Gas Nozzle Research Articles

Influence of feedstock powder and cold spray processing parameters on microstructure and mechanical properties of Ti-6Al-4V cold spray depositions

A high pressure cold spray system was used to deposit three Ti-6Al-4V feedstock powders (i.e., hydride de-hydride, plasma atomized, and gas atomized) on Ti-6Al-4V substrates while varying gas temperature and nozzle length. Particle impact temperature and particle velocity were calculated using a 1-D axial model. The microstructure of the feedstock powders and the cold spray depositions were characterized via optical and scanning electron microscopy. The hardness of the as-received powders was determined using nanoindentation. To assess deposition quality, coatings were characterized in terms of porosity, microhardness, and adhesion strength. Results showed that hydride de-hydride powders were characterized by an equiaxed alpha grain structure with intergranular beta phase regions while atomized powders were characterized by martensitic α phase structures. Cold sprayed coatings revealed two distinct microstructures. Regions that experienced low/moderate plastic strain retained the as-received powder microstructure while regions that experienced significant plastic strain were characterized either by a featureless microstructure (atomized coatings) or the presence of fine, elongated beta precipitates (hydride de-hydride coatings). Depositions performed using a long nozzle resulted in the best deposition quality, with porosity as low as 0.3% and adhesion strengths >69MPa. While atomized powders resulted in comparatively higher quality coatings for all process conditions, hydride de-hydride coatings of excellent quality (average porosity≈0.6%, adhesion strength >65MPa) were achieved under optimal conditions. Thus, hydride de-hydride powders may hold promise as a cost effective alternative to atomized powders for Ti-6Al-4V cold spray depositions.

Methane Explosion Mitigation in Coal Mines by Water Mist

Statistics shows that the majority of accidents with fatal outcome are caused by methane and/or coal dust explosion. This leads to assume that contemporary counter-explosion systems of various designs cannot be considered effective. Considering the growing threat of methane explosion in the coming years along with the development of deeper levels, the improvement of a system for protecting people in underground opening appears urgent.This paper focuses on technical solutions to be used in designing a protective system for minimizing the consequences of methane explosions in coalmines. The new protective system consists of three main modules: i) a high-speed shock wave suppression section; ii) a suppression section with a long-term action and iii) a system activating device. The shock wave suppressor contains a 200 litre volume water tank with a built-in gas generator and nozzles. It is activated after 12ms from the blast moment, the duration of discharge is 40 s. The suppression section with a long-term action contains a 2000 litre volume water tank, a high-pressure pump, a hydraulic accumulator, solenoid valves, and a system of pipes with built-in nozzles. It is activated after 4 s from the blast moment, the duration of discharge is 8 min. The activation device includes a detection block containing sensors, an emergency signal generation module, a signal transmission module, a signal receiving module and a power supply module. The system operates in a waiting mode and activates immediately upon the receipt of the start signal generated by the detector. The paper also addresses the preliminary results of the system prototype testing in the tunnel.

Performance of an electrohydrodynamic gas pump fitted within a nozzle

In this study, an EHD gas pump fitted within a conical nozzle is examined for three diameter ratios (DR = 1/2, 1/3, and 1/4). It has been tested for an applied voltage ranging from corona threshold up to sparkover. The results are critically examined to reveal the velocity profile of the corona jet at the downstream of the pump exit as well as the relation between the pump performance and diameter ratio. It has been found that three nozzle configurations have their own characteristics and performs differently under various conditions. A pump with a diameter ratio of 1/2 performs the best in maintaining a velocity profile that can extend the longest distance downstream of the pump while a pump with a diameter ratio of 1/4 can produce the highest velocity with the smallest increase in corona current. The maximum performance of 3 L/min/W is achieved by the pump with a diameter ratio of 1/2 operating at 15 kV. It is found that the flow and electric characteristic are not linearly dependent on the diameter ratio of the nozzle. As such, the design of an EHD nozzle gas pump for a specific application needs to consider an optimal combination of these parameters.

