Radial Distributions Of Gas Temperature Research Articles

Determination of 915-MHz Atmospheric Pressure Air Microwave Plasma Torch (MPT) Parameters

The gas temperature, electron temperature, and electron density are critical parameters that affect microwave plasma chemistry processes in industrial applications. Using optical emission spectroscopy (OES), the gas temperature and electron density of a 915-MHz atmospheric pressure air microwave plasma torch (MPT) were investigated at various absorbed power levels and radial positions. In addition, the variation in the electron temperatures of 915-MHz atmospheric pressure argon microwave plasma filaments was analyzed as a function of the absorbed power. The experimental results showed that: 1) the absorbed power had little effect on the radial gas temperature or electron density; 2) the skin effect was present in the 915-MHz atmospheric pressure air MPT, where it causing caused hollowing in the center of the radial gas temperature distribution; 3) the electron density reached approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times10$ </tex-math></inline-formula> 13 cm−3 and was almost insensitive to variations in the absorbed power in the center of the 915-MHz atmospheric pressure air MPT; and 4) the upper limit of the 915-MHz atmospheric pressure microwave plasma filament electron temperature increased from approximately 1 to approximately 3 eV as the absorbed power increased from 2.0 to 6.3 kW.

Imaging Diagnostics and Gas Temperature Measurements of Atmospheric-Microwave- Induced Air Plasma Torch

In this article, the core of an atmospheric-microwave-induced air plasma torch is resolved and measured by adjusting the exposure time of a high-speed camera. Gas temperature measurements of the microwave plasma core are achieved by molecular emission spectrometry of the ${A}^{2}{\Sigma }^{+}\to {X}^{2}{\Pi }_{r}$ electronic system of OH radicals. How the geometric features and gas temperature of the plasma core are related to the magnetron power and gas flow rate is explored, and the radial temperature distribution of the microwave plasma is measured. In these experiments, the magnetron power is 1033–2023 W and the gas flow rate is 10–20 L/min. The results show that microwave plasma has two parts, namely, its core and outer shell. The core radius increases approximately linearly with the magnetron power, whereas it does not change substantially with the gas flow rate. Gas temperature can be used to distinguish the core from the outer shell because the former can reach 8000 K, while the latter cools down from 5500 K. Moreover, the core temperature changes with neither the magnetron power nor the gas flow rate. Finally, a method to control the radial distribution of gas temperature of microwave plasma torch is presented.

Thermocouple and electric probe measurements in a cold atmospheric-pressure microwave plasma jet

A cold atmospheric-pressure plasma jet was studied using the novel microwave plasmatron recently developed. Cold plasma jet was generated in Ar flow by electrode 2.45 GHz discharge of up to 200 W power in the portable plasmatron burner (torch) with 2.5 cm diameter outlet. Oscillograms and floating potential dependences on distance from the torch outlet were measured by planar electric probe. Axial and radial distributions of gas temperature in a cold plasma jet were obtained by means of thermocouple method.

Computer study of the gas temperature profile in copper and copper vapor halide lasers

Due to their unique radiation properties, metal vapor lasers find a variety of applications, including being used as a high- brightness amplifier in new active optical systems. This type of systems has been actively developed in recent years and is applied for visual control of fast processes in screening the background illuminations. A computer model is built and applied to an existing laser source allowing to determine the radial distribution of gas temperature in the cross section of the laser tube. Computations are performed using a preset qualitative type radial distribution of the electric power supplied to the gas discharge. The influence of the electric power supplied to the gas discharge and the wall temperature on the thermal resistance of the gas discharge was evaluated by means of computer simulations. The proposed methodology allows the planning of experiments and developing new laser sources with improved output characteristics.

