Gas Jet Research Articles

Simulation of the Jet Fire Using Atmospheric Dispersion Modeling (ALOHA): A Case Study of Natural Gas Pipeline in Istanbul, Türkiye

Natural gas is known as a widely used energy source in residential, business and industrial areas. During the transportation of natural gas by pipelines, accidents occur due to various reasons, which can also lead to gas output. These accidents are events that have the potential to pose important risks in terms of life and property safety, particularly in urban areas and surrounding of pipeline routings. In this study, accident scenarios were generated based on a natural gas distribution pipeline fire that occurred in Istanbul (NW Türkiye) on 28 April 2020 and the impact areas of the jet fire were calculated using the ALOHA program. The effects of source release factors (i.e., pipe length and diameter) and atmospheric conditions (i.e., wind speed, cloud cover, air temperature and relative humidity) on the thermal radiation threat distances associated with jet fire were calculated for the current and worst scenarios. As a result, it was found that pipe length and diameter have a significant effect on threat distances. In addition to the role of the synoptic circulation mechanism on the jet fire for the selected episodic event (position of low/high pressure centers), local atmospheric conditions also have an effect on the threat distance. From the modeling analysis, significant impact of wind speed, air temperature and relative humidity values on the threat distances were found. In the worst scenario, if there were strong northeasterly winds reaching 30.9 m per hour at the time of the jet fire, the threat distances would have been 21 m (red), 28 m (orange) and 42 m (yellow). This case shows that if a natural gas jet fire occurs under the influence of strong northeasterly winds (passing over the Black Sea without encountering any topographic obstacles), poisonous gas will be transported to long distances in a short time and will negatively affect social life and economy.

An XCT study on three-dimensional characteristics of a spout-fluid bed

Spout-fluid beds are widely used in the chemical and petrochemical industries for excellent mixing and heat and mass transfer properties. Understanding the behavior of jets in spout-fluid beds is crucial for optimizing these processes. In this paper, we present a novel experimental method for studying the three-dimensional characteristics of jets in spout-fluid beds using X-ray computed tomography. By employing a gas–solid flow parameter measurement system, we propose an accurate experimental fitting method for voxel voidage values, enabling the three-dimensional reconstruction of the time-averaged voidage in the entire flow field of a spout-fluid bed. These data are then used to develop an image processing algorithm for identifying and quantifying gas jets in the flow field, allowing for measures of jet length, volume, and diameter. We further investigate the effects of static bed height, spouting gas velocity, and fluidizing gas flowrate on the three-dimensional characteristics of jets.

An experimental platform for investigation of the Zeeman effect in strong magnetic fields.

An experimental platform is developed for the investigation of the Zeeman effect in strong magnetic fields. Mega-Gauss magnetic fields are generated by a 1 MA Zebra pulsed power machine using metal rod loads. A gas jet or CH oil on the load is the source of hydrogen. Excited hydrogen atoms are backlit by black body radiation from the rod load. Hydrogen absorption spectra are recorded with a grating spectrometer and intensified gated CCD camera. The experimental platform enables the observation of the quadratic Zeeman effect in hydrogen gas jets using the spectral shift of the central line in the Zeeman triplet. Other gases can be studied using the gas jet method.

Proton acceleration from optically tailored high-density gas jet targets

Laser-driven ion acceleration is well established using solid targets mainly in the target normal sheath acceleration regime. To follow the increasing repetition rate available on high-intensity lasers, the use of high-density gas targets has been explored in the past decade. When interacting with targets reaching densities close to the critical one, the laser pulse can trigger different acceleration mechanisms such as Collisionless Shock Acceleration (CSA) or hole boring. Particle-in-cell simulations using ideal target profiles show that CSA can accelerate a collimated, narrow energy spread and few hundreds of megaelectronvolts ion beam on the laser axis. Nevertheless, in real experiments, the laser will not only interact with an overcritical, thin plasma slab with sharp density gradients, but also with lower density regions surrounding the core of the gas jet, extending to several hundreds of micrometres. The interaction of the laser with these lower density wings will lead to nonlinear effects that will reduce the available energy to drive the shock in the high-density region of the target. Optically tailoring this target could mitigate that issue. Recent experiments conducted on different laser facilities aimed at testing several tailoring configurations. We first tested a scheme with a copropagating picosecond prepulse to create a lower density plasma channel to facilitate the propagation of the main pulse, while the second one was a transverse tailoring driven by nanosecond laser pulses to generate blast waves and form a high-density plasma slab. The main results will be presented here and the methods compared.

