scholarly journals Small Bubbles Generation With Swirl Bubblers for SNS Target

2018 ◽  
Author(s):  
C. Barbier ◽  
E. Dominguez-Ontiveros ◽  
R. Sangrey
Keyword(s):  
Pressure Wave ◽  
Proton Accelerator ◽  
Pressure Waves ◽  
Negative Effects ◽  
Cavitation Damage ◽  
Pressure Losses ◽  
Oak Ridge ◽  
Micron Diameter ◽  
Rapid Temperature ◽  
Small Bubbles

Oak Ridge National Laboratory’s (ORNL) Spallation Neutron Source (SNS) uses a mercury target to generate neutrons. When the powerful 1.4 MW, 60Hz proton beam hits the target, a strong pressure wave propagates in the mercury and into the vessel wall due to the rapid temperature rise in mercury. These pressure waves induce cavitation damage on the target container and high stresses, which both limit the lifetime of the target. Since October 2017, helium gas has been injected into the mercury flow in order to mitigate the negative effects of pulse-induced pressure waves. The preliminary strain measurements suggest that gas injection is indeed efficient at mitigating the pressure wave. Tiny nozzles (8-micron diameter) at choked condition are used to generate small bubbles. The bubblers can theoretically inject a total mass flow rate of 0.75 SLPM. However, during operation the bubblers were capable of injecting only approximately 0.45 SLPM, which suggests that some of the nozzles may have become clogged. Since there is a strong desire to inject a larger quantity of gas in the target to, hopefully, mitigate even more the pressure wave, SNS has been looking at implementing swirl bubblers in the target, similar to the ones used in the Japan Proton Accelerator Research Complex (J-PARC) mercury target. In this paper, results with prototypical bubblers tested in water and mercury are presented. Bubblers were installed in prototypical targets and bubble size distributions were measured in both water and mercury. It was found that swirl bubblers can generate a large number of small bubbles, but some compromises were made to keep the pressure losses across them reasonable.

Choked-Flow Inlet Orifice Bubbler for Creating Small Bubbles in Mercury

2013 ◽  
Author(s):  
Mark Wendel ◽  
Ashraf Abdou ◽  
Bernard Riemer
Keyword(s):  
National Laboratory ◽  
High Surface ◽  
Population Data ◽  
Science Center ◽  
Cavitation Damage ◽  
Oak Ridge ◽  
Choked Flow ◽  
Test Loop ◽  
High Level ◽  
Small Bubbles

Pressure waves created in liquid mercury pulsed spallation targets like the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, induce cavitation damage on the target container. The cavitation damage is thought to limit the lifetime of the target for power levels at and above 1 MW. One way to mitigate the damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating a bubble size distribution that is sufficiently large and disperse in mercury is challenging due to the high surface tension. Also, measuring the population is complicated by the opacity and the high level of turbulent mixing. Recent advances in bubble diagnostics by batch sampling the mercury made it possible to compare bubble populations for different techniques in a SNS-1/20th scale test loop. More than 10 bubblers were tested and the most productive bubblers were taken for in-beam testing at the Los Alamos Neutron Science Center (LANSCE) WNR user facility. One bubbler design, referred to as the inlet-orifice bubbler, that showed moderate success in creating populations also has an added advantage that it could easily be included in the existing SNS full-scale mercury target configuration. Improvements to the bubbler were planned including a reduction of the nozzle size to choke the gas injection, thus steadying the injected mass flow and allowing multiple nozzles to work off of a common plenum. For the first time, reliable bubble population data are available in the prototypical target geometry and can be compared with populations that mitigated cavitation damage. This paper presents those experimental results.

