Axial Injection Research Articles

Images of the Electromagnetic-Field Distribution in a Microwave Reactor Excited by an Axial Injection Torch

The study of the electromagnetic (em) field with a microwave-driven reactor excited by an axial injection torch (TIA) provides direct information about the power coupled to the device. A numerical simulation tool has been developed to calculate the 2-D em fields with a TIA-reactor system in the presence of plasma. The field images are used to monitor the variations of its distribution pattern with changes in the device dimensions, providing general guidelines for device optimization.

Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine

This paper presents an experimental investigation of a novel approach for controlling the rotor tip leakage and secondary flow by injecting cooling air from the stationary casing onto the rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the rotor tip region and its impact on the rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly loaded, high pressure gas turbine stage. Measurements conducted with a two-sensor fast-response aerodynamic probe have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the rotor. Cooling air has been injected in the circumferential direction at a 30 deg angle from the casing tangent, opposing the rotor turning direction through a circumferential array of ten equidistant holes per rotor pitch. Different cooling air injection configurations have been tested. Injection parameters such as mass flow, axial position, and size of the holes have been varied to see the effect on the rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the rotor tip leakage vortex and the rotor tip passage vortex reduce. Both vortices move toward the tip suction side corner of the rotor passage. With an appropriate combination of injection mass flow rate and axial injection position, the isentropic efficiency of the stage was improved by 0.55 percentage points.

Ion source and low energy injection line for a central region model cyclotron

At CIAE, a 100 MeV H(-) cyclotron (CYCIAE-100) is under design and construction. A central region model (CRM) cyclotron was built for various experimental verifications for the CYCIAE-100 project and for research and development of high current injection to accelerate milliampere H(-) beam. The H(-) multicusp source built in 2003 has been improved recently to make the source operation more stable. A new injection line for axial low energy high current injection has been designed and constructed for the CRM cyclotron.

IC-100 accelerator complex for scientific and applied research

Industrial production of nuclear filters has been implemented at the IC-100 cyclotron complex of the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. After the complete upgrade, the cyclotron was equipped with the superconducting ECR ion source and the system of external axial beam injection. The implantation complex was equipped with the special transportation channel with the beam scanning system and the setup for irradiation of polymer films. Intense beams of heavy ions Ne, Ar, Fe, Kr, Xe, I, and W with an energy of ∼1 MeV/nucleon were obtained. the properties of irradiated crystals were studied, different polymer films were irradiated, and several thousands of square meters of track membranes with pore densities varying in a wide range were produced. Other scientific and applied problems can be solved at the cyclotron complex.

A Stark broadening method to determine simultaneously the electron temperature and density in high-pressure microwave plasmas

The aim of this work is to analyse and discuss a spectroscopic method of diagnosis based on the Stark broadening of emission lines to determine the electron density and temperature in atmospheric-pressure plasmas. Usually, when the electron temperature is previously known, the Stark broadening of certain spectral lines spontaneously emitted by the plasma is used to determine the electron density in a rapid and inexpensive way. However, comparing two or more broadening of lines can allow us to diagnose the electron density and temperature simultaneously. To carry out this cross-point method, we must know the Stark broadening dependence on the electron temperature and density for different lines. In this work we have used the first three Balmer series hydrogen lines, whose Stark broadenings were calculated by means of a recent micro-field model existing in the bibliography. The experimental study was made in argon and hydrogen plasma flames. The plasmas were produced at 2.45 GHz by an axial injection torch, which can operate at atmospheric pressure under different experimental conditions to produce appropriate plasmas in ‘open air’. The flame produced in this way is a two-temperature plasma, so it is not in local thermodynamic equilibrium. Moreover, by means of the Boltzmann-plot modified with the p−6 law, we found for the hydrogen plasma that most of the observable atomic states were ruled by the excitation–saturation balance. With this method we could also determine the electron temperature.

Energy balance of a plasma opening switch in the conduction stage

The energy balance of a plasma opening switch (POS) in the stage of conduction is calculated for a system, in which the dominating process is the magnetic field penetration into the plasma bridge volume due to the snowplow effect. This mechanism is typical of a microsecond POS for the megaampere range. The energy and momentum distribution over plasma components in POS with axial and radial injection of multispecies plasma are considered.

