Numerical investigation of transient, low-power metal vapour discharges occurring in near limit ignitions of flammable gas

Abstract

This article presents an investigation of a transient (30 µs -5 ms) electrical discharge in metal vapour with low voltage (≤ 30 V) and current (≤ 200 mA), drawn between two separating electrodes. Discharges of this type are rarely studied, but are important in electrical explosion safety, as they can ignite flammable gasses. An empirical model is developed based on transient recordings of discharge voltages and currents and high speed broadband image data. The model is used for predicting the electrical waveforms and spatial power distribution of the discharge. The predicted electrical waveforms show good accuracy under various scenarios. To further investigate the underlying physics, the model is then incorporated into a simplified 3-D gas dynamics simulation including molecular diffusion, heat transfer and evaporation of metal from the electrode surface. The local thermodynamic equilibrium (LTE) assumption is next used to calculate electrical conductivity from the simulated temperature fields, which in turn is integrated to produce electrical resistance over time. This resistance is then compared to that implied by the voltage and current waveforms predicted by the empirical model. The comparison shows a significant discrepancy, yielding the important insight that the studied discharge very likely deviates strongly from LTE.

Measurement of medium-voltage AC air arc temperature and particle number density based on dual-wavelength Moiré deflection technology

“…The characteristic time of the chemical reaction between arc particles is considered to be shorter than the characteristic time of the physical movement of the particles under the action of an external electric field, and in this scenario, the arc will be in the LCE state. An arc can be generally described using the 'two-temperature magnetohydrodynamic model,' which includes two variables related to the temperature: the electron temperature and heavy particle temperature [9][10][11]. The evolution of the particle components and physical fields of the arc under LCE can be obtained using macroscopic thermodynamic statistical laws [12].…”

Computational fluid dynamics simulation of cryogenic safety analysis in an liquefied natural gas powered ship during liquefied natural gas leakage

“…Thus, the safety design analysis for LNG-powered ships is necessary, preferably in the basic design stage (Paik et al, 2011). Many researchers have developed the safety analysis simulation of LNG leakage hazards and established several models, such as zone models, integral models (Puttock, 1987;Shekhar et al, 2018), semiempirical models (Zhou et al, 2013), and computational fluid dynamics (CFD) models (Pula et al, 2005;Blanco and Zingg, 2007;Luketa-Hanlin et al, 2007). Among them, CFD simulation has been widely applied to analyze the leakage risk of LNG-powered ships under various conditions such as cryogenic impact, gas diffusion and explosion progress (Rigas and Sklavounos, 2006;Gavelli et al, 2008).…”

Simulation of the flow of an explosive atmosphere exposed to a hot surface

“…Due to the development of numerical tools and the increase of computational power, simulations represent today an attractive approach to study ignition-related processes (for example Esmaeelzade et al (2019);Shekhar et al (2018)). As regards hot surfaces, Griffiths and Barnard (2012) analyzed the influence of the size of the surface on the ignition temperature.…”