Publication detail

Fast framing imaging and modelling of vapour formation and discharge initiation in electrolyte solutions

ASIMAKOULAS, L. GRAHAM, W.G. KRČMA, F. DOSTÁL, L. STALDER, K.R. FIELD T.A.

Original Title

Fast framing imaging and modelling of vapour formation and discharge initiation in electrolyte solutions

English Title

Fast framing imaging and modelling of vapour formation and discharge initiation in electrolyte solutions

Type

journal article in Web of Science

Language

en

Original Abstract

The formation of vapour and initiation of electrical discharges in normal saline and other NaCl solutions has been observed and modelled. Millisecond pulses of −160 to −300 V were applied to a sharp tungsten carbide electrode immersed in the liquid. A fast framing camera was used to observe vapour layer growth around the electrode by shadowgraphy. Images were also taken without backlighting to observe emission accompanying breakdown. The conductivity of the vapour layer has been estimated by comparison of experimentally measured impedances with impedances calculated by finite element modelling of the liquid and vapour around the electrode observed by shadowgraphy. The conductivity of the vapour layer is estimated to vary between ∼1 and 10−3Sm−1, which are orders of magnitude higher than expected for water vapour. The reason for the high conductivity is not clear, but may be due to injection of charge carriers into the vapour by corona discharge at the sharp tip and/or the presence of cluster ions in the vapour. Alternatively, the vapour layer may be a foam mixture of high conductivity liquid and low conductivity vapour bubbles. Discharge formation does not occur primarily at the sharp tip of the electrode, but rather at the side. Finite element models of the vapour layer show that the highest electric fields are found close to the sharp tip of the electrode but that the field strength drops rapidly moving away from the tip. By contrast slightly lower, but consistently high, electric fields are often observed between the side of the electrode and the liquid vapour boundary where plasma emission is mostly observed due to the shape of the vapour liquid boundary. The electron number density in the discharge is estimated to be ∼1021m−3. There is evidence from the shadowgraphy for different boiling mechanisms; nucleate boiling at lower voltages and film boiling at higher voltages. A rule of thumb based on a simplistic model is suggested to predict the time to discharge based on electrode area, initial current, and electrolyte temperature, density, conductivity and heat capacity. Supplementary material for this article is available online

English abstract

The formation of vapour and initiation of electrical discharges in normal saline and other NaCl solutions has been observed and modelled. Millisecond pulses of −160 to −300 V were applied to a sharp tungsten carbide electrode immersed in the liquid. A fast framing camera was used to observe vapour layer growth around the electrode by shadowgraphy. Images were also taken without backlighting to observe emission accompanying breakdown. The conductivity of the vapour layer has been estimated by comparison of experimentally measured impedances with impedances calculated by finite element modelling of the liquid and vapour around the electrode observed by shadowgraphy. The conductivity of the vapour layer is estimated to vary between ∼1 and 10−3Sm−1, which are orders of magnitude higher than expected for water vapour. The reason for the high conductivity is not clear, but may be due to injection of charge carriers into the vapour by corona discharge at the sharp tip and/or the presence of cluster ions in the vapour. Alternatively, the vapour layer may be a foam mixture of high conductivity liquid and low conductivity vapour bubbles. Discharge formation does not occur primarily at the sharp tip of the electrode, but rather at the side. Finite element models of the vapour layer show that the highest electric fields are found close to the sharp tip of the electrode but that the field strength drops rapidly moving away from the tip. By contrast slightly lower, but consistently high, electric fields are often observed between the side of the electrode and the liquid vapour boundary where plasma emission is mostly observed due to the shape of the vapour liquid boundary. The electron number density in the discharge is estimated to be ∼1021m−3. There is evidence from the shadowgraphy for different boiling mechanisms; nucleate boiling at lower voltages and film boiling at higher voltages. A rule of thumb based on a simplistic model is suggested to predict the time to discharge based on electrode area, initial current, and electrolyte temperature, density, conductivity and heat capacity. Supplementary material for this article is available online

Keywords

plasma discharge, electrolyte, fast framing camera, electric fields, simulations, boiling regimes, bubbles

Released

04.03.2020

Publisher

IOP

Location

Bristolv

ISBN

0963-0252

Periodical

PLASMA SOURCES SCIENCE & TECHNOLOGY

Year of study

29

Number

3

State

GB

Pages from

035013-1

Pages to

035013-19

Pages count

19

URL

Documents

BibTex


@article{BUT165977,
  author="František {Krčma} and Lukáš {Dostál}",
  title="Fast framing imaging and modelling of vapour formation and discharge initiation in electrolyte solutions",
  annote="The formation of vapour and initiation of electrical discharges in normal saline and other NaCl
solutions has been observed and modelled. Millisecond pulses of −160 to −300 V were applied to a
sharp tungsten carbide electrode immersed in the liquid. A fast framing camera was used to observe
vapour layer growth around the electrode by shadowgraphy. Images were also taken without
backlighting to observe emission accompanying breakdown. The conductivity of the vapour layer
has been estimated by comparison of experimentally measured impedances with impedances
calculated by finite element modelling of the liquid and vapour around the electrode observed by
shadowgraphy. The conductivity of the vapour layer is estimated to vary between ∼1 and
10−3Sm−1, which are orders of magnitude higher than expected for water vapour. The reason for
the high conductivity is not clear, but may be due to injection of charge carriers into the vapour by
corona discharge at the sharp tip and/or the presence of cluster ions in the vapour. Alternatively, the
vapour layer may be a foam mixture of high conductivity liquid and low conductivity vapour
bubbles. Discharge formation does not occur primarily at the sharp tip of the electrode, but rather at
the side. Finite element models of the vapour layer show that the highest electric fields are found
close to the sharp tip of the electrode but that the field strength drops rapidly moving away from the
tip. By contrast slightly lower, but consistently high, electric fields are often observed between the
side of the electrode and the liquid vapour boundary where plasma emission is mostly observed due
to the shape of the vapour liquid boundary. The electron number density in the discharge is estimated
to be ∼1021m−3. There is evidence from the shadowgraphy for different boiling mechanisms;
nucleate boiling at lower voltages and film boiling at higher voltages. A rule of thumb based on a
simplistic model is suggested to predict the time to discharge based on electrode area, initial current,
and electrolyte temperature, density, conductivity and heat capacity.
Supplementary material for this article is available online",
  address="IOP",
  chapter="165977",
  doi="10.1088/1361-6595/ab2cab",
  howpublished="print",
  institution="IOP",
  number="3",
  volume="29",
  year="2020",
  month="march",
  pages="035013-1--035013-19",
  publisher="IOP",
  type="journal article in Web of Science"
}