Update on Progress in Creating Stabilized Gas Layers in Flowing Liquid Mercury

2009 ◽  
Author(s):  
Mark Wendel ◽  
David Felde ◽  
Ashraf Abdou ◽  
Bernard Reimer
Keyword(s):  
High Speed ◽  
National Laboratory ◽  
Protective Layer ◽  
Two Phase ◽  
Flowing Liquid ◽  
Cavitation Damage ◽  
Oak Ridge ◽  
Liquid Mercury ◽  
Materials Research ◽  
Gas Layer

The Spallation Neutron Source (SNS) facility in Oak Ridge, Tennessee uses a liquid mercury target that is bombarded with protons to produce a pulsed neutron beam for materials research and development. In order to mitigate expected cavitation damage erosion (CDE) of the containment vessel, a two-phase flow arrangement of the target has been proposed and was earlier proven to be effective in significantly reducing CDE in non-prototypical target bodies. This arrangement involves covering vulnerable surfaces with a protective layer of gas. The difficulty lies in establishing a persistent gas layer that is oriented vertically and holds up to the strong buoyancy force and the turbulent mercury flow. Several new multiphase experiments have been completed at the Oak Ridge National Laboratory toward developing such layers. The gas hold-up is accomplished by machining regular features (grooves or pits) into the wall with dimensions on the order of 1 mm. The thickness of the gas layer varies, and it is currently unknown how thick a layer must be in order to successfully mitigate the damage, although this aspect is also under investigation. The paper includes a description of the various tests, a presentation of high-speed video images of the gas/mercury interaction viewed through a transparent window, and a discussion of how the results can be used to design a new SNS target that might be resistant to cavitation damage erosion.

Measurements of Gas Bubble Size Distributions in Flowing Liquid Mercury

2012 ◽  
Author(s):  
Mark Wendel ◽  
Bernard Riemer ◽  
Ashraf Abdou
Keyword(s):  
Bubble Size ◽  
High Speed ◽  
National Laboratory ◽  
Size Distributions ◽  
Flow Loop ◽  
Proton Beam Irradiation ◽  
Flowing Liquid ◽  
Cavitation Damage ◽  
Oak Ridge ◽  
Liquid Mercury

Pressure waves created in liquid mercury pulsed spallation targets have been shown to induce cavitation damage on the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, measuring such a population in mercury is difficult since it is opaque and the mercury is involved in a turbulent flow. Ultrasonic measurements have been attempted on these types of flows, but the flow noise can interfere with the measurement, and the results are unverifiable and often unrealistic. Recently, a flow loop was built and operated at Oak Ridge National Labarotory to assess the capability of various bubbler designs to deliver an adequate population of bubbles to mitigate cavitation damage. The invented diagnostic technique involves flowing the mercury with entrained gas bubbles in a steady state through a horizontal piping section with a glass-window observation port located on the top. The mercury flow is then suddenly stopped and the bubbles are allowed to settle on the glass due to buoyancy. Using a bright-field illumination and a high-speed camera, the arriving bubbles are detected and counted, and then the images can be processed to determine the bubble populations. After using this technique to collect data on each bubbler, bubble size distributions were built for the purpose of quantifying bubbler performance, allowing the selection of the best bubbler options. This paper presents the novel procedure, photographic technique, sample visual results and some example bubble size distributions. The best bubbler options were subsequently used in proton beam irradiation tests performed at the Los Alamos National Laboratory. The cavitation damage results from the irradiated test plates in contact with the mercury are available for correlation with the bubble populations. The most effective mitigating population can now be designed into prototypical geometries for implementation into an actual SNS target.