Scaling of Conduction and Opening Stages of Microsecond Megaampere Plasma Opening Switches

This paper presents the analysis of experiments carried out on the GIT-4 and GIT-12 installations with microsecond megaampere plasma opening switches. Switches with axial and radial plasma injection are considered. It is shown that the conduction current, depending on the switch geometry and plasma density, is given by the magnetohydrodynamic scaling. The experimentally observed switch features in the opening stage can be explained in frame of the modified erosion model of switch opening.

Two-dimensional electromagnetic model of a microwave plasma reactor operated by an axial injection torch

This paper presents a two-dimensional electromagnetic model for a microwave (2.45 GHz) plasma reactor operated by an axial injection torch. The model solves Maxwell’s equations, adopting a harmonic time description and considering the collision dispersion features of the plasma. Perfect-conductor boundary conditions are satisfied at the reactor walls, and absorbing boundary conditions are used at the open end of the coaxial waveguide powering the system. Simulations yield the distribution of the electromagnetic fields and the average power absorbed by the system for a given spatial profile of the plasma density (tailored from previous experimental measurements), with maximum values in the range 1014−1015 cm−3. Model results reveal that the system exhibits features similar to those of an air-filled, one-end-shorted circular metal waveguide, supporting evanescent or oscillatory solutions for radial dimensions below or above a critical radius, respectively. Results also show that the fractional average power absorbed by the plasma is strongly influenced by the system dimensions, which play a major role in defining the geometry pattern of the electromagnetic field distribution. Simulations are used to provide general guidelines for device optimization.

Ultrasonic properties of granular media saturated with DNAPL/water mixtures

We present the results of four experiments investigating the ultrasonic properties of granular materials partially saturated with trichloroethylene (TCE), a dense non‐aqueous contaminant. P‐wave velocity measurements were made under in situ effective stress conditions using a pulse transmission cell at ≈250 kHz. Two synthetic samples and two natural aquifer cores were fully saturated with water and then subjected to an axial injection of TCE. The resulting measurements show reductions in P‐wave velocity of up to 15% due to contaminant saturation. A theoretical model combining Gassmann fluid substitution and Hill's equation was used to estimate the effects of DNAPL saturation; this model underpredicted observed reductions in velocity at high TCE saturations. A linear relationship, expressed in terms of volumetric contaminant fraction, provided an excellent empirical fit to the laboratory measurements.

Suspension Plasma Spraying of Intermediate Temperature SOFC Components Using an Axial Injection DC Torch

Intermediate temperature SOFC components, such as dense, nanostructured SDC electrolytes (samarium doped ceria) and porous anode sublayers were fabricated by suspension plasma spraying using an axial feed dc plasma torch. The liquid carrier employed in this approach allowed for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a refined microstructure. Dense, thin (<10(m) and non-fractured electrolytes were created. Various processing routes for SOFC half-cells, using tape-cased, plasmasprayed and suspension-sprayed anodes, were explored. Loss of integrity and non-continuous coverage of the anode constituted the principal difficulties in the subsequent electrolyte deposition. The role of suspension feedstock particle size is discussed. Amongst various schemes investigated, a processing route that employs sequential suspension plasma spraying steps for both the electrolyte and the anode, using relatively large primary particles in the feedstock, constituted the most promising approach.

Effect of Gun Nozzle Geometry, Increase in the Entrance Convergent Section Length and Powder Injection Position on Cold Sprayed Titanium Coatings

Nozzle geometry influences gas dynamics, such as gas density, velocity and temperature, making sprayed particle behavior one of the most important parameters in cold spray process. Gas flow at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour (convergent -divergent and convergent-divergent-barrel), entrance geometry of convergent-divergent nozzle and powder injection position at nozzle on the cold spray process. The process changes inside the nozzle were observed through numerical simulation studies and the results were used to find a correlation with coating properties. A titanium powder was usedin the experiments. Working gas (is nitrogen) pressure and temperature at nozzle-intake were 3MPa and 626K, respectively. In addition, the change in the nozzle contour and the change in the convergent section length of the gun nozzle were found to have a slight effect on the coating microstructure. Powder injection position was also found to influence deposition efficiency and coating porosity with titanium powder. Deposition efficiency using axial injection was found to be higher than that using radial injection.

