The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Yang Cao - One of the best experts on this subject based on the ideXlab platform.
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Study of wall ablation on low-voltage arc interruption: The effect of Stefan Flow
Journal of Applied Physics, 2019Co-Authors: Jindong Huo, Svetlana Selezneva, Linda Jacobs, Yang CaoAbstract:Low-voltage circuit breakers provide essential protection for industrial and residential power installations, by taking advantage of the voltage drop at the electrode–plasma interface to force current zero. This is accomplished by using the magnetic force and unbalanced pressure on the arc as the contacts open to push the arc toward a stack of steel plates that break the arc into subarcs and thereby multiply the number of voltage drops. As the fault current can be high, substantial energy can be dissipated, which results in interactions among the arc and solid counterparts in terms of wall ablation and metal evaporation. In this study, ablation experiments are conducted to demonstrate its great influence on the arc voltage and on the pressure field. Significant progress has been accomplished in the computation of arc dynamics through the coupling of fluid motion with electromagnetics, although an important mechanism in arc breaking simulation, the effect of Stefan Flow caused by species generation, has not been considered. We report out a numerical approach for taking into account the effect of Stefan Flow, particularly for the breakers with high gasifying wall materials. This approach accounts for the diffusion induced convection due to added-in species from the evaporation surfaces, which will largely influence the Flow field and the properties of the plasma mixture. Apart from the voltage drop, this mechanism plays an important role in simulating arc interruption. The ability of conducting Stefan Flow computation further enhances the understanding of arc behaviors and improves the design of practically oriented low-voltage circuit breakers.
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Low- Voltage Arc Interruption Computation: the Effect of Stefan Flow
2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), 2018Co-Authors: Jindong Huo, Svetlana Selezneva, Linda Jacobs, Yang CaoAbstract:Low-voltage circuit breakers provide essential protection for industrial and residential power distribution, by taking advantage of cathode drop to force current zero. This is accomplished by using the magnetic force and pressure on the arc as the contacts open to push the arc towards a stack of steel plates which break the arc into sub-arcs and thereby multiply the number of cathode drops. As the fault current can be high, substantial energy can be dissipated, which results in interactions among the arc and solid materials: ablation of wall materials. Comprehensive CFD/MHD studies have been conducted for arc running and splitting, although an important mechanism in arc breaking computation, the effect of Stefan Flow induced by species generation, has not been considered. In this work, we report out a simulation approach for taking into account the effect of Stefan Flow, particularly for the breakers with highly gasified wall materials. This approach accounts for the initial velocity of added-in species from the surface of the polymer wall and electrodes' surface, which will largely influence the Flow field and the property of plasma mixture. The ability of conducting computation with considering Stefan Flow effect will further enhances the accuracy of arc simulation in low-voltage circuit breakers.
V Dimal - One of the best experts on this subject based on the ideXlab platform.
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Continuum regime motion of a growing droplet in opposing thermo-diffusiophoretic and gravitational fields of a thermal diffusion cloud chamber
Journal of Aerosol Science, 2001Co-Authors: S Bakanov, J Smolik, S Zaripov, V DimalAbstract:A model for the motion of aerosol particles by Stefan Flow, thermo-diffusiophoresis and gravity in a continuum regime is described, which considers a phase change on the particle surface. It is tested in a thermal diffusion cloud chamber where a droplet formed by nucleation quickly grows and simultaneously moves upwards due to vertical temperature and concentration gradients. Kinetic coefficients are assumed to be constant. Model predictions of the height where the droplet reverses its motion are in satisfactory agreement with the experimental results of Ždimal et al. ((1996). Colloids Surfaces A, 106, 119). The droplet motion seems to be predicted well at higher gradients and vapor fluxes, but model underestimates droplet motion at lower ones. For those cases also the free-molecule and transition regimes need to be included.
Kuan Zhou - One of the best experts on this subject based on the ideXlab platform.
