The Experts below are selected from a list of 2814 Experts worldwide ranked by ideXlab platform
Denis Hellebuyck - One of the best experts on this subject based on the ideXlab platform.
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functional performance criteria for comparison of less flammable transformer oils with respect to fire and explosion risk
LUTVDG TVBB; (2013), 2013Co-Authors: Denis HellebuyckAbstract:Power grids worldwide are expanding not only driven by ambitious clean energy, but also because of the rising need for reliable energy. Key components of these power grids are transformers. Transformers are traditionally filled with mineral oil, to serve as a coolant and dielectric insulator. Now globally a rising trend is observed towards the adoption of less flammable, biodegradable transformer Liquids at ever increasing voltages and power ratings. The objective of this report is to discuss past, current and future attempts to quantify the fire and explosion risk in less flammable Liquid filled high voltage transformers. Testing procedure standards that give a reliable assessment of the fire behavior of electro technical insulating Liquid based on relevant physical characteristics of the fluids are currently under development, such as IEC 60695-8-3. However more effort is required in order to provide meaningful information concerning the relation between small-scale tests and large-scale tests and that between the tests and failure scenarios in real life applications. The experimental focus of this report, small-scale comparative tests in the Cone Calorimeter and other settings, is limited to pool fires. Spray and vapour/gas cloud fires and explosions, even though of great importance, are not considered. In total 5 Liquids were tested: mineral oil, silicone Liquid, synthetic ester and 2 natural esters. The comparative tests display a wide range of fire properties for the respective Liquids. The higher the fire point the longer it takes for a Liquid to ignite. Polluting the samples with 3% mineral oil decreased the time to ignition, especially for the natural esters. The heat release rate calculated from the cone experiments show analogies with the heat of combustion values tabled, except for the silicone Liquid where a crust formation on the Liquid’s surface impeded combustion. Heat losses from the burning surface to Cooler Liquid below or boundaries greatly also affect the burning behaviour. These complexities result in the fact that great care should be taken when scaling this small scale burning behaviour to use in fire safety applications.
Christensen Weston - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Natural Convection Flow in a Detector Using Computational Fluid Dynamics
Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange, 2019Co-Authors: Christensen WestonAbstract:The goal of this research was to simulate the flow, temperature, and impurity concentration within the Deep Underground Neutrino Experiment (DUNE) Single Phase Far Detector using a commercially available computational fluid dynamics (CFD) solver. DUNE is a research collaborative investigating properties of neutrinos in an effort to better understand the origins of matter and behavior of subatomic particles. The Far Detector is a geometrically complex neutrino detector containing: anode plane arrays and cathode plane arrays which induce an electric field within the detection region that causes electrons to drift to the sensing equipment, field cage planes to enclose the neutrino detection region, inlets and outlets for Liquid argon flow, ground planes to ground the electric field outside the detection region, a service floor, and other smaller features. High-fidelity models are required to accurately simulate the flow patterns within the detector. This research investigated the effects of: 1) mesh refinement, 2) turbulent Schmidt number, and 3) the boundary condition employed at the Liquid-ullage interface, i.e. slip vs. no slip. The effect of mesh refinement was analyzed by comparing the results of six levels of mesh refinement, ranging from 40.8 to 151.6 million cells. The simulation was also completed for turbulent Schmidt numbers of 0.5, 0.9, and 2.0 to determine how this property, which is difficult to quantify, impacted the results. Finally, the results of the simulation were compared for using a slip boundary condition at the Liquid-ullage interface to the simulations using a no-slip boundary condition. It was expected that these factors would significantly impact the flow, temperature and impurity concentration within the cryostat and that by comparing the simulation results to experimental data the ideal simulation parameters could be identified and implemented. The computationally generated results of this research are validated using the results of the prototype experimental and simulation data. This thesis research led to three distinct findings. First, appropriate mesh refinement in critical areas, such as near walls or surrounding inlets and outlets led to the outcome that all levels of mesh refinement investigated in this work are able to appropriately capture the movement of Liquid argon within the detector. By capturing the complex flow features with local mesh refinements, the impact of global mesh refinement was minimized. Second, the effect of changing the turbulent Schmidt number was negligible, with the impurity concentrations varying less than 0.17% for all turbulent Schmidt numbers in this study. This contradicted the hypothesis that lower turbulent Schmidt numbers would results in greater impurity variance within the detector. This may be due to the extreme purity conditions of the detector but confirms that greater study is necessary to determine to optimum turbulent Schmidt guidelines. Third, the selection of a slip vs. no-slip boundary condition at the ullage-Liquid interface yields significantly different flow and consequently different thermal profiles. The no-slip boundary condition leads to the predictions of significantly warmer temperatures in the Liquid volume. The slip condition provided results much more consistent with those seen in experiments than the no-slip condition. This is most likely due to the reduced mixing between the warmer gaseous argon and Cooler Liquid argon caused by forcing the fluid along the interface to remain stationary. The slip condition allows the simulated fluid to move along this interface, which is consistent with conditions in the actual detector
K Nissen - One of the best experts on this subject based on the ideXlab platform.
