Helium-air Mixture Research Articles

Features of achievement of limiting speed values of track tests of ballistic type aircraft

The development of high-speed ballistic aircraft with speeds exceeding 1000 m/s is currently a priority abroad and in Russia. The effectiveness of new such products is confirmed by track tests at the speed of their use. Test sites with rail tracks exist in almost all countries, for example in the USA there are more than 15 of them. Double-rail, monorail and various combinations thereof, differing in length, width of the rail pair, rails and the design of the track itself, including a sealed shell over the rail track to fill it with a lighter one environment. The longest track in the USA is Holloman AFB, located in New Mexico with a length of 15536 m. They have track ranges with different lengths and their own special design in England, France, Germany, Canada, Italy, Japan, India, China, Korea, Turkey and other countries, including African continent. High-speed range tests in Russia are carried out on the experimental installation “Rocket Rail Track 2500”, located on the territory of the FKP “GkNIPAS named after L. K. Safronov”. The experimental installation consists of a rail track placed on a special base, providing the necessary vertical profile of the track with sections of ascent and straight horizontal movement, as well as a technological descent section for braking moving technological equipment. The product under test is placed on a rocket track sled moving along rails on sliding supports. To accelerate the track carriage, solid fuel rocket engines are used, the thrust of which is selected based on ballistic calculations to achieve the required test speed. The length of the track plays an important role in achieving the maximum acceleration speeds of moving track equipment. The enormous aerodynamic drag, proportional to the square of the speed of movement of the carriage, when tested at high speeds, leads to the need to reduce the midsection and mass of the mobile unit. An increase in engine thrust leads to an increase in the weight and cost of track equipment, as well as to the need to increase the safety margin of sliding supports. However, an increase in test speed can be achieved by replacing the air medium with gases that have a significantly lower density, for example, helium. Track testing of new aircraft or their elements, although cheaper than flight testing, is quite expensive. In this regard, work on the theoretical assessment of replacing the medium from ambient air with helium, as well as with a mixture of helium and air at different concentrations in an indoor gallery on a track rail track, is a new, relevant and practically useful task. The work performed a numerical simulation of the problem of supersonic flow around a helium-air mixture at different volumetric ratios. Numerical values of aerodynamic resistance were obtained at a sled speed of 830 m/s. The results of numerical calculations of the motion dynamics of a 3D model of monorail track equipment, which are planned for use in conducting full-scale fire experiments, are presented.

Dynamics of multilayer Rayleigh–Taylor instability at moderately high Atwood numbers

This paper investigates the multilayer Rayleigh–Taylor instability (RTI) using statistically stationary experiments conducted in a gas tunnel. Employing diagnostics such as particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF), we make simultaneous velocity–density measurements to study how dynamics and mixing are linked in this variable density flow. Experiments are conducted in a newly built, blow-down three-layer gas tunnel facility. Mixing between three gas streams is studied, where the top and bottom streams are comprised of air, and the middle stream is an air–helium mixture. Shear is minimized between these streams by matching their inlet velocities. The four experimental conditions investigated here consist of two different density ratios (Atwood numbers 0.3 and 0.6), each investigated at two instability development times (or equivalently, two streamwise locations), and all experiments are with the same middle stream thickness of 3 cm. The growth of the middle layer is measured using laser-based planar Mie scattering visualization. The mixing width is found to grow linearly with time at late times. Various quantitative measures of molecular mixing indicate a very high degree of molecular mixing at late times in the multilayer RTI flow. The vertical turbulent mass flux$a_y$is calculated. In addition to mostly negative values of$a_y$, typical of buoyancy-dominated flows due to negative correlation between velocity and density fluctuations, positive regions are also observed in profiles of$a_y$due to entrainment and erosion at the lower edge of the mixing region. Global energy budgets are calculated for the multilayer RTI flow at late times and it is found that the majority of potential energy released has been dissipated due to viscous effects, and a large value of mixing efficiency ($\sim$60 %) is observed.

