Gas Flow Field Research Articles

Experimental and Numerical Investigation of Shielding Gas Behaviors in Laser Welding of TC4 Alloy.

Gas protection is a crucial part of quality control in laser welding, especially for titanium alloy, which oxidizes easily at high temperatures. Substantial experiments concerning shielding gas characteristics in the welding process have been implemented. However, the common analysis conducted is simplistic and lacks a theoretical basis. This paper presented an investigation of the shielding gas behaviors based on numerical simulation and a titanium alloy laser welding experiment. The numerical model was established and validated by experiment. Subsequently, the temperature field and gas flow fields were calculated. By combining the two fields, the threshold temperature of gas protection was determined, and the influence of shielding gas parameters on the protection effect was examined. The results revealed that the protection of the high-temperature zone was primarily influenced by the nozzle height, nozzle inner diameter, and nozzle angle, while the plasma suppression effect was mainly correlated with the nozzle inner diameter and gas flow rate. These initial findings provide scientific guidance for the better quality production of laser beam welded components made of not only titanium alloy but also other metallic materials.

Missile thermal emission flow field under the synergistic effect of deep reinforcement learning and wireless sensor network

AbstractThe vehicle-mounted missile vertical thermal emission not only has excellent maneuverability, randomness, and concealment, but also has a short response time, good versatility, and high reliability, so it is widely used. In order to explore the gas flow field of thermal emission of the vehicle-mounted missile, firstly, this study introduces the theoretical basis of deep reinforcement learning (DRL) algorithm and wireless sensor network (WSN). Secondly, combining WSN and DRL, a WSN technology based on DRL is proposed. Finally, the DRL-based WSN technology is applied to the vertical thermal emission of the vehicle-mounted missile. In addition, the flow field simulation software is employed to simulate and compare the influence of the single-side and double-side diversion schemes of the gas flow discharged by the diverter on the open ground field flat collection launcher, and the diversion characteristics of the two schemes are obtained. The results show that in the single-side diversion scheme, the impact and ablation area of the gas jet on the ground mainly appear at the rear side of the diversion device, and the ablation area of the gas jet on the launcher vehicle is mainly at its tail end. While the ablative site and shock of the double-side diversion scheme on the ground mainly appear on both sides of the diversion, and the ablative part of the gas jet to the launcher is mainly present at the bottom of the frame and the inside surface of the tire. The study of missile thermal emission flow fields based on DRL and WSN has certain theoretical significance for the flow field variation of missile launching.

Perspectives on instrumentation development for chemical species tomography in reactive-flow diagnosis

Chemical species tomography (CST) has been deployed in a wide range of applications in the last two decades for multi-dimensional measurement of gaseous flow fields. CST offers unique capability for spatiotemporally resolved imaging of multiple thermochemical parameters. It is fundamentally robust, highly sensitive, and adaptable to industrial processes and large-scale combustion systems. The instrumentation methods used to implement CST measurements are critical in determining the physical and chemical variables that may be imaged by CST. In this perspective, we have three main objectives: (a) discuss recent advances in CST instruments from the viewpoint of optics and electronics; (b) highlight the on-going challenges for systems to address the ever-increasing requirements on temporal and spatial resolutions; and (c) consider potential developments for next-generation CST instrumentation.

Study on the characteristics of the transient flow field under different underwater environments

The underwater muzzle transient flow field is an unsteady, multiphase complex flow field interacting with projectiles and containing various shock wave structures. The turbulent mixing of gunpowder gas and water has a significant impact on the development of the muzzle gas flow field. Moreover, the muzzle gas flow field disturbs the motion of the projectile, thereby affecting shooting accuracy. As part of this research, an unsteady multiphase flow model of the underwater muzzle transient flow field is established by combining the theories of multiphase flow and turbulent mixing. The volume of fluid model is employed to trace the two-phase interface, while the gas–liquid turbulent mixing is described by the standard k–ε turbulence model. Furthermore, the cavitation model is used to describe the cavitation phenomenon caused by the motion of the projectile. The established numerical model is validated by comparing underwater launching experimental results. Accordingly, the muzzle flow field of a 30 mm underwater gun under different water depth conditions is numerically calculated. The results demonstrate that, as the water depth increased, the gunpowder gas is exposed to relatively high water pressure during the expansion process, resulting in a continuous decrease in the core area of the gas, and the Mach disk is also increasingly closer to the muzzle. At different water depths, the diameter of the Mach disk conforms to the binomial law with time, while the displacement of the Mach disk from the muzzle increases exponentially with time.