Injector design for liner-on-target gas-puff experiments.

We present the design of a gas-puff injector for liner-on-target experiments. The injector is composed of an annular high atomic number (e.g., Ar and Kr) gas and an on-axis plasma gun that delivers an ionized deuterium target. The annular supersonic nozzle injector has been studied using Computational Fluid Dynamics (CFD) simulations to produce a highly collimated (M > 5), ∼1 cm radius gas profile that satisfies the theoretical requirement for best performance on ∼1-MA current generators. The CFD simulations allowed us to study output density profiles as a function of the nozzle shape, gas pressure, and gas composition. We have performed line-integrated density measurements using a continuous wave (CW) He-Ne laser to characterize the liner gas density. The measurements agree well with the CFD values. We have used a simple snowplow model to study the plasma sheath acceleration in a coaxial plasma gun to help us properly design the target injector.

On the evolution of substrate's residual stress during cold spray process: A parametric study

A comprehensive study was undertaken to determine the effects of carrier gas temperature, pressure, and nozzle speed on the residual stresses induced by cold spray coating of aluminum 7075 powder onto AZ31B-H24 magnesium substrate. Embedded Fiber Bragg Grating sensors and thermocouples were employed for simultaneous in-situ measurements of strain and temperature during cold spray process. A statistical model was then developed based on the significance and interactions of the cold spray parameters on the residual stress field. This model demonstrated that the induced temperature is the most significant parameter to the final formation of residual stress. It is also shown that the peening effect plus the temperature resulted from the cold spray yields to the dynamic recrystallization of the substrate near the surface, and generates nano-size grains at the interface. This research validates that the final size of the refined grains and the level of induced residual stress depend heavily on the process' thermal energy.

Microstructure-scaled active sites imaging of a solid oxide fuel cell composite cathode

Active sites for oxygen reduction reaction in strontium-doped lanthanum manganite (LSM)/scandia-stabilized zirconia (ScSZ) composite cathode of solid oxide fuel cell (SOFC) is visualized in microstructure scale by oxygen isotope labeling. In order to quench a reaction, a SOFC power generation equipment with a nozzle for direct helium gas impinging jet to the cell is prepared. A typical electrolyte-supported cell is operated by supplying 18O2 at 1073 K and abruptly quenched to room temperature. During the quench, the temperature of the cell is decreased from 1073 K to 673 K in 1 s. The 18O concentration distribution in the cross section of the quenched cathode is obtained by secondary ion mass spectrometry (SIMS) with a spatial resolution of 50 nm. The obtained 18O mapping gives the first visualization of highly distributed active sites in the composite cathode both in macroscopic and particle scales.

Supersonic turbine stator design using dense gas with numerical method

In recent years, interest in renewable energy as a substitute for power generation using coal has increased. As a next-generation power system, the Organic Rankine cycle (ORC) system, which requires a multi-stage turbine or a supersonic turbine to generate a high power, has been shown to have high potential for such uses. In this paper, a dense gas is chosen as a working fluid and a supersonic nozzle is designed for a supersonic turbine with advantages in terms of cost, power density and layout. Two stators are designed using the Method of characteristics (MOC) for air and dense gas. To validate the numerical model, the nozzle designed for the air is compared to that of a PIV experiment from the open literature, and the results indicate a reasonable agreement. The nozzle for the dense gas is different as that needed for air. Therefore, the modified MOC is applied based on a polytropic assumption. In conclusion, an estimation of the performance is implemented with loss coefficients for a different number of blades. The number of blades is shown to be proportional to the loss coefficient. For example, the case with the biggest numbers of blades is affected the most by the shock effect that occurs at the trailing edge.

