Gas Nozzle Research Articles

Effect of grinding nozzles pressure on particle and fluid flow patterns in a spiral jet mill

Spiral jet mills utilise high-pressure gas jets, which induce particle breakage by collisions. Appropriately angled jets force particles to circulate in dense phase near the wall due to the centrifugal field. Moving radially inwards towards the mill centre, the two-phase dense flow is transformed into a lean phase and fine particles are entrained out by the fluid drag. Here we analyse the effect of grinding nozzles pressure on the particle dynamics and fluid flow by numerical simulation. The average velocity gradient in the radial direction is very steep for low mass loadings, indicative of rapid shearing, but it decreases significantly as the particle mass loading is increased. The dissipated collisional energy, accountable for size reduction, is strongly influenced by the jet penetration through the circulating bed, which in turn depends on the mass loading and operating pressure of grinding gas nozzles. As a result of jet penetration, the grinding gas nozzles pressure becomes less effective at high pressures. The analysis developed here elucidates the coupled effect of mass loading and grinding nozzles pressure on the dissipated collisional energy, which accounts for particle breakage.

Modeling of liftoff heights of non-premixed turbulent flames in co-flows having various temperatures and O2 concentrations

Lifted flames in combustion furnaces are diluted with burned gas entrained into the fuel jet. The reduced concentrations of reactants resulting from this dilution increase the liftoff height, while the associated temperature increase decreases the height. The aim of the present study was to develop a premixed model capable of predicting the variation in the liftoff height resulting from entrainment. A triple concentric burner incorporating fuel gas, oxidizer and co-flow gas nozzles was employed to simulate a combustion furnace. Prior to combustion tests, the fraction of the fuel gas in the non-reactive jets forming on the burner was determined, to allow an evaluation of parameters affecting the entrainment rate of the co-flow gas. The flame liftoff height above the burner was found to increase with decreases in the O2 concentration in the co-flow gas and was decreased with increases in temperature. Three premixed models were examined: a conventional premixed model, a DP1 model including only the effect of decreasing reactant concentrations and a DP2 model including the effects of both decreasing concentrations and temperature increases. Validations of these models demonstrated that the conventional model failed to predict variations in the liftoff height at a variety of co-flow gas O2 concentrations and temperatures. The DP1 model also provided insufficient correlations between the bulk velocity and liftoff height, such that the correlation line at a high co-flow gas temperature separated from that at room temperature. In contrast, the DP2 model provided excellent correlations in conjunction with different virtual origin positions.

Mitigation of magneto-Rayleigh-Taylor instability growth in a triple-nozzle, neutron-producing gas-puff Z pinch

The gas-puff Z-pinch is a well-known source of x-rays and/or neutrons, but it is highly susceptible to the magneto-Rayleigh-Taylor instability (MRTI). Approaches to MRTI mitigation include density profile tailoring, in which nozzles are added or modified to alter the acceleration trajectory, and axial pre-magnetization, in which perturbations are smoothed out via magnetic field line tension. Here, we present two-dimensional magnetohydrodynamic simulations of loads driven by an 850 kA, 160ns driver that suggest these mitigation strategies can be additive. The initial axial magnetic field, B_{z0}, to stabilize a 2.5-cm-radius Ne gas liner imploding onto an on-axis deuterium target can be reduced from 0.7T to 0.3T by adding a second liner with a radius of 1.25cm. Because MRTI mitigation tends to increasingly lower yield with higher B_{z0}, the use of a lower field is advantageous. Here, we predict a reduction in yield penalty from >100× with the single liner to <10× with a double liner. A premagnetized, triple nozzle gas puff could therefore be an attractive source for intense neutrons or other fusion applications.

