Jet Operating Research Articles

Ion fluxes and memory effects in an Ar–O2 modulated radiofrequency-driven atmospheric pressure plasma jet

In this work we used molecular beam mass spectrometry to characterize ion fluxes produced by a modulated radiofrequency (RF)-driven atmospheric pressure plasma jet operating in a homogeneous gas environment (Ar + 1% O2). The influence of the RF modulation frequency (100 Hz to 20 kHz) on the ion fluxes was investigated by time-resolved measurements, and the lifetimes of the dominant ions, O2 +, NO+, O−, O2 − and O3 −, were found to be 28 ± 2, 117 ± 8, 7.3 ± 0.4, 17 ± 1 and 23 ± 2 μs, respectively. The absolute ion densities in the near afterglow region were found to be of the order of 1011 cm−3. Significant differences in the dynamics of the positive and negative ions were found; these are explained by the presence of electrons at similar densities in the afterglow produced by electron detachment reactions from negative ions due to the large concentrations of atomic oxygen and singlet delta oxygen. Transitions in ion flux dynamics for different modulation frequencies and at the startup of the plasma were analyzed together with intensified charge coupled device images recording the plasma propagation in order to assess the dynamics of plasma plume propagation and how it is impacted by ‘memory effects’. Quantitative measurements of the ion densities enabling these memory effects are reported. The results in this paper highlight the tremendous impact of memory effects on plasma propagation and the corresponding pre-ionization.

Atomic oxygen density determination in the effluent of the COST reference source using in situ effective lifetime measurements in the presence of a liquid interface

Spatially resolved, absolute densities of atomic oxygen are measured for several helium-based admixtures in the effluent of the COST Reference Microplasma Jet using two-photon absorption laser induced fluorescence (TALIF). Admixtures investigated include a helium-only admixture, four helium/oxygen admixtures (0.1, 0.5, 0.6, and 1.0 oxygen), and a helium/water admixture (2500 ppm water), chosen to coincide with previously published characterizations of plasma-treated liquid. The atomic oxygen TALIF signal is calibrated for density using the noble gas xenon, which possesses a very similar two-photon excitation and fluorescence scheme. Measurements are conducted for the jet operating in ambient air with both an open effluent and a liquid surface present, allowing for comparison with liquid phase measurements conducted under similar conditions. The presence of a water surface does not appear to alter the background chemistry in the effluent but reduces O densities close to the liquid interface when compared to a similar distance from the nozzle in an open effluent case. This may be the result of a reduction in flow velocity caused by the liquid obstructing the gas flow. Additionally, measurements near the liquid surface revealed a region of atomic oxygen well outside of where the core of the effluent impinges on the liquid. This is likely relevant for applications as it considerably expands the surface area subject to O absorption. Critically, in situ measurements of the effective lifetimes of the laser-excited 3p3PJ state of atomic oxygen were recorded in the effluent by employing a picosecond (ps) laser and a nanosecond (ns) ICCD. By experimentally determining the contribution from collisional quenching via the in situ effective lifetime measurements, significant improvements in the accuracy of the atomic oxygen density calibration were made, with differences of approximately 30 from existing methods of estimating quenching rates at atmospheric pressure. Finally, spatially resolved atomic oxygen densities allow for an investigation of O formation and extinction pathways in the effluent and a comparison between admixtures.

Cylindrical inertial electrostatic confinement plasma source for surface treatment

The inertial electrostatic confinement (IEC) has been commonly researched in the scope of application for space propulsion and fusions reactors since many years. The utilization as thruster is possible due to a free emitting stream in a so-called jet mode of the IEC source. Depending on the setup, this jet can be operated as high energetic electron beam (tight jet) with electron energies of several keV or as low energetic plasma jet close to quasineutrality (spray jet). These modes are of high interest for thin film applications and plasma treatment. However, the IEC source is still not used in this field of application. Relevant application scopes can be electron substrate heating, surface plasma pretreatment, ionized physical vapor deposition and plasma enhanced chemical vapor deposition. In this paper, a cylindrical IEC source is presented that emits the plasma in both known jet modes, spray jet and tight jet. The jet emission occurs in radial outlet direction along the entire source height (“curtain-like” emission). Furthermore, an ignition test and operational behavior test is introduced. A stable spray jet operation region was examined and dependencies on pressure and voltage are investigated.