Numerical Analysis for Determination of Hydrodynamic Characteristics of a Gimbaled Thrust Vectoring Nozzle

Gimbaled thrust vectoring nozzles are employed in Solid Rocket Motors (SRM) to account for the aspects of maneuverability of the flight vehicle. The flow field of such a solid pulsed rocket motor is explored numerically (from dome-closeout onward) by solving Reynolds-averaged Navier-Stokes equations with Menter’s Shear Stress Transport (SST) k - ? turbulence model using a Computational Fluid Dynamics (CFD) tool. Parametric studies are carried out to find out the thermochemical and hydrodynamic characteristics of the hot gas in the rocket motor nozzle. The performances of different supersonic and subsonic sections were studied in terms of the hydrodynamic aspects such as static pressure and Mach number distribution. It is observed that the tradeoff of implementing thrust vectoring mechanism amounts to an additional pressure loss of 10.06% in the rocket motor. Such analyses are specific to certain types of Short Range Ballistic Missiles (SRBM) having solid state propellant (primary stage) in radial boost, end burning pulsed configuration with exacting demands on maneuverability and control implied upon payload and mission criterion.Journal of Bangladesh Academy of Sciences, Vol. 41, No. 1, 69-84, 2017

Effects of nozzle structure on the gas mixture uniformity of marine gas engine

Natural gas is a preferred fuel choice owing to its easy availability, clean combustion, and low emission levels, especially in the field of marine engines. Recently, manifold multi-point gas injection technology was adopted by engine manufactures to improve the response of the marine gas engine to load changes and the consistency of gas fuel supplied to each cylinder. The characteristics of manifold gas injection have a significant influence on the combustion and emissions of marine gas engines. It is therefore vital to investigate the effect of gas nozzle structures on the gas mixture formation and combustion process. In this study, based on the validation through experimental method, a computational fluid dynamics simulation method was adopted to analyze the influence of the nozzle structure on the uniformity of the intake gas mixture in a natural gas engine, and the combustion process was analyzed to show the further effects of nozzle structure on combustion characteristics. The results show that, at high engine load, the structure of the cross multi-hole gas nozzle can help achieve a more homogeneous gas mixture, which is beneficial to the in-cylinder combustion; it yet yields higher NO emission. The single-hole gas nozzle structure yields an inhomogeneous mixture during the intake stroke and has negative effects on combustion. However, at lower engine load, employing a cross multi-hole gas nozzle results in the deposition of gas fuel residue in the intake port during the intake process, thereby inhibiting complete combustion. The structure of the single-hole gas nozzle can provide higher kinetic energy, which has positive effects on fuel intake efficiency and combustion intensity, although there is still an increased NO emission associated with it, owing to a higher cylinder temperature.

The characteristic analysis of high-pressure gas jets for natural gas engine based on shock wave structure

High gas injection pressure leads to the formation of under-expanded gas jet at nozzle exit. The shock wave structure near the nozzle affects gas jet injection and mixing characteristics, which affects the combustion and emission performance of the engine. Gas jet injection process and shock wave structure evolution law under different nozzle pressure ratio (NPR) and orifice diameter have been investigated with the application of Schlieren imaging and numerical simulation. Results show that long injection duration exists in gas injection process after the end of injection. It is attributed to the slow pressure reduction velocity in the nozzle. This phenomenon is one of the key factors which influence the high HC emission of gas fuel port injection natural gas engines. The change of pressure inside the nozzle also affects the shock wave structure (Mach disk) near the nozzle. It is found that the increase of Mach disk width leads to a large jet near-field angle which promotes the spatial distribution and turbulent mixing of gas jet. In addition to experimental results, numerical simulation is used to analyze the injection characteristics of gas injection system. Increasing gas nozzle flow area and shortening gas nozzle length are regarded as effective ways to improve the responsiveness of gas injection system and reduce gas injection duration. The range of Reynolds number at exit of the nozzle is 0.5–2.5×105 under various gas injection pressures and orifice diameters. This presents that gas jet is easily influenced by air turbulence in intake manifold. Strong air turbulence in intake manifold is needed in a gas fuel port injection natural gas engine in order to obtain homogeneous gas/air mixture.