Direct-simulation Monte Carlo modeling of reactor-scale gas-dynamic phenomena in a multiwafer atomic-layer deposition batch reactor

Atomic layer deposition (ALD) using multiwafer batch reactors has now emerged as the manufacturing process of choice for modern microelectronics at a massive scale. Stringent process requirements of thin film deposition uniformity within wafer (WiW) and wafer–wafer (WTW) in the batch, film conformity along submicrometer wafer features, thin film quality, and the utilization of expensive precursors in the reactor dictate ALD reactor design and process parameter optimization. This paper discusses a particle-based direct-simulation Monte Carlo (DSMC) of the full reactor scale simulation that overcomes the low Knudsen number limitation of typical continuum computational fluid dynamics approaches used for modeling low-pressure ALD reactors. A representative industrial multiwafer batch reactor used for the deposition of Si-based thin films with N2 and Si2Cl6 (hexachlorodisilane) as process feed gases with pressures in the range 43–130 Pa and a uniform reactor temperature of 600 °C is simulated. The model provides detailed insights into the flow physics associated with the transport of the precursor species from the inlets, through wafer feed nozzles, into the interwafer regions, and finally through the outlet. The reactor operating conditions are shown to be in the slip/transitional flow regime for much of the reactor volume and especially the feed gas nozzle and interwafer regions (where the Knudsen number approaches ∼0.2), justifying the need for a high-Knudsen number DSMC approach as in this work. For the simulated conditions, the nonuniformity of precursor species immediately above the wafer surface is predicted to be within &amp;lt;1% for a given wafer and &amp;lt;2% across the entire multiwafer stack. Results indicate that higher pressure degrades WiW and WTW uniformity. A reactor flow efficiency is defined and found to be ∼99%, irrespective of the chamber pressure.

Multiparameter Optimization of Thrust Vector Control with Transverse Injection of a Supersonic Underexpanded Gas Jet into a Convergent Divergent Nozzle

The optimal design of the thrust vector control system of solid rocket motors (SRMs) is discussed. The injection of a supersonic underexpanded gas jet into the diverging part of the rocket engine nozzle is considered, and multiparameter optimization of the geometric shape of the injection nozzle and the parameters of jet injection into a supersonic flow is developed. The turbulent flow of viscous compressible gas in the main nozzle and injection system is simulated with the Reynolds-averaged Navier–Stokes (RANS) equations and shear stress transport (SST) turbulence model. An optimization procedure with the automatic generation of a block-structured mesh and conjugate gradient method is applied to find the optimal parameters of the problem of interest. Optimization parameters include the pressure ratio of the injected jet, the angle of inclination of the injection nozzle to the axis of the main nozzle, the distance of the injection nozzle from the throat of the main nozzle and the shape of the outlet section of the injection nozzle. The location of injection nozzle varies from 0.1 to 0.9 with respect to the length of the supersonic part of the nozzle; the angle of injection varies from 30 to 160 degrees; and the shape of the outlet section of the injection nozzle is an ellipse with an aspect ratio that varies from 0.1 to 1. The computed fluid flow in the combustion chamber is compared with experimental and computational results. The dependence of the thrust as a function of the injection parameters is obtained, and conclusions are made about the effects of the input parameters of the problem on the thrust coefficient.

DEVELOPMENT AND RESEARCH OF SYNTHESIS TECHNOLOGY CONVERSION OF VEHICLE DIESEL TO GAS ENGINES WITH SPARK IGNITION

The expediency of converting transport diesel engines into gas internal combustion engines with spark ignition has been substantiated. A multifunctional synthesis technology Avenir Gaz has been developed, designed to convert diesel engines of vehicles in operation into spark-ignited gas internal combustion engines operating on a cheaper and environmentally friendly gas fuel - LPG. The synthesis technology is based on three electronic microprocessor control units Avenir Gaz 37 of level "A", Avenir Gaz 37 of level "B" and Avenir Gaz 37 of level "C". It is shown that Avenir Gaz synthesis technology of level "A" allows converting diesel engines into gas internal combustion engines with LPG supply through a gas-air mixer into the intake pipeline, and level “B” provides group or sequential LPG injection by electromagnetic gas nozzles (common rail injection system ) into the intake manifold. Avenir Gaz synthesis technology of level "C" allows the use of an electronic inductive spark ignition system with an immovable voltage distributor (with two-spark or individual ignition coils).