Preliminary demonstration on JET of an ITER neutron environment-compatible quadrupole mass-spectrometer✰

Strict limits recently imposed on neutron exposure to electronics for critical diagnostic systems on ITER, the fusion reactor demonstration facility under construction in the south of France, has led to the development of a quadrupole mass spectrometer with an exceptionally long cable. An 80 m cable exceeds the last state-of-the art limit of 15 m, imposed by the normally required proximity of the RF supply to the analyzer, and will allow locating the electronics in a neutron safe environment. This breakthrough, a joint development of ORNL with Hiden Analytical Ltd., was enabled by the use of an intermediate, RF-matching unit, free of silicon-based electronics, and using only vacuum tubes and an air-core transformer, rendering it resilient both to ionizing radiation and to fringing magnetic fields. After successful testing of the prototype unit, both at ORNL and Hiden's laboratories, the unit was installed on the JET tokamak, as part of a multi-sensor, divertor effluent gas analysis system, similar to one also under design for ITER. As such, the prototype will be tested both before and during the next nuclear (D-T) operation of JET, planned for mid-2021. In this paper, the prototype development, laboratory testing and first results from non-nuclear plasma pulse testing on JET are presented. The latter include not only successful detection of fusion fuel cycle and impurity species, but also improved resolution and stability over the state-of-the-art, 15m-cable units on the same analysis station.

The comparative study of linear shaped charges

The fireground tests are the best method for verifying the operation effectiveness of the entire shooting device or its component parts in real conditions. The purpose of the fireground tests presented herein was the physical verification of linear shaped charge (LSC) ability to perforate multi-layered target, reflecting the material and geometrical conditions of a borehole. The series of shooting tests included tests of three types of linear shaped charges selected for use in perfo-fracturing devices. The following shaped charges were tested: LSC in lead enclosure, having φ = 40 mm circular cross-section with shaped recess; LSC with copper liner in 20/30 mm steel trapezoid enclosure; LSC with liner made of solid copper, in 20/40 mm steel trapezoidal enclosure.During testing, the cumulative jet velocity was recorded using voltage type probes, arranged between the individual layers of a target composed of steel and concrete materials. The research method adapted for the project purposes was aimed at verification of the following thesis: whether the proposed shaped charges fulfil the technical and performance conditions for their effective application in the oil industry. The criterion adopted was the ability – or lack of ability – to perforate the multi-layered barrier in the form of two steel plates and concrete casting. The testing stand, single-use by its nature, was each time composed of concrete block having 400 mm ´ 250 mm ´ 150 mm dimensions and 20 MPa static compressive strength, on which two steel plates were placed parallel to each other with 20 mm spacing. The thickness of the plates was 5 mm and 10 mm respectively. The tested shaped charge was placed on the top steel plate at a distance of one calibre – that is the distance equal to the opening of the trapezoidal shaped charge and full diameter of circular cross-section charge. Furthermore, within media interface planes (steel/air, air/steel; steel/concrete), the set of voltage-type measuring probes was installed, in the form of single electric wires (φ = 0.25 mm). At an instant when they break (circuit break) as a result of cumulative jet operation, voltage drop in the subsequent measuring probes will act as a logical gate of start-stop type, or in other words the zero-one (0–1) type gate. The readings of individual probes breakage times allowed in addition to determine the velocity of the cumulative jet and to estimate its braking dynamics while passing through the subsequent elements of multi-layered target.

PIV investigation of high Reynolds number submerged water jets at high-pressure ambient conditions

High-pressure water jets bear a great technological potential to enhance geothermal deep drilling. Compared to existing water cutting technologies, significantly different operation conditions are encountered under deep-drilling conditions, such as high ambient pressures. The fundamental fluid mechanics are significantly affected by those operation conditions. In this work we examine the influence of increasing ambient pressure of up to 12.0 MPa on the water jet characteristics under submerged drilling conditions. PIV measurements of the jet flow field at changing cavitation numbers reveal two characteristic regimes, which are distinguished by a critical cavitation number. In the cavitating regime, the jet decays considerably faster with increasing distance to the nozzle than in the non-cavitating regime. In addition to that, an increasing cavitation intensity shortens the potential core length of the water jet and increases the jet spreading angle and with this has a similar effect on the jet as increasing turbulence intensity in single-phase flows. Related to the decreasing kinetic energy of the jet in the cavitating regime, the resulting impact force of the water jet on the specimen surface decreases with increasing cavitation intensity. Our investigations indicate that a technology transfer from water jet cutting to submerged jet drilling requires adjustments of both nozzle geometries and jet operation conditions.Graphic abstract

Cold atmospheric pressure plasma inactivation of dairy associated planktonic cells of Listeria monocytogenes and Staphylococcus aureus

