Coaxial Gas Flow Research Articles

An Optimization of Manufacturing Process of SS304L Using Direct Energy Deposition Method

The direct energy deposition (DED) method is an emerging manufacturing technique that has been recently highlighted due to its capabilities to coat materials with complex geometry for high temperature and highly corrosive environmental applications, such as steam turbine blade. Amongst metallic materials, SS304L has been reported to have superior corrosion resistance in such environments. Therefore, 3D printing of complex-shaped parts using SS304 maybe a promising strategy to introduce 3D printing techniques for nuclear industry application. To obtain robust and stable products that can withstand extreme environments, optimization of the SS304 manufacturing process conditions is required. This study investigated the effects of process parameters including laser power, scan speed, coaxial gas flow, and feeder rate using the DED method with a 4 way nozzle. It was found that laser power has an effect on grain growth behaviors. If the other variables are fixed and the scan speed is above a certain value, then the scan speed does not affect surface oxidation. The feeder rate is related to height. As the feeder rate increases, the height increases. Coaxial gas works to prevent oxidation and damage to the optic components and is not a critical factor in determining the size of the deposited material. These results can be utilized in future studies to accelerate the process design time of other 3D printed materials and future applications using SS304L

Two-fluid coaxial atomization in a high-pressure environment

We study the dynamics of atomization of a liquid column by a coaxial gas flow with varying gas pressures. Specifically, we analyse how the gas density increase associated with elevated gas pressures in the ambient and co-flowing gas jet influences the liquid destabilization and breakup process, as well as the resulting droplet formation and dispersion. We present new experimental results for a coaxial liquid–gas atomizer operating in a high-pressure environment, with gas–liquid momentum ratio in the range $M = 5\unicode{x2013}56$ and pressurized gas densities $\rho _g/\rho _0 = 1\unicode{x2013}5$ , where $\rho _0$ is the ambient gas density at standard conditions. High-speed shadowgraphy images are used to quantify the spatially and temporally varying liquid–gas interface in the spray near-field. Liquid core lengths, spreading angles and other spray metrics are presented, and the influence of gas density is identified from the comparison with atomization at atmospheric conditions. In the spray mid-field, phase Doppler interferometry is used in conjunction with laser Doppler velocimetry to quantify the droplet size and velocities, as well as their radial variations across the spray. Results show an increase in droplet size at elevated ambient pressures, when keeping the gas–liquid momentum ratio constant. Finally, we show that these observations are in line with predictions from the Kelvin–Helmholtz and Rayleigh–Taylor instabilities, both of which are relevant to the gas–liquid atomization process.

A study on mechanical properties of CuNi2SiCr layered on nickel–aluminum bronze via directed energy deposition

Nickel-aluminum bronze (NAB) is a widely used copper alloy for the fabrication of marine propellers owing to its excellent corrosion resistance in seawater. The repairing process of damaged propellers is an important research topic. This study proposes a repair method that employs the directed energy deposition (DED) technique and copper alloy powder (CuNi2SiCr). This study focused on and mechanical properties of CuNi2SiCr deposited on an NAB substrate through DED. First, the optimal process parameters of the DED process were established by varying the laser power, powder feed rate, scanning speed, coaxial gas flow, and powder gas flow rate. In addition, the mechanical properties of the deposited material and substrate were studied through microhardness measurements and mechanical tests. The results showed that the microstructure of the deposited layers was α-Cu, characterized by low strength, hardness and high toughness. The microstructure of the NAB substrate exhibited higher hardness and strength than the deposited CuNi2SiCr, because the substrate was composed of a typical α + β solid solution and different intermetallic κ phases. Moreover, the tensile strength and elongation of the deposited specimens were lower than those of the substrate because the deposition layers have micropores. The wear resistance of the deposited specimens was lower than that of NAB owing to low hardness and plastic deformation during wear. This study demonstrates the feasibility of the DED deposition of copper alloy—CuNi2SiCr—and proposes a novel method that repairs NAB parts using the metal additive manufacturing process.