Stacking of Flowcells for the CO2-to-CO Electrolysis

The low-temperature CO2-to-CO electrolysis is one of the most mature CO2 electrolysis processes regarding technical and economical readiness. For this rather young technology Ag is established as a stable and highly selective catalyst. Research focus is therefore on increasing the process´ energy efficiency as well as the space-time yield. Promising results were reported for continuous single flowcells in lab scale size operating with aqueous electrolytes and gas diffusion electrodes (GDE) [1,2].This work specifically addresses the performance optimization of such flowcells under the condition of designing a stackable flowcell architecture. For two different flowcell concepts, short-stacks were designed and tested.Media flow compartments in a catholyte buffered GDE-flowcell operating with a proton exchange membrane were modified on two levels. The feed gas distribution over the GDE was optimized by introducing gas flowfields in the gas chamber, which supports the GDE from the far side of the anode and provides electrical contact. In the catholyte chamber, which separates the membrane from the cathode, an ionically conductive spacer was introduced. This spacer suppressed gas bubble-induced noise during cell voltage measurements and thus enabled a more stable process. The anode was mounted directly to the membrane (Zero-Gap) eliminating the second electrolyte gap (Figure1). In combination, these three modifications provided a supporting structure all the way from the anode flowfield to the cathode flowfield and thus force closure within the cell. Additionally these modifications ensured electric and ionic contact through the entire active cell area and provide mechanical support for the GDE and the membrane. By assembling and successfully testing a two-cell short-stack, it was demonstrated that the applied modifications yielded a stackable flowcell concept. [3]As catholyte buffered flowcells are limited in reaching high energy efficiencies (e.g. 35%) due to the ohmic resistance in the electrolyte gap, a flowcell containing a membrane electrode assembly (MEA) was designed applying the lessons learned previously and stackability as a design requirement. These flowcells operate with anion exchange membranes as polymer electrolytes rendering the catholyte buffer redundant. The electrodes can be mated directly on the membrane which minimized the electrode distance to the thickness of the membrane. The MEA flowcells, therefore, show low cell voltages and hence high energy efficiencies (e.g. 45%). Furthermore, the number of media flows that are to be managed within a single flowcell and hence in a stack is reduced. Aside from this simplification, anolytes with low ionic conductivity (e.g. 10mM KHCO3) can be used, reducing shunt currents within the stack and thus simplifying the electrolyte manifolds.A modular bipolar plate consisting of two plates was designed, which allows a free combination of different coated flowfields for the anode and cathode sides. For instance, the anode plates were coated with an Ir-MMO coating to enhance the OER appearing at the anode and thus to increase the single-cell performance. The bipolar plates were implemented in a three-cell short-stack containing MEA cells (Figure1). The results from electrochemical experiments with the short-stack showed that the results obtained with the single flowcell (200 mA/cm²; 3.2 V; FE(CO) >90%) could be adapted to the three-cell short-stack.

Numerical study on thermal-hydro coupling characteristics of underground coal combustion under heterogeneous void fraction

Coal seam mining will lead to the movement and fissures of the overlying strata, which makes a complex void condition between the mining area and the ground surface. The void condition plays a key role in the occurrence and expansion of underground coal fires. In this study, the void rate model and the coupled thermal-hydro model of the underground coal fire were constructed. The COMSOL Multiphysics was used to study the coupling law of the temperature field and gas flow field of coal seam spontaneous combustion. By setting different oxygen content and inlet gas velocity, the influence of the external environmental parameters on the expansion law of underground coal fire is analyzed. The results show that the void characteristics of the mining area and the overlying strata have an obvious influence on the expansion of underground coal fire, and there is also a two-way coupling effect of the temperature field and gas flow field. The analyses of the influencing parameters show that reducing the oxygen content or increasing the inlet gas velocity will have a certain inhibitory effect on the expansion of underground coal fires, which can reduce the risk of spontaneous combustion.