The effect of cold atmospheric pressure plasma (CAPP) on three strains of Staphylococcus aureus and one strain of Listeria monocytogenes on gel discs was studied. A plasma jet operating in argon was used and exposure times were from 5 to 120 s. Bacteria had been isolated from dairy environments. In comparison, peracetic acid (PAA, 0.5% v/v) applied on cell suspensions at the same treatment times was studied. The cell viability was measured by flow cytometry and the culturable cells were determined by plate count technique. PAA reduced nearly 7 log cycles of both microorganisms after a short time (10 s). Concurrently, membrane permeabilization, RNA and DNA damage, and lack of esterase activity could be demonstrated. CAPP showed a mild biocidal effect with a maximum reduction of 1–2 log cycle after 120 s, and no significant impact on membrane permeabilization, RNA and DNA damage, or esterase activity. Therefore, for the selected processing parameters, PAA remains as more effective treatment in terms of inactivating pathogenic bacteria in dairy environments, reaching ~7 log cycles reductions. Further studies should determine the effect of higher CAPP exposure times on S. aureus and L. monocytogenes strains.

Progress in preparing real-time control schemes for Deuterium-Tritium operation in JET

Operation of a magnetic fusion experiment, such as JET, relies on the availability of real-time (RT) control schemes, which supervise the plasma as it approaches the expected target performance while maintaining the integrity of the machine and its subsystems. At JET, there have been a series of recent efforts since (Lennholm M. et al 2017 Fusion Engineering and Design 123 535–540) to develop and test RT control schemes in preparation for the upcoming Deuterium-Tritium (DT) campaign. When operating JET in DT, each plasma discharge will in fact be a precious resource, being both T and neutron budget limited. Among the developed control schemes, this paper deals with the isotope ratio controller, which will maintain the required 50:50 DT ratio needed to favor nuclear fusion processes; the dud detector (L. Piron et al 2019 Fusion Engineering and Design 146 1364–1368), which will terminate a discharge moving toward controllers for detecting excessive radiation. Moreover, brand-new detectors, also based on machine learning approaches, have been implemented for detecting off-normal events or pre-disruptive states and have been included in the Plasma Event TRiggering and Alarms system (C.I. Stuart et al 2020 SOFT conference). Work is also ongoing to deploy into JET the RAPTOR suite, a RT observer for plasma state monitoring (C. Piron et al 2020 SOFT conference), and to identify control schemes within RAPTOR capabilities, which could contribute to support the development of high performance plasma scenarios.

Fluid Dynamics of a Bistable Diverter Under Ultrasonic Excitation—Part I: Performance Characteristic

Abstract This paper investigates an ultrasonically driven bistable fluidic diverter at inlet nozzle Mach numbers of up to Mn = 0.3 and operating pressure ratios of up to Pr = 1.1. Part I examines the switching characteristics with respect to nondimensional parameters of excitation amplitude, frequency, required energy, switching time and inlet total pressure. It is shown that to promote switching at turbulent jet Mach numbers of up to Mn = 0.3 it is necessary to excite a jet preferred mode of St = 0.45 which differs from previously reported laminar jet operation of the similar device. For the reference case the switching time amounts to 1.2 ms suggesting oscillation frequencies of up to 500 Hz. Part II is a combined experimental and numerical study that examines the triggered instability modes in the free shear layer using large eddy simulations (LES) and visualizes the flow field using Particle Image Velocimetry (PIV).

Comparison of atmospheric pressure argon producing O(1S) and helium plasma jet on methylene blue degradation

A solution of methylene blue dye was degraded under an atmospheric pressure plasma jet operating in a linear field configuration with pure argon or pure helium as working gases. Optical emission spectroscopy was carried out to understand the reactive species present with and without dye treatment. Both plasma jets contain reactive species such as OH, N2, and atomic oxygen (O). However, atomic oxygen takes a greatly different form depending on the working gas. In the argon plasma jet, we observe that most of the atomic oxygen produced is the O(1S)–O(1D) transition that also leads to the green colored plasma plume. On the other hand, the helium plasma jet produces the well known triplet states of oxygen at 777 and 844 nm. The absorption spectra confirmed the faster and more energy efficient degradation of the methylene blue dye when treated by the argon plasma jet. Argon plasma with enhanced atomic oxygen content can be utilized as a cheaper and efficient method for waste water treatment.

