Abstract:
Argon TIG arc temperatures have been measured for a wide range of
arc
parameters using the 'Fowler-Milne' spectroscopic method. Prompted by
widespread disagreement amongst temperatures published by previous
groups, a detailed investigation has been carried out into those experimental
and theoretical
aspects of the measurement process that may have led to
incorrect results. The tests have included the variation of
experimental
parameters, the choice of Abel inversion procedure, and the calculation of
argon species number densities and partition functions.
The existence of
equilibrium within the TIG arc has been investigated by
determining temperatures with a number of argon emission lines. Significant
differences 'in derived values of the
temperatures were observed within 1mm
of the
tungsten cathode tip, smaller variations were observed over the
remainder of the arc. The results indicate that
large scale departures from a
Boltzmann distribution
amongst argon atom excited states exists close to the
tungsten tip, deviations decrease with increasing distance from the tip but do
not
disappear completely. lt is believed that the breakdown of equilibrium
within the
argon TIG arc may help to explain the disagreement in temperatures
obtained
by past groups that have used spectroscopic methods.
Despite evidence for non-equilibrium within the arc. results from
previous groups suggest that derived values of .the temperatures are
substantially correct in the main body of the arc. The detailed temperature
maps provide useful information on temperature changes with arc parameters
for the
purposes of modelling and understanding of the arc.