Disintegration co-flowing gas-liquid jet coupled with forced perturbation

In this study, numerical simulation is employed to diagnose the behavior of round liquid jet under forced perturbation with the low-velocity coaxial gas flow. A sinusoidal longitudinal perturbation with high amplitude and infinite frequency is imposed on the inlet of the liquid jet. An annular gas with lower velocity flows coaxially. The volume of fluid (VOF) approach is used to capture the liquid-gas interface. Various circumstances are considered such as properties of the liquid, the ratio of gas velocity to liquid velocity, and the properties of perturbation. Different cap formations, ligament breakup, and the droplet generation processes are depicted. The results indicate that the slower gas flow can affect the liquid jet breakup behavior and droplet generation. Also, liquid properties can considerably influence the cap formation and morphology of breakup. This investigation is validated by other numerical and experimental research in the basic conditions, while co-flowing gas-liquid jet considered in the present study is completely novel.

BEHAVIOR OF CO-FLOW JETS COUPLED WITH A LONGITUDINAL PERTURBATION

In this study, a numerical simulation is used to show the physics of a coupled forced perturbation and liquid jet in the presence of a low-velocity coaxial gas flow. The volume of fluid (VOF) approach is employed to capture the liquid–gas interface. A sinusoidal velocity with a finite frequency and amplitude is applied at the liquid jet inlet to define a forced perturbation. An annular gas flow with a velocity lower than that of the liquid jet is imposed to examine its influence on the liquid jet breakup mechanism. The annular gas flow is modulated by the sinusoidal velocity inlet, and the effect of this flow on the liquid jet breakup mechanism is analyzed. Different ratios of the gas velocity to liquid velocity are studied. The results indicate that the low-velocity gas flow can considerably affect the behavior of the liquid jet, and this effect becomes more significant as the amplitude of the forced perturbation increases.

Nano-additively manufactured gold thin films with high adhesion and near-bulk electrical resistivity via jet-assisted, nanoparticle-dominated, room-temperature microsputtering

Abstract Microsputtering is a novel additive manufacturing technique that takes a completely new approach to the printing of conductors, directly writing on an arbitrary substrate with the use of a microplasma, i.e., a plasma generated at atmospheric pressure by an arrangement of electrodes with millimeter-scale or smaller spacing. Conductors deposited via microsputtering promise significantly improved electrical conductivity over traditional extrusion ink-based methods. This study investigates, via a design of experiments, the deposits created by a 3D printer-compatible write head that encompasses an atmospheric-pressure gold microsputterer with strong coaxial gas flow. In addition to attaining 1 nm/s deposition rates—on par with traditional (i.e., vacuum) sputtering, the microplasma sputterer creates ~100 nm-thick gold films with near-bulk electrical resistivity (down to 2.9 µΩ cm, i.e., 120% the bulk value) and excellent adhesion—without employing an adhesion layer, annealing, or any other pre/post-processing steps. It is concluded that the strong gas flow promotes the formation of nanoparticles in the plasma plume out of the originally microsputtered gold atoms, which in turn, deposit and create films with excellent adhesion and conductivity.

Stability of Thermocapillary Flow in High-Prandtl-Number Liquid Bridges Exposed to a Coaxial Gas Stream

The stability of thermocapillary flow in a liquid bridge made from 5cSt silicone oil (Pr = 68) is computed numerically. To improve the numerical model as compared to the standard approach, we consider the flow in the liquid bridge fully coupled to the flow in the ambient gas, temperature-dependent material parameters, and a dynamically deforming liquid–gas interface. We address the full two-phase-flow problem of interest for the space experiment JEREMI and investigate the effect of a steady axisymmetric coaxial gas flow which is imposed at the inlet of the annular gap between the liquid bridge and the outer confining cylinder. Under zero-gravity the flow is primarily driven by the imposed temperature gradient with viscous stresses from the gas phase being small. However, the heat transfer between liquid and the gas, and thus the temperature fields are strongly affected by the forced flow in the gas phase. As a result the stability of the steady axisymmetric flow depends sensitively on the flow direction and the temperature of the gas. If the temperature of the gas is identical to that of the support rod of the liquid bridge a gas stream opposing the thermocapillary stresses strongly destabilizes the basic flow. In a co-flow configuration the basic state is stabilized. Curves of neutral Reynolds numbers as functions of the strength of the annular gas flow are discussed for two aspect ratios of the liquid bridge.