A Numerical Simulation of a Low-Temperature Argon Plasma Jet

A plasma jet at atmospheric pressure using a dielectric barrier discharge (DBD) can be very useful in the biomedical field. In this article, a numerical simulation of such plasma jet operating in argon gas and launched in the open air was developed using COMSOL Multiphysics software. Three coupled models are considered in this study. A hydrodynamic investigation is conducted and the dilution of argon in air is considered an initial value in the plasma model. An electrostatic study is developed in order to preview the initial electric field. Finally, a plasma study is carried out and discussed in terms of electron density, electric field distribution, and plasma length. This study is validated by comparing the results to those measured in a similar system in the literature. The results are in good agreement with the literature and correspond to the physics of the plasma jet.

Tribocorrosion Behavior of Inconel 718 Fabricated by Laser Powder Bed Fusion-Based Additive Manufacturing

Additive manufacturing (AM) by laser powder bed fusion (LPBF) has gained significant research attention to fabricate complex 3D Inconel alloy components for jet engines. The strategic advantages of LPBF-based AM to fabricate jet components for aerospace applications are well reported. The jet components are exposed to a high degree of vibration during the jet operation in a variable aqueous environment. The combined vibration and the aqueous environment create a tribological condition that can accelerate the failure mechanism. Therefore, it is critical to understand the tribocorrosion behavior of the Inconel alloy. In the present work, tribocorrosion behavior of the LPBF fabricated standalone coating of Inconel 718 in the 3.5% NaCl aqueous solution is presented. The LPBF fabricated samples are analyzed to determine the impact of porosity, generated as a result of LPBF, on the triobocorrosion behavior of AM Inconel 718. The study includes potentiodynamic tests, cathodic polarization, along with OCP measurements. The corrosive environment is found to increase the wear by 29.24% and 49.5% without the initiation of corrosion in the case of AM and wrought Inconel 718, respectively. A corrosion accelerated wear form of tribocorrosion is observed for Inconel 718. Additionally, the corrosive environment has a significant effect on wear even when the Inconel 718 surface is in equilibrium potential with the corrosive environment and no corrosion potential scan is applied. This study provides an insight into a critical aspect of the AM Inconel components.

Cooling performance of an impinging synthetic jet in a microchannel with nanofluids: An Eulerian approach

Numerical investigations of heat transfer enhancement in a three-dimensional micro-channel with a single synthetic jet were conducted using Al2O3-water, CuO-water and TiO2-water nanofluids. The effects of different types of nanoparticles at particle volume concentrations of 1%, 2% and 5% on the thermal performance in the micro-channel were examined. The numerical tool was validated against existing experimental data on the heat transfer characteristic of nanofluids in micro-channel. Heat transfer enhancement using nanofluids based on the Eulerian single-phase model was assessed for the cases with and without the operation of the synthetic jet. In general, the overall thermal performance was greatly influenced by the thermal conductivity and dynamic viscosity of the working nanofluids. The former corresponds to thermal enhancement by conduction whilst the latter corresponds to convective enhancement due to the periodic oscillation of the synthetic jet diaphragm. As the particle volume concentration of a nanofluid increased, effectiveness of the synthetic jet to provide convective cooling became poorer on account of higher viscosity. Nevertheless, in some cases, this can be overcome by the enhancement in thermal conductivity, depending on the Peclet number of the working fluid. Synthetic jet microchannel with Al2O3-water nanofluid at φ = 5% showed the best overall cooling performance whereas TiO2-water nanofluid at φ = 5% failed to improve the thermal performance.

Проектирование газореактивного привода с системой управления тягой при помощи вихревого клапана

The article is devoted to the design of a gas-jet drive with a traction control system using a vortex valve. A diagram is given and the principle of operation of a vortex jet device designed to control the gas flow is considered. The selected scheme of a vortex jet device with a distributed supply of a feed and a concentrated supply of control gas flows, designed to control the thrust of a gas-jet engine. The profiling of the Laval nozzle was carried out using a simplified technique from [G. N. Abramovich, Applied Gas Dynamics]. Computational and theoretical studies of the gas flow from a gas-jet drive with a vortex valve in the maximum thrust mode and in the thrust control mode have been carried out

Experimental investigation on abrasive water jet polishing of stainless steel: a preliminary study

Abrasive water jet (AWJ) is a versatile machining technique for the production of components in various applications. In this paper, AWJ machining technique is extended to polishing operations on stainless steel 304. The polishing operations were carried out in the OMAX-AWJ machining centre by controlling the process parameters, namely, the traverse rate and the abrasive mesh size. The single and double pass roster method was considered for the production of polished surface by AWJ. In this study, in-depth analysis of 3D surface topography and surface morphology has been done on various polished surfaces. The experimental results indicated the yield of a surface texture with beneficial roughness features for the double pass jet operation through the employment of an abrasive mesh size of #300 and a traverse rate of 39.96 mm/min.

