Test Gas Research Articles

Spectroscopic investigations on impurities and their effect on the electron number density in the shock tube

An accurate estimation of electron number density is significant in many plasma physics studies. In this paper, the effect of impurities in test gas on the electron number density of the plasma generated in the hypersonic flow of a free-piston driven hypersonic shock tube has been studied using optical emission spectroscopy. Emission spectra of argon plasma showed the presence of following impurities: sodium, potassium, nitrogen, oxygen and hydrogen. The electron number density calculated from the spectral broadening of argon emission lines, is one order of magnitude higher than the electron number density calculated from the thermochemical equilibrium flow model that does not include the impurities. Hence the results show that the presence of impurities has a significant impact on the shock tube plasma and warrants the need to include these effects in the thermochemical equilibrium flow model while investigating magneto-aerodynamic interaction flows and communication blackout studies in the hypersonic ground-based test facilities.

Driving Force of Molecular/Ionic Superfluid Formation

Driving Force of Molecular/Ionic Superfluid Formation

Experimental investigation on aerothermal effects of forward-facing cylindrical and parabolic cavity in hypersonic flow

Thermal protection of hypersonic vehicles is of great concern during ascent and re-entry conditions due to higher aerothermal loads. The passive forward-facing cavity is exhibited a substantial reduction of aero heating effects. The experimental studies on unsteady aspects of the flow considering the cavity geometries and heat transfer effects within the cavity are not abundant. In the present study, we investigated the heat transfer variations and nature of shock around a blunt body with cylindrical and parabolic cavity geometries. Experiments are conducted in hypersonic shock tunnels using air as the test gas for flow enthalpy conditions of 3.2 and 5.4 MJ/kg for a free-stream Mach number of 10.9 and 10.2 respectively. The cavity flow is established by verifying the measured heat flux, pressure, and shock oscillation results. The unsteady heat flux measurements and high-speed schlieren imaging is performed to study the effects. The results reveal that the flow with the parabolic cavity geometry shows a significant increase in the mean shock standoff position of about 14% and 30% compared to the blunt-nosed body, and about 7%–18% compared to the cylindrical cavity geometry, with a reduction of bow shock oscillations. As a result, a substantial reduction of heat flux about 34%–59% on the nose surface is noticed and found it is effective for mitigating the aerodynamic heating at higher flow enthalpy conditions. The flow with a cylindrical cavity geometry indicated the substantial increase in the heat flux due to the shock interaction and the significant heat flux variation in the cavity region is recognized and observed that such effects were not prevalent with the parabolic cavity geometry.

Research on Main Controlling Factors of Fracturing Reformation of Ancient Sandstone Horizontal Wells in Jingbian Gas Field

From 2015 to 2019, a total of 7 wells in the Shan 28 well area of the Jingbian gas field used pumped bridge plug staged fracturing technology. The average test gas daily gas production rate is 8.13×104m3/d, and the average unblocked flow rate is 46.06×104m3/d, Demonstrating the superiority of the staged fracturing reconstruction process of pumping bridge plugs, However, due to the short time of using the pumped bridge plug staged fracturing process, the main controlling factors of fracturing reformation are not clear, resulting in a large gap between the gas production effect of the reformed well and the expected. Therefore, based on the site construction parameters, this paper uses single factor analysis and grey correlation analysis methods to determine the main control factors for fracturing reformation of the ancient sandstone horizontal well in the Jingbian gas field. Research shows that the length of gas layer, liquid type, average sand ratio, and sand volume are the main factors affecting the open flow and daily gas production of horizontal wells. The research results in this paper have certain guiding significance for the effective development of ancient sandstone horizontal wells.