On amplitudes of disk flutter vibrations in helium-air mixture gas filled hard disk drives with flow mitigation devices

On amplitudes of disk flutter vibrations in helium-air mixture gas filled hard disk drives with flow mitigation devices

CFD analysis on stratification dissolution and breakup of the air-helium gas mixture by natural convection in a large-scale enclosed vessel

This paper describes the computational fluid dynamics (CFD) analysis and validation works from the previous experimental study on the natural convection driven by outer surface cooling in the presence of density stratification consisting of air and helium (as a mimic gas of hydrogen). The experiment was conducted in the Containment InteGral effects Measurement Apparatus (CIGMA) facility at Japan Atomic Energy Agency (JAEA). CIGMA vessel is a large cylindrical stainless steel with an inner diameter of the main cylindrical part 2.5 m and an overall height of 11 m. The mass fraction proportion of helium in the whole vessel was 11% and the helium molar fraction at the top vessel was 48%. Two experiments were performed and the numerical simulation was carried out to analyze the detailed effect of the cooling region on the erosion of the helium stratification layer. First test was named CCLP30 or case 1 and second test was named CCPL34 or case 2. The main difference between case 1 and case 2 was the cooling area of case 1 was narrower than case 2. In case 1, cooling area was only located at the one-fourth of outer vessel. Whereas, in case 2, cooling area was located at one-half of outer vessel. The temporal and spatial evolution of the helium concentration and the gas temperature inside the containment vessel was predicted and validated against the experimental data. The results indicated that the numerical predictions fairly agreed with the experimental data. However, the predicted erosion rate showed discrepancies compare with the experimental data. The relative errors time required for the complete dissolution of the helium gas were within 15%. In addition, two stratification behaviors that depend on the cooling location were presented and discussed. The CFD simulation confirmed that an upper head cooling caused two counter-rotating vortexes in the helium-rich zone. Meanwhile, the upper half body cooling caused two counter-rotating vortexes in the helium-poor zone. These findings are important to understand the mechanism of the density stratification process driven by natural convection in the containment vessel.

A modern view on the treatment of acute bronchiolitis in pediatric intensive care units: a review

INTRODUCTION. The literature has accumulated enough data on the treatment of children with acute bronchiolitis (OB). However, this information is formed mainly on the general population of patients with OB and is often not applicable to patients with a severe course of the disease. From the standpoint of evidence-based medicine, routine use of medications is not recommended in modern consent documents, and there are also no clear recommendations on respiratory support and certain aspects of intensive care in children with OB. OBJECTIVES. To analyze approaches to therapy in children with severe acute course in need of intensive care, and to assess the validity, effectiveness and safety of the use of the analyzed groups of drugs and respiratory strategies. MATERIALS AND METHODS. The analysis of publications in the electronic databases PubMed and the Russian Scientific Citation Index on the keywords “bronchiolitis”, “intensive care units”, “critical care”, “fluid therapy”, “respiratory therapy”, “ventilation”, “co-morbidity”; “respiratory syncytial virus”; “hypertonic saline” was carried out, “corticosteroids”; “epinephrine”; “high-flow oxygen therapy”, “inhalation”, “infant”, “bronchiolitis in children”. The date of the last search is January 15, 2022. RESULTS. This systematic review provides information on the etiology and risk factors of severe acute respiratory syndrome in children, from the standpoint of evidence-based medicine, studies on the treatment of severe acute respiratory syndrome are characterized, including in the intensive care unit with glucocorticosteroids, inhalations of bronchodilators, epinephrine, 3 % hypertonic sodium chloride solution, respiratory support, high-flow oxygenation, noninvasive ventilation, artificial ventilation, antibiotics, air-helium mixture. CONCLUSIONS. Currently, there is more information that infants with OB show a high degree of heterogeneity, while the main uncertainty lies in a misunderstanding of the processes, which patients will benefit most from a particular treatment method. Further research is needed to fill the research deficit in children with a severe course of OB.

Numerical Simulation of Enrichment of the Air-Helium Mixture with a Bifunctional Sorbent Based on Glass Microspheres

Numerical Simulation of Enrichment of the Air-Helium Mixture with a Bifunctional Sorbent Based on Glass Microspheres

Experimental investigation of natural convection and gas mixing behaviors driven by outer surface cooling with and without density stratification consisting of an air-helium gas mixture in a large-scale enclosed vessel

This paper describes an experimental investigation of natural convection driven by outer surface cooling in the presence of density stratification consisting of an air and helium (as mimic gas of hydrogen) gas mixture in an enclosed vessel. The unique cooling system of the Containment InteGral effects Measurement Apparatus (CIGMA) is used, and findings reveal that the cooling location relative to the stratification plays an important role in determining the interaction behavior of the heat and mass transfer in the enclosed vessel. When the cooling region is narrower than the stratification thickness, the density-stratified region expands to the lower part while decreasing in concentration (stratification dissolution). When the cooling region is wider than the stratification thickness, the stratification is gradually eroded from the bottom with decreasing layer thickness (stratification breakup). This knowledge is useful for understanding the interaction behavior of heat and mass transfer during severe accidents in nuclear power plants.