Analytical calculation of the gas temperature and measurement of the electron temperature for gas discharges in Ne and He mixtures with copper, bromine, hydrogen and strontium

Thermal conductivities of binary gas systems are calculated on the basis of 12-6 Lennard-Jones and rigid sphere inter-atomic interaction approximations for the case of gas discharges in He and Ne with small admixtures of copper, bromine, hydrogen and strontium. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, analytical solutions of the steady-state heat conduction equation are found for two cases of uniform and non-uniform power input, respectively. For both cases the average gas temperature is found by averaging the radial gas temperature distribution over the radius. Measurement of the relative intensities of some He and Ne spectral lines originating from different upper levels has enabled us to determine the average electron temperature.

Theoretical and experimental determination of gas and electron temperatures for gas discharges in Ne and He mixtures with copper, bromine, hydrogen and strontium

Thermal conductivities of binary gas systems are calculated on the basis of 12-6 Lennard-Jones and rigid sphere inter-atomic interaction approximations for the case of gas discharges in He and Ne with small admixtures of copper, bromine, hydrogen and strontium. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, an analytical solution of the steady-state heat conduction equation is found for two discharge tube constructions. Two cases of uniform and non-uniform power input are considered. For both cases the average gas temperature is found by averaging the radial gas temperature distribution over the radius. Measurement of the relative intensities of some He and Ne spectral lines, originating from different upper levels, has enabled us to determine the average electron temperature.

Theoretical and experimental study of some basic processes in He-TlI and Ne-TlI plasma - asymmetric charge transfer, penning ionization and diffusion

The diffusion coefficients of thallium and iodine atoms in a binary system with helium and neon are calculated on the basis of 12-6 Lenard-Jones and rigid sphere models. Cross-sections and rate constants for thermal energy charge transfer into some Tl+ and I+ excited states are theoretically and experimentally obtained for a gas discharge in He-TlI and Ne-TlI mixtures. Cross-sections and rate constants for Penning ionization into Tl+ and I+ ground and excited states are calculated for Penning collisions with the He and Ne metastable atoms. Since the characteristic constants studied depend on the gas temperature, the radial gas temperature distribution is also calculated through solving the heat conduction equation.

Multiple growth and characterization of thick diamond single crystals using chemical vapour deposition working in pulsed mode

In this paper, the fast growth of three thick diamond single crystals using the chemical vapour deposition (CVD) method working in a pulsed mode is reported. After 48 h, a total of half a carat of uncoloured synthetic diamond was obtained. These crystals, exhibiting thicknesses of 430, 570 and 900 μm, were then thoroughly analysed by a wide range of characterization techniques, such as Raman spectroscopy, UV and IR absorption, photoluminescence (PL) and cathodoluminescence (CL). All three samples turned out to be of relatively high quality but small differences in purity and quality could be detected. These appeared to be directly related to the slight inconsistence of the substrate temperature during growth that ranged from 800 to 900 °C due to non-uniformity in the radial distribution of gas temperature. A higher contamination by residual nitrogen impurities has been evidenced for the two samples that were grown with the lowest temperature as confirmed by the PL and UV absorption spectra, as well as a lower free excitonic emission in CL. Finally a 900 °C growth temperature was shown to be more favourable to good quality and fast growth rate.

Spectroscopic Diagnostics of Atmospheric Pressure Helium Dielectric Barrier Discharges in Divergent Fields

AbstractSummary: We present optical emission spectroscopy studies of atmospheric pressure glow discharges in flowing pure helium (He), and He/nitrogen (N2) mixtures. Two different metallic high‐voltage electrode geometries have been examined, namely needle and cylindrical, the grounded dielectric‐covered electrode being planar. The axial and radial distributions of gas temperature have been evaluated from rotational spectra of molecular nitrogen ion emissions as a function of the electrode geometries, the gap spacings and the partial pressure of N2 in He. Also, the spatiotemporal distribution of discharge species in the needle‐plane geometry and the link between gas temperature and light emission intensity are presented. The physical interpretations of these results are discussed with reference to recent work reported by the present authors and by others.Axial and time‐dependent intensity distribution of the total light emission during the positive voltage half‐cycle, across a needle‐ (dielectric) plane gap.magnified imageAxial and time‐dependent intensity distribution of the total light emission during the positive voltage half‐cycle, across a needle‐ (dielectric) plane gap.