A high temperature engine materials test facility.

Gas turbine engines subject materials to extreme conditions. Their high temperature materials and co-developed coatings must survive combustion gas temperatures currently approaching 1800 °C, large thermal gradients, severe thermal shock, and static and fatigue inducing applied stresses, all the while operating in highly reactive, high-pressure, high-speed combustion gas flows containing significant partial pressures of water vapor, oxygen, and other reactive species for many tens of thousands of hours. We describe the design and development of a test facility for the study of materials under individual and combinations of test parameters similar to those experienced within legacy and future engines. A hydraulic load frame capable of applying static or cyclic tension-compression stresses up to 400 MPa to flat-dog bone-shaped test specimens is integrated within an environmental test chamber capable of sustaining gas pressures from 0.1 to 1.2 MPa (1-12 atm). An adjustable0.1-2 kW power CO2 laser whose 10.6 µm wavelength radiation is strongly absorbed by ceramic coating materials is used to heat sample surfaces to temperatures of 1800 °C and above, while rear surface air jet cooling establishes through-thickness thermal gradients. Rapid laser heating in conjunction with transiently applied front and/or rear-side air cooling is used to create hot or cold thermal shock effects. This is accompanied by the impingement of a high pressure (up to 1.3 MPa) reactive gas jet upon the sample with speeds up to 300m/s by preheating dry air, mixing it with steam to the desired humidity, heating to 850 °C, and then expanding it through a converging nozzle. Thermal imaging pyrometers measure specimen front and back surface temperature fields, while environmental test chamber view ports permit digital image correlation and strain mapping.

Research of Fuel-air Thermal Tools for Extraction and Processing of Block Stone

The stages of development of thermal tools with intensifiers of combustion of fuel components are described. Studies for obtaining the manifestation of detonation in the free stream of thermal tools during combustion of fuel components have been performed. The design features of the development of gasoline-air thermal tools, which allow intensifying the combustion processes of fuel components, are presented. However, due to the simplicity of operation and organization of feeding fuel components with gasoline-air burners, their use as working bodies of mechanized equipment is urgent. Increasing the power of gasoline-air burners without considerable development of their overall dimensions and increasing the size of the burner flame is possible due to intensification of combustion processes. The use of gasoline-air burners as working bodies of mechanized thermal units is restrained by their relatively low power, the increase of which quickly increases their overall dimensions. Also, the thermal tools with supersonic flare for various technological operations, for rock destruction during slot excavations are considered. The experiments have shown that with the increase in the number of ejection windows, the size of the flare and the power of shock waves increase. To determine the heat transfer parameters of supersonic high-temperature gas jets, a special burner was developed with the possibility of using gasoline, diesel fuel and propane gas as fuel. Gasoline-air burners allow using detonation combustion in them to increase the productivity of thermal destruction of rocks, and to automate the start-up of the burners in operation. Experimental studies have shown that gasoline-air burners, with a combustion intensifier, allow using detonation combustion in them to increase the productivity of thermal destruction of rocks, to automate the start-up of thermal tools in operation

Experimental Study on Atomization Characteristics of Swirl Nozzle under Annular Airflow Impingement

