Effect Of Ambient Gas Research Articles

Study of the Effects of Different Ambient Gases and Buoyancy on Hydrogen Jet Characteristics.

Substituting nitrogen with inert gases in an inert gas cycle engine can not only effectively improve engine efficiency but also eliminate NOX emissions in the combustion products. Owing to the low density of hydrogen, jet development is affected by buoyancy. This study explored the effects of different ambient gases, such as Ar, N2, and He, as well as buoyancy, on the hydrogen jet and mixing characteristics based on Schlieren. The results indicated that as the pressure ratio increases, the penetration length and volume of the hydrogen jet increase, whereas the dispersion angle and entrainment ratio decrease. The penetration capacity of the hydrogen jet is strongest in He, followed by N2, and weakest in Ar. Additionally, in He, the hydrogen jet exhibits the smallest dispersion angle, fastest jet volume growth, and largest entrainment ratio. The entrainment ratio of the H2 jet in He is 2.75-3.84 times that of N2 and 4.72-8.3 times that of Ar. In N2 and Ar, the penetration length of the inverted jet after 2.5 ms is approximately 2-4 mm longer than that of the upright jet, indicating that buoyancy has a certain influence on jet development.

The detection of elemental content changes in electrode coating using laser-induced breakdown spectroscopy

The elemental content of battery electrode coating is prone to change due to the production technology and ambient factors. To ensure the consistent performance and safety of a lithium battery, the elemental content of the electrode coating needs to be kept strictly consistent. This study proposes an internal mixed matrix method that combines laser-induced breakdown spectroscopy and chemometric method to achieve rapid and accurate detection of elemental content changes in electrode coating. The stoichiometric ratios of analytical elements are calculated by using the spectra of laser-induced breakdown spectroscopy. The relationships between that stoichiometric ratios and the actual content of analytical elements are studied and show that they are linear. Thus, the content change of the analytical element can be determined by calculating the change of the stoichiometric ratio. The average relative errors for content changes of iron, lithium, and phosphorus are 6.43%, 2.96%, and 4.12%, respectively, and the lowest detection limits are 278.2 mg/kg, 20.5 mg/kg, and 105.4 mg/kg, respectively. Furthermore, the internal reference method is proposed to correct the effect of ambient gases and improve detection accuracy. The results are that when Fe I 372.751 nm and Fe I 373.485 nm are used as analytical lines, after correcting for the effect of ambient gases, the average relative errors of Fe content changes are reduced by 62% and 72%, respectively, and the lowest detection limits are increased by 67% and 71%, respectively.

Effect of injection pressure on low-temperature fuel atomization characteristics of diesel engines under cold start conditions

Exploring the atomization characteristics and spray impingement characteristics of low-temperature fuel under different injection pressures has important practical significance for improving the cold start performance of diesel engines. In this study, based on LIEF-PIV combined laser testing technology, a fuel atomization experimental system for diesel engine cold start was established. The concentration and velocity fields of low-temperature fuel with the temperature from 20 to - 40 ℃ were experimentally analyzed within the injection pressures of 40-80MPa. The results showed that the increase of injection pressure increased the initial kinetic energy of the diesel droplets, whereas the concentration gradient of spray decreased significantly. Meanwhile, the mixing effect of spray and ambient gas increased. When the fuel temperature decreased from 0 ℃ to - 20 ℃, the values of the average equivalence ratio in the near-wall region decreased from 0.52 to 0.21. The change of injection pressure had an obvious effect on the macro morphology of wall-impinging spray and the flow characteristics of the fuel/air mixture. When the injection pressure increased from 40MPa to 80MPa, the difference of maximum turbulent kinetic energy among various temperatures increased from 0.66 m2/s2 to 0.90 m2/s2.

Effect of ambient gas and crystal features on Doppler ultrasound twinkling of pathological mineralizations.