Enhancement of light transmission through nanoslit in a circular metallic film flanked by parallel periodic gratings

ABSTRACTWe investigate the potential of a slit grating structure on a silver film embedded in a high index dielectric film, as a Plasmonic optical antenna in infrared region. Using FDTD calculations it is demonstrated that the transmission properties of the structure has strong dependence on the dimension of dielectric film. By tapering the height of output gratings directionality of the emitted beam has been improved. We propose the application of the Plasmonic antenna and examine its performance in axial injection of light from single mode fiber to photonic crystal waveguide.

Temperature diagnostics in a high-pressure hydrogen microwave plasma torch I: experimental characterization

We present preliminary results of an experimental study of a hydrogen plasma flame produced using a microwave axial injection torch (torche à injection axiale or TIA). This device usually runs in argon or helium at atmospheric pressure providing a stable discharge at high HF power levels and a two-temperature plasma. In the current work, hydrogen plasma is launched in a helium filled chamber to prevent hydrogen-air explosive reactions. Seven spectroscopic hydrogen lines have been detected in the visible spectrum (the Balmer series of hydrogen). Using a Boltzmannplot representation it is shown that the plasma is far from equilibrium, but the electron temperature still can be obtained from a modified plot via a p−x-correction, which shows that the lower energy levels of Balmer series of the hydrogen system is ruled by the excitation-saturation balance (ESB).

Characterization of a high-pressure hydrogen microwave plasma torch using the method of dBR

A hydrogen plasma flame produced by an axial injection torch powered at the microwave frequency of 2.45 GHz is studied using the method of disturbed Bilateral Relations (dBR). The application of this method which relates the influence of equilibrium disturbing, as produced by transport, to equilibrium restoring processes, reveals that the most dominant excitation balance is the Excitation Saturation Balance. Moreover, a global discharge model leads to an electron density of ne = 4.1020m−3 and an electron temperature of Te = 0.86 eV. The gas temperature was estimated to be Th = 0.3 eV. The values of ne and Te were found to be in good agreement with the value obtained with the modified Boltzmann-plot and the crossing method of Stark broadening. The dBR method points out that the first level in partial local Saha equilibrium will be the level with principal quantum number p = 10 which is in fair agreement with experimental results.

Near field flow structure of isothermal swirling flows and reacting non-premixed swirling flames

Two confined lean non-premixed swirl-stabilized flame typologies were investigated in order to achieve detailed information on the thermal and aerodynamic field in the close vicinity of the burner throat and provide correlation with the exhaust emissions. Previous finding indicated the generation of a partially premixed flame with radial fuel injection and a purely diffusive flame with co-axial injection in a swirling co-flow. In the present work, the experimental study is reported which has been conducted on a straight exit laboratory burner with no quarl cone, fuelled by natural gas and air, and fired vertically upwards with the flame stabilized at the end of two concentric pipes with the annulus supplying swirled air and the central pipe delivering the fuel. Two fuel injection typologies, co-axial and radial (i.e., transverse), leading to different mixing mechanisms, have been characterized through different techniques: particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) for a comprehensive analysis of the velocity field, still photography for the detection of flame front and main visible features, and thermocouples for the temperature distribution. Isothermal flow conditions have been included in the experimental investigation to provide a basic picture of the flow field and to comprehend the modifications induced by the combustion process. The results indicated that, although the global mixing process and the main flame structure are governed by the swirl motion imparted to the air stream, the two different fuel injection methodologies play an important role on mixture formation and flame stabilization in the primary mixing zone. Particularly, it has been found that, in case of axial injection, the turbulent interaction between the central fuel jet and the backflow generated by the swirl can induce an intermittent fuel penetration in the recirculated hot products and the formation of a central sooting luminous plume, a phenomenon totally absent in the case of radial injection.