Pressure nozzles are widely used in spray drying and other industries. In order to improve the atomization characteristics of pressure cyclone nozzles, a new type of annular jet gas impingement atomization device is developed. We use high-speed imaging and digital image processing and other methods to analyze the spray characteristics of the different annular device configurations (using four, six, and eight tubes) and under different gas–liquid mass flow rates. It is shown that with an increase in the Air–Liquid mass Ratio (ALR), the liquid film breakup process changes from undulating sheet breakup to perforated sheet breakup and the breakup length decreases. The breakup length decreases the most under the condition of six-tube airflow with the range of 31–55%, while the Sauter mean diameter (SMD) basically does not change. With the increase in ALR and the Weber number of liquid (Wel), the droplet size distribution becomes more uniform. The spray characteristics of the atomizer assisted by gas jets reaches the best state when Wel = 4596.3 and m˙g = 1.97 g/s. The experimental conclusions have some guiding significance for the design and optimization of the atomization devices in spray drying towers.

Theoretical and experimental analysis of the critical velocity of interface instability in gas jet forming

Gas jet forming can be used for creating optical reflectors, but under certain conditions, the surface shape fluctuation of the gas-liquid interface, that is, interface instability, may occur during the forming process. This study investigated the mechanism of interface instability in gas jet forming by combining the Kelvin-Helmholtz instability and the gas jet flow velocity distribution law. Theoretical analysis revealed that when the nozzle height is fixed, interface instability occurs when the gas flow rate reaches a certain value, which increases with the distance between the nozzle and the liquid surface. In order to verify the results of the theoretical analysis, experiments were carried out within the range of nozzle height from 0 to 42 mm, based on the formulas of the transition section between the potential core region and the self-similarity region in the gas jet. Within this range, the critical velocity of interface instability was found to be the minimum, 9.946 m/s, when the nozzle height was 0 mm, and the maximum, 15.562 m/s, when the nozzle height was 42 mm. The results of the theoretical analysis and experiments were used to establish a predictive model for the critical condition of interface instability, with a mean prediction deviation of 0.119 m/s. This model can provide a basis for selecting parameters for gas jet forming.

Oxygen Distribution at the Hot Spot in BOF Steelmaking

The distribution of oxygen between the gaseous and liquid oxidation products at the hot spot is modeled. The simplified model accurately describes the interaction of the gas jet exiting the lance nozzles with the gaseous surrounding of the jet. This interaction changes the chemical composition of the gas jet influencing the subsequent interaction with the hot spot. The iterative procedure then calculates the chemical composition of the gas exiting the cavity. The characterization of the exiting gas flowing past the lance head as well as the generation rate of FeO is attained by combining the modeled gas composition exiting the cavity with an oxygen mass balance based on a quasi-stationary BOF operation.

Particle removal from solid surfaces via an impinging gas jet pulse: Comparison between experimental and CFD-DEM modeling results

Computational and experimental studies are performed to investigate the influence of a gas jet pulse impinging perpendicularly onto a flat solid surface seeded with a monolayer of spherical particles. A numerical resuspension model is derived to predict particle release into the gas phase during jet impingement. To this end, discrete particles are immersed in a continuous gas phase modeled via Large Eddy Simulation to capture the effect of jet turbulence on the particle detachment process. Two-way coupling between particulate and gas phase is established via a near-wall particle drag model and a lift model. Direct particle–wall interactions are captured with adhesion, rolling friction and sliding friction models. To validate the overall modeling approach, numerical results are compared with resuspension experiments for monodisperse polystyrene particles placed on a glass slide. Simulations show that the particles preferentially mobilize by rolling, followed to a limited extend by lift off from the solid surface driven by aerodynamic forces and particle–particle collisions. Resuspension occurs in the first instants after jet impingement. Computational and experimental results for removal efficiency Γ are in good agreement in terms of the location of their r50 parameter, i.e., the radial position where 50% of the particles have been removed by the jet; both results show a linear dependence between the r50 value and the jet Reynolds number of the impinging jet. However, experimental Γ(r) curves generally have a smooth sigmoidal shape whereas numerical results predict a sharp transition. Some model shortcomings are identified which lead to an underprediction of particle lift-off and which explain the observed differences. Furthermore, the experimental Γ curves nearly collapse onto each other when plotted over the predicted local wall-shear stress.

