L. Pershin, L. Chen, J. Mostaghimi, Centre for Advanced Coating Technology, University of Toronto, Toronto, ON, Canada
Thermal spray torches commonly use argon for plasma generation. Low thermal properties of argon, however, limit the thermal efficiency of the torches. Use of molecular gases, which must dissociate before ionization, requires larger energy input resulting in enthalpy increase of the plasma.
In this paper, the effect of various gas compositions ( Ar, Ar+H2, and CO2+CH4) on a torch voltage-current characteristics, power and thermal efficiency were studied. At the same time, YSZ particle conditions in-flight were compared. Higher thermal conductivity and efficiency of CH4+CO2 gas mixture reflect in more favorable sprayed particle conditions, particle temperature in particular. At 50mm spray distance YSZ particle temperatures were 2470°C and 2896°C for Ar+H2 and CH4+CO2 correspondingly. Typical arc voltage for the torch operating in CO2+CH4 was 130-180V in comparison with 45-60 V for Ar+H2 and thermal efficiency also was up to 20-40% higher.
Summary: In this work, plasma flow inside a cascaded DC torch, effect of a plasma gas composition (Ar or CO2+CH4) and torch performance were studied. Both, laminar model and k-å turbulence model were employed and compared in the simulations.