A Numerical and Experimental Analysis of Cardiovascular Stent Design Considerations

2003 ◽  
Author(s):  
John J. Charonko ◽  
Saad A. Ragab ◽  
Pavlos P. Vlachos
Keyword(s):  
Pressure Wave ◽  
Wave Reflection ◽  
Numerical Models ◽  
Gradual Transition ◽  
First Year ◽  
Pressure Waves ◽  
Negative Effects ◽  
Design Considerations ◽  
Stent Length

Stents have proven very effective in opening the lumens of blocked and diseased arteries, leading to an increased quality of life for thousand of patients. Due to their success, stents have grown into a $1.5 billion dollar industry, but unfortunately still suffer from failure rates of 20–30% in the first year. Many of these failures can be traced back to restenosis or thrombosis of the stented arteries, a problem which conventional self-expanding or balloon-expanded stents have not proved effective in combating. Mathematical and experimental research shows that stents create adverse flow conditions and increase the stresses found around the implants, and trials of designs intended to reduce these effects have proven effective in combating restenosis. The goal of this research was to investigate mathematically design considerations for an improved stent that can reduce these negative effects. This was accomplished through the construction of a onedimensional numerical model for the fluid mechanics of the artery that was implemented using FEA and a combination of WENO and Runge-Kutta methods. The output from this model was compared with solutions from the literature and with in-vitro experimental results. Based on these tests it was concluded that the model accurately predicted the behavior of the pressure waves in a vessel. These numerical models were then used to evaluate several proposed designs. The pressure wave reflection was found to be controlled entirely by the design of the stent ends; mid-length variations in stent compliance provided no change in the model behavior. Also, a region of gradual transition between the low stiffness of the artery and the increased stiffness of the stent, while useful for reducing wall stresses, proved ineffective in reducing the magnitude of the reflected pressure waves. The best design for minimizing pressure wave reflection was found to be one that minimized total stent length.

A Compact Gas Liquid Separator for the SNS Mercury Process Loop

2021 ◽  
Author(s):  
Charlotte Barbier ◽  
Elvis Dominguez-Ontiveros ◽  
Justin Weinmeister ◽  
Jeremy Slade ◽  
Dustin Ottinger ◽  
...  
Keyword(s):  
Proton Beam ◽  
Pressure Wave ◽  
National Laboratory ◽  
Beam Power ◽  
Target Station ◽  
Pressure Losses ◽  
Oak Ridge ◽  
Helium Bubbles ◽  
Successful Design ◽  
Liquid Separator

Abstract Upgrades at the Spallation Neutron Source (SNS) accelerator at Oak Ridge National Laboratory are underway to double its proton beam power from 1.4 to 2.8 MW. About 2MW will go to the current first station while the rest will go to the future Second Target Station. The increase of beam power to the first target station is especially challenging for its mercury target. When the short proton beam hits the target, strong pressure waves are generated, causing cavitation erosion and challenging stresses for the target's weld regions. SNS has successfully operated reliably at 1.4 MW by mitigating the pressure wave with the injection of small Helium bubbles into the mercury. To operate reliably at 2MW, more gas will be injected into mercury to mitigate the pressure wave further. However, the mercury process loop was not originally designed for gas injection, and the accumulation of gas in the pipes is a concern. Due to space constraints, a custom Gas Liquid Separator (GLS) was designed to fit a 90-degree horizontal elbow space in the SNS mercury loop. Simulations and experiments were performed, and a successful design was developed that has the desired efficiency while keeping the pressure losses acceptable.

Propagation of Pressure Waves, Caused by a Thermal Shock, in Liquid Metals Containing Gas Bubbles

2005 ◽  
Author(s):  
K. Okita ◽  
Y. Matsumoto ◽  
S. Takagi
Keyword(s):  
Thermal Shock ◽  
Void Fraction ◽  
Pressure Wave ◽  
Cavitation Erosion ◽  
Liquid Metals ◽  
Bubble Radius ◽  
Gas Bubbles ◽  
Pressure Waves ◽  
Lower Natural Frequency ◽  
Small Bubbles

Propagation of pressure waves caused by a thermal shock in liquid metals containing gas bubbles is performed by a numerical simulation. The present study examined the influences of bubble radius and void fraction on the absorption of thermal expansion of liquid metals and attenuation of pressure waves. As the result of the calculation, since the large bubbles which have a lower natural frequency than the small bubbles cannot respond to the heat input, the peak pressure at the heated region increases with increasing bubble radius. Especially, when the bubble radii are around 500 μm, the pressure wave propagates through the mixture not with the sonic speed of the mixture but with that of liquid mercury. On the other hand, decreasing the void fraction makes behavior of bubbles nonlinear and a collapse of bubble produces a high pressure wave. However, the calculation shows that the method of introducing micro gas bubbles into liquid metals is effective to prevent cavitation erosion on the wall.