A designed flow-through microsystem for accurate and fast measurement of gas sensors at the ppb level

The characteristic parameters of gas sensors depend highly on the method used to evaluate them. This paper presents a flow-through microsystem for accurate and fast measurement of gas sensors, especially for the sensor with a fast response and high sensitivity at the ppb level. The microsystem consists of four parts, i.e. a dynamic multiple gas handling unit, a test gas preheater, an olive-like test chamber with an inner volume of 4.98 ml and data analysis apparatus. Thereinto, the multiple gas handling unit was constructed to meet the needs of dynamical sensor response tests, and the olive-like test chamber was designed based on the principles of low background interference and fast replacement of ambient conditions, which was optimized by computational fluid dynamics simulation and verified by its airtightness and applicable flow rate range. For a flow rate of 300 ml min−1, it can discern that the replacement time for the chamber ambient gas test was about 1 s. Finally, performance tests for two commercial sensors and one home-made sensor were carried out on this microsystem. The results showed that this system can serve as a means of highly sensitive (ppb level) and fast gas sensor evaluation, and the measured values obtained by this system can be considered to be closer to a sensor’s true values.

Synthesis of VO2 thin films from vanadium powder and determination of room-temperature NH3 sensing properties

VO2 nanomaterials were synthesized directly from vanadium powder and NH4OH solution. The effect of annealing temperature on the formation of VO2 and V2O5 phases of materials after synthesis was investigated and analyzed. The material is composed of nanoparticles with an average size of about 2 nm. The gas sensing properties of VO2 samples at room temperature were studied. The VO2 nanomaterial was selective toward NH3 at 25 °C among other test gases such as C2H5OH, CH3COCH3, and C3H8. The effects of moisture, stability, and gas-sensing mechanism of VO2 nanomaterials were also investigated and discussed. VO2 nanomaterials have simple fabrication and superior air sensitivity and thus have great potential as NH3 sensors at room temperature.

Two-Dimensional Numerical Study of the Transient Flow Conditions in Complete Shock Tunnel

In the current research, an axisymmetric model is developed to study high-speed unsteady flow in the test section of a 7 meter-long shock tunnel. The computational calculations of the shock tunnel are conducted using the Fluent CFD solver. The Finite Volume Method (FVM) is used to discretize the governing equations of mass, momentum, and energy. The accuracy of the numerical model is investigated with first-order upwind, second-order upwind, and third-order MUSCL schemes. Adaptive mesh refinement is implemented to resolve the shock wave and contact surface regions accurately. The numerical results are compared with theoretical calculations and experimental data from experimental tests and the comparison shows good agreement. Different test gases of Helium, Air and CO2, are utilized in the current study. The results show that steady test conditions are maintained for a longer test time by adjusting the pressure ratio and gas combination across the diaphragm. The highest shock wave speed and strength are achieved for a gas combination of Helium-CO2, but a longer test duration is observed when using Air as the test gas.

Flow Regime Visualization and Identification of Air–Water Two-Phase Flow in a Horizontal Helically Coiled Rectangular Channel

Experiments of flow regime visualization and identification of air–water two-phase flow were conducted in a horizontal helically coiled rectangular channel. The test superficial liquid and gas velocities are 0.09–2 m/s and 0.18–16 m/s, respectively. Flow regimes were observed with a high-speed video camera and the corresponding local and average void fractions were measured with an electric conductivity probe method and with a quick-close valve method, respectively. Four main flow regimes including unsteady pulsating flow, bubbly flow, intermittent flow, and annular flow were observed. The bubbly flow identification criteria depend on more than 90% bubbles whose chord length was smaller than the channel equivalent diameter. The annular flow identification criteria is the local void fraction in the gas core larger than 0.97. Then the flow regimes and their transition mechanisms are analyzed. Furthermore, new transition criteria among these flow regimes have been proposed. The results show that the critical transition average void fraction from bubbly to intermittent flow is 0.23. A complete air–water flow regime map has been developed for the horizontal helically coiled rectangular channel and the map predicts the observed flow regimes well.