Color Doppler twinkling on kidney stones and other pathological mineralizations is theorized to arise from stable microbubbles, which suggests twinkling will be sensitive to ambient gas. Here, lab-grown cholesterol, calcium phosphate, and uric acid crystals were imaged with ultrasound in water while varying oxygen, carbon dioxide, and nitrogen levels. Twinkling was found to increase on cholesterol in elevated oxygen, cholesterol and calcium phosphate in elevated carbon dioxide, and no crystals in elevated nitrogen. These results support the crevice microbubble theory of twinkling and suggest gases may be varied to enhance twinkling on some mineralizations.

LIBS plasma in atmospheric pressure argon, nitrogen and helium: Spatio-temporal distribution of plume emission and Hα linewidth

Laser Induced Breakdown Spectroscopy (LIBS) method is considered for assessing the retention of hydrogen isotopes in the ITER plasma-facing components during the maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or inert gas. At these conditions, the broadening of the spectral lines of hydrogen isotopes and the reduction of line intensities complicates the distinguishing of hydrogen isotopes. The aim of the present study was to investigate the effect of atmospheric pressure nitrogen, argon and helium ambient gas on the spatio-temporal distribution of the LIBS plasma plume emission and linewidths of Hα line, representing the hydrogen isotopes. Nd:YAG laser with 8 ns pulse width was used to ablate the molybdenum (Mo) target with hydrogen impurity. The development of the formed plasma plume was investigated by time and space-resolved emission spectra in the 20 nm range around the 656.28 nm Hα line. For all gases used in the experiments, the intensity and linewidth of Hα line decreased with the delay time between the laser pulse and the spectral registration. At the same linewidth values, the highest intensities were obtained in the helium atmosphere while the lowest intensity was obtained in nitrogen. According to spatially resolved spectral measurements, the Hα line was most intense near the Mo target while the Mo lines peaked farther away. In the case of the helium atmosphere, the plasma plume emission was observed at a longer distance from the target and it decayed faster than in argon and nitrogen atmospheres. According to these results, helium is the most beneficial ambient gas for hydrogen isotope detection by atmospheric pressure LIBS. The use of argon ambient gas may be required when LIBS is used for the simultaneous determination of fuel and He retention in the wall material.

The Effect of Ambient Pressure and Gas–Liquid Ratio on the Spray Characteristics of an Effervescent Atomizer

The Effect of Ambient Pressure and Gas–Liquid Ratio on the Spray Characteristics of an Effervescent Atomizer

Effect of ambient gas on grain growth of CZTS layer: study on device efficiency

Effect of ambient gas on grain growth of CZTS layer: study on device efficiency

Surface morphology evolution mechanisms of laser polishing in ambient gas

Laser polishing, as an effective surface finishing process, is significantly affected by ambient gas. Previous studies on the contribution of ambient gas to laser polishing mostly focused on experiments, but rarely on numerical simulations. Given this, this paper proposes an improved model capable of analyzing the effects of ambient gas on the laser-polished surface's morphology evolution mechanisms, by expanding an existing laser polishing model with the influences of mass transfer, solutocapillary forces, and chemical reactions. Argon and air were used as ambient gasses for comparison. Through this model, the surface morphology evolution of laser polishing in air was compared with that in argon in terms of the velocity field, temperature field, concentration field, melt surface velocity, molten pool surface profile, and surface forces. The respective contributions of chemical reaction heat, oxygen mass flux, mass transfer, and surface forces were also presented. Furthermore, the numerical model was verified on 304 stainless steel from the perspectives of polished surface roughness, molten pool depth, and oxygen element distribution.