Influence and Suppression of Harmful Effects Due to By-Product in CVD Reactor for 4H-SiC Epitaxy

Suppression of harmful effect due to by-product on homo-epitaxial growth of 4H-SiC films using a high speed wafer rotation vertical CVD method was demonstrated. Influence of by-product, such as 3C-SiC deposit on a hot-wall and Si deposit on gas nozzles, formed during the epitaxial growth was investigated in two comparative studies. The analysis of triangular defects with 3C-SiC down-falls on the films revealed that the most of the down-falls which were peeled from the hot-wall adhered to the wafers before the epitaxial growth. By increasing the wafer rotation speed to 300 rpm just after wafer loading into the reactor, the down-falls dropped towards the wafer surface were effectively eliminated, and the maintenance period of the reactor could be increased more than 4 times compared to the case of maintaining the wafer rotation speed of 50 rpm until just before epitaxial growth step. Additionally, the relationship between Si deposit formed on the gas nozzles in the gas inlet and fluctuation of thickness and doping concentration of the films suggested that Si deposit formed on the gas nozzles acts as a trap site of Si source gas. By suppression of the Si deposit using optimizing gas flow condition, no significant fluctuation of thickness and doping concentration of the films were observed and the maintenance period of the gas nozzles could be increased more than 3 times compared to the epitaxial growth using the nozzles on which Si deposit was formed.

Influence of nozzle gas inlets on properties of GTD222 superalloy powders for additive manufacturing

The GTD222 superalloy powders for the additive manufacturing were prepared by the vacuum inert gas atomization (VIGA) with the close-coupled nozzle system in this paper. The effects of nozzle gas inlets on the chemical composition, particle size distribution, sphericility, fluidity, loose packed density, and surface morphology of the GTD222 superalloy powders were studied. The results show that, using the nozzle with an “outer straight inner tangent” structure enhances the suction effect of the nozzle and improves the stability of the closed-coupled gas atomization process. In addition, the tangent inlet system enhances the gas shear effect, therefore improves the yield of the fine powders (15~53 μm). The optimized process parameters are found in the conditions of 200 ℃ superheat and 3 MPa atomization pressure. The oxygen mass fraction of the powders prepared in the optimized conditions is 0.02%, the medium diameter is 57.98 μm, the degree of sphericility is 0.77, the fluidity is 26.15 g/(50 s), and the loose packed density is 4.63 g/cm3, which meet the requirements of the metal additive manufacturing technology.

Work Envelope Expansion and Parametric Optimization in WAAM with Relative Density and Surface Aspect as Quality Constraints: The Case of Al5Mg Thin Walls with Active Cooling

The successful and efficient production of parts with specific features by Wire + Arc Additive Manufacturing (WAAM) strongly depends on the selection of proper and typically interrelated deposition parameters. This task might be particularly challenging in the making of thin walls, which might be highly impacted by processing conditions and heat accumulation. In this context, this study aims at expanding the work envelope and optimizing the parametric conditions in WAAM with relative density and surface aspects of the preforms as quality constraints. The experimental approach was based on the deposition of thin Al5Mg walls by the CMT process on its standard welding setup and with an active cooling technique to enhance the deposition robustness. Internal voids were estimated by Archimedes’ method. The surface quality of the walls was assessed through the visual aspect and the surface waviness by cross-section analysis. All the conditions presented relative density higher than 98%. The upgrade of the standard welding hardware to WAAM purposes through the addition of a supplementary shielding gas nozzle to the torch and the intensity of the heat sinking from the part significantly expanded the process work envelope, with its applicability being successfully demonstrated with multi-objective optimization. To sum up, a decision-making procedure is presented towards achieving intended preform quality.

A novel structure of throttle trap valve for self-adjustment of discharge capacity in high pressure heat exchangers

A novel self-adjusting throttle trap valve (TTV) for use in high pressure heat exchangers was developed based on multiphase flow theory. The discharge capacity of liquid water is self-adjusted by the effective flow area occupied by the water vapor. The effect of the pressure difference (△p), gas nozzle outlet diameter (Φ3), gas nozzle inlet diameter (Φ2), and the distance between throttle and gas nozzle (L) on the self-adjusting capacity was investigated by means of CFD simulation and validation experiments. The self-adjusting capacity of the TTV increases with an increase in △p, Φ3, and with a decrease in L, but is relatively unaffected by Φ2. To evaluate the contribution of different structural parameters to the self-adjusting ability, the dimensionless self-adjusting capacity index (SACI) was constructed, based on the relation between the self-adjusting capacity and the gas flow rate. Using the SACI, it was determined that to optimize the self-adjusting capacity, a lower value of Φ3 should be chosen, while the optimal value for L was approximately 6 mm for this simulation model. This research provides new technology for the development and design of a high-efficiency TTV.