Synthesis of ZnAl2O4 and Evaluation of the Response in Propane Atmospheres of Pellets and Thick Films Manufactured with Powders of the Oxide.

ZnAl2O4 nanoparticles were synthesized employing a colloidal method. The oxide powders were obtained at 300 °C, and their crystalline phase was corroborated by X-ray diffraction. The composition and chemical structure of the ZnAl2O4 was carried out by X-ray and photoelectron spectroscopy (XPS). The optical properties were studied by UV-vis spectroscopy, confirming that the ZnAl2O4 nanoparticles had a direct transition with bandgap energy of 3.2 eV. The oxide’s microstructures were microbars of ~18.2 nm in size (on average), as analyzed by scanning (SEM) and transmission (TEM) electron microscopies. Dynamic and stationary gas detection tests were performed in controlled propane atmospheres, obtaining variations concerning the concentration of the test gas and the operating temperature. The optimum temperatures for detecting propane concentrations were 200 and 300 °C. In the static test results, the ZnAl2O4 showed increases in propane response since changes in the material’s electrical conductance were recorded (conductance = 1/electrical resistance, Ω). The increases were ~2.8 at 200 °C and ~7.8 at 300 °C. The yield shown by the ZnAl2O4 nanoparticles for detecting propane concentrations was optimal compared to other similar oxides categorized as potential gas sensors.

Effect of annealing temperature on a highly sensitive nickel oxide-based LPG sensor operated at room temperature

In the present work, nanostructured nickel oxide (NiO) powder has been synthesized using the sol–gel method and is annealed at different temperatures to study the impact of annealing temperature on its structural, optical, morphological, and LPG sensing properties. The obtained powder was analyzed by several characterization techniques such as field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV–Visible spectroscopy (UV–Vis), particle analyzer, and Fourier-transform infrared spectroscopy. XRD patterns show that NiO nanoparticles have a cubic unit cell structure. The average crystallite size for each of the samples was calculated to be 27–77 nm using the Debye–Scherrer formula and Williamson-Hall uniform deformation model plot. FESEM images revealed the mesoporous morphology of prepared NiO nanoparticles and found that the particle size increases with an increase in annealing temperature. The UV–Vis absorption spectrum shows that the energy band gap decreases with an increase in annealing temperature for NiO nanoparticles. Liquefied petroleum gas (LPG) sensing properties of the prepared pellets were also examined at room temperature (300 K) in the range of 0.5–2.0 vol% concentration of LPG. The gas sensing response of the NiO:500 sample is 244.4% which is the highest among all the samples due to the combined effect of nanocrystal defects and specific surface area. The sensing response of the synthesized material increased significantly as the concentration of the test gas rose.

The value of endobronchial cryotherapy in the management of malignant endobronchial obstruction in patients with inoperable NSCLC: a prospective analysis of clinical and survival outcomes

BackgroundMalignant endobronchial obstruction (MEBO) is the most debilitating complication in non-small cell lung cancer (NSCLC). The therapeutic role of cryotherapy and its impact on survival has not been well addressed. This is to clarify whether the combination of endobronchial cryotherapy (EBCT) and chemoradiotherapy (CRT) improved symptoms, respiratory functions, performance status, and survival outcomes in inoperable NSCLC with symptomatic MEBO compared to that obtained by CRT alone.ResultsA prospective cohort study included 60 cases presented to Qena University Hospital, Egypt, between December 2016 and May 2019. They were divided into two groups. Group A included 30 patients who were managed with EBCT plus CRT. Group B included 30 patients who were managed with CRT alone. The outcomes assessed were symptoms relief, respiratory function tests (RFT), performance status, and survival outcomes at baseline and 4 weeks of follow-up. Group A patients showed a highly significant improvement in symptoms (cough, dyspnea, and hemoptysis), RFT, 6MWD test, and arterial blood gases, compared to group B. The mean Karnofsky score increased from 57.33±5.67% at baseline to 60.67±6.39% post-EBCT (P=0.036); group A was significantly improved compared to group B (P=0.04). The Kaplan-Meier median survival for all patients was 9.7±0.4 months (95% CI= 8.86–10.54), and group A cases (10.77±0.44 months, 95% CI= 9.9–11.6) was significantly longer than that of group B cases (8.6±0.68 months, 95% CI= 7.3–9.97; T test = 2.631, P=0.011).ConclusionThe use of EBCT with CRT for the management of MEBO in symptomatic patients with inoperable NSCLC is an efficient and safe procedure. EBCT improves clinical outcomes, RFT, performance status, and median survival.Trial registrationClinTrial.Gov registration: NCT04710459 on 4/3/2021.