Impact of process flow conditions on particle morphology in metal powder production via gas atomization

Additive manufacturing processes as for instance selective laser melting or electron beam melting are becoming more common and just turning into standard manufacturing processes for metal components. Nevertheless, these processes are still new compared to classic powder metallurgy manufacturing routes such as pressing and sintering. Hence not all necessary requirements for the powders in use are fully known yet. This makes an increase in control of the powder properties a crucial task to achieve. To reach this goal one must understand the different influences on the powder production process from the beginning of the whole production route. In this work, the influence of the spray chamber flow on the particle morphology is examined. The nozzle system used to produce the metal powders is a close-coupled atomization system with a convergent-divergent gas nozzle configuration. The particle morphology as well as the particle size distribution have been analyzed to examine the influence of the atomization gas flow compared to an additional use of a coaxial gas flow. To review the changes of the flow patterns, computational fluid dynamic simulations have been performed. The particle trajectories were calculated to assess the change in particle behavior as well. Atomization experiments have been conducted with an AISI 52100 (1.3505) steel in a small batch atomization plant to evaluate the influence of the change in flow on the particle size distribution and circularity. The experimental results show that a use of additional coaxial gas leads to an increase in particle circularity up to 10% for relevant particle sizes. An approach for the quantification of satellite occurrence is given by examination of the shift of the particle size distribution to smaller diameters.

High-viscosity sample-injection device for serial femtosecond crystallography at atmospheric pressure.

A sample-injection device has been developed at SPring-8 Angstrom Compact Free-Electron Laser (SACLA) for serial femtosecond crystallography (SFX) at atmospheric pressure. Microcrystals embedded in a highly viscous carrier are stably delivered from a capillary nozzle with the aid of a coaxial gas flow and a suction device. The cartridge-type sample reservoir is easily replaceable and facilitates sample reloading or exchange. The reservoir is positioned in a cooling jacket with a temperature-regulated water flow, which is useful to prevent drastic changes in the sample temperature during data collection. This work demonstrates that the injector successfully worked in SFX of the human A2A adenosine receptor complexed with an antagonist, ZM241385, in lipidic cubic phase and for hen egg-white lysozyme microcrystals in a grease carrier. The injection device has also been applied to many kinds of proteins, not only for static structural analyses but also for dynamics studies using pump-probe techniques.

Liquid jet formation during a suspended liquid suction process

In the tubular co-flowing gas-liquid jet, liquid is sucked through a nozzle suspended above the flat gas-liquid interface. The liquid hump can be induced by the sudden pressure change just beneath the nozzle entrance. At a sufficiently fast initial gas superficial velocity, the interface undergoes a transition and liquid starts to be sucked. The suction flow is in the form of an axisymmetric liquid jet surrounded by an upwards coaxial gas flow. In the present study, we discuss the evolution and characteristics of the suspended liquid suction flow. The jet dynamics include the interface deformation and development (the hump stage), the tubular co-flowing jet (the spout state) and the destabilization of the liquid jet (the jet state). Tube inner diameter, suspension height, and initial gas superficial velocity are three important parameters that influence the suction flow. Due to the inward gas flow, a relatively large amount of pressure gradients is imparted to a small mass of liquid near a free surface, which leads to interface deformation. The lateral boundary of the liquid hump circumferentially shrinks and the top liquid gradually rises following the shrinkage. There is a comparatively stable axisymmetric liquid jet surrounded by an upwards coaxial gas flow inside the tube. Surprisingly, no evidence is shown the dependence of jet spout with initial gas axisymmetric superficial velocity below the nozzle through plenty of experiment figures and statistical analysis. On the other hand, the velocity difference between the fast light gas flow and the slow dense liquid is critical to the destabilization of the liquid jet.

Diagnostics of powder particle parameters under laser radiation in direct material deposition

A comparative analysis is presented for the particle velocity and temperature in the light field of a continuous wave (CW) or pulsed CO2-laser in a coaxial jet gas flow. The problems of measuring the particle velocity and temperature in the light field are solved using noncontact registration methods based on a spectrometer and a combination of laser and optical devices. Alumina, molybdenum, nickel and aluminum powders are used with standard size distributions of the particles. It is shown that, in the field of laser radiation, powder particles get an extra acceleration due to the reactive force resulting from the recoil pressure in evaporation from particles. Laser radiation essentially influences the in-flight velocity of particle velocity and temperature.