Investigation on the flow and heat transfer characteristics in a flame deflector with different water injection schemes

The thermal–hydraulic performance of flame deflector in a reduced-scale rocket engine testing platform with different water spray schemes is analyzed. The standard k-ε turbulent model and Eddy-Dissipation Concept (EDC) model are applied to solve the characteristic of the flow and combustion and the discrete ordinates (DO) model is adopted to simulate the thermal radiation. Model validation shows that the predicted results are in good agreement with the experimental data. In addition, the flow and temperature field of the exhaust gas impinging on the flame deflector under different water injection location, mass flow rate, hydrogen ratio and vertical panel height are numerically investigated. The results reveal that the scheme of centre water spray performs better than other schemes in terms of maximum and area-averaged temperatures. In terms of the flow performance, the case of annulus water spray performs best, followed by centre water spray and bottom water spray worst. With the increase of hydrogen ratio, the reburning of hydrogen results in the amplification of the high-temperature region in the flame deflector. The temperature on the bottom surface decreases gradually but the temperature on the vertical panel increases with the increase of the vertical panel height.

Dust transport law and deposition characteristic in coal workers' respiratory tract based on CFD simulations

During the coal mining process, the particle produced enters the worker's body with breathing and likely leads to lung diseases such as pneumoconiosis. In this paper, an idealized model of the human respiratory tract is established, and the gas flow field is simulated using CFD for both steady and unsteady human respiration, followed by analysis of the trajectory and deposition of particle. Results show that during steady state breathing, airflow produces complex changes in the larynx, particles are mainly deposited in the pharynx, and the main deposition factors are impact and particle inertia. In non-steady respiration, the fraction of particles deposited in the inhalation phase is much greater than in the exhalation phase. Exhaling immediately after inhaling in a dusty room and holding the breath after inhaling when using inhaled drug therapy. This paper has positive implications for the study of the pathogenesis and treatment of lung diseases.

Research on the Structure Optimization Design of Automobile Intake Pipe

As the front end of the intake system, the intake dirty pipe is responsible for delivering sufficient and stable air to the air filter. Therefore, in order to meet the requirements of low intake resistance, it is necessary to correspondingly improve the flow resistance performance of the intake dirty pipe. In this study, the main research object was the intake pipe in the intake system of gasoline engine vehicles, and the internal gas flow field was simulated and analyzed. The results show that there are clear discrete velocity regions at the inlet and elbow, which affect the uniformity of the overall fluid flow and cause a certain pressure loss. After structural optimization, the total pressure difference at the inlet and outlet of the pipeline was reduced by 22.67% compared to the original model, and the total pressure loss was significantly reduced. A simplified model was used to make samples of the intake dirty pipes before and after performance improvement, and flow resistance tests were conducted respectively. The difference between test data and simulation data is within a reasonable range, and the simulation results are relatively reliable.

Research on the Cooling Effect of Water Injection of the Deflector on Flame of the Vertical Launch Missile

The high-temperature gas generated by the missile launch will cause serious ablation to the launcher. In order to study the thermal protection of the launch device, a scheme of arranging vertical upward water spray pipes in the deflector is proposed, which realizes the thermal protection of the launcher by the vaporization and heat absorption principle of liquid water and the impact effect. Based on the Mixture multiphase flow model, coupled with the vaporization equation of liquid water and the component transport model, the cooling mechanism and effect of the proposed scheme are analyzed. Meanwhile, the numerical simulation of gas flow field under different water injection speed conditions is carried out, and the change law between different water injection speed and cooling effect is obtained. The results show that after the water sprayed by the pipes laid in the deflector, a water film will be formed on the surface of the deflector and the wall of the launch vehicle, which plays a role in the isolation of the high-temperature gas. The temperature of the launch device drops significantly. With the increase of water injection speed, the thickness of the water film formed on the surface of the deflector and the wall of the launch vehicle becomes larger, and the isolation effect on the gas becomes more obvious. When the water injection speed increases to 55m/s, the vaporization rate of liquid water in the direct impact area of the gas jet reaches the maximum, the heat absorption is the most at the same time, and the temperature in this area reaches the lowest level. The cooling effect of the water spray speed of 55m/s on the flow field is the best. This conclusion can provide a theoretical reference for the thermal protection design of missile launcher.