Progress in Creating Stabilized Gas Layers in Flowing Liquid Mercury

2008 ◽  
Author(s):  
Mark Wendel ◽  
David Felde ◽  
Bernard Riemer ◽  
David West ◽  
Brian D’Urso ◽  
...  
Keyword(s):  
Solid Wall ◽  
High Surface ◽  
Protective Layer ◽  
Porous Wall ◽  
High Energy ◽  
Two Phase ◽  
Flowing Liquid ◽  
Oak Ridge ◽  
Liquid Mercury ◽  
Gas Layer

The Spallation Neutron Source (SNS) facility in Oak Ridge, Tennessee uses a liquid mercury target that is bombarded with protons to produce a pulsed neutron beam for materials research and development. In order to mitigate expected cavitation damage erosion (CDE) of the containment vessel, a two-phase flow arrangement of the target has been proposed and was earlier proven to be effective in significantly reducing CDE in non-prototypical target bodies. This arrangement involves covering the beam “window”, through which the high-energy proton beam passes, with a protective layer of gas. The difficulty lies in establishing a stable gas/liquid interface that is oriented vertically with the window and holds up to the strong buoyancy force and the turbulent mercury flow field. Three approaches to establishing the gas wall have been investigated in isothermal mercury/gas testing on a prototypical geometry and flow: (1) free gas layer approach, (2) porous wall approach, and (3) surface-modified approach. The latter two of these approaches show success in that a stabilized gas layer is produced. Both of these successful approaches capitalize on the high surface energy of liquid mercury by increasing the surface area of the solid wall, thus increasing gas hold up at the wall. In this paper, a summary of these experiments and findings is presented as well as a description of the path forward toward incorporating the stabilized gas layer approach into a feasible gas/mercury SNS target design.

Experiments and Simulations With Large Gas Bubbles in Mercury Towards Establishing a Gas Layer to Mitigate Cavitation Damage

2006 ◽  
Author(s):  
Mark Wendel ◽  
David Felde ◽  
Thomas Karnowski ◽  
Bernard Riemer ◽  
Arthur Ruggles
Keyword(s):  
Liquid Metal ◽  
Solid Wall ◽  
National Laboratory ◽  
Large Bubble ◽  
Cavitation Damage ◽  
Oak Ridge ◽  
Beam Experiment ◽  
Order Of Magnitude ◽  
Protective Gas ◽  
Gas Layer

One option that shows promise for protecting solid surfaces from cavitation damage in liquid metal spallation targets involves introducing an interstitial gas layer between the liquid metal and the containment vessel wall. Several approaches toward establishing such a protective gas layer are being investigated at the Oak Ridge National Laboratory including large bubble injection and methods that involve stabilization of the layer by surface modifications to enhance gas hold-up on the wall or by inserting a porous media. It has previously been reported that using a gas layer configuration in a test target showed an order-of-magnitude decrease in damage for an in-beam experiment. Video images that were taken of the successful gas/mercury flow configuration have been analyzed and correlated. The results show that the success was obtained under conditions where only 60% of the solid wall was covered with gas. Such a result implies that this mitigation scheme may have much more potential. Additional experiments with gas injection into water are underway. Multi-component flow simulations are also being used to provide direction for these new experiments. These simulations have been used to size the gas layer and position multiple inlet nozzles.

CFD Validation of Gas Injection Into Stagnant Water

2007 ◽  
Author(s):  
Ashraf Ibrahim ◽  
David Felde ◽  
Bernard Riemer ◽  
Mark Wendel
Keyword(s):  
Acoustic Waves ◽  
High Speed ◽  
Two Phase Flow ◽  
Gas Injection ◽  
Phase Flow ◽  
Cfd Model ◽  
Stagnant Water ◽  
Two Phase ◽  
Oak Ridge ◽  
Liquid Mercury

Investigations in the area of two-phase flow at the Oak Ridge National Laboratory’s (ORNL) Spallation Neutron Source (SNS) facility are progressing. It is expected that the target vessel lifetime could be extended by introducing gas into the liquid mercury target. As part of an effort to validate the two-phase computational fluid dynamics (CFD) model, simulations and experiments of gas injection in stagnant water have been completed. The volume of fluid (VOF) method as implemented in ANSYS-CFX was used to simulate the unsteady two-phase flow of gas injection into stagnant water. Flow visualization data were obtained with a high-speed camera for the comparison of predicted and measured bubble sizes and shapes at various stages of the bubble growth, detachment, and gravitational rise. The CFD model is validated with these experimental measurements at different gas flow rates. The acoustic waves emitted at the time of detachment and during subsequent oscillations of the bubble were recorded with a microphone. The acoustic signature aspect of this validation is particularly interesting since it has applicability to the injection of gas into liquid mercury, which is opaque.