Embedded direct ink writing of freeform ceramic components

Direct ink writing, a widely used additive manufacturing technique, has some disadvantages in fabricating suspended ceramic structures due to instabilities in the ink caused by surface tension and gravity forces, requiring a strict optimization of the rheology of the feedstock. To overcome this problem, freeform 3D printing was achieved in this work by performing printing inside a supporting medium composed of vegetable oil and fumed silica. The rheological properties of the supporting medium as well as the printability of the ink as a function of the solid content were investigated. Printing parameters such as gas pressure and nozzle movement speed were optimized for a selected diameter of the printed filament. With this method, several suspended structures were fabricated, such as coils with different pitches, hollow cylinders and 3D letters, showing no shape distorting both after printing and the thermal treatment. A preceramic polymer was used as the primary material for the tests, but we also demonstrated that with this approach it is possible to print using inks containing either metal or ceramic powders, thereby showcasing the large potential of this approach for being used in different applications.

Numerical simulation on the emission of NOx from the combustion of natural gas in the sidewall burner

The NOx produced from industrial facilities is a serious environmental problem in China. In this work, the NOx emission from the combustion of natural gas in the sidewall burner was investigated by using CFD method. To achieve the low NOx emission, the sidewall burner structure was optimized involving the width of the primary premixed gas outlet, the secondary fuel gas nozzles number and angular spacing. The mixing rate of fuel gas and air could be improved by increasing the width of primary premixed gas outlet, and the lowest NOx emission of 32.8 ppm was achieved at the width of 8 mm. The NOx emission was remarkably reduced with the increasing of nozzles number, where 28.33 ppm of NOx emission and 357.35 ppm of CO were obtained at four nozzles. The combustion performance and NOx emission was improved as well as NOx emission was reduced at the angular spacing of 55?, compared to that of 30?, 35?, 40?, 45?, 50?, and 60?.

Experimental investigation on the effect of melt delivery tube position on liquid metal atomization

Metal powders are often made by gas atomization of liquid metal. During the process, liquid metal which flows from a melt delivery tube (MDT) is atomized by high speed gas discharging from a gas nozzle. In this work, the effect of the melt delivery tube position on atomization outcomes such as the yield, mass median diameter, and spread of the particle size distribution, is studied experimentally. A melt atomization setup (pilot-scale) is used to produce tin powder by gas-atomization. Three MDT positions, namely, intruded, extruded and flush with respect to the gas nozzle, are chosen for this study. Three pressure regimes (atmospheric, aspiration and pressurization) are established by varying the relative distance between the MDT and the gas nozzle exit for the three positions. Experimental investigations revealed that the intruded position produces powder with lower mean particle sizes and lower spread than the extruded configuration. The intruded position also gives a significantly higher yield compared to the extruded and flush positions at low gas flow rates, and hence appears to be the most suited for metal atomization using a free-fall configuration.

Parameters Optimization of Auxiliary Gas Process for Double-Wire SS316L Stainless Steel Arc Additive Manufacturing

Serious heat accumulation limits the further efficiency and application in additive manufacturing (AM). This study accordingly proposed a double-wire SS316L stainless steel arc AM with a two-direction auxiliary gas process to research the effect of three parameters, such as auxiliary gas nozzle angle, auxiliary gas flow rate and nozzle-to-substrate distance on depositions, then based on the Box–Behnken Design response surface, a regression equation between three parameters and the total score were established to optimized parameters by an evaluation system. The results showed that samples with nozzle angle of 30° had poor morphology but good properties, and increasing gas flow or decreasing distance would enhance the airflow strength and stiffness, then strongly stir the molten pool and resist the interference. Then a diverse combination of auxiliary process parameters had different influences on the morphology and properties, and an interactive effect on the comprehensive score. Ultimately the optimal auxiliary gas process parameters were 17.4°, 25 L/min and 10.44 mm, which not only bettered the morphology, but refined the grains and improved the properties due to the stirring and cooling effect of the auxiliary gas, which provides a feasible way for quality and efficiency improvements in arc additive manufacturing.