Determination of Hazardous Zone of Coal Spontaneous Combustion in Ultra-Long Working Face Based on the Gob Porosity Evolution and Flow Field Distribution

Coal fire remains one of the main hazards of underground work. Spontaneous coal fires cause serious casualties and property losses. At present, most of the studies on coal spontaneous combustion have been conducted on working faces shorter than 200 m. However, the ultra-long working face gob of shallow buried coal seam is much larger, the distribution of its flow field is more complex, and, thus, risk of spontaneous combustion in the gob is higher. Exploring the evolution law of the gob flow field of ultra-long working face to quickly determine the range of the coal spontaneous combustion hazardous zone is of great significance to the safe production of similar mines. In this study, the gas flow field distribution in the gob of an ultra-long working face was measured by buried pipeline method and oxygen concentration was used as the index. It is found that the oxygen concentration decreases with the advance of the working face. Based on the flow field distribution, the oxidation zone of the gob was determined. Meanwhile, a three-dimensional (3D) numerical model of the working face was established, and the overlying stratum collapse and porosity evolution in the gob were simulated using the particle flow software, PFC3D discrete element software, for the porosity distribution law of the gob. The obtained porosity data were then imported into FLUENT using the custom function UDF to construct a 3D grid model. The flow field distribution in the gob was then numerically simulated for the seepage and migration law of the wind flow in the gob. The results reveal an arch-shaped wind flow field distribution with a swirl shape on the intake airway side. In the strike direction, the wind flow gradually becomes weaker with the advance of the working face. In the dip direction, the wind flow seepage range on the return airway side is obviously higher than that on the intake airway side. In the vertical direction, the wind flow range in the upper gob is larger than that in the middle and lower gob. The spontaneous combustion and oxidation zone of the gob is determined to be at 140.4–313.3 m on the intake airway side, 201.2–351.6 m in the middle of the gob, and 153.2–328.1 m on the return airway side. Finally, the residual coal distribution was superimposed onto the oxygen concentration distribution to obtain the spontaneous residual coal combustion hazardous zone in the gob.

A CFD-based porous medium model for simulating municipal solid waste incineration grates: A sensitivity analysis

This study starts from a generalized CFD-based porous medium model developed in previous work simulating the combustion of municipal solid waste (MSW) on incineration grates. In this paper, three specific bed models are compared: a newly developed whole moving bed model, a newly developed multi-zone model, and a fixed bed model. Although the whole moving bed model covers the entire gas flow field, this advantage is offset by a high computational cost. In the multi-zone model, different zones of the waste bed are computed consecutively. This helps to reduce the computational time by about 75% but causes a loss of accuracy in predicting the gas flow field at the transition between the zones. For the fixed bed model, the walking column approach is needed. Additional accuracy loss is introduced but the computational time is significantly reduced even further compared to the multi-zone model. Because of the trade-off between computational cost and accuracy and the great uncertainty of the model parameters in industrial practice, the fixed bed model is suggested for simulating industrial grate-firing systems. In addition to these moving bed modeling strategies, this study also investigates how sensitive model results are to the assumed minimum and maximum solid fractions, which determine the evolution of porosity along the grate. The results show that the conversion rates are relatively insensitive to these criteria within the investigated range. Conversely, the effective surface area greatly influences the combustion characteristics as it affects the drying and char conversion rate and governs the temperature difference between the solid and gas phases. This finding calls for a better understanding of the evolution of the effective surface area and equivalent particle diameter during the combustion of MSW.