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work loss during compression of a saturated mixture in a compressor
1997Co-Authors: D Tootle, K Annamalai, K NissenAbstract:It is idealized that when compressing a vapor/Liquid mixture inside the saturation dome adiabatically and quasi-statically, there is not entropy generation. In fact, the process is inherently irreversible due to temperature gradients created during the compression process between the Liquid and vapor portions of the mixture. During compression, the vapor portion of the mixture will increase in pressure and temperature rapidly while the Liquid portion of the mixture will remain relatively constant acting as an incompressible Liquid. After the compression, the hotter vapor will transfer heat irreversibly to the Cooler Liquid drops to achieve thermal equilibrium creating more vapor, thereby changing the quality of the mixture and causing an increase in entropy. This paper analyzes the extent of the irreversibility in the process by modeling the saturated mixture to undergo adiabatic compression and then letting the mixture achieve adiabatic equilibration. Estimates are presented for the highest possible work loss (or irreversibility) and parametric studies are conducted for the effect of quality and compression ratio. The results can be used to address an ideal operating condition for a compressor that experiences this situation, such as the transient operation during startup where a saturation condition of the working substance can exist.
D Tootle - One of the best experts on this subject based on the ideXlab platform.
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work loss during compression of a saturated mixture in a compressor
1997Co-Authors: D Tootle, K Annamalai, K NissenAbstract:It is idealized that when compressing a vapor/Liquid mixture inside the saturation dome adiabatically and quasi-statically, there is not entropy generation. In fact, the process is inherently irreversible due to temperature gradients created during the compression process between the Liquid and vapor portions of the mixture. During compression, the vapor portion of the mixture will increase in pressure and temperature rapidly while the Liquid portion of the mixture will remain relatively constant acting as an incompressible Liquid. After the compression, the hotter vapor will transfer heat irreversibly to the Cooler Liquid drops to achieve thermal equilibrium creating more vapor, thereby changing the quality of the mixture and causing an increase in entropy. This paper analyzes the extent of the irreversibility in the process by modeling the saturated mixture to undergo adiabatic compression and then letting the mixture achieve adiabatic equilibration. Estimates are presented for the highest possible work loss (or irreversibility) and parametric studies are conducted for the effect of quality and compression ratio. The results can be used to address an ideal operating condition for a compressor that experiences this situation, such as the transient operation during startup where a saturation condition of the working substance can exist.
K Annamalai - One of the best experts on this subject based on the ideXlab platform.
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work loss during compression of a saturated mixture in a compressor
1997Co-Authors: D Tootle, K Annamalai, K NissenAbstract:It is idealized that when compressing a vapor/Liquid mixture inside the saturation dome adiabatically and quasi-statically, there is not entropy generation. In fact, the process is inherently irreversible due to temperature gradients created during the compression process between the Liquid and vapor portions of the mixture. During compression, the vapor portion of the mixture will increase in pressure and temperature rapidly while the Liquid portion of the mixture will remain relatively constant acting as an incompressible Liquid. After the compression, the hotter vapor will transfer heat irreversibly to the Cooler Liquid drops to achieve thermal equilibrium creating more vapor, thereby changing the quality of the mixture and causing an increase in entropy. This paper analyzes the extent of the irreversibility in the process by modeling the saturated mixture to undergo adiabatic compression and then letting the mixture achieve adiabatic equilibration. Estimates are presented for the highest possible work loss (or irreversibility) and parametric studies are conducted for the effect of quality and compression ratio. The results can be used to address an ideal operating condition for a compressor that experiences this situation, such as the transient operation during startup where a saturation condition of the working substance can exist.