Oxygen sensor errors in helium-air mixtures

Oxygen sensors play a vital role in ensuring the safety of employees and users at the National High Magnetic Field Laboratory. While most oxygen sensors have accurate and linear responses in nitrogen/argon environments, studies have highlighted a phenomenon in helium-air mixtures with certain types of oxygen sensors. A controlled experiment was performed to observe the behavior of two types of oxygen sensors: orifice and membrane. The orifice sensor showed a large deviation of up to 13% of measured reading above the actual oxygen content in the helium-air mixture test, while the membrane sensor remained accurate to within 3% of the actual value throughout its range.

Electric field distributions along helium plasma jets

Results of simulations of streamers propagating along the atmospheric-pressure helium plasma jets ejected from a thin tube into ambient air are presented. The computational model includes the equations governing the helium–air mixture composition along and across the jet, as well as the equations, describing streamer propagation in the mixture, for the electric field and the charged species densities. Streamer velocity and spatial–temporal profiles of plasma parameters are obtained for various values of the helium flow rate. It is shown, in agreement with available experimental data, that the electric field values in the heads of streamers increase nearly linearly with the distance from the tube exit and that the slope of this dependence decreases with the growth of the helium flow rate.

Atmospheric pressure plasma jets generated by the DBD in argon-air, helium-air, and helium-water vapour mixtures

Plasma jets are increasingly used in plasma medicine, in microelectronics and for surface treatment due to their unique properties, such as low gas temperature and high concentration of active species. This paper presents the results of a study of plasma jets generated by the atmospheric pressure dielectric barrier discharge while passing through it of argon-air, helium-air and helium-water vapor mixtures. Comparison of the plasma jets characteristics shows that the gas flow rate at which the maximum power of UV radiation is achieved increases in the series of He-H2O, He-air, Ar-air. Replacing Ar-air working mixture with He-air mixture leads to an increase in the plasma jet radiation power in ∼ 3 times. The maximum overall radiation power achieved in the He-air plasma jet was 0.07 W. The emission spectra of the plasma jets were identified in the spectral region of 270–900 nm, it was found that the molecular bands of the second positive and first negative systems of nitrogen predominate in the UV region of spectrum and lines of He I or Ar I prevail in the visible region. The distributions of the radiation intensity of excited plasma species along the jet length were measured. The analysis of difference in the emission spectra of the plasma jet in pure Ar and He and in their mixtures with air, as well as in a He-H2O mixture, has been performed taking into account values of the mean electron energy and rate constants of elementary processes in the plasma calculated using the Bolsig + code. The molecular and ionic reactions responsible for emission of radiation in the UV range of spectrum are considered.

Optical Radiation of Atmospheric Pressure Plasma Jets Excited by a Barrier Discharge

The luminescence spectra of plasma jets formed by a barrier discharge at atmospheric pressure in argon–air and helium–air mixtures have been studied experimentally in the spectral region of 270–900 nm. It is shown that the emission spectra of plasma jets are represented mainly by electronic-vibrational transitions of the second positive system of neutral nitrogen molecules in the ultraviolet range of the spectrum. The radiation powers of the studied mixtures are compared.

Investigation of lubricant transfer and distribution at head/disk interface in air-helium gas mixtures

Lubricant transfer and distribution at the head/disk interface in air-helium gas mixtures is investigated using a developed model that combines an air-bearing model with a molecular dynamics model. The pressure distribution is calculated by the air-bearing model at the head/disk interface with respect to the helium content and the pressure obtained is then input to the molecular dynamics model to understand the lubricant transfer mechanism. Finally, the effects of pressure at the boundary condition and disk velocity on lubricant transfer are discussed in relation to the helium fraction within the air-helium gas mixtures. Results show there is a decrease in the pressure difference with an increase in the helium percentage, which leads to a decrease in the volume of the lubricant transferred. The results also suggest that the lubricant is not easily to transfer in gas mixtures with a high percentage of helium, even when both higher disk velocities and pressure boundary conditions are applied.

Estudio del régimen de combustión sin llama ante la variación de la carga térmica

El presente estudio evaluó numérica y experimentalmente en un horno de 20 kW (a gas natural y con un factor de aireación de 1.2) la estabilidad del régimen de combustión sin llama ante la variación de la carga térmicausando diferentes flujos de aire (43 scfm, 63 scfm y 83 scfm) y una mezcla de Aire-Helio (Aire 82.02 scfm y Helio 7.06 scfm); esta última se utilizó con el fin de evaluar el comportamiento del sistema ante un incremento en el calor especifico del fluido de carga. El estudio se dividió en dos par-tes, una parte numérica y otra experimental. A partir de la simulación numérica se calculó el perfil de temperatura, el perfil de CO, el factor de recirculación Kv y la masa de productos de combustión recirculados. En la fase experimental los perfiles de temperatura mostraron una disminución en la temperatura de la cámara de combustión a medida que el flujo de aire de carga incrementaba, sin embargo, esta disminución no afectó la uniformidad térmica dentro del horno. Además la eficiencia útil mostró un incremento al pasar de un flujo de aire de carga de 43 scfm a 63 scfm,seguido de una disminución al incrementar la carga térmica.

