Test Gas Research Articles

Convective heat-transfer rate and surface pressure distribution over a cone model at hypersonic speeds

In this article, experiments are carried out in a hypersonic shock tunnel with helium as driver gas and air as the test gas to obtain the convective heating rate and surface pressure distribution on a cone model placed at hypersonic speed. Test is performed in hypersonic shock tunnel for a flow Mach number of 6.5 at two different angles of attack, 0° and 5°. The sputtered thin film platinum sensors are used to measure the heat flux on a cone model. The measured heat-transfer rate compares well with theoretically estimated values using reference enthalpy method and computational fluid dynamics (CFD) simulation. The measured surface pressure compares well with CFD.

Test methodologies for hydrogen sensor performance assessment: Chamber vs. flow-through test apparatus

Certification of hydrogen sensors to meet standards often prescribes using large-volume test chambers [1,2]. However, feedback from stakeholders such as sensor manufacturers and end-users indicates that chamber test methods are often viewed as too slow and expensive for routine assessment. Flow-through test methods are potentially an efficient and cost-effective alternative for sensor performance assessment. A large number of sensors can be simultaneously tested, in series or in parallel, with an appropriate flow-through test fixture. The recent development of sensors with response times of less than 1s mandates improvements in equipment and methodology to properly capture the performance of this new generation of fast sensors; flow methods are a viable approach for accurate response and recovery time determinations, but there are potential drawbacks. According to ISO 26142 [1], flow-through test methods may not properly simulate ambient applications. In chamber test methods, gas transport to the sensor is dominated by diffusion which is viewed by some users as mimicking deployment in rooms and other confined spaces. Conversely, in flow-through methods, forced flow transports the gas to the sensing element. The advective flow dynamics may induce changes in the sensor behaviour relative to the quasi-quiescent condition that may prevail in chamber test methods. The aim of the current activity in the JRC and NREL sensor laboratories [3,4] is to develop a validated flow-through apparatus and methods for hydrogen sensor performance testing. In addition to minimizing the impact on sensor behaviour induced by differences in flow dynamics, challenges associated with flow-through methods include the ability to control environmental parameters (humidity, pressure and temperature) during the test and changes in the test gas composition induced by chemical reactions with upstream sensors. Guidelines on flow-through test apparatus design and protocols for the evaluation of hydrogen sensor performance have been developed. Various commercial sensor platforms (e.g., thermal conductivity, catalytic and metal semiconductor) were used to demonstrate the advantages and issues with the flow-through methodology.

Fabrication and characterization of ZnO-TiO2-PANI (ZTP) micro/nanoballs for the detection of flammable and toxic gases.

The present paper reports the in-situ chemical polymerization of nanocomposites thin film composed by titanium dioxide (TiO2), zinc oxide (ZnO) and polyaniline (PANI). It was found that nanocomposites sensor is highly selective and shows response to low concentration. To improve the sensing response characteristics of ZT thin film, PANI is incorporated. Thin film based LPG sensor of ZnO-TiO2-PANI composite was fabricated by spin coating of ZnO-TiO2 nanoparticles doped with PANI over inter digital electrodes (IDEs). The thin film was characterized by using XRD, SEM, TEM, UV-vis, BET and FTIR. It was also tested for gas sensing properties of LPG/NO2 which are well known flammable and toxic gases. The measured response for ZnO-TiO2-PANI based sensor was 87 for 2000 ppm of LPG and 412 for 20 ppm of NO2 at room temperature towards other testing gases together with Acetone, IPA, NH3 and CO2.

Forced expiratory volume in 1-second and blood gas analysis in children during asthma attacks

Background Asthma is the most common chronic disease in the world, with a high incidence in children. Blood gas analysis and pulmonary function test using spirometry are recommended to evaluate the degree of asthma in children. Spirometry test is non-invasive and easier to implement compared to blood gas analysis.
 Objective To evaluate for a possible correlation between forced expiratory volume in 1 second (FEV1) measured by spirometry test and blood gas analysis (pO2 and pCO2 levels) in children during an asthma attack.
 Methods This cross-sectional study was done in children with asthma attacks who were admitted to Sanglah Hospital, Denpasar, Bali, between November 2016 and April 2017. Subjects underwent spirometry tests and blood gas analyses. Potential correlations between FEV1 and pO2 and pCO2 levels were analyzed by Spearman’s correlation test.
 Results A total of 50 subjects, consisting of children aged 6 to 12 years, were diagnosed with asthma attacks during the study period. Subjects’ mean FEV1 level was 43.6%, mean pCO2 was 38.36 mmHg, and mean pO2 was 121.92 mmHg. There were no significant correlations between FEV1 and pCO2 level (r=0.206; P=0.152) or FEV1 and pO2 (r=0.157; P=0.277) found in this study.
 Conclusion FEV1 does not correlate with pCO2 and pO2 level in children during asthma attacks.

A Method and Apparatus for Direct Enthalpy Rise Measurement for Gas Compression

Gas property prediction is necessary for proper design of compressors. Equations of state are utilized to predict the thermo-physical gas properties needed for such calculations. These are semi-empirical models that allow the calculation of thermodynamic properties such as density, enthalpy, and speed of sound of gas mixtures for known pressures and temperature. Currently, there is limited or no data publically available to verify the results of these equation of state calculations for the range of pressures, temperatures, and gas compositions relevant to many oil and gas applications. Especially for isentropic enthalpy head (i.e., the enthalpy rise along constant entropy lines), which is a critical parameter required to accurately design and performance test compressors, limited public domain data are available for equation of state validation. In this paper, a method and test apparatus is described to measure compression enthalpy rise directly. In this apparatus, a test gas is compressed using a fast acting piston inside an adiabatic autoclave. Test results are then corrected using calibration efficiencies from a known reference gas compression process at a similar Reynolds number. The paper describes the test apparatus, calibration, measurement methodology, and test results for one complex hydrocarbon gas composition at elevated temperatures and pressures. An uncertainty analysis of the new measurement method is also presented and results are compared to several equations of state. The results show that commonly used equations of state significantly underpredicted the compression enthalpy rise for the test gas case by more than 6%.

