Modeling heat dominated electric breakdown in air, with adaptivity to electron or ion time scales

Agnihotri, Ashutosh; Hundsdorfer, Willem; Ebert, Ute

doi:10.1088/1361-6595/aa8571

Cited by 7 publications

(7 citation statements)

References 28 publications

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“…From Figure 4, it can be seen that the maximum temperature is consistent with that reported in the literature for similar discharge types [13,20,22,23]. An interesting difference between panels a and b in Figure 4 is that the maximum gas temperature, equal to 1,745 and 2,563 °C in panels a and b, respectively, is located at the middle of the discharge gap instead of the tip of the electrode as shown in panel a, which is in contrast to that shown in panel b and what is typically expected in such type of discharges20 22.…”

Section: Gas Temperature and Gas Rarefactionsupporting

confidence: 88%

“…While multiple studies examined the spatial distribution of temperature in discharge configurations common for activating water [13,[20][21][22][23], very few focused on the temperature distribution in the liquid phase and its consequences on the gas phase, which is the focus of this work. To conduct this analysis, a numerical model developed in an earlier work of the group was upgraded to account for heat transfer and water vaporization at the plasma-liquid interface [24].…”

Section: Introductionmentioning

confidence: 99%

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Resolving the spatial scales of mass and heat transfer in direct plasma sources for activating liquids

Silsby

Dickenson²,

Walsh³

et al. 2022

Front. Phys.

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When plasma is in direct contact with liquid, an exchange of mass and heat between the two media occurs, manifested in multiple physical processes such as vaporization and multiphase heat transfer. These phenomena significantly influence the conditions at the plasma–liquid interface and interfere with other processes such as the multiphase transport of reactive species across the interface. In this work, an experimentally validated computational model was developed and used to quantify mass and energy exchange processes at a plasma–liquid interface. On the liquid side of the interface, it was shown that a thin film of liquid exists where the temperature is approximately three times higher than the bulk temperature, extending to a depth of 10 μm. As the depth increased, a strongly nonlinear decrease in the temperature was encountered. On the plasma side of the interface, plasma heating caused background gas rarefaction, resulting in a 15% reduction in gas density compared to ambient conditions. The combined effect of gas rarefaction and liquid heating promoted vaporization, which increased liquid vapor density in the plasma phase. When water is the treated liquid, it is shown that water vapor constitutes up to 30% of the total gas composition in the region up to 0.1 mm from the interface, with this percentage approaching 70–80% of the total gas composition when the water’s temperature reaches its boiling point.

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Section: Gas Temperature and Gas Rarefactionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Resolving the spatial scales of mass and heat transfer in direct plasma sources for activating liquids

Silsby

Dickenson²,

Walsh³

et al. 2022

Front. Phys.

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show abstract

“…By coupling the fluid equations of discharge dynamics and the hydrodynamic equations for the air flow, Agnihotri et al observed that ambient air heats up to approximately 800 K within tens of nanoseconds within a mean ambient field of 17 kV/cm. This heating process and the induced pressure waves are effective enough to initiate electrical breakdown without the streamer mechanism with locally enhanced electric field tips (Agnihotri et al, 2017). Beyond air perturbations induced by shock waves and heating processes, civil transport aircraft, high-speed air vehicles, or the wind flow around (sharp) objects (Corda, 2017;Fleming et al, 2001;Gu & Lim, 2012;Gumbel, 2001;Lawson & Barakos, 2011) can initiate large pressure and thus air density gradients.…”

Section: Introductionmentioning

confidence: 99%

High‐Energy Emissions Induced by Air Density Fluctuations of Discharges

Köhn

Chanrion

Neubert

2018

Geophysical Research Letters

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Bursts of X‐rays and γ‐rays are observed from lightning and laboratory sparks. They are bremsstrahlung from energetic electrons interacting with neutral air molecules, but it is still unclear how the electrons achieve the required energies. It has been proposed that the enhanced electric field of streamers, found in the corona of leader tips, may account for the acceleration; however, their efficiency is questioned because of the relatively low production rate found in simulations. Here we emphasize that streamers usually are simulated with the assumption of homogeneous gas, which may not be the case on the small temporal and spatial scales of discharges. Since the streamer properties strongly depend on the reduced electric field E/n, where n is the neutral number density, fluctuations may potentially have a significant effect. To explore what might be expected if the assumption of homogeneity is relaxed, we conducted simple numerical experiments based on simulations of streamers in a neutral gas with a radial gradient in the neutral density, assumed to be created, for instance, by a previous spark. We also studied the effects of background electron density from previous discharges. We find that X‐radiation and γ‐radiation are enhanced when the on‐axis air density is reduced by more than ∼25%. Pre‐ionization tends to reduce the streamer field and thereby the production rate of high‐energy electrons; however, the reduction is modest. The simulations suggest that fluctuations in the neutral densities, on the temporal and spacial scales of streamers, may be important for electron acceleration and bremsstrahlung radiation.

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“…where the energy density S vt stored in vibrational states, is relaxed in τ vt = 20 µs [86]. The equation of states for perfect gases, p = (ρ g /m g )k B T, closes equations ( 8)- (10).…”

Section: Initial and Boundary Conditionsmentioning

confidence: 65%

Numerical approaches in simulating Trichel pulse characteristics in point-plane configuration

Shaygani

Adamiak

2023

J. Phys. D: Appl. Phys.

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In this work, a detailed comparison is made of a few different approaches to numerical modeling of non-equilibrium gas discharge plasmas in dry ambient air at atmospheric conditions, leading to Trichel pulse discharge. Simulation models are based on a two-dimensional axisymmetric finite element discretization of point-plane geometry. The negative corona discharge and the hydrodynamic approximation for generic ionic species (electrons, positive and negative ions) are used. The models account for the drift, diffusion, and reactions of the species. They comprise continuity equations coupled to Poisson’s equation for the electric field. Three different formulations were used to specify the ionic reaction rate coefficients. In the first one, the reaction coefficients are approximated by the analytical expressions as a function of the electric field intensity. Two others extract the reaction coefficients from the solution of the Boltzmann equation as a function of the reduced electric field or the electron energy. The effect of gas flow and heating on the pulse characteristics is also investigated. The accuracy of the models has been validated by comparing them with the experimental data.

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Modeling heat dominated electric breakdown in air, with adaptivity to electron or ion time scales

Cited by 7 publications

References 28 publications

Resolving the spatial scales of mass and heat transfer in direct plasma sources for activating liquids

Resolving the spatial scales of mass and heat transfer in direct plasma sources for activating liquids

High‐Energy Emissions Induced by Air Density Fluctuations of Discharges

Numerical approaches in simulating Trichel pulse characteristics in point-plane configuration

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