Gas dynamics of stationary supersonic gas jets with inert particles exhausting into a medium with low pressure

Issues related to the development of tools for mathematical modeling of stationary supersonic flows of an ideal compressible gas with inert particles are considered. A mathematical model is constructed that describes the flow of an inviscid compressible gas with inert particles in a jet flowing from an axisymmetric nozzle into a flooded space. Provided that the flow is supersonic along one of the spatial coordinates, the Euler equations are hyperbolic along this coordinate. For numerical calculations of the gas flow field, the finite volume method and the marching method are used. For integration over the marching direction, the three-step Runge–Kutta scheme is used. The procedure for calculating the flows includes the reconstruction of the values of the desired functions on the faces of the control volumes from the average values over the control volumes and the solution of the problem of the decay of an arbitrary discontinuity (the Riemann problem). The Lagrangian method of test particles is used to describe the dispersed phase. The effects of the reverse influence of particles on the flow of the carrier gas are not taken into account. The effects of viscosity and rarefaction of the gas flow are taken into account only when the gas interacts with particles. Calculation of the trajectories of inert particles is carried out in a known flow field of the carrier gas. The motion trajectories of discrete inclusions in jet flows with strong underexpansion are presented. The influence of the particle size and the coordinates of the particle entry point into the flow on the features of their transfer by the jet stream are discussed. Efficient means of numerical simulation of stationary supersonic flows of an ideal compressible gas with particles in nozzles and jets have been developed. The calculation results are of interest for studying supersonic gas suspension flows around bodies and for calculating oblique shock waves.

Characteristics of segmented dielectric window inductively coupled plasma

In this study, a novel inductively coupled plasma (ICP) system is proposed. It comprises a segmented dielectric window and a metal frame. For the proposed ICP system, a thin window can be designed, thereby compensating for the power loss caused by the metal frame. The proposed ICP system has two potential advantages: it can enhance the controllability of the gas flow field and it can reduce the capacitive power coupling. These characteristics enable the superior uniformity and reliable operation of ICP systems for semiconductor processes. The characteristics of the proposed ICP system are investigated using three-dimensional fluid self-consistent plasma simulations and experiments. The proposed ICP system exhibits performance similar to that of the conventional ICP system currently used in etching and deposition processes.

Effect of Electrode Induction Melting Gas Atomization on Powder Quality: Satellite Formation Mechanism and Pressure

Electrode induction melting gas atomization (EIGA) is a wildly applied method for preparing ultra-clean and spherical metal powders, which is a completely crucible-free melting and atomization process. Based on several experiments, we found that although the sphericity of metal powders prepared by EIGA was higher than that of other atomization methods, there were still some satellite powders. To understand the formation mechanism of the satellite, a computational fluid dynamics (CFD) approach FLUENT and a discrete particle model (DPM) were developed to simulate the gas atomization process, and several EIGA experiments with different argon pressures (2.5-4.0 MPa) were designed. A numerical simulation of the gas-flow field verified the formation trajectory of satellites, and the Hall flow rate of the powder produced under different pressures was 13.3, 13.8, 15.6, and 16.8, which were consistent with the prediction of the numerical simulation. This study provides theoretical support for understanding the satellite formation mechanism and improving powder sphericity in the EIGA process.

Large-scale physically accurate modelling of real proton exchange membrane fuel cell with deep learning

Proton exchange membrane fuel cells, consuming hydrogen and oxygen to generate clean electricity and water, suffer acute liquid water challenges. Accurate liquid water modelling is inherently challenging due to the multi-phase, multi-component, reactive dynamics within multi-scale, multi-layered porous media. In addition, currently inadequate imaging and modelling capabilities are limiting simulations to small areas (<1 mm2) or simplified architectures. Herein, an advancement in water modelling is achieved using X-ray micro-computed tomography, deep learned super-resolution, multi-label segmentation, and direct multi-phase simulation. The resulting image is the most resolved domain (16 mm2 with 700 nm voxel resolution) and the largest direct multi-phase flow simulation of a fuel cell. This generalisable approach unveils multi-scale water clustering and transport mechanisms over large dry and flooded areas in the gas diffusion layer and flow fields, paving the way for next generation proton exchange membrane fuel cells with optimised structures and wettabilities.