Interaction of soliton gases in deep-water surface gravity waves.

Soliton gases represent large random soliton ensembles in physical systems that display integrable dynamics at leading order. We report hydrodynamic experiments in which we investigate the interaction between two beams or jets of soliton gases having nearly identical amplitudes but opposite velocities of the same magnitude. The space-time evolution of the two interacting soliton gas jets is recorded in a 140-m-long water tank where the dynamics is described at leading order by the focusing one-dimensional nonlinear Schrödinger equation. Varying the relative initial velocity of the two species of soliton gas, we change their interaction strength and we measure the macroscopic soliton gas density and velocity changes due to the interaction. Our experimental results are found to be in good quantitative agreement with predictions of the spectral kinetic theory of soliton gas despite the presence of perturbative higher-order effects that break the integrability of the wave dynamics.

Primary and secondary breakup of molten Ti64 in an EIGA atomizer for metal powder production

Electrode Induction melting Gas Atomization (EIGA) is a free-fall gas atomization process used to produce metal powders, where a swirling supersonic gas jet hits a molten metal stream atomizing it into droplets through various fragmentation mechanisms. Fragmentation mechanisms of molten Ti64 are investigated by high-speed video visualization. The role of gas pressure and melting chamber overpressure on the fragmentation mechanisms and on the particle size distribution is determined. The mechanisms observed are fiber breakup, bag breakup and Rayleigh breakup for primary fragmentation and bag breakup and shear breakup for secondary fragmentation. Increasing the gas pressure promotes shear breakup and creates finer droplets. A model based on log-stable law is proposed to fit the mass distribution according to the dominant fragmentation regime. A good agreement is observed between the different analysis (dominant atomization regime, mass cumulative distribution evolution, parameters of log-stable law). A criterion for prediction of nozzle clogging is devised.

Development of a double-grating differential interferometer for plasma diagnostics.

A special differential interferometer consisting of two gratings was developed for diagnostics of plasma density. Compared with other differential interferometers, our system has an important advantage that the shear distance, shear direction, and fringe width can be adjusted independently, enabling easy control of the parameters. This feature allows precise tuning of the two probe beams in the interferometer for rigorous differential phase diagnosis and more accurate information of the plasma density can be obtained. The double-grating-based differential interferometer was tested for diagnostics of the laser-produced plasma which was generated by focusing a 1 TW/35 fs Ti:sapphire laser pulse in a gas jet with a 100 μm orifice diameter. It was confirmed that our differential interferometer can provide more reliable and accurate plasma density information, especially for plasmas with a high spatial gradient in density.

Effects of wall cavity and fuel injection pressure on the performance of a non-reacting supersonic combustor

This study numerically investigates the flow field of a non-reacting cavity-configured scramjet (Supersonic Combustion Ramjet) combustor at various fuel injection pressures by solving the 2D Reynolds-Averaged Navier-Stokes (RANS) equations, species transport equations, and Menter SST k-ω model. The aim of this research is to reveal the effects of wall cavity insertion and fuel injection pressure (FIP) on the crucial performance parameters i.e., fuel-air mixing efficiency (MxE), total pressure recovery (TPR), and mass-averaged Mach number (MAMN). Accordingly, two trapezoidal cavities of aspect ratio 7 are introduced on the opposite walls of a rectangular combustor. The combustor entrance is configured with rearward-facing steps and it intakes finite parallel air streams through finite-width inlets. Gaseous hydrogen jets are injected 30 mm downstream from the combustor entrance and 10 mm upstream from the cavity leading edge. FIP is varied according to the fuel-to-freestream pressure ratios (FFPR) of 4.5, 9.0, 13.5, and 18.0. The results of the cavity-configured combustor are then compared with the performance of the combustor in the absence of the wall cavities. The results delineate the change in flow structures with the inclusion of wall cavities and variation in FIP. Insight physics of mixing, total pressure loss, and MAMN in different regions of the combustor are studied and the results are quantified for comparison. MxE in a cavity-configured combustor does not monotonically increase with decreasing FFPR as found in the combustor without wall cavities. The shock-shear layer interactions (SSLIs) play a dominant role in mixing inside the cavity-configured combustor. The results also demonstrate that the insertion of wall cavities can increase fuel-air MxE through the formation of cavity recirculation zones. In the cavity-configured combustor, a maximum of 45% MxE is achieved for FFPR 4.5, which is 4% higher than the value obtained from the combustor without the cavities with an expense of 3% greater total pressure loss.