Vorticity dynamics in a spatially developing liquid jet inside a co-flowing gas

A three-dimensional transient round liquid jet within a low-speed coaxial outer gas flow is numerically simulated and analysed via vortex dynamics ($\unicode[STIX]{x1D706}_{2}$ analysis). Two types of surface deformations are distinguished, which are separated by a large indentation on the jet stem. First, there are those inside the recirculation zone behind the leading cap – directly affecting the cap dynamics and well explained by the local vortices. Second, deformations upstream of the cap are mainly driven by the Kelvin–Helmholtz (KH) instability, unaffected by the vortices in the behind-the-cap region (BCR), and are important in the eventual atomization process. Different atomization mechanisms are identified and are delineated on a gas Weber number ($We_{g}$) versus liquid Reynolds number ($Re_{l}$) map based on the relative gas–liquid velocity. In a frame moving with the liquid velocity, this result is consistent with prior temporal studies. A simpler and clearer portrait of similarity of the atomization domains is shown by using the relative gas–liquid axial velocity, i.e. $We_{r}$ and $Re_{r}$, and avoiding the widely used velocity ratio as a third key parameter. A detailed comparison of vorticity along the axis in an Eulerian frame versus a frame fixed to a surface wave reveals that the vortex development and surface deformations are periodic in the upstream region, but this periodicity is lost closer to the BCR. In the practical range of the density ratio and for early times in the process, axial vorticity is mainly generated by baroclinicity while streamwise vortex stretching becomes more important at later times and only at lower relative velocities when pressure gradients are reduced. The inertia, vortex, pressure, viscous and surface tension forces are analysed to delineate the dominant causes of the three-dimensional instability of the axisymmetric KH structure due to surface acceleration in the axial, radial and azimuthal directions. The inertia force related to the axial gradient of kinetic energy is the main cause of the axial acceleration of the waves, while the azimuthal acceleration is mainly caused by the pressure and viscous forces. The viscous forces are negligible in the radial direction and away from the nozzle exit in the axial direction. It is interesting to note that azimuthal viscous forces are important even at high $Re_{l}$, indicating that inertia is not totally dominant in this instability occurring early in the atomization cascade.

Influence of a coaxial gas flow on the evolution of oscillatory states in a liquid bridge

We present an experimental and complementary computational study of a two-phase flow in a liquid bridge that develops under the action of buoyant and Marangoni forces in the presence of a gas stream parallel to the interface. The gas flow is counter-directed with respect to the steady flow in liquid. The forced gas flow along the interface provides actions on the system via shear stresses and heat exchange. For the experimental fluids (n-decane, nitrogen) the ratio of viscosities is large, about 40, and the gas Reynolds number is moderate, Reg = 120. Thus, heat transfer is the prevailing mechanism by which gas affects the flow in a liquid. The effect of gas temperature on the evolution of flow states is examined. The study reveals that in the supercritical region, ΔT>1.25ΔTcr, the flow dynamics can be divided in three regimes relative to the gas temperature. When the gas is colder than the temperature of the supporting disk, multiple transitions between the oscillatory states occur: periodic, quasi-periodic with two frequencies, quasi-periodic with three frequencies and noisy quasi-periodic with three frequencies. In the case, when the gas temperature approaches the temperature of the cold disk and goes up to the mean temperature, the flow remains periodic up to the largest tested ΔT. In the case of hotter gas, the flow also remains periodic far above the threshold of hydrothermal instability, but the azimuthal mode of the periodic oscillatory flow is changed. The stability window is found to exist between these two azimuthal modes and its location is sensitive to the gas parameters as well as to the geometry of a liquid bridge. It opens a possibility that oscillatory instability can be stabilized by choosing specific temperatures and velocities of counter-current gas.

Preparation and Characterization of Quaternized Chitosan Coated Alginate Microspheres for Blue Dextran Delivery.