Energetic Characteristics of Oxygen Plasma

AbstractA low‐temperature oxygen plasma is studied using the thermocouple, probe and spectral method in the range of 2–8 Torr pressure, 30–100 mA discharge currents, 0, 5, 10 m/s pumping velocity. The gas temperature, concentrations of electrons and oxygen atoms in the 3p5P state, and the longitudinal electric field are measured. Radial distributions of gas temperature and electron concentration are obtained. Ranges of pressures and currents are found in which considerable increases in electric field, discharge voltage, temperatures of gas and electrons are observed at pumping switched on. An estimate of the rate constant of the steplike ionization through the O2(a1Δg) state is given. The concentration of atomic oxygen in the ground state and excitation constant of the triplet O(3p5P) by electron impact are obtained from the solution of the balance equations and our experimental data.

The gas temperature in and the gas expulsion from a graphite furnace used for atomic absorption spectrometry

A simplified model for heat transfer based on thermal conduction is used to calculate the radial gas temperature distribution inside a semi-enclosed, commercial graphite tube furnace used for atomic absorption spectrometry. In the absence of a forced convective flow of a purge gas, the gas temperature inside the graphite furnace during its heating is lower than the wall temperature. After the wall temperature has attained a steady-state value, the gas temperature approaches the wall temperature and the radial temperature gradient in the gas decreases. The difference between the wall temperature and the gas temperature depends on the temperature program used, the thermal properties of the purge gas, and the atomizer geometry. The residence time of relatively volatile analyte elements is largely controlled by expulsion when wall atomization at high heating rates and high atomization temperatures are used. Analytical sensitivities are often enhanced by vaporizing the analyte into a gas having an approximately constant temperature.

The radial gas-temperature distribution in a positive column in neon

Abstract The radial gas-temperature distribution in the positive column in neon is determined with the aid of a differential interferometer. The essential part of the interferometer was a double slit illuminated by a He-Ne laser. The results are compared with the gas temperatures given by Mouwen, which were obtained from thermocouple measurements.

Transient temperature distributions in cylindrical arc columns following abrupt current changes

Using the shock wave technique, radial distributions of gas temperature have been measured in cylindrical, wall stabilized, arc columns under both steady state and transient conditions. The arc atmosphere was air and the current range 0·5-100 A. The transient measurements included the case of free recovery following sudden current interruption.The temperature profiles have been used in conjunction with published electrical conductivity data to determine electrical conductance values and these show good agreement with direct electrical measurements and theory. This result confirms that the arc plasma is in approximate thermal equilibrium so that the column behaviour may be described solely in terms of thermal processes.The importance of natural radial flow under transient conditions has been estimated by calculating flow velocity profiles from the measured temperature distributions and published gas density data. The results are in good agreement with theory, and show the increasing importance of the radial flow at higher currents.

The constricted positive column in neon

The radial gas temperature distribution in a constricted positive column in neon was measured. The shape of this distribution function can be understood by assuming a thermal constriction model.

Radial temperature measurements of alternating current arcs

Using the shock-wave technique, measurements of the radial distribution of gas temperature of free-burning alternating current arc columns have been determined. Temperature distributions have been determined at different times in the current cycle for arcs of 8 to 25 A r.m.s.The results show that at any point in the arc column the temperature has a mean value on which is superimposed an oscillatory component having a phase and amplitude dependent upon the spatial position. The alternating current arc exhibits, therefore, a cyclic heat-wave phenomenon. From the variations of phase and amplitude of temperature oscillation, thermal diffusivity values have been deduced.The results show that the a.c. arc has a lower temperature, lower conductance and greater power dissipation than the comparable d.c. arc. Consideration indicates that these effects result from the cyclic radial gas flow generated by the oscillatory nature of the discharge.