Dissecting recorded gunshot sounds

Gunshot audio recordings are composites of multiple sound sources, including blast, ballistic, mechanical, and environmental sounds. The existence of each sound and its distinguishing features depend on the source characteristics, the propagation environment, and the recording system. Controlled recordings show the situational dependence of these sound sources and the recording system. Knowledge of the physics and these dependences is critical in forensic analysis and the ability to dissect, separate, and identify sources in recorded gunshots. Multiple blast sources (muzzle blast, gas jet, mechanical impact, and primer explosion), ballistic sources (shockwave and subsonic flow), and environmental sources (reflections and terminal impact) will be shown from both controlled experiments and uncontrolled forensic recordings.

Numerical simulation of the underwater gun using gas-curtain launch

A novel gas-curtain launch technique is proposed to enhance the interior ballistic performance for underwater guns. The size of the initial gas curtain in front of the projectile is a critical factor in determining the subsequent behavior of the gunpowder gas jet flow field once the projectile leaves the muzzle. Hence, a validated two-dimensional unsteady multiphase model is built for the flow field at the muzzle of an underwater gas-curtain launch. The calculation involves determining the development of the initial gas curtain sizes for a 30 mm underwater gun, specifically focusing on the evolution of the precursor jet and gunpowder gas jet flow field. The results indicate that a double three-wave point structure forms within the bottle-shaped shock wave structure of the precursor jet when the initial gas curtain length equals the barrel. As the initial gas curtain size increases, the “bottle” structure elongates along the axial direction and compresses radially. After the projectile exits the muzzle, the gunpowder gas quickly expands toward the front, causing the collapse of the Mach disk of the precursor jet. The gunpowder gas jet then reforms a new bottle-shaped shock wave structure. A larger initial gas curtain can facilitate the expansion of the gunpowder gas, resulting in an increased size of the bottle, delayed formation, and weakened intensity of the Mach disk. Additionally, increasing the size of the initial gas curtain decreases the resistance experienced by the projectile outside the barrel. The initial gas curtain can also affect the cavitation bubble evolution process on the projectile sidewall, showing a growth-(attenuation)-stability trend.

Gas–liquid twin-fluid atomization from non-circular orifices

Passive control of twin-fluid atomization can be achieved by changing the orifice shape of the injector. In this study, the characteristics of twin-fluid atomization in the outside-in-liquid injector with circular, square, and rectangular orifices at various aspect ratios were investigated experimentally and computationally. The morphology of the spray was captured by shadowgraph, the diameter and velocity of the droplets were measured by the phase Doppler particle analyzer, and numerical simulations were performed for the central gaseous core. Comparing the sprays with square and circular orifices, droplets from the non-circular orifice are generally smaller with less disparities in droplet sizes due to the more intensive turbulent disturbances and corner effect. Furthermore, the non-circular orifice also results in better spatial distribution of the spray. The droplet diameters of the spray with a square orifice do not satisfy the log-normal distribution near the orifice along the centerline of the spray, which may be attributed to the different entrainment of spray droplets by the central gas flow for the sprays with circular and non-circular orifices. The twin-fluid sprays produced by the rectangular orifice also exhibit the same axial switching effect as in the high-pressure gaseous jet flow, in which the spray diffusion in the minor axis is more extensive than that in the major axis. Moreover, the droplets' Sauter mean diameter produced by the rectangular orifice is more sensitive to the size in the minor axis of the orifice and decreases as the aspect ratio of the orifice increases given the same cross-sectional area.