The Feasibility Study of Plasma-activated Water as a Physical Therapy to Induce Apoptosis in Melanoma Cancer Cells In-vitro.

Low-temperature plasma (LTP) has demonstrated great potential in biomedicine, especially in cancer therapy in-vivo and in-vitro. Plasma activated water (PAW) as an indirect plasma therapy is a significant source of reactive oxygen and nitrogen species (RONS) which play an important role in apoptosis induction in cancer cells. In this study, Helium (He) plasma jet operating in 0.75 W and 20 kHz as dissipated power and frequency, respectively, is used as the cold plasma source. The electrical, thermal, and spectroscopic properties of (He) plasma jet and pH as well as the conductivity and temperature of PAW samples, are investigated. The concentration of hydrogen peroxide (H2O2), nitrite (NO2-) and nitrate (NO-3), which are produced in water as long-lived anticancer RONS, was measured 471.6, 7.9 and 93.5 μM, respectively after 6 min of plasma treatment. Alamar Blue and flow cytometry assays were employed to investigate the B16F10 cancer metabolic activity and apoptosis. These data support that cold atmospheric plasma (CAP) can produce a certain concentration of anti-cancer agents in water and induce apoptosis in melanoma cancer cells due to RONSs via activating the caspase 3 pathway.

Electric field dynamics in an atmospheric pressure helium plasma jet impinging on a substrate

Time and spatially resolved electric field measurements by Stark polarization spectroscopy in a nanosecond pulsed atmospheric pressure helium jet operating in ambient air and impinging on a indium tin oxide coated glass slide are reported. An automatic fitting procedure of the Stark shifted spectra taking into consideration constraints regarding Stark components' positions and intensities as well as molecular nitrogen emission subtraction was implemented. This allowed electric field vector component measurements both in the gas phase and at the interface when the jet impinges on the substrate and during the development of a surface ionization wave. The obtained results show an increase in the axial electric field in the jet effluent in the gas phase with a peak magnitude from 12 to 18 kV cm−1 before the ionization wave impinges on the substrate. A steep electric field enhancement to a peak value of about 24 kV cm−1 was observed when the ionization wave impinges on the surface. A peak radial electric field of about 27 kV cm−1 was measured off-axis in the surface ionization wave. These results are consistent with previously reported modelling predictions. While Stark polarization spectroscopy is limited to electric field measurements from regions with emission, we illustrate that the capability to measure near surface electric fields in helium makes it a valuable complementary technique for the electric field-induced second harmonic (EFISH) technique.

The von Kármán street behind a circular cylinder: flow control through synthetic jet placed at the rear stagnation point

Abstract

Modeling of the energy of a smelt-water explosion in the recovery boiler dissolving tank

The explosion energy generated as molten smelt droplets interact with water was evaluated as a function of smelt distribution, water temperature, and smelt temperature using a thermodynamic model. The results show that increasing smelt-to-water volume ratio and water temperature significantly increases the explosion energy, converting a larger proportion of the thermal energy of smelt into mechanical work. To reduce the chance of violent smelt-water explosions, it is important to: i) optimize the shatter jet design and operation to uniformly distribute the smelt over a large area in the dissolving tank; ii) avoid high green liquor temperature and ensure adequate liquor mixing; and iii) avoid upsets that may cause heavy smelt runoff or jellyroll smelt.

Ionization wave propagation in a He plasma jet in a controlled gas environment

Characterizing ionization wave propagation in low temperature plasma jets is critical to predicting production of reactive species and plasma–surface interactions for biomedical applications and surface functionalization. In this paper, results from optical emission and laser induced fluorescence measurements of the ionization wave in a He plasma jet operating in a controlled gas environment are discussed and used for comparison with numerical modeling. The ionization wave was observed using ICCD (Intensified Charge Coupled Device) imaging and characterized by time and spatially resolved electron density measurements using laser-collision-induced fluorescence. The plasma jet was initially characterized using pure He (nominally at 200 Torr), while varying pressure and voltage. When operating in pure He, the ionization wave broadly expands exiting the plasma tube. Increasing the operating pressure reduces the speed and isotropic expansion of the ionization wave. The jet operated with a humid He shroud was also studied. The humid He shroud results in the electron density increasing and having an annular profile due to the lower ionization potential of H2O compared to He and localized photoionization in the mixing region. Numerical modeling highlighted the importance of resonance radiation emitted by excited states of He, photoelectron emission from the quartz tube, and the kinetic behavior of the electrons produced by photoionization ahead of the ionization front.