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Mass transfer coefficients considering boundary layer reaction in oxy-fuel combustion of coal char
Fuel, 2014Co-Authors: Kuan ZhouAbstract:Abstract In comparison with conventional air combustion, char particle reacts with higher concentrations of O 2 and CO 2 in the oxy-fuel combustion. At higher temperatures, strong Stefan Flow is formed at the char surface and the CO gas-reaction occurs in the boundary layer, which have significant effects on the char reaction and the mass transfer. But Stefan Flow and CO gas-phase reaction are often neglected in the study of conventional coal combustion. In this work, with the consideration of CO oxidation and Stefan Flow in the boundary layer of a char particle, modifications to the mass transfer coefficients were presented for the coal oxy-fuel combustion. Better improvement was achieved in predicting the mass transfer coefficient by comparing with the experimental data. Further analyses indicated that the mass transfer coefficient of O 2 decreases and that of CO 2 , increases in the presence of CO gas-phase reaction. Moreover, the closer the CO flame sheet is to the char surface, the smaller the correction factor of O 2 mass transfer coefficient and the larger the correction factor of CO 2 . If only considering the oxidation reaction at the particle’s surface, the minimum correction factor of O 2 is 0.5 which is 32.5% lower than that in the absence of CO gas-phase reaction. If only the surface gasification reaction is considered, the correction factor for CO 2 will increase rapidly at the flame location of about ten times the particle radius, and reach 1.0 at three times the particle radius which means that it is unnecessary to correct the diffusion coefficient. This is very different from the case neglecting the boundary layer reaction. If the surface oxidation and surface gasification are considered simultaneously, the increase of the number of surface reaction will decrease the mass transfer coefficients for both O 2 and CO 2 , and will have greater influence on CO 2 transfer than on O 2 . These changes of reactive gas mass transfer indicate the significant impacts of CO homogeneous reaction in the oxy-fuel combustion of coal char.
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mass transfer coefficients considering effects of steam in oxy fuel combustion of coal char
Fuel, 2013Co-Authors: Kuan ZhouAbstract:Considering the effects of Stefan Flow and steam in the oxy-fuel combustion of char, correction factors for the mass transfer coefficients of gas reactants, O2, CO2, and H2O, are derived in the present work. By comparisons with the experimental data, the rigid continuous-film model, and the uncorrected single-film model, it is concluded that the corrections greatly improve the predictions of the particle temperature, combustion rates and burnout time. The correction factors are related to the gas components, reaction numbers and rate ratios. Generally, the increase of number and rate of surface reaction will result in the enhancement of Stefan Flow and hence decrease the mass transfer coefficients. But discussion under the typical conditions of oxy-fuel combustion shows that different reaction has different impacts on the mass transfer of reactive gases. In the presence of steam, the correction for O2 is nearly the same as cases neglecting the steam, owing to the low gasification rate of H2O and the accelerative diffusion transfer of O2 in H2O and H2. The correction for CO2 increases slightly by about 3% because the gasification rate of H2O is only a little higher than that of CO2. On the contrary, the participation of O2 and CO2 reactions plays considerable role in the mass transfer coefficient of H2O. Especially, the high rate reaction, like O2 oxidation, has more remarkable effects on the mass transfer of gas reactants. Therefore, more attention should be paid to the modification of mass transfer coefficients when the O2 oxidation reaction is prevailing in the char oxy-fuel combustion, for the transfer coefficients will be greatly changed.
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Effects of Stefan Flow on Ignition and Heat Transfer of a Char Particle in O2/CO2 Atmospheres
Energy & Fuels, 2013Co-Authors: Kuan ZhouAbstract:Stefan Flow, occurring at the surface of a carbon particle, is often neglected or simply regarded as a mass transfer phenomenon in pulverized-coal combustion. In this work, considering the Stefan f...
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effects of Stefan Flow on ignition and heat transfer of a char particle in o2 co2 atmospheres
Energy & Fuels, 2013Co-Authors: Kuan ZhouAbstract:Stefan Flow, occurring at the surface of a carbon particle, is often neglected or simply regarded as a mass transfer phenomenon in pulverized-coal combustion. In this work, considering the Stefan f...
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effects of Stefan Flow and co oxidation on char particle combustion in o2 co2 atmosphere
Fuel, 2013Co-Authors: Juan Yu, Kuan Zhou, Wei OuAbstract:Abstract Stefan Flow occurring at the surface of char and CO oxidation in the boundary layer are often neglected in the conventional pulverized-coal air combustion. In this work, effects of Stefan Flow and CO oxidation in the oxy-fuel burning are investigated numerically and experimentally. A mathematical model is firstly developed for the combustion of a carbon particle. Comparisons with the experiment data exhibit better agreement for the present model than that neglecting the effects of Stefan Flow and CO oxidation. Predictions also show that neglect of the Stefan Flow and CO oxidation results in overestimating the particle temperature, shortening the burnout time, and especially, being unable to predict the particle extinguishment and the final burnout rate correctly. Notable effects of Stefan Flow and CO oxidation on the burnout time generally appear under conditions of lower O 2 concentration, lower reactivity, lower gas temperature and larger particle size where the combustion is prone to be controlled by reaction kinetics and gas diffusion simultaneously (Regime II). On the contrary, the effects of Stefan Flow and CO oxidation are relatively insignificant on the burnout time in the diffusion-controlled combustion (Regime III). However, whether the Stefan Flow and CO oxidation could be neglected in such cases still depends on the actual combustion conditions and simulation results.
Alain Berlemont - One of the best experts on this subject based on the ideXlab platform.