Effect of Cu2+ concentration on MnFe2O4 nano-crystals in its NH3 sensing property

This work is focused on the field of gas sensor for sensing the toxic gases which is highly harmful to environment. The semiconductor metal oxide nanoparticles of manganese ferrites and copper doped manganese ferrite (MnFe2O4 and Cu: MnFe2O4) was successfully developed. The characterization like crystal structure, surface morphology, optical bandgap, elemental composition and functional group analysis for the developed materials were carried out using X-ray Diffraction (XRD), Scanning electron microscope (SEM), Diffused reflectance spectroscopy (DRS), Energy dispersive X-Ray analysis (EDAX) and Fourier Transform (FT-IR) studies respectively. The ammonia gas (NH3) was taken as test gas and the sensitivity of prepared samples were analyzed with different ppm (200–400) of gas molecules at room temperature. The sensing percentage gradually improved with the increase in Cu2+ concentration also with the increase in ppm of the gas. However, the recovery time of the material is increased with increase in the ppm.

Superplastic forming characteristics of AZ41 magnesium alloy

An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming parameters. Formability was assessed using elevated temperature tensile testing and hot gas bulging, across a range of strain rates (1×10 −1 −1×10 −3 s −1 ) and temperatures (350−450 °C). Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming processes. Post forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability, with dynamic recrystallization being clearly evident. Peak elongation of 520% was achieved at 450 °C and 1×10 −3 s −1 ; industrially relevant elongation was achieved at 1×10 −2 s −1 at both 450 °C (195%) and 400 °C (170%).

Expansion Tube Test Flow Design for Magnetohydrodynamic Aerobraking

This paper explores the operating envelope for the University of Queensland’s free-piston driven X2 expansion tube to determine if flow conditions can be produced that generate a significant magnetohydrodynamic interaction. Numerical calculations are presented to demonstrate the existence of viable operating conditions to study magnetohydrodynamics. Argon is selected as the test gas due to its simple chemistry and low ionization enthalpy. A candidate flow condition is selected for detailed analysis and experimental validation. Finite-rate reacting argon numerical simulations indicate that relatively short shock-layer length scales for the models tested in X2 limit the degree of argon ionization that is generated. However, a strong interaction remains available, and use of a larger facility can fully mitigate this issue. It is shown that expansion tubes are capable of generating the required flowfield for these experiments, and important considerations for design of suitable test flows are identified.

Room temperature ammonia sensing of α-MoO3 nanorods grown on glass substrates

We report the fabrication of ammonia gas sensors operating at room temperature using aligned one-dimensional orthorhombic molybdenum trioxide (α-MoO3) nanorods. α-MoO3 nanorods were fabricated on glass substrates by thermal evaporation under vacuum condition and subsequent annealing at ambient air. The selectivity of fabricated sensors was performed with different test gases viz. ammonia, xylene, acetone, toluene, isopropanol, 2-methoxyethanol, n-butanol, methanol, and ethanol. Highest sensitivity for ammonia gas at room temperature (28°C, 35% relative humidity) for a concentration of 100 ppm, was achieved. The sensors annealed at 400 °C showed response to lower concentrations of ammonia (1 ppm) with high repeatability. The sensing response dropped only less than 1% after one year of stable performance. The change in morphology and the structural modifications of α-MoO3 nanorods with annealing had improved the sensing response.