Numerical and experimental investigation of gas flow field variations in three-dimensional printed gas-dynamic virtual nozzles

Gas-dynamic virtual nozzles (GDVNs) play a vital role in delivering biomolecular samples during diffraction measurements at X-ray free-electron laser facilities. Recently, submicrometer resolution capabilities of two-photon polymerization 3D printing techniques opened the possibility to quickly fabricate gas-dynamic virtual nozzles with practically any geometry. In our previous work, we exploited this capability to print asymmetric gas-dynamic virtual nozzles that outperformed conventional symmetric designs, which naturally leads to the question of how to identify the optimal gas-dynamic virtual nozzle geometry. In this work, we develop a 3D computational fluid dynamics pipeline to investigate how the characteristics of microjets are affected by gas-dynamic virtual nozzle geometry, which will allow for further geometry optimizations and explorations. We used open-source software (OpenFOAM) and an efficient geometric volume-of-fluid method (isoAdvector) to affordably and accurately predict jet properties for different nozzle geometries. Computational resources were minimized by utilizing adaptive mesh refinement. The numerical simulation results showed acceptable agreement with the experimental data, with a relative error of about 10% for our test cases that compared bell- and cone-shaped sheath-gas cavities. In these test cases, we used a relatively low sheath gas flow rate (6 mg/min), but future work including the implementation of compressible flows will enable the investigation of higher flow rates and the study of asymmetric drip-to-jet transitions.

Experiment on gas flow field of large-caliber hypersonic balance gun in half-space

As one of the main methods to study the characteristics of an object, experiment is the main way to verify the correctness and reliability of numerical results. The hypersonic projectile near the ground launch involves many complex physical phenomena, so the ground surface has an important impact on the flight stability of the projectile and the structural characteristics of the gas flow field. In this paper, we carried out a whole process experiment of a hypersonic projectile from the bottom of the tube to the muzzle based on the 300 mm balance gun. The muzzle pressure and the initial velocity of the muzzle were monitored by the data acquisition system. We obtained the influence of the ground on the gas flow field of the hypersonic projectile through the overpressure data on the ground near the muzzle. Meanwhile, the dynamic characteristics of the launch process are recorded by high-speed photography. The experimental results show that the muzzle shock wave meets the ground, and the reflection phenomenon occurs, forming a wavefront with opposite directions of propagation. It makes the pressure in the lower half of the domain significantly higher than that in the upper half. By analyzing the experimental phenomena and experimental data, this paper shows the development characteristics of the projectile’s flow field, as well as the influence of the ground on the flow field and the motion stability of the projectile.

Experimental Analysis of Degradation in Insulation Performance After Arc-Preconditioning in High-Voltage Circuit Breaker

In the capacitive current switching duty of high-voltage circuit breakers, arc-preconditioning has been standardized to check insulation performance after short-circuit current interruption. Therefore, it is necessary to consider the degradation in insulation performance due to the wear of electrodes and insulators caused by arc-preconditioning. Since insulation performance depends on the electric field and gas density, we evaluated the effects of gas flow and electric field on the stroke position for a product-sized model circuit breaker through fluid and electric field analyses. The impact of arc-preconditioning on insulation performance was analyzed from the breakdown voltage changes before and after arc-preconditioning. The gas density in the high electric field at the tip of the electrode depends on the stroke position, and the electron behavior emitted from the electrode changes with the polarity of the applied voltage. The effects of stroke position and arc-preconditioning on dielectric breakdown performance were systematically evaluated by analyzing a breakdown model that takes into account electron propagation from the electrode tip and changes in breakdown voltage before and after arc-preconditioning. It was found that the degradation in electrodes and insulators due to arc-preconditioning does not uniformly degrade insulation performance, but the degradation effect differs depending on the stroke position, such as when the breakdown voltage does not change.

Unrelaxed tensile stress impacts on the instability of viscoelastic sheets with the gas velocity oscillation

A temporal instability analysis of a viscoelastic liquid sheet with unrelaxed tensile stresses in the oscillation gaseous flow field has been studied with the Floquet method in the present research. Effects of the oscillated amplitude and frequency of incoming gaseous flow on the instability features in the different instability regions are analyzed systematically. Results reveal that the unrelaxed tensile stress has a positive effect on stabilizing the liquid sheet, while the higher oscillation amplitude would promote the sheet breakup. Besides, it is indicated that when the stress tensor would be controlled by the viscoelastic effects, elastic impacts would suppress the breakup, while it shows an opposite impact when the stress tensor is dominated by the tensile stress. The existence of parametric instability regions is influenced by the oscillated and elastic parameters as well.