Electronic excitation temperature profiles in an air microwave plasma torch

Abstract

A 0.9 to 1.5 kW, 2.45 GHz atmospheric pressure air microwave plasma torch has been operated efficiently with less than 1 % reflected power. The plasma is sustained in a 28 mm internal diameter fused quartz tube which penetrates perpendicularly through the wide walls of a tapered and shorted WR-284 (72 x 17 mm cross-section) waveguide. A study has been made of the effects of power and airflow on the electronic excitation temperature, T exc. Abel inversion of radial profile chord averaged Fe I emission lines in the 370 to 377 nm range have been used to obtain localized profile measurements of T exc inside the waveguide excitation region. In general, temperature profiles peak on axis with no evidence of a skin effect in the large diameter (10 mm FWHM emission intensity) plasmas. A maximum central T exc of 6550 K ± 350 K is observed at an airflow rate of 28 lpm. When maintaining a constant flow rate of 14 lpm, a 55 % increase in microwave power from 0.9 to 1.4 kW causes a ~100 % increase in plasma volume without any noticeable effect on the central T exc value. At a constant microwave power of 1.4 kW, an increase in total flow rate from 11 to 28 lpm decreases the volume of the plasma by ~25 % and increases the central T exc by ~13 %. The axially peaked temperature profiles are consistent with an electron density of ~ 10 13 cm-3 .

Plasma Flame Sustained by Microwaves and Burning Hydrocarbon Fuel: Its Applications

“…A number of experimental results in atmospheric microwave plasmas have been reported (Green et al, 2001;Moon et al, 2002). For example, Green et al measured the torch flame temperature inside a discharge tube by making use of the Fe I emission lines in the 370-377 nm range (Green et al, 2001).…”

“…Furthermore, in previous works, the microwave plasma torch has been investigated in various applications such as the abatement of CF 4 , NF 3 and SF 6 , the elimination of chemical and biological warfare agents, and synthesis of carbon nanotube, titanium dioxide, titanium nitride, and zinc oxide (Hong et al, 2004;Kim et al, 2007). Although the microwave plasma torch in air discharge provides high plasma density and high gas temperature in inexpensive ways (Green, 2001), the plasma volume and temperature of the microwave plasma torch decrease drastically outside the discharge tube, thereby limiting its capability of bulk treatment of waste. For example, the gas flow rates in the treatment experiments of CF 4 and phosgene were only tens of liters per minute (lpm), although high destruction and removal efficiency more than 96% had been accomplished Hong et al, 2005).…”

Investigation of Synthesis‐Gas Production via CH4O2Ar Gas Mixture Using Microwave Plasma Torch

“…Moreover, typical MW plasma torch operated at 2.45 GHz produced maximum temperature of 6 000 K at atmospheric pressure while operated by 2 000 W power. [16] For Ar MW plasma at 1 atm with power range of 650-950 W, the thermocouple and optical emission spectroscopy showed temperature of 1 030-2 200 K. [17] In other literature for up to 600 W MW power, lower temperature plasma zone of 500-1 000 K at low pressure near the discharge volume have been estimated. [1] However, regarding our experimental set-up running with maximum MW power of 300 W, regarding ref.…”

“…[1] However, regarding our experimental set-up running with maximum MW power of 300 W, regarding ref. [16] at atmospheric pressure we expect maximum temperature of 2 000-3 000 K for our plasma flame. Obviously, far from the flame, the temperature decreases drastically, where at the distance of 2 cm we measured only 299, 303, and 308 K at 100, 200, and 300 W, respectively.…”

Synthesis of SiOx Nano-Powders Using a Microwave Plasma Torch at Atmospheric Pressure

“…The microwave plasma torch provides a highly unusual and reactive chemical environment at high temperatures. For example, the air microwave plasma torch produces plasma with a high temperature of ~6000 K and a high plasma density of ~10 13 /cm 3 [14]. All the gas flows in Figure 1 were controlled by mass flow controllers (MFCs).…”