UoC‐4: A MOF Based on Octahedral ScO 6 Nodes and Fluorinated Trimesate Ligands

A new MOF (metal-organic framework), [Sc(dF-BTC)6/6]⋅solvent with dF-BTC3−=2,4-difluoro-1,3,5-benzene-tricarboxylate, termed UoC-4 (UoC≡University of Cologne), was synthesized by solvothermal reaction in an ethanol/water solvent mixture. The crystal structure of UoC-4 was solved and refined from X-ray single crystal data (I41/amd, Z=8). In the crystal structure each of the three carboxylate groups of the dF-BTC3− linker coordinates to two Sc3+ cations, resulting in an almost ideal ScO6 octahedron. The connectivity of these ScO6 and dF-BTC3− building units leads to a 3D framework structure with a new unprecedented topology. Small voids with a diameter of <5 Å are formed, in which most likely disordered ethanol molecules reside. UoC-4 is stable against moisture, but in water a slow hydrolysis occurs. Thermal decomposition in an inert atmosphere starts above 400 °C. Activation of the material failed so that no gas sorption isotherm with N2 as test gas could be recorded. The small pores within UoC-4 are obviously not accessible for gases like N2 due to very small opening windows.

In situ nozzle reservoir thermometry by laser-induced grating spectroscopy in the HELM free-piston reflected shock tunnel

Experimental determination of test gas caloric quantities in high-enthalpy ground testing is impeded by excessive pressure and temperature levels as well as minimum test timescales of short-duration facilities. Yet, accurate knowledge of test gas conditions and stagnation enthalpy prior to nozzle expansion is crucial for a valid comparison of experimental data with numerical results. To contribute to a more accurate quantification of nozzle inlet conditions, an experimental study on non-intrusive in situ measurements of the post-reflected shock wave stagnation temperature in a large-scale free-piston reflected shock tunnel is carried out. A series of 20 single-shot temperature measurements by resonant homodyne laser-induced grating spectroscopy (LIGS) is presented for three low-/medium-enthalpy conditions (1.2–2.1 MJ/kg) at stagnation temperatures 1100–1900 K behind the reflected shock wave. Prior limiting factors resulting from impulse facility recoil and restricted optical access to the high-pressure nozzle reservoir are solved, and advancement of the optical set-up is detailed. Measurements in air agree with theoretical calculations to within 1–15%, by trend reflecting greater temperatures than full thermo-chemical equilibrium and lesser temperatures than predicted by ideal gas shock jump relations. For stagnation pressures in the range 9–22 MPa, limited influence due to finite-rate vibrational excitation is conceivable. LIGS is demonstrated to facilitate in situ measurements of stagnation temperature within full-range ground test facilities by superior robustness under high-pressure conditions and to be a useful complement of established optical diagnostics for hypersonic flows.