Formation and steady flow characteristics of ventilated supercavity with gas jet cavitator

Substantial discrepancies in the formation and attainment conditions for different ventilated cavities are the characteristics of the cavitator and ventilation condition. In this study, a systematic experimental investigation on the concept of using a gas nozzle at the tip of the object as both the cavitator and the ventilation hole to form a supercavity was performed in a gravity water tunnel. The formation, elimination process and steady shape of the gas jet ventilated supercavity, were observed and measured. The dependence relationship of the dimensionless parameters of gas jet length, maximum cavity diameter, cavitation number, Froude number and ventilation coefficient were provided based on the experimental data. With the velocity increases in the test section, the irregular cloud cavitation, evolving with a gas jet wake, appears, and the gas jet wake flows to the back upper location. After that, an ellipsoidal bubble located in front of the gas jet cavitator within a certain distance is observed. Eventually, the ellipsoidal bubble gradually grows to a large bubble and cavity, then develops to a supercavity with increasing of the incoming flow velocity in the test section.

DC Microplasma Jet for Local a:C-H Deposition Operated in SEM Chamber.

A DC micro plasma jet for local micro deposition of a:C-H film in the ambient vacuum of scanning electron microscope (SEM) chamber is proposed. Acetylene (C2H2) gas was locally fed into the chamber through an orifice shaped gas nozzle (OGN) at 6.6 sccm in flow rate by applying 80 kPa-inlet pressure with an additional direct pumping system equipped on the SEM chamber. As a cathode, a cut of n-type silicon (Si) wafer was placed right in front of the OGN at 200 μm gap distance. By applying a positive DC voltage to the OGN, C2H2 plasma was generated locally between the electrodes. During discharge, the voltage increased and the current decreased due to deposition of insulating film on the Si wafer with resulting in automatic termination of discharge at the constant source voltage. A symmetric mountain-shaped a:C-H film of 5 μm height was deposited at the center by operation for 15 s. Films were deposited with variation of gas flow rate, gap distance, voltage and current, and deposition time. The films were directly observed by SEM and analyzed by surface profiler and by Raman spectroscopy.

Faster, More Reproducible DESI-MS for Biological Tissue Imaging

A new, more robust sprayer for desorption electrospray ionization (DESI) mass spectrometry imaging is presented. The main source of variability in DESI is thought to be the uncontrolled variability of various geometric parameters of the sprayer, primarily the position of the solvent capillary, or more specifically, its positioning within the gas capillary or nozzle. If the solvent capillary is off-center, the sprayer becomes asymmetrical, making the geometry difficult to control and compromising reproducibility. If the stiffness, tip quality, and positioning of the capillary are improved, sprayer reproducibility can be improved by an order of magnitude. The quality of the improved sprayer and its potential for high spatial resolution imaging are demonstrated on human colorectal tissue samples by acquisition of images at pixel sizes of 100, 50, and 20 μm, which corresponds to a lateral resolution of 40–60 μm, similar to the best values published in the literature. The high sensitivity of the sprayer also allows combination with a fast scanning quadrupole time-of-flight mass spectrometer. This provides up to 30 times faster DESI acquisition, reducing the overall acquisition time for a 10 mm × 10 mm rat brain sample to approximately 1 h. Although some spectral information is lost with increasing analysis speed, the resulting data can still be used to classify tissue types on the basis of a previously constructed model. This is particularly interesting for clinical applications, where fast, reliable diagnosis is required.Graphical ᅟ

Damper opening optimization and performance of a co-firing boiler in a 300 MWe plant