Optimization of extreme ultraviolet vortex beam based on high harmonic generation

In high harmonic generation (HHG), Laguerre–Gaussian (LG) beams are used to generate extreme ultraviolet (XUV) vortices with well-defined orbital angular momentum (OAM), which have potential applications in fields such as microscopy and spectroscopy. An experimental study on the HHG driven by vortex and Gaussian beams is conducted in this work. It is found that the intensity of vortex harmonics is positively correlated with the laser energy and gas pressure. The structure and intensity distribution of the vortex harmonics exhibit significant dependence on the relative position between the gas jet and the laser focus. The ring-like structures observed in the vortex harmonics, and the interference of quantum paths provide an explanation for the distinct structural characteristics. Moreover, by adjusting the relative position between the jet and laser focus, it is possible to discern the contributions from different quantum paths. The optimization of the HH vortex field is applicable to the XUV, which opens up a new way for exploiting the potential in optical spin or manipulating electrons by using the photon with tunable orbital angular momentum.

Gas–liquid coaxial atomization with swirl in high-pressure environments

We present recent experimental results on the dynamics of atomization of a liquid column by a coaxial turbulent gas jet, under varying air angular momentum (swirl) conditions and densities. We compare between atomization under atmospheric conditions and in a pressurized environment where the atomizing and ambient air density is 5 times the atmospheric level. For both conditions, the parameter space includes a gas-to-liquid momentum ratio in the range of M=25−56 and swirl ratios of SR=0−1. High-speed shadowgraphy images in the spray near-field are used to quantify the spatial and temporal evolution of the liquid–gas interface. In the mid-field, Phase Doppler Interferometry, collected radially across the spray, quantify droplet size, velocity, and number density distributions. At high pressure and with increasing M, we observe a decrease in spray angle when SR=0 but a spray angle increase when SR>0.5 (critical swirl). We reconcile these observations with the crown de-wetting mechanism, first observed in X-ray shadowgraphs of the spray. Crown de-wetting depends on gas inertia relative to the liquid, which increases linearly with atomization environment pressure, leading to this switch in behavior. This mechanism also explains the modified droplet radial distribution in the mid-field, with critical transition from concave to convex-shaped trends in the mean droplet size profile. Finally, we reconstruct the full spray droplet population from radial measurements, showing that swirl not only modifies the transport of droplets in the spray cross-section, but also enhances break-up and reduces the Sauter Mean Diameter globally, for all momentum ratios and pressure conditions tested.

Thermodynamic analysis of nano-electrospray induced gas jets

Nano-electrospray (nES) produces a plume of charged liquid droplets which have drag interactions with the surrounding gas after they are emitted from a source capillary. The resulting induced gas flow has often been considered unimportant, but we have demonstrated that a gas microjet of significant velocity up to 10s of m/s can be produced. In this work we present a thermodynamic framework that enables analysis of gas jet generation from electrosprays and introduce the important metrics for such analysis, effectiveness (a measure of momentum transfer from the electrosprayed aerosol to gas) and efficiency (a measure of energy conversion from electrical energy generating the electrospray to gas kinetic energy). This analytical framework is applicable to any two-phase flows consisting of discrete conservative-force-driven particles which exchange momentum with an inert, otherwise quiescent fluid medium to yield a co-flowing two-phase jet. We apply this framework to sprays of water from nano-electrospray emitters to demonstrate that increasing the applied electrical potential difference, increasing liquid mass flowrate, and decreasing droplet size all can increase electrospray induced gas jet strength, but only the latter two do so while also increasing the momentum transfer effectiveness and energy conversion efficiency.