The Influence of Helium And Cavitation on the Yeast Life Process

Purpose of the study is to іnvestigate the simultaneous effect of cavitation and helium on the viability of yeast of the genus Saccharomyces cerevisiae in water. To study the change in the number of cells during cavitation treatment of the water system in the gas atmosphere. Methods. Yeast of Saccharomyces cerevisiae type were used as test microorganisms. Freshly prepared distilled desaerated water was used for the research, to which yeast cells were introduced with a microbiological loop. The volume of the model medium was cooled in a glass reactor with tap water, the temperature of which corresponded to 298 ± 1 K. The total duration of the process was 2 hours. The cavitation source was an ultrasonic generator UZDN-2T with frequency of 22 kHz and power of 35 W. The test water was bubbled with gas throughout the process. The test gas was helium. The number of microorganisms per unit volume of test water was determined by the total number of colonies on the nutrient medium on Petri dishes and expressed in colony-forming units (CFU). Results. In the experimental part of the work the process of water treatment with the content of yeast cells under cavitation conditions with simultaneous supply of helium is proposed. The efficiency of water purification from yeast as a result of the combined action of helium/cavitation has been established. The value of the effective rate constant of microorganisms destruction according to the kinetic reaction equation of the first order is calculated. The viability of yeast under cavitation conditions and bubbling of helium through the water system has been studied. The proportion of destroyed cells during the two-hour action of yeast-contaminated water at different treatment regimes was calculated and compared. An active decrease in the number of Saccharomyces cerevisiae in the aqueous medium at the beginning of the process with the achievement of the proportion of destroyed cells (Dd) 40.48% after 30 min of combined He/cavitation action at the initial microbiological water contamination of 4.2 · 103 CFU/cm3. NMend = 100 CFU/cm3 after 90 minutes of water treatment, that corresponds to the water purification degree &gt; 97%. The end result is almost pure water, which allows to discharge treated water into natural water. Conclusions. The obtained results indicate intensive cavitation purification of water from the studied microorganisms in the experimental conditions. The influence of the studied gas nature on the process of destruction of microbiological contaminants in water is described.

Дія гелію на очищення води з різною концентрацією мікроорганізмів

The influence of bubbled inert gas on the viability process of rod-shaped microorganisms in the water has been studied. The micro-objects were resistant sporogenic cells of Bacillus cereus type, which belong to the Bacillaceae family, and the test gas was helium. Helium was fed at a rate of 0.2 cm3/s. Bacteria were added to distilled deaerated water, creating model aqueous media with different initial numbers of microorganisms (NM). The concentration of microorganisms per unit volume of water was within the same order: NM01 = 3.4&nbsp;·&nbsp;104 CFU/cm3, NM02 = 4.8 · 104 CFU/cm3 and NM03 = 7 · 104 CFU/cm3. An in-depth method of culturing bacterial cells was used. Conditions for culturing microorganisms was temperature of 37&nbsp;°C, duration of 48 hours. NM values before and after experiments was determined by counting the colonies that grew on the nutrient medium on Petri dishes. The calculated number of cells was expressed in colony-forming units (CFU). During microscopic examinations, cells of the fixed preparations culture (1-day and 3-day) were studied. Fixed cell preparations at x1200 are shown. The shape and size of the cells of the fixed preparation are shown, as well as the shape and location of the spores inside the cells. Illustrative material shows the oval shape of the spores. It was found that the diameter of the spores is smaller than the cell diameter. The results of experimental studies show a change of NM values over time, during which there was a decrease of the cells number per unit volume of water during the two-hour duration of the process, regardless of the different NM0. The proportion of destroyed cells for each of their concentrations after every 30 minutes of water treatment was calculated and the values of the initial NM ratio to the current NM after each water sampling were given. The dependences of the proportion of destroyed cells of the treatment duration of microbial water with helium are graphically constructed. An increase in the proportion of destroyed cells with a decrease in the initial concentration of cells in the water was observed. The highest percentage of destroyed bacilli was reached at NM01 = 3.4 · 104 CFU/cm3, which was 77.06&nbsp;%, while for NM02 = 4.8 · 104 CFU/cm3 and NM03 = 7 · 104 CFU/cm3 are 72.92&nbsp;% and 47.72 %, respectively. Thus, a sufficiently high efficiency of helium alone during the treatment of microbial water containing resistant sporogenic bacteria has been experimentally shown.

Research on Formaldehyde Release Rate of Car mats

The environmental test cabin method was used to simulate the actual use environment of car mats to collect test gas, The formaldehyde content in the collected gas was measured by ultraviolet spectrophotometer, and the formaldehyde release rate was calculated. The results indicated that formaldehyde was released in all 30 batches of samples at a rate ranging from 0.02 to 0.13mg/ m2 (m2•h).