Characteristics of Disk Flutter in Mixture Gas of Helium and Air

In this paper, characteristics of disk flutter (natural frequency of disk modes, modal damping ratios, and modal excitation caused by flow) were studied by using a HDD filled with air, helium, and their mixture gas. In our experiments, amplitude of disk flutter decreased as the fraction of helium in the mixture gas increased but was not simply proportional to the gas density. This contradicts the general understanding that the amplitude of disk flutter is proportional to density of fluid in a HDD. Analysis of modal parameters showed disk flutter excitation varied with respect to the helium-air mixture ratio in the same manner as the disk flutter amplitude. From the behavior of the excitation factor, we categorized three regions on the basis of the gas density ratio, i.e., the ratio of gas density to air density in 1 atm. at room temperature: the transitional region is helium-rich, the critical region is mid-way between the other regions and the turbulent flow region is air-rich.

The influence of vehicular obstacles on longitudinal ventilation control in tunnel fires

The effect of the vehicular blockage in a tunnel under longitudinal ventilation smoke control was systematically studied using a small-scale tunnel (1:30 of a standard tunnel section) with a helium-air mixture as the buoyant plume. The experimental results showed excellent agreement with full-scale data and reference correlations from former studies. When there are vehicular obstacles in the tunnel, the critical velocity decreased as a function of the blockage ratio. Notwithstanding, it was found that the relative size of the vehicular obstacle and the relative location of the fire source can have a reversed effect, inasmuch as the presence vehicular obstacle exerted an influence on the critical and confinement velocities. Moreover, the backlayering distance was evidently affected by the vehicular blockage. A parallel analysis was carried out for the backlayering distance for lower and upper regimes of the dimensionless heat release rate, where the current data was compared against data from other studies. The method and experimental set-up proved their ability to reproduce several phenomena and thus also their capability to supply relevant and valuable information on the effect of the vehicular blockage on tunnel fire dynamics.

Experimental and numerical investigation of the emergency helium release into the LHC tunnel

An unexpected ejection of cryogen into large confined spaces can result in hazardous consequences. This paper presents the experimental results of the controlled release of liquid helium into the LHC tunnel at CERN. The experiment was designed to measure the oxygen concentration, temperature, and propagation of the helium-air mixture cloud in the LHC tunnel. This required the usage of novel, in-house manufactured, ultrasonic helium detectors. The experimental results showed an advantage of the ultrasonic sensors over traditional electrochemical sensors. Next, a minimal mathematical model was presented and implemented numerically. The experimental results contributed to the validation of the numerical model. A number of numerical calculations were performed in order to examine the consequences of a helium spill with different mass flows. This assisted in the evaluation of the critical helium mass flow, above which the oxygen concentration could drop below the safety limit. A satisfactory comparison of the experimental results and numerical calculations showed the accuracy of the assumptions of the proposed mathematical model.

Dynamics of buoyancy-driven flows at moderately high Atwood numbers

Simultaneous density and velocity turbulence statistics for Rayleigh–Taylor-driven flows at a moderately high Atwood number ($A_{t}$) of $0.73\pm 0.02$ are obtained using a new convective type or statistically steady gas tunnel facility. Air and air–helium mixture are used as working fluids to create a density difference in this facility, with a thin splitter plate separating the two streams flowing parallel to each other at the same velocity ($U=3~\text{m}~\text{s}^{-1}$). At the end of the splitter plate, the two miscible fluids are allowed to mix and the instability develops. Visualization and Mie-scattering techniques are used to obtain structure shape, volume fraction profile and mixing height growth information. Particle image velocimetry (PIV) and hot-wire techniques are used to measure planar and point-wise velocity statistics in the developing mixing layer. Asymmetry is evident in the flow field from the Mie-scattering images, with the spike side showing a more gradual decline in volume fraction than the bubble side. The spike side of the mixing layer grows 50 % faster than the bubble side. PIV is implemented for the first time in these moderately high-Atwood-number experiments ($A_{t}>0.1$) to obtain root-mean-square velocities, anisotropy tensor components and Reynolds stresses across the mixing layer. Overall, the turbulence statistics measured have shown different scaling compared to small-Atwood-number experiments. However, the total probability density functions for the velocities and turbulent mass fluxes exhibit behaviour similar to small-Atwood-number experiments. Conditional statistics reveal different values for turbulence statistics for spikes and bubbles, unlike small-Atwood-number experiments.