In this study, 2-[(Acryloyloxy)ethyl]trimethylammonium chloride was graft polymerized onto chitosan (CS) to form quaternary ammonium CS (QAC) by using ammonium persulfate as a redox initiator. Alginate (ALG) microspheres loaded with a water-soluble macromolecular model drug, blue dextran (BD), were obtained by corporation of coaxial gas-flow method and ionic gelation process. CS and QAC were then coated on the surfaces of ALG microspheres to generate core/shell structured CS/ALG and QAC/ALG microspheres, respectively. The experiment result showed that QAC/ALG microspheres had a smaller particle size due to the stronger electrostatic interactions between QAC and ALG molecules. In vitro drug release studies at pH 7.4 and pH 9.0 exhibited that the release rate of BD was significantly decreased after ALG microspheres coating with CS and QAC. Moreover, ALG microspheres coated with QAC showed a prolonged release profile for BD at pH 9.0. Therefore, QAC/ALG microspheres may be a promising hydrophilic macromolecular drug carrier for a prolonged and sustained delivery.

Simulation of the primary breakup of a high-viscosity liquid jet by a coaxial annular gas flow

The conversion of low-grade fossil and biogenic energy resources (petcoke, biomass) to a synthesis gas in a high pressure entrained flow gasification process opens a wide spectrum for high efficient energy conversion processes. The synthesis gas can be used for production of methane (SNG), liquid fuels (BtL, CtL) or as fuel for operation of a gas turbine in a combined cycle power plant (IGCC). The production of a tar free high quality syngas is a challenging objective especially due to the fact that typical liquid or suspension fuels for entrained flow gasifiers feature viscosities up to 1000 mPas. Fuel droplet conversion at typical entrained flow gasification conditions is characterized by heat up, evaporation and subsequent degradation of the vapour phase. To guarantee a high fuel conversion rate in the gasifier an efficient atomization of the fuel is required. Mainly twin-fluid burner nozzles are used for atomization of those typically high viscous fuels. The present study is focused on the assessment of the accuracy of CFD computations for the primary breakup of high-viscosity liquids using an external mixing twin fluid nozzle. In a first step experiments were performed with a Newtonian glycerol-water-mixture featuring a liquid viscosity of 400 mPas. Jet breakup was investigated using a high speed camera as well as PIV and LDA-System for a detailed investigation of the flow field. In a second step the experimental results serve as reference data to assess the accuracy of CFD computations. Compressible large eddy simulations (LES) were performed to capture the morphology of the primary breakup as well as the important flow field characteristics. A Volume of Fluid (VOF) approach was used to track the unsteady evolution and breakup of the liquid jet. Comparison of experimental and numerical results showed good agreement with respect to breakup frequency, velocity fields and morphology.

Dopant Enriched Nitrogen Gas Combined with Sheathless Capillary Electrophoresis-Electrospray Ionization-Mass Spectrometry for Improved Sensitivity and Repeatability in Glycopeptide Analysis.

Over the last years, numerous strategies have been proposed to enhance both ionization efficiency and spray stability in electrospray ionization (ESI), in particular for nanospray applications. In nano-liquid chromatography-mass spectrometry (nano-LC-ESI-MS), a better ESI performance has been observed when a coaxial gas flow is added around the ESI emitter. Moreover, enrichment of the gas with an organic dopant has led to an improved desolvation and ionization efficiency with an overall enhanced sensitivity. In this study, the use of a dopant enriched nitrogen (DEN)-gas combined with sheathless capillary electrophoresis (CE)-ESI-MS was evaluated for glycopeptide analysis. Using acetonitrile as a dopant, an increased sensitivity was observed compared to conventional sheathless CE-ESI-MS. Up to 25-fold higher sensitivities for model glycopeptides were obtained, allowing for limits of detection unachieved by state-of-the-art nano-LC-ESI-MS. The effect of DEN-gas on the repeatability and intermediate precision was also investigated. When compared to previously reported nano-LC-ESI-MS measurements, similar values were found for CE-ESI-MS with DEN-gas. The enhanced repeatability fosters the use of DEN-gas sheathless CE-ESI-MS in protein glycosylation analysis, where precision is essential. The use of DEN-gas opens new avenues for highly sensitive sheathless CE-ESI-MS approaches in glycoproteomics research, by significantly improving sensitivity and precision.

