Effects of Anode Nozzle Geometry on Ambient Air Entrainment Into Thermal Plasma Jets Generated by Nontransferred Plasma Torch

Abstract

Abstract-The geometrical effects of an anode nozzle in a nontransferred plasma torch on air entrainment are examined by measurements of plasma composition using a quadruple mass spectrometry. In addition, the radial and axial distributions of plasma enthalpy, temperature, and velocity are measured by using an enthalpy probe method. Two types of anode nozzle geometry, i.e., cylindrical and stepped nozzles, are employed for the torch in this experiment. As a result of gas composition measurements, the new stepped nozzle turns out to produce a thermal plasma jet having lower air content in it compared with the conventional cylindrical nozzle. The plasma jet produced by the stepped nozzle exhibits higher enthalpy and temperature, especially around the core of the plasma flame, due to less intrusion of ambient air. Furthermore, the axial velocity distribution with a slowly changing variation is observed in the stepped nozzle case because of the plasma flow less disturbed by air entrainment. From these experimental results of thermal plasma characteristics and nozzle geometry effects on air entrainment, a high quality of coating products are expected in plasma spraying by using the stepped nozzle due to higher plasma enthalpy and temperature and lower velocity drop along the plasma jet.Index Terms-Air entrainment, enthalpy probe, nozzle geometry effects, plasma spraying, plasma torch, quadruple mass spectrometry.

Thermal Plasma Decomposition of Fluorinated Greenhouse Gases

“…In the numerical simulation, the governing fluid equations consisting of mass, momentum, and energy conservation are solved under the steady-state, twodimensional, and axis-symmetric conditions. Although the turbulent thermal plasma is an inherently threedimensional time transient phenomena, a time averaged axis-symmetric modeling on thermal plasma jets have been in good agreement with experimentally measured results [50][51][52]. Since the k-ε turbulence model is widely used for turbulent thermal plasma flow modeling, it is also incorporated to include turbulence effects [53].…”

“…Therefore, enhancement of gas mixing between cold waste gas and high temperature plasma jet is required for an efficient decomposition of non-degradable fluorinated compounds. The intrinsic turbulent nature of thermal plasma enhances the mixing process between the plasma jet and waste gas through the entrainment process [51,61,62]. Turbulent intensities are compared in Fig.…”

Thermal Plasma Synthesis of Nano-Sized Powders

“…For example, non-transferred DC torches with hot cathodes normally produce a hot ionized flame with temperatures in the range of 8,000~16,000 K at the torch exit [2]. The velocities of this flame can reach to hundreds m/s or to several thousand m/s depending on the torch nozzle structures at a given gas flow rate [2,[12][13][14]. On the other hand, RF plasma torches produce relatively large flame of 5,000~10,000 K moving at mild velocities of up to several tens m/s [2,5,[15][16][17].…”

Time-resolved tomographic measurements of temperatures in a thermal plasma jet

“…The entrainment may be diagnosed by Thomson scattering [21], by spectrally resolved measurements detecting the radiation of the core and surrounding gases [22] or by enthalpy probes [23].…”