Two-Phase Flow Simulations of Protective Gas Layer for Spallation Neutron Source Target

2011 ◽  
Author(s):  
Ashraf Abdou ◽  
Mark Wendel ◽  
Bernard Riemer ◽  
Eric Volpenhein ◽  
Robert Brewster
Keyword(s):  
Neutron Source ◽  
Vessel Wall ◽  
Pressure Waves ◽  
Spallation Neutron Source ◽  
Two Phase ◽  
Flowing Liquid ◽  
Liquid Mercury ◽  
Helium Gas ◽  
Protective Gas ◽  
Gas Layer

The Spallation Neutron Source (SNS) is an accelerator-based neutron source at Oak Ridge National Laboratory (ORNL). The nuclear spallation reaction occurs when a proton beam hits liquid mercury. This interaction causes thermal expansion of the liquid mercury which produces high pressure waves. When these pressure waves hit the target vessel wall, cavitation can occur and erode the wall. Research and development efforts at SNS include creation of a vertical protective gas layer between the flowing liquid mercury and target vessel wall to mitigate the cavitation damage erosion and extend the life time of the target. Since mercury is opaque, computational fluid dynamics (CFD) has been used to visualize the general behavior of a protective gas layer arising from various delivery and retention concepts as a guide for design of experimental efforts. Recent advancements in capacity for large scale CFD modeling via the high performance compute systems of ORNL now enable high-fidelity simulation approaching full geometric scale. Accordingly, in this study, CFD simulations of three dimensional, unsteady, turbulent, two-phase flow of helium gas injection in flowing liquid mercury over textured walls are carried out for target design purposes with the commercially available CFD code STARCCM+. The Volume of Fluid (VOF) model is used to track the helium-mercury interface. Different combinations of conical pits and V-shaped straight grooves at different orientations with respect to the gravity vector are simulated at the SNS proton beam window to increase the helium gas holdup. Time integration of predicted helium gas volume fraction over time is done for the design alternatives considered to compare the gas coverage and average thickness of the helium gas layer.

Development of a gas layer to mitigate cavitation damage in liquid mercury spallation targets

2008 ◽  
Vol 377 (1) ◽  
pp. 155-161 ◽  
Author(s):  
David Felde ◽  
Bernard Riemer ◽  
Mark Wendel
Keyword(s):  
Cavitation Damage ◽  
Liquid Mercury ◽  
Gas Layer

Survey of Recent Research Results for New Fluor Materials

1999 ◽  
Vol 560 ◽  
Author(s):  
William A. Hollerman ◽  
Gary A. Glass ◽  
Steven A. Allison
Keyword(s):  
High Speed ◽  
High Performance ◽  
National Laboratory ◽  
Fluorescence Decay ◽  
Particle Accelerators ◽  
Oil Well ◽  
Positioning Systems ◽  
Oak Ridge ◽  
Fluorescence Efficiency ◽  
Large Material

ABSTRACTThere is worldwide interest in the use of fluor materials that emit visible light when exposed to ionizing radiation. Typically, fluors are used as components in high performance electromagnetic calorimeters, down-hole oil well loggers, temperature sensors for equipment with high speed moving parts, and beam positioning systems for large particle accelerators. A candidate fluor should have a large fluorescence efficiency, small reduction in output as a function of exposure, intense visible fluorescence spectrum, large material density, and small prompt fluorescence decay time.Over the last few years, new fluor materials have been located by organizations such as Oak Ridge National Laboratory, Lawrence Berkeley National Laboratory, and the Department of Defense. These new fluors, such as YAIO3:Ce, YSiO5:Ce, GdSiO5:Ce, Y2O2S doped with Tb, Pr, and Eu, and Gd2O0S doped with Th, Pr, and Eu, show a great deal of promise for use in the applications listed above.This paper will present a summary of fluor research completed by the authors over the last ten years. These results will be used to establish a fluor characterization program at the Acadiana Research Laboratory (ARL) that will move it to the front of this developing technology.

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