Calculation of Pressure Wave Propagation Through a Tube Junction

1996 ◽  
Vol 210 (3) ◽  
pp. 239-244 ◽  
Author(s):  
M J P William-Louis ◽  
C Tournier
Keyword(s):  
Wave Propagation ◽  
Pressure Wave ◽  
Method Of Characteristics ◽  
Subsonic Flow ◽  
New Method ◽  
Superposition Method ◽  
Pressure Waves ◽  
Incoming Flow ◽  
Governing Equations ◽  
Pressure Losses

This paper describes a new method for the calculation of pressure wave propagation through a junction. The unsteady model, valid for subsonic flow, takes into account the fluid compressibility and pressure losses according to the type of junction. A new method called the ‘branch superposition method’ is used for the numerical calculation, and consists of uncoupling the system of governing equations. During the propagation of pressure waves through a three-tube junction, two branches are inlet or outlet. Therefore, to uncouple the system, one of the two branches with incoming flow is modelled as a source or one of the two branches with outgoing flow as a sink. This method, combined with the method of characteristics, gives the possibility of predicting the propagation of pressure waves through a junction, where the fluid may be initially at rest or not. The model is validated by a comparison with experimental results.

Transient Analysis on Helium Coolant Tube Break Accident of Dual-Functional Lithium Lead Test Blanket Module

2016 ◽  
Author(s):  
Qian Sun ◽  
Tianji Peng ◽  
Zhiwei Zhou ◽  
Zhibin Chen ◽  
Jieqiong Jiang
Keyword(s):  
Pressure Wave ◽  
Transient Analysis ◽  
Structural Integrity ◽  
Maximum Pressure ◽  
Pressure Waves ◽  
Operating Pressure ◽  
Pressure Shock ◽  
Dual Functional ◽  
Short Time ◽  
Helium Coolant

Dual-functional Lithium Lead Test Blanket Module (DFLL-TBM) was proposed by China for testing in the International Thermonuclear Experimental Reactor (ITER).When an in-TBM helium coolant tube breaks, high pressure helium will discharge into the Pb-Li breeding zones. The pressure shock in the TBM will threaten the structural integrity and safety of ITER. Simulation and analysis on helium coolant tube break accident of DFLL-TBM was performed, and two cases with different break sizes were considered. Computational results indicate that intense pressure waves spread quickly from the break to the surrounding structures and the variation of pressure in the TBM breeding box is drastic especially when the pressure wave propagation encounters large resistance such as at the bending corner of the flow channel, the inlet and outlet of Pb-Li, etc. The maximum pressure in the TBM breeding box which is even higher than the operating pressure of helium also occurs in these zones. Although the pressure shock lasts for a very short time, its effect on the structural integrity of DFLL-TBM needs to be paid attention to.

Effect of Gas Microbubble Injection and Narrow Channel Structure on Cavitation Damage in Mercury Target Vessel

2021 ◽  
Vol 1024 ◽  
pp. 111-120
Author(s):  
Takashi Naoe ◽  
Hidetaka Kinoshita ◽  
Hiroyuki Kogawa ◽  
Takashi Wakui ◽  
Eiichi Wakai ◽  
...  
Keyword(s):  
Average Power ◽  
Narrow Channel ◽  
Channel Structure ◽  
Pressure Waves ◽  
Target Vessel ◽  
Original Design ◽  
Cavitation Damage ◽  
Service Operation ◽  
Damage Depth ◽  
Design Type

The target vessel, which enclosing liquid mercury, for the pulsed spallation neutron source at the J-PARC is severely damaged by cavitation caused by proton beam-induce pressure waves in mercury. To mitigate the cavitation damage, we adopted a double-walled structure with a narrow channel for the mercury at the beam window of the target vessel. The narrow channel disturbs the growth of cavitation bubbles due to the pressure gradient. In addition, gas microbubbles are injected into the mercury to suppress the pressure waves. After finishing service operation, the front end of the target vessel was cut out to inspect the effect of those cavitation damage mitigation technologies on the interior surface. The damage depth of the cutout specimens for the original design type and double-walled target vessels were quantitatively investigated by the replica method. The results showed that the double-walled target facing mercury with gas microbubbles operate 1812 MWh for an average power of 434 kW is equivalent to the damage of original design target operated 1048 MWh for average power of 181 kW. The erosion depth due to cavitation in the narrow channel is clearly smaller than on the wall facing bubbly mercury.