Effects of secondary air and separated overfire air on boiler performance were experimentally investigated in a 300MWe utility boiler co-firing coal with blast furnace gas and coke oven gas. Moreover, an objective function aiming at simultaneously calculating NOx emissions and boiler efficiency from thirty-seven operating parameters was represented by a back propagation neural network model which was optimized by genetic algorithm, and the nineteen levels damper openings of secondary air and separated overfire air were optimized by adopting genetic algorithm so as to simultaneously achieve low NOx emissions and high boiler efficiency. Damper openings of secondary air located at blast furnace gas nozzles zone (GAA/GA/GBB) and coal combustion zone (AS/BS/CS and AA/AB/BC/CC) were adjusted from 10 to 100% in specially designed burner, and the better damper openings were experimentally obtained. The damper openings of separated overfire air were also changed from 10 to 100%, but it hard to evaluate the better damper openings due to the boiler efficiency and NOx emissions simultaneously decrease with the increase of separated overfire air. Finally, the optimal operation of secondary air and separated overfire air were achieved by using optimization model, which could provide references for the adjustment of secondary air and separated overfire air.

Global entropy solutions to the compressible Euler equations in the isentropic nozzle flow for large data: Application of the generalized invariant regions and the modified Godunov scheme

We study the motion of isentropic gas in nozzles. This is a major subject in fluid dynamics. In fact, the nozzle is utilized to increase the thrust of rocket engines. Moreover, the nozzle flow is closely related to astrophysics. These phenomena are governed by the compressible Euler equations, which are one of crucial equations in inhomogeneous conservation laws.In this paper, we consider its unsteady flow and devote to proving the global existence and stability of solutions to the Cauchy problem for the general nozzle. The theorem has been proved in Tsuge (2013). However, this result is limited to small data. Our aim in the present paper is to remove this restriction, that is, we consider large data. Although the subject is important in Mathematics, Physics and engineering, it remained open for a long time. The problem seems to rely on a bounded estimate of approximate solutions, because we have only method to investigate the behavior with respect to the time variable. To solve this, we first introduce a generalized invariant region. Compared with the existing ones, its upper and lower bounds are extended constants to functions of the space variable. However, we cannot apply the new invariant region to the traditional difference method. Therefore, we invent the modified Godunov scheme. The approximate solutions consist of some functions corresponding to the upper and lower bounds of the invariant regions. These methods enable us to investigate the behavior of approximate solutions with respect to the space variable. The ideas are also applicable to other nonlinear problems involving similar difficulties.

Decreasing the surface roughness of aluminum alloy welds fabricated by a dual beam laser

Decreasing the surface roughness of visible laser welds on aluminum automotive closure panels is of critical importance in the automotive industry. During welding, surface roughness is strongly influenced by the interaction of filler wire, laser, and gas. Observation by CCD camera revealed that placement of the filler wire tip at the front wire-feeding position could effectively mitigate humping phenomenon on the weld surface. Visualization of the gas flow and detection of the plasma intensity demonstrated that optimizing the shielding gas parameters could further reduce the rippling phenomenon by affecting the molten pool surface tension and the pressure differential acting upon the molten pool. The surface quality could be improved via optimization of nozzle outlet geometry, gas flow rate, inclination angle of gas tube, and distance between the nozzle and laser beam. After shrinking the processing parameter window through the single factor investigation, a Taguchi L9 orthogonal array was designed to optimize the shielding gas parameters. The weld surface roughness, Ra, could be effectively reduced to below 1μm when a circular gas nozzle was positioned 5mm behind the laser beam, delivering pure argon gas at 30SCFH with an inclination angle of 45° to the horizontal plane.

Optimization of dehydration process to improve stability and efficiency of supersonic separation

