beam diameter of 520 μm, laser power of 220 W, and a scanning velocity of 100 mm/s. In order to create surface structures, simultaneously, superimposed pulsed laser radiation with a laser beam diameter of 65 μm, pulse duration of 60 ns, a maximum pulse energy of 0.35 mJ, and a pulse frequency of 50 kHz was used to evaporate small amounts of Molten Material from the melt pool. This localized evaporation of Molten Material is assumed to create vapor pressure that deforms the melt pool surface and therefore leads to surface structures. Our results indicate that by pulsed laser radiation capillary surface waves with a wavelength of the doubled laser beam diameter are excited on the melt pool surface. This forced excitation of capillary surface waves result in surface structures that are analyzed after solidification by means of white light interferometry. Based on this analysis we derived an oscillation frequency of ν = 2.27 (± 0.16) kHz for the excited capillary surface wave as well as an effective kinematic viscosity of μ = 0.1328 cm2 s−1 for the damping of this surface oscillation during solidification. In terms of structural features, we achieved surface structures with heights of up to 100 μm. Furthermore, structure height controllably scales in dependence on pulse energy and number of laser pulses as long as no ejection of Molten Material takes place. Finally, a comparison of the redistributed Material volume per time shows that we achieved a volume redistribution rate of 28.37 mm3/min, which is significantly bigger than has been achieved with other laser texturing techniques so far and demonstrates the high potential of this new hybrid technique not only for surface structuring purposes.