A unified correlation for steam condensation rates in the presence of air–helium mixtures under naturally driven flows

Steam condensation in the presence of multiple noncondensable gases is critical in many nuclear plant safety applications, not the least of which are hypothetical severe accidents where H2 is present in addition to the containment air inventory. Experimentalists have used helium as a surrogate for H2, and have proposed a number of correlations and/or databases to estimate steam condensation rates in the presence of binary air–helium mixtures under free convection regimes typical of reactor flows. These studies are purely empirical, and hence do not allow to draw clear dependencies of the heat transfer rate on critical thermal-hydraulic parameters. In this study, we do away with the particular forms of the correlations, and go back to the original experimental data, consolidate them in a single database, and propose a unified correlation that is compatible with the heat and mass transfer analogy. This best-estimate correlation for steam–air–helium mixtures, based on four different investigations and 180 data points, covers ranges of conditions expected in nuclear severe accidents. The consolidated raw data gather around a curve with a standard deviation of 20%, which is within typical experimental error bands. We show in addition that the correlation can directly be used to estimate steam condensation rates in the presence of binary hydrogen–air mixtures.

Computational fluid dynamics analysis of the initial stages of a VHTR air-ingress accident using a scaled-down model

An air-ingress accident is considered to be one of the design basis accidents of a very high-temperature gas-cooled reactor (VHTR). The air-ingress accident is initiated, in its worst-case scenario, by a complete break of the hot duct in what is referred to as a double-ended guillotine break. This leads to an initial loss of the primary helium coolant via depressurization. Following the depressurization process, the air–helium mixture in the reactor cavity could enter the reactor core via the hot duct and hot exit plenum. In the event that air ingresses into the reactor vessel, the high-temperature graphite structures in the reactor core and hot plenum will chemically react with the air, which could lead to damage of in-core graphite structures and fuel, release of carbon monoxide and carbon dioxide, core heat up, failure of the structural integrity of the system, and eventually the release of radionuclides to the environment.Studies in the available literature focus on the phenomena of the air ingress accident that occur after the termination of the depressurization, such as density-driven stratified flow, molecular diffusion, and natural circulation. However, a recent study shows that flow reversal could occur due to Taylor wave expansion near the end of the depressurization, which could affect subsequent stages of the air ingress accident scenario. Therefore, to properly understand and evaluate the depressurization effects, numerical simulations are performed for the double-ended guillotine break of the Gas Turbine-Modular Helium Reactor (GT-MHR) cross vessel with a computational fluid dynamics (CFD) tool, ANSYS FLUENT.A benchmark and error quantification study of the depressurization shows that the ANSYS FLUENT model can predict the depressurization problem with relatively low uncertainty. In addition, the computational results show that the depressurization of a double-ended guillotine break behaves as an isentropic process. The observed flow oscillations near the end of the depressurization promote mixing of helium gas and air near the break. The results of the CFD analyses also show that the density-driven stratified flow, which is postulated to be the next stage of the air-ingress accident scenario, is strongly dependent on the density difference between the air–helium mixture in the containment and the helium in the reactor vessel. Therefore, the flow oscillations near the end of the depressurization stage may have a minor, yet notable, effect to slow down the air ingress due to density-driven stratified flow by decreasing the bulk density of the gas mixture in the containment through the addition of helium and increasing the bulk density in the reactor vessel through the addition of air.

RANS analyses on erosion behavior of density stratification consisted of helium–air mixture gas by a low momentum vertical buoyant jet in the PANDA test facility, the third international benchmark exercise (IBE-3)

Density stratification in the reactor containment vessel is an important phenomenon on an issue of hydrogen safety. The Japan Atomic Energy Agency (JAEA) has started the ROSA-SA project on containment thermal hydraulics. As a part of the activity, we participated in the third international CFD benchmark exercise (IBE-3) focused on density stratification erosion by a vertical buoyant jet in containment vessel. This paper shows our approach for the IBE-3, focusing on the turbulence transport phenomena in eroding the density stratification and introducing modified turbulence models for improvement of the CFD analyses. For this analysis, we modified the CFD code OpenFOAM by using two turbulence models; the Kato and Launder modification to estimate turbulent kinetic energy production around a stagnation point, and the Katsuki model to consider turbulence damping in density stratification. As a result, the modified code predicted well the experimental data. The importance of turbulence transport modeling is also discussed using the calculation results.