Supersonic gas-liquid separation is considered as one of the novel methods for natural gas conditioning that removes either water or heavy hydrocarbons from the natural gas without using chemical ingredients. The expansion of natural gas stream in a supersonic nozzle increases the fluid velocity to supersonic level and makes low pressure and temperature conditions in which nucleation of the liquid phase and condensation initiate. The process includes two isentropic processes with an intermediate shockwave. This research is the first serious attempt for controlling the supersonic separation units and applies the stability concept for actual conditions and disturbances in the gas pressure and composition during the lifecycle of a gas well. The article explores how the optimal performance of a supersonic nozzle can be saved with variations in the nozzle input gas pressure or composition. As the phase change and condensation are mainly occur at the shockwave position, the geometry configuration of supersonic nozzle is of high importance so that the drain location should be aligned with the shockwave location. An algorithm is employed to find a control function to compensate the backpressure of the nozzle within the feed pressure variation. It guarantees the equipment to be kept effectively in the optimal operating condition. In a case study, it is explained how the proposed solution enables the system to keep the dew point within ±2.5 °C drift from the desired criteria following a ±18% disturbance in the inlet pressure. Moreover, investigation on the effect of natural gas composition shows that the separation system is intrinsically robust to variations in the main natural gas composition.

Effects of dimensional size and surface roughness on service performance for a micro Laval nozzle

Nozzles with large and small dimensions are widely used in various industries. The main objective of this research is to investigate the effects of dimensional size and surface roughness on the service performance of a micro Laval nozzle. The variation of nozzle service performance from the conventional macro to micro scale is presented in this paper. This shows that the dimensional nozzle size has a serious effect on the nozzle gas flow friction. With the decrease of nozzle size, the velocity performance and thrust performance deteriorate. The micro nozzle performance has less sensitivity to the variation of surface roughness than the large scale nozzle does. Surface quality improvement and burr prevention technologies are proposed to reduce the friction effect on the micro nozzle performance. A novel process is then developed to control and depress the burr generation during micro nozzle machining. The polymethyl-methacrylate as a coating material is coated on the rough machined surface before finish machining. Finally, the micro nozzle with a throat diameter of 1 mm is machined successfully. Thrust test results show that the implement and application of this machining process benefit the service performance improvement of the micro nozzle.

The minimum in-line coalescence height of bubbles in non-Newtonian fluid

The minimum in-line coalescence height of bubbles generated from a submerged nozzle was investigated experimentally in shear thinning non-Newtonian fluid at lower Reynolds number (2∼60). Carboxymethyl cellulose sodium (CMC) aqueous solution and carbon dioxide were used as the liquid phase and the gas phase, respectively. The process of the formation, movement and in-line coalescence of bubbles was visualized and recorded by a high-speed digital camera. The influences of bubble size, bubble generation frequency and liquid property on the minimum in-line coalescence height of bubbles were investigated by changing nozzle diameter, gas flow rate and the mass concentration of CMC aqueous solutions. For a given liquid, the generating frequency and size of bubbles increased but the minimum coalescence height of in-line bubbles decreased when the nozzle diameter and gas flow rate were increased. When the nozzle diameter and gas flow rate were fixed, the shear-thinning effect of CMC aqueous solution became stronger with increasing CMC mass concentration, which led to the increase in both the terminal rise velocity and average acceleration of the trailing bubble, consequently, the minimum in-line coalescence height of bubbles decreased. An empirical correlation for estimating the minimum in-line bubble coalescence height was proposed, the calculating values accords well with experimental data with a mean relative deviation only 7.6%.

Analysis of nozzle gas speed on the performance of the zoned and staged gas-fired radiant tube

In this study, the nozzle characteristics of zoned and staged double P-type gas-fired radiant tube were improved to optimize combustion efficiency. A three-dimensional finite element model was established, and a grid-independence study was conducted to guarantee the accuracy of the calculation results. Corresponding experiments were designed to prove the reliability and accuracy of the simulation model. Then, the developed mode was used to determine the flow field characteristics of the zoned and staged gas-fired radiant tube. Moreover, the gas and wall temperatures were calculated by altering the gas speeds in the main and branch tube nozzles respectively. The effects of nozzle gas speed on the radiant tube were compared. Results showed that increasing the air speed of the main tube nozzle could decrease the maximum temperature and the wall temperature difference, improve temperature uniformity, and slightly increase thermal efficiency. Increasing the air speed of the branch tube nozzle could reduce the maximum wall temperature and enhance surface temperature uniformity; but these effects were relatively not significant.