Effect of ambient gas on cavity formation for sphere impacts on liquids

Formation of a splash crown and a cavity following the impact of a sphere on a body of liquid is a classical problem. In the related problem of a droplet splashing on a flat surface, it has been established that the properties of the surrounding gas can influence the splashing threshold. At lower impact speeds, this is due mainly to the influence of gas kinetic effects, since the height of the gas lubrication film which is displaced during dynamic wetting is often comparable to the mean free path of the gas. At higher Weber and Reynolds numbers, on the other hand, inertial effects dominate and the density of the gas becomes important in determining whether a splash occurs. In this article, sphere impacts on a liquid body are investigated in a rarefied atmosphere using high-speed photography. It is found that the threshold entry speed for cavity formation is influenced by the density of the surrounding gas, whereas changing the mean free path of the gas has no effect. We attribute this phenomenon to the gas slowing the sealing of the thin crown sheet behind the sphere. This assertion is supported with experimental measurements of the liquid sheet thickness. In the range of parameters considered, the splash crown influences the movement of the contact line, an effect not previously observed.

A molecular dynamics study of evaporation of multicomponent stationary and moving fuel droplets in multicomponent ambient gases under supercritical conditions

The evaporation of a six-component fuel droplet under supercritical conditions is investigated using molecular dynamics (MD) simulations. The focus here is on effects of multicomponent ambient gases and the relative motion between the droplet and the ambient. The ambient pressure ranges from 8 MPa to 36 MPa and the ambient temperature ranges from 750 K to 3600 K. In the lower range of the temperature and pressure, the average displacement increment (ADI) per fuel atom gradually increases with time and the classic evaporation is observed. In the higher range of the temperature and pressure, the ADI profile has a unimodal distribution with time and the diffusive mixing between the droplet and the ambient gases dominates. Based on the ADI profile of fuel atoms, a criterion (τ0.9P) for mode transition from evaporation to diffusion is proposed. Among the ambient gases investigated, the mode transition is the most difficult in the nitrogen ambient but the easiest in combustion exhaust gases. For multicomponent fuel droplets close to or in diffusion mode, with higher relative velocities, the relative difference between evaporation rates for light/heavy fuel components is reduced. This study demonstrates that supercritical conditions alone are insufficient for mode transition of evaporation.

Effect of aging, temperature, and ambient gases on the complex impedance of As2Te13Ge8S3 glassy films

The work is focused on the application of the impedance spectroscopy method to provide evidence and study the effects of aging, temperature, and gas adsorption in chalcogenide-based thin films. The experiments are carried out with thin films of glassy quaternary composition As2Te13Ge8S3 in a wide frequency range at different temperatures under different environmental conditions, in particular, either dry or wet air or their mixtures with NO2 or CO2. It is found that aging has a significant effect on the impedance spectra of Pt–As2Te13Ge8S3–Pt functional structures, which make evidence for the presence of substantial spatial and compositional disordering. This effect can be stabilized by the post-preparation annealing of the sample. The effect of temperature on impedance spectra consists in a variation in the both real and imaginary parts of impedance that appear to be extremely sensitive to adsorptive processes. Adsorption of nitrogen dioxide results in a significant frequency-dependent decrease in the impedance parameters, which is attributed to an effective “strong” chemisorption process due to the interaction of "odd" electrons of NO2 molecules with lone pair electrons of chalcogen atoms. The effect of water vapors leads only to an increase in the real part of impedance, while the imaginary part abruptly decreases; this fact is attributed to a “weak” form of chemisorption. The effect of carbon dioxide on the impedance spectra is attributed to the physical adsorption of CO2 molecules. This effect is weak; however, it is reversible and clearly observed even at room temperature.