Neutron macromolecular crystallography

2018 ◽  
Vol 2 (1) ◽  
pp. 39-55 ◽  
Author(s):  
Matthew P. Blakeley ◽  
Alberto D. Podjarny
Keyword(s):  
Neutron Diffraction ◽  
Fluorescent Proteins ◽  
National Laboratory ◽  
Direct Determination ◽  
Drug Binding ◽  
Proton Accelerator ◽  
Biological Macromolecules ◽  
Macromolecular Crystallography ◽  
Neutron Sources ◽  
Oak Ridge

Neutron diffraction techniques permit direct determination of the hydrogen (H) and deuterium (D) positions in crystal structures of biological macromolecules at resolutions of ∼1.5 and 2.5 Å, respectively. In addition, neutron diffraction data can be collected from a single crystal at room temperature without radiation damage issues. By locating the positions of H/D-atoms, protonation states and water molecule orientations can be determined, leading to a more complete understanding of many biological processes and drug-binding. In the last ca. 5 years, new beamlines have come online at reactor neutron sources, such as BIODIFF at Heinz Maier-Leibnitz Zentrum and IMAGINE at Oak Ridge National Laboratory (ORNL), and at spallation neutron sources, such as MaNDi at ORNL and iBIX at the Japan Proton Accelerator Research Complex. In addition, significant improvements have been made to existing beamlines, such as LADI-III at the Institut Laue-Langevin. The new and improved instrumentations are allowing sub-mm3 crystals to be regularly used for data collection and permitting the study of larger systems (unit-cell edges >100 Å). Owing to this increase in capacity and capability, many more studies have been performed and for a wider range of macromolecules, including enzymes, signalling proteins, transport proteins, sugar-binding proteins, fluorescent proteins, hormones and oligonucleotides; of the 126 structures deposited in the Protein Data Bank, more than half have been released since 2013 (65/126, 52%). Although the overall number is still relatively small, there are a growing number of examples for which neutron macromolecular crystallography has provided the answers to questions that otherwise remained elusive.

Cinematographic Analysis of Counter Jet Formation in a Single Cavitation Bubble Collapse Flow

2011 ◽  
Vol 27 (2) ◽  
pp. 253-266 ◽  
Author(s):  
S.-H. Yang ◽  
S.-Y. Jaw ◽  
K.-C. Yeh
Keyword(s):  
Flow Field ◽  
Cavitation Bubble ◽  
Pressure Wave ◽  
Bubble Surface ◽  
Bubble Collapse ◽  
Solid Boundary ◽  
Liquid Jet ◽  
Pressure Waves ◽  
Field Variation ◽  
Critical Position

ABSTRACTThis study utilized a U-shape platform device to generate a single cavitation bubble for the detail analysis of the flow field characteristics and the cause of the counter jet during the process of bubble collapse induced by pressure wave. A series of bubble collapse flows induced by pressure waves of different strengths are investigated by positioning the cavitation bubble at different stand-off distances to the solid boundary. It is found that the Kelvin-Helmholtz vortices are formed when the liquid jet induced by the pressure wave penetrates the bubble surface. If the bubble center to the solid boundary is within one to three times the bubble's radius, a stagnation ring will form on the boundary when impacted by the penetrated jet. The liquid inside the stagnation ring is squeezed toward the center of the ring to form a counter jet after the bubble collapses. At the critical position, where the bubble center from the solid boundary is about three times the bubble's radius, the bubble collapse flows will vary. Depending on the strengths of the pressure waves applied, either just the Kelvin-Helmholtz vortices form around the penetrated jet or the penetrated jet impacts the boundary directly to generate the stagnation ring and the counter jet flow. This phenomenon used the particle image velocimetry method can be clearly revealed the flow field variation of the counter jet. If the bubble surface is in contact with the solid boundary, the liquid jet can only splash radially without producing the stagnation ring and the counter jet. The complex phenomenon of cavitation bubble collapse flows are clearly manifested in this study.

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