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A Level Set Method for vaporizing two-phase Flows
Journal of Computational Physics, 2007Co-Authors: Solenne Tanguy, Timothy Menard, Alain BerlemontAbstract:Development and applications of numerical methods devoted to reactive interface simulations are presented. Emphasis is put on vaporization, where numerical difficulties arise in imposing accurate jump conditions for heat and mass transfers. We use both the Level Set Method and the Ghost Fluid Method to capture the interface motion accurately and to handle suitable jump conditions. A local vaporization mass Flow rate per unit of surface area is defined and Stefan Flow is involved in the process. Specific care has been devoted to the extension of discontinuous variables across the interface to populate ghost cells, in order to avoid parasitic currents and numerical diffusion across the interface. A projection method is set up to impose both the velocity field continuity and a divergence-free condition for the extended velocity field across the inter- face. The d2 law is verified in the numerical simulations of the vaporization of an isolated static drop. Results are then presented for a water droplet moving in air. Vapor mass fraction and temperature fields inside and outside the droplet are presented.
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A level set method for vaporizing two-phase Flows
Journal of Computational Physics, 2007Co-Authors: Sebastien Tanguy, Thibault Menard, Alain BerlemontAbstract:Development and applications of numerical methods devoted to reactive interface simulations are presented. Emphasis is put on vaporization, where numerical difficulties arise in imposing accurate jump conditions for heat and mass transfers. We use both the Level Set Method and the Ghost Fluid Method to capture the interface motion accurately and to handle suitable jump conditions. A local vaporization mass Flow rate per unit of surface area is defined and Stefan Flow is involved in the process. Specific care has been devoted to the extension of discontinuous variables across the interface to populate ghost cells, in order to avoid parasitic currents and numerical diffusion across the interface. A projection method is set up to impose both the velocity field continuity and a divergence-free condition for the extended velocity field across the interface. The d(2) law is verified in the numerical simulations of the vaporization of an isolated static drop. Results are then presented for a water droplet moving in air. Vapor mass fraction and temperature fields inside and outside the droplet are presented. (c) 2006 Elsevier Inc. All rights reserved.
Jindong Huo - One of the best experts on this subject based on the ideXlab platform.
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Study of wall ablation on low-voltage arc interruption: The effect of Stefan Flow
Journal of Applied Physics, 2019Co-Authors: Jindong Huo, Svetlana Selezneva, Linda Jacobs, Yang CaoAbstract:Low-voltage circuit breakers provide essential protection for industrial and residential power installations, by taking advantage of the voltage drop at the electrode–plasma interface to force current zero. This is accomplished by using the magnetic force and unbalanced pressure on the arc as the contacts open to push the arc toward a stack of steel plates that break the arc into subarcs and thereby multiply the number of voltage drops. As the fault current can be high, substantial energy can be dissipated, which results in interactions among the arc and solid counterparts in terms of wall ablation and metal evaporation. In this study, ablation experiments are conducted to demonstrate its great influence on the arc voltage and on the pressure field. Significant progress has been accomplished in the computation of arc dynamics through the coupling of fluid motion with electromagnetics, although an important mechanism in arc breaking simulation, the effect of Stefan Flow caused by species generation, has not been considered. We report out a numerical approach for taking into account the effect of Stefan Flow, particularly for the breakers with high gasifying wall materials. This approach accounts for the diffusion induced convection due to added-in species from the evaporation surfaces, which will largely influence the Flow field and the properties of the plasma mixture. Apart from the voltage drop, this mechanism plays an important role in simulating arc interruption. The ability of conducting Stefan Flow computation further enhances the understanding of arc behaviors and improves the design of practically oriented low-voltage circuit breakers.
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Low- Voltage Arc Interruption Computation: the Effect of Stefan Flow
2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), 2018Co-Authors: Jindong Huo, Svetlana Selezneva, Linda Jacobs, Yang CaoAbstract:Low-voltage circuit breakers provide essential protection for industrial and residential power distribution, by taking advantage of cathode drop to force current zero. This is accomplished by using the magnetic force and pressure on the arc as the contacts open to push the arc towards a stack of steel plates which break the arc into sub-arcs and thereby multiply the number of cathode drops. As the fault current can be high, substantial energy can be dissipated, which results in interactions among the arc and solid materials: ablation of wall materials. Comprehensive CFD/MHD studies have been conducted for arc running and splitting, although an important mechanism in arc breaking computation, the effect of Stefan Flow induced by species generation, has not been considered. In this work, we report out a simulation approach for taking into account the effect of Stefan Flow, particularly for the breakers with highly gasified wall materials. This approach accounts for the initial velocity of added-in species from the surface of the polymer wall and electrodes' surface, which will largely influence the Flow field and the property of plasma mixture. The ability of conducting computation with considering Stefan Flow effect will further enhances the accuracy of arc simulation in low-voltage circuit breakers.