On the expansion dynamics of plasma plume produced by laser ablation of LiYF4 crystal in a helium atmosphere

The effect of helium ambient gas on the expansion dynamics of plasma plume produced by ablating the LiYF4 crystal with 355 nm laser pulses is investigated. To study the expansion dynamics, the time-resolved optical signals from the plume constituents, either neutral or ionized, were recorded as a function of various experimental parameters, including laser fluency, at different distances, d, from the target along the expansion direction of the plume and at various angles with reference to the target normal. The analysis of the plume constituents at different distances from the target was used to derive the expansion velocities of the species. Depending on the species and on d, the shifted Maxwell–Boltzmann distribution component of the fit gave the values of the expansion velocities in the range 1.0 × 104 m s−1–4.0 × 104 m s−1. The effect of laser fluency on the expansion velocities of the plume species was also investigated. With the exception of Y and Y+, the expansion velocities of all the plume species, increased linearly with increasing laser fluency up to ∼8 J cm−2. Beyond this value, a saturation regime is observed. The angular distribution of the plume constituents in 1 Pa of He evidenced that all the plume species were focused along the target normal, and the FWHM of the angular distribution curve resulted reduced when compared with the vacuum.

Structural, Optical, and Electrical Characteristics of Thermal Treated ZnO Thin Films Deposited by RF Sputtering on Glass Substrates

The effects of post-annealing treatment temperature and ambient gas on the properties of ZnO thin films were investigated. The results showed that the properties of the ZnO thin film depended on the crystal quality, the type and density of the intrinsic defects. Treating the ZnO thin films at 300°C, regardless of the ambient gas, affected only on the crystal quality of the thin films. When the samples were treated at 500°C and 600°C, the structural properties were significantly improved, accompanied by changes in the optical and electrical properties. The extent of improvements varied with the treatment ambient. These variations in the optical and electrical properties of the thin films were attributed to the different reaction mechanisms when ZnO was treated under different ambient conditions. The thin films, treated at 600°C under N2O ambient, exhibited the best structural, optical, and electrical properties for metal-semiconductor-metal photodetector (MSM-PD) applications.

Effect of annealing ambient gases on the bias stability of amorphous SnSiO thin-film transistors

The effect of different annealing ambient gases on the initial electrical properties and bias stability of amorphous tin silicon oxide (a-SnSiO) thin-film transistors (TFTs) is examined in this study. At an annealing temperature of 350 °C, the SnSiO film remained amorphous with excellent transmittance regardless of the annealing environment. The presence of oxygen during annealing (such as in air and O2) could reduce the mobility of the TFTs and create more oxygen-related defect states, thereby reducing the bias stability. In contrast, nitrogen-annealed TFTs showed maximum mobility and optimal bias stability. The corresponding mobility reached 8.6 cm2V−1s−1, the threshold voltage was 0.2 V and the subthreshold swing value was 0.7 V dec−1.

Wavelength modulation-direct absorption spectroscopy combined with improved experimental strategy for measuring spectroscopic parameters of H2O transitions near 1.39 μm

The wavelength modulation-direct absorption spectroscopy (WM-DAS) was used to measure the spectroscopic parameters for 8 H2O absorption transitions near 1.39 μm at 300–900 K. A reference light path was introduced to eliminate the effect of ambient gas and inherent fluctuation of laser intensity. Experimental results at high temperatures for the transition at 7185.597 cm−1 showed that the WM-DAS enhanced noise rejection by extracting the characteristic frequencies of modulated laser intensity. The SNR was enhanced to 1800 for the peak absorbance of 20% and remained 380 around the peak absorbance of only 0.5% by using this method, showing its huge potential in situ gas sensing in harsh engineering fields. The Voigt, Rautian, Galatry and quadratic speed-dependent Voigt profiles were used to recover the absorbance and determine the best-fit spectroscopic parameters and their temperature dependence. The measured N2-broadening coefficients compare well with the available values listed in the HITRAN/HITEMP database. The Dicke narrowing and speed-dependent coefficients were also determined with analyses of the uncertainties in these measured parameters.