In-flight aggregation and deposition behaviour of particles in low pressure cold spray

Low pressure cold spray (LP-CS) is a kind of cold spray (CS) technology. Due to lower gas pressure, particles are difficult to deposit using LP-CS. The particles should be softened by heating of the carrier gas (200 °C–600 °C) in the Laval nozzle to compensate for this deficiency. In this study, the morphology of particles ejected from the Laval nozzle was observed using a scanning electron microscope (SEM), and the aggregation phenomenon between particles was obtained for the first time. With increasing the carrier gas temperature, the particle morphology tended to be irregular gradually due to aggregation and this phenomenon cannot be ignored. Based on this phenomenon, an aggregated particle model was established and the deposition behaviour was investigated by a coupled thermomechanical Eulerian method. The results show that the equivalent plastic strain (PEEQ) of the aggregated particle mainly depends on the particle velocity, and the change of temperature depends more on the original particle temperature. Compared with the individual particles, the bonding between the aggregated particle and substrate is poor at the middle position. In addition, the multi-particles deposition simulation indicates that the formation of coating pores could be inhibited to some extent by the phenomenon of aggregation between particles.

Experimental investigation of a cavitating Venturi and its application to flow metering

An experimental investigation has been carried out to evaluate the performance of a cavitating Venturi flow. For that purpose, a closed loop circuit with a centrifugal pump and a transparent asymmetric converging-diverging test section has been built which allows to set the pressure level and the flow rate. The system is instrumented with several pressure sensors and temperature probes that are continuously monitored during the tests. The experiments have consisted in generating non-cavitating and cavitating flows inside the Venturi under controlled conditions. The obtained results, which have been characterized as a function of the Venturi's discharge coefficient, pressure ratio and pressure loss coefficient, are in good agreement with previous studies carried out with standard Venturi geometries, specially under non-cavitating flows. The Venturi's performance under cavitation flows has been found to be dependent on the Venturi's inlet pressure and similar to a chocked flow condition with constant volumetric flow rate. On the basis of these observations and the analogous behaviour with compressible gas nozzles, a new flow coefficient has been derived which remains constant at any cavitating regime. Thus, this coefficient permits to use a Venturi as a flow meter on cavitation conditions.

Effect of gas temperature and nozzle traverse speed on the deposition efficiency in cold spraying

Effect of gas temperature and nozzle traverse speed on the deposition efficiency in cold spraying

SIMULATION OF AN ANNULAR LIQUID JET WITH A COAXIAL SUPERSONIC GAS JET IN A MEDICAL INHALER

Medical inhalers have been used for the treatment of a wide range of respiratory diseases including COVID-19. In this study, we investigate the annular liquid jet breakup with a coaxial supersonic gas jet using large eddy simulations. This contributes to a further understanding and improvement of medical inhaler designs. The liquid is sucked in by the low pressure as a result of the high velocity gas jet and breaks up due to the interaction with the gas jet. This type of spray nozzle configuration is commonly used in medical inhalers. Two different gas nozzle diameters are studied. The simulated liquid structure is compared with preliminary, qualitative experimental results. The gas jet pressure and radial velocity of the liquid are found to be coupled and the interaction between them plays an important role in formation of the liquid structure. The effect of gas nozzle diameter on flow rate, mean radius of the liquid, and mean radial velocity, as well as its oscillation behavior has been investigated. The power development of dominate frequencies of averaged radial liquid velocity along the flow direction is shown. The growth of the instabilities can be observed from these results.