Heat transfer enhancement with the use of nanofluids in radial flow cooling systems considering temperature-dependent properties

Heat transfer enhancement capabilities of coolants with suspended metallic nanoparticles inside typical radial flow cooling systems are numerically investigated in this paper. The laminar forced convection flow of these nanofluids between two coaxial and parallel disks with central axial injection has been considered using temperature dependent nanofluid properties. Results clearly indicate that considerable heat transfer benefits are possible with the use of these fluid/solid particle mixtures. For example, a Water/Al 2O 3 nanofluid with a volume fraction of nanoparticles as low as 4% can produce a 25% increase in the average wall heat transfer coefficient when compared to the base fluid alone (i.e., water). Furthermore, results show that considerable differences are found when using constant property nanofluids (temperature independent) versus nanofluids with temperature dependent properties. The use of temperature-dependent properties make for greater heat transfer predictions with corresponding decreases in wall shear stresses when compared to predictions using constant properties. With an increase in wall heat flux, it was found that the average heat transfer coefficient increases whilst the wall shear stress decreases for cases using temperature-dependent nanofluid properties.

Controlled synthesis of alumina nanoparticles using inductively coupled thermal plasma with enhanced quenching

Synthesis of alumina nanoparticles in an Ar–O 2 inductively coupled radio frequency (rf) plasma controlled by axial quench gas injection was investigated. The flow and temperature fields for various quench gas flow rates in the plasma reactor, as well as the corresponding quench rates, were predicted using a renormalization group (RNG) k– ε turbulence model. Nanosize alumina particles were synthesized from the vapor phase by oxidation of aluminum in the plasma. The collected products were characterized by means of field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), and BET surface area analysis. The dependences of particle size and shape on the injection position and the flow rate of the quench gas were discussed.

Air Plasma Spraying of LSM/YSZ SOFC Composite Cathodes

Porous composite cathodes containing (La0.8Sr0.2)0.98MnO3 (LSM) and yttria stabilized zirconia (YSZ) for use in solid oxide fuel cells (SOFCs) have been produced by air plasma spraying. Deposition was carried out using axial powder injection for increased deposition efficiency and composition control. A number of composite cathodes were produced using different combinations of parameter values within the identified range. Successful coatings were then characterized for composition and porosity using EDX and SEM. As a result of these tests, combinations of input parameter values were identified that are best suited to the production of coatings with microstructures appropriate for use in SOFC composite cathodes.

Thermal inequilibrium of atmospheric helium microwave plasma produced by an axial injection torch

The population density of several excited states has been obtained spectroscopically in a helium plasma sustained by a torch device at atmospheric pressure as a function of the radius in the plasma for different conditions of microwave power and plasma gas flow. The ground-state atom density is determined from the gas temperature, which is deduced from the rotational temperature of the molecular nitrogen ions. The population distribution is fitted to the theoretical results of a collisional-radiative model that includes particle transport. A large deviation of the measured populations is found from the theoretical populations for local thermodynamic equilibrium. The plasma at any radial position is far from local thermodynamic equilibrium; the equilibrium deviation parameter of the ground state is larger than 10 000. The equilibrium deviation parameters of the measured excited-state populations obey the theoretical pk−6 exponential law.

Radial description of excitation processes of molecular and atomic species in a high-pressure helium microwave plasma torch

In this paper, the radial distributions of emissivity of the species present in the helium–nitrogen, helium–oxygen and helium–argon plasmas sustained by the axial injection torch at atmospheric pressure are studied by optical emission spectroscopy using the Abel inversion procedure. The spectrum was scanned for atomic and ionic lines together with rotational bands of neutral and ionic molecules of such species. The variation of the emissivity with different mixture composition was also studied. No emission from oxygen molecular species (O2, ) was found in the discharge or from the atomic ions N+ or O+. The interaction processes between helium and the introduced species are discussed. A decrease in helium emissivity when compared with the pure helium plasma was found for every plasma gas mixture composition.