Early spray development at high gas density: hole, ligament and bridge formations

Three-dimensional temporal instabilities, leading to spray formation of a round liquid jet segment with an outer, coaxial high-density gas flow, are studied with Navier–Stokes and level-set computations. These computations predict the liquid surface shape showing the smaller structures on the conical wave crests, i.e. lobes, holes, bridges and ligaments, which are the precursors to droplet and spray formations. These structures and their time scales affect droplet size and velocity distributions as well as spray cone angles. The gas-to-liquid density ratio, liquid Reynolds number ($Re$) and liquid Weber number ($We$) range between 0.02–0.9, 320–16 000 and 2000–230 000, respectively, which cover three distinct physical domains. (1) At higher $Re$ and $We$, ligaments and then drops develop following hole and liquid bridge formations. (2) At higher gas densities throughout the $Re$ range, several holes merge forming two bridges per lobe before breaking to form ligaments; this hole merging is explained by slower development of hairpin vortices and lobe shape. (3) In cases where both gas density and $Re$ or $We$ are lower, the well-ordered lobes are replaced by more irregular, smaller-scale corrugations along the conical wave crest edge; ligaments form differently by stretching from the lobes before holes form. Thicker ligaments and larger droplets form in the low $Re$, low gas density range. The surface wave dynamics, vortex dynamics and their interactions are explained. Understandings of liquid stream break up and concurrent smaller structure formation are built upon an examination of both translation and rotation of the fluid. In all cases, hole formation is correlated with hairpin and helical vortices; fluid motion through a perforation in the thin sheet near the wave crest corresponds to these vortices. The hole formation process is dominated by inertial forces rather than capillary action, which differs from mechanisms suggested previously for other configurations. Circulation due to streamwise vorticity increases while the lobes thin and holes form. For larger surface tension, cavities in the jet core rather than perforations in a sheet occur. The more rapid radial extension of the two-phase mixture with increasing gas density is explained by greater circulation in the ring (i.e. wave crest) region. Experimental descriptions of the smaller structures are available only at lower $Re$ and lower density, agreeing with the computations. Computed scales of bridges, ligaments, early droplets and emerging spray radii agree qualitatively with experimental evidence through the high $Re$ and $We$ domains.

Generation Control of ZnO Nanoparticles Using a Coaxial Gas-Flow Pulse Plasma Ar/O2 Plasma

Generation of ZnO nanoparticles was investigated using a coaxial gas-flow pulse plasma. We studied how zinc atoms, sputtered from a zinc target, reacted with oxygen in a plasma and/or on a substrate to form ZnO nanoparticles when the discharge parameters, such as applied pulse voltage and gas flow rate, were controlled in an O2/Ar plasma. The formation processes were estimated by SEM, TEM, and EDX. We observed many ZnO nanoparticles deposited on Si substrate. The particle yield and size were found to be controlled by changing the experimental parameters. The diameter of the particles was typically 50–200 nm.

Three-dimensional large eddy simulation of round liquid jet primary breakup in coaxial gas flow using the VOF method

Large eddy simulation (LES) was performed on a liquid primary breakup process of twin-fluid atomizers with various dimensions. Volume of fluid (VOF) method was applied to track the unsteady evolution and breakup of the liquid jet. It was observed that the liquid primary breakup morphology of the thin central tube nozzle was more sensitive to the liquid inlet velocity distribution than that of the thick central tube nozzle, and the possible reasons were analyzed. The effect of liquid inlet velocity distributions on the primary breakup morphology was explored in detail. A criterion parameter was defined to assess the relative importance of liquid inlet velocity distributions on the liquid breakup shape of a selected atomizer. The combination of the present numerical scheme and the proper liquid inlet velocity distribution, which was determined by the dimensions of atomizers, was reliable and efficient for the numerical investigation of coaxial atomizer with various dimensions.

Heat Transfer Through the Interface and Flow Regimes in Liquid Bridge Subjected to Co-Axial Gas Flow

We present results of an extensive numerical study on the thermocapillary (Marangoni) convection and a heat transfer through the interface in a liquid bridge of Pr = 68. The geometry of the physical problem is a cylindrical and non-deformable liquid bridge concentrically surrounded by an annular gas channel under conditions of zero gravity. The gas flow is co- or counter-directed with respect to the Marangoni flow. The forced gas flow along the interface provides two actions: via shear stresses and heat exchange. Usually the cooling of the interface enhances the flow while the heating slows down. This general trend may not hold when shear and thermocapillary stresses are comparable. The results show that when gas enters from the cold side the heat transfer through the interface is considerably larger than that when gas enters from the hot side.