DEVELOPMENT OF PROMISING SYNTHESIS - TECHNOLOGY AVENIR GAZ CONVERTING DIESELS TO GAS ENGINES WITH SPECIAL IGNITION

The object of research is the multifunctional synthesis technology Avenir Gaz (of various levels of complexity), intended for converting transport diesel engines into spark-ignited gas internal combustion engines (ICE) for operation on liquefied petroleum gas (LPG). Investigated problem: the creation of an affordable synthesis technology in terms of complexity and price, which allows converting operating diesel engines into gas internal combustion engines operating on cheaper and environmentally friendly gas fuel - LPG. Main scientific results: Avenir Gaz synthesis technology (two levels of complexity, qualified as levels "A" and "B") for converting diesel engines into gas internal combustion engines is developed and created. It is shown that the conversion of diesel engines according to the Avenir Gaz synthesis technology is carried out on the basis of the developed electronic microprocessor control systems. And the basis of the control systems is the developed and manufactured two electronic microprocessor control units Avenir Gaz 37 (hereinafter – ECU Avenir Gaz 37). ECUs in accordance with the levels of complexity of synthesis technology are qualified as – ECUs Avenir Gaz 37 "A" and Avenir Gaz 37 "B". It is shown that Avenir Gaz synthesis technology of level "A" allows converting diesel engines into gas internal combustion engines with LPG supply through a gas-air mixer into the inlet pipeline. At the same time, the Avenir Gaz 37 "A" ECU, using the signal from the Hall sensor of the distributor, limits the maximum speed of the gas engine, thereby ensuring its safe operation. And the synthesis technology Avenir Gaz 37 of level "B" allows converting diesel engines into gas internal combustion engines providing group or sequential injection of LPG by electromagnetic gas nozzles (injection system of the Common Rail type) into the intake manifold in the area close to the intake valve. Area of practical use of the research results: converting diesel vehicles, including agricultural machinery (powerful wheeled and tracked tractors, combines, etc.) into spark-ignited gas combustion engines operating on LPG. An innovative technological product: Avenir Gaz synthesis technology, which allows converting the transport diesel engines in operation into gas internal combustion engines for operation on LPG. Scope of application of the innovative technological product: naturally aspirated and supercharged diesel engines with the number of cylinders from one to six, in-line and V-shaped, with a uniform alternation of working strokes.

Research basic parameters and justification of choice of gas injectors for alternative biogas fuel

In connection with the trend of shortage of commercial fuels for engines in Ukraine and the world, the production of alternative fuels is developing, including biogas. The use of biogas fuel on a modern internal combustion engine equipped with gas equipment of 4-5 generations can create a number of difficulties. This is due to the low heat of combustion of untreated biogas, the presence of moisture and the specifics of the operation of the nozzles. And, therefore, for the correct choice of nozzles, it is necessary to conduct a study and analysis of a number of basic indicators of their operation and, based on the data obtained, recommend their optimal parameters. In gas nozzles, as in gasoline ones, there are a number of important parameters on which stability and uniformity of engine operation, fuel consumption, reliability, etc. depend. These include: linear operation; nozzle reaction time; coil resistance; response time; ability to maintain factory performance; resource of work. For research, we selected nozzles of 4 generations of common manufacturers, namely: Matrix; Barracuda; Valtek; Hana; Keihin. In terms of linea-rity, Valtek nozzles have low performance, and therefore use on engines can lead to increased biogas consumption, reduced engine performance and valve burnout. Keihin nozzles have high rates in this aspect of research, and therefore they will provide maximum efficiency of biogas combustion on the engine. High reaction time in Keihin nozzles. Barracuda nozzles are very close to working with Keihin, which means that their use will not impair engine performance. The factory characteristics of the nozzles, namely the coil resistance is the optimal Keihin nozzle, and the lowest values ​​in Valtek nozzles, the response (response) time of the Matrix, Hana and Keihin nozzles is quite close to 2 ms, which will provide quick response and wear, and the Barracuda and Valtek nozzles Keihin, Matrix and Barracuda nozzles provide the ability to maintain factory characteristics in the range from 2 to 5%, and the worst performance in Valtek is up to 20%, the service life of the nozzles, subject to timely servicing, is the largest Keihin nozzle, Matrix and Hana, which is from 200 to 250 thousand km, and the lowest indicator in Valtek and Matrix injectors is a resource from 70 to 100 thousand km. So, according to the results of the research, Keihin nozzles are recommended for use on engines in the process of their conversion to gas fuel. Their application will provide maximum efficiency and economy of the engine.