Nanosecond laser-metal ablation at different ambient conditions

Ablation of metals under different ambient conditions and laser fluences, was investigated through series of experiments. A 1064nm, 6ns Nd:YAG laser was used to ablate 1mm thick metal targets with laser energy ranging from 2mJ to 300mJ. The experiments were designed to study the effect of material properties, laser fluence, ambient gas, and ambient pressure on laser-metal ablation. The first experiment was conducted under vacuum to study the effect of laser fluence and material properties on metal ablation, using a wide range of laser fluences (2J/cm2 up to 300J/cm2) and two different targets, Al and W. The second experiment was conducted at atmospheric pressure using two different ambient gases air and argon, to understand the effect of ambient gas on laser-metal ablation process. The third experiment was conducted at two different pressures (10Torr and 760Torr) using the same ambient gas to investigate the effect of ambient pressure on laser-metal ablation. To compare the different ablation processes, the amount of mass ablated, ablation depth, crater profile and melt formation were measured using White Light Profilometer (WLP). The experimental results show that at low laser fluence: the ablated mass, ablation depth, and height of molten layer follow a logarithmic function of the incident laser fluence. While, at high laser fluence they follow a linear function. This dependence on laser fluence was found to be independent on ambient conditions and irradiated material. The effect of ambient pressure was more pronounced than the effect of ambient gas type. Plasma shielding effect was found to be very pronounced in the presence of ambient gas and led to significant reduction in the total mass ablation.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

Indium selenide: an insight into electronic band structure and surface excitations

We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.

Preferential triplet over singlet emission of Zn in laser-induced plasmas

An experimental study is performed on the time-dependent intensity variations of Zn emission focusing on the triplet (Zn I 481.0 nm) and singlet (Zn I 636.2 nm) emission lines induced under three experimental conditions. A single nanosecond (ns) Nd:YAG laser in standard laser-induced breakdown spectroscopy (LIBS) setup is employed for the investigation of direct shock wave-induced emission characteristics with N2 ambient gas at 0.4 kPa and the different effects of He ambient gas at 2 kPa. An additional two-laser system consisting of ns and picosecond (ps) lasers in an orthogonal setup is used to study the exclusive role of a He-assisted excitation (HAE) process for the generation of those two Zn emission lines. The results of this study consistently exhibit the dominant triplet emission over the singlet emission marked by initial maximum intensity ratios of 8 and 12 obtained from the experiments using a single-laser setup in N2 and He ambient gases, respectively, indicating the significant contribution of the HAE mechanism to the enhanced and longer lasting Zn emission in He gas. The experiment using the special two-laser setup further demonstrates the exclusive role of the HAE process in the Zn emission featuring an even markedly higher triplet/singlet intensity ratio of 22. Thus, the results of this study suggest the possibly more general nature of dominant triplet emission phenomena previously found in laser-induced He and Ca emission spectra.

Experimental Study on Acoustic Attenuation Due to Solid Particles

ABSTRACTHigh-frequency pressure waves present in rocket motors can be dampened by solid or liquid particles produced from their propellant combustion depending on conditions. The present study conducted an experimental investigation into the effects of particle sizes, ambient gases, and pressure wave frequencies on the attenuation of acoustic energy. Aluminum oxide powders of single-peak broad distributions with average diameters of 5.1 μm, 7.6 μm, 16.5 μm, and 36.2 μm were used to simulate condensed particles in solid rocket combustion environment. Attenuation of excited pressure waves traveling through the fixed cylindrical volume full of particle-laden helium or nitrogen gas has been measured. The number densities of particles floating in gases have been determined by use of processing of images from a high-speed camera. It is observed that alumina particles surely have attenuation effects of pressure waves. The particles in helium show approximately two times greater pressure wave attenuation than those in nitrogen, which indicates the effect of gas density on the attenuation of pressure wave by particles. The optimal particle diameter for the maximal attenuation varies with the frequency of pressure wave. Pressure wave attenuation reaches maximal values at an average particle diameter of 7.6 μm in helium and 16.5 μm in nitrogen over frequencies. Particle diameters showing maximal attenuation become shifted and so do the attenuation characteristics for both cases of helium and nitrogen for high frequency waves greater than 2500 Hz.