Gas Sealing Performance Analysis of Metal Rubber Seals

In this paper, the gas sealing properties of the metal rubber seals is analyzed. The gas leak rate formula for metal rubber seals is derived. The gas seal performance test of metal rubber seals is conducted and the relationship between gas leakage and temperature and pressure is obtained under different test temperatures and gas pressures. The results provide the basis for the optimization and improvement of sealing performance.

Unique Differences in Breath Test Gas Patterns in Inflammatory Bowel Disease (IBD) Compared to Non-IBD Patients: A Large-Scale Database Linkage Analysis

Introduction: Breath testing (BT) has gained interest for diagnosing small intestinal bacterial overgrowth (SIBO) in IBD patients with overlapping irritable bowel syndrome (IBS)-like symptoms. We aimed to characterize BT gas patterns in IBD patients compared to non-IBD patients and assess antibiotic response. Methods: A database of 14,847 consecutive lactulose BTs performed between November 2005 and October 2013 was developed from patients with IBS-like symptoms. Repeated BTs were excluded using probabilistic record linkage. BTs were classified into 5 categories: Normal: CH4 <10 parts per million (ppm) and H2 rise <20ppm within 90 min. H2predominant: CH4 <10ppm and H2 rise >20 ppm within 90 min, CH4 predominant: CH4 ≥10 ppm, Flatline: CH4 =0 ppm and H2≤3 ppm with variation ≤1 ppm within 120 min, Equivocal: H2 >20ppm at baseline. BT data was linked to our electronic health records to identify IBD patients and their disease course through manual chart review. Response to antibiotics was determined by reported improvement in symptoms. Poisson loglinear model was used assess differences in gas patterns between IBD and non-IBD patients. Results: After probabilistic linkage, we identified 455 IBD and 10,505 non-IBD patients with BT. Demographics and disease phenotypes are summarized in Table 1 and Table 2. SIBO was present in 58% (n=264) of IBD patients with IBS overlap. (Fig 1) Patients with Crohn's disease (CD) (effect size (ES) -1.48, [95% confidence interval (CI) -0.84- -2.13], p<0.001) and ulcerative colitis (UC) (ES -0.80, [95%CI -0.19- -1.14], p=0.01) were significantly less likely to produce excessive CH4 compared to non-IBD patients. When combined, IBD patients were more likely to be flatliner than non-IBD patients (ES 0.49, [95%CI 0.04-0.95], p=0.03). CH4predominant SIBO was significantly more prevalent in UC patients with constipation than other gas patterns (50%, p=0.001). In IBD patients with SIBO, 57% responded to antibiotics independent of disease activity, location, and behavior.679_A Figure 1. Cohort demographics of non-IBD patients compared to IBD patients.Conclusion: IBD patients with ongoing IBS-like symptoms have high prevalence of SIBO and demonstrate symptomatic improvement with antibiotics. Methanogenesis is suppressed in IBD patients. Flatline BT is more prevalent in IBD patients, suggesting excessive hydrogenotrophic bacteria. These findings suggest CH4 producing and hydrogenotrophic microorganisms as potential therapeutic targets. Future prospective studies are needed to validate these findings.679_B Figure 2. Disease phenotype of IBD patients.679_C Figure 3. Comparison of breath test patterns of CD, UC and non-IBD patients. Methanogenesis is significantly suppressed in CD and UC patients with IBS-like symptoms compared to non-IBD patients. There is no statistically significant difference between breath test patterns of CD and UC patients.

Long-term stability of oxygen surface exchange kinetics of Pr0.8Ca0.2FeO3-δ against SO2-poisoning

The long-term stability of the oxygen exchange kinetics of the Sr- and Co-free solid oxide fuel cell (SOFC) and solid oxide electrolyser cell (SOEC) air electrode material Pr0.8Ca0.2FeO3-δ (PCF82) is investigated by in-situ dc-conductivity relaxation measurements. The chemical oxygen surface exchange coefficient kchem is determined as a function of time at 700 °C under ideal (O2-Ar atmosphere) and accelerated ageing conditions (O2-Ar with 2 ppm SO2). In pure O2-Ar PCF82 shows fast oxygen surface exchange kinetics with kchem = 6 × 10−4 cm s−1 and excellent stability for 1000 h. Due to the addition of 2 ppm SO2 to the test gas only a moderate degradation occurs with kchem decreasing to 8 × 10−5 cm s−1 during further 1000 h. Post-test analyses by scanning (transmission) electron microscopy and X-ray photoelectron spectroscopy show S-rich secondary phases in the near-surface region of the SO2-poisoned sample. These inactive phases occur in an island-like arrangement of relatively large crystals, whereas significant amounts of the surface remain unaffected. This effect explains the high stability of the oxygen exchange kinetics of PCF82 against SO2-poisoning in comparison to state-of-the art materials like La0.6Sr0.4CoO3-δ (LSC64).

Experimental research on high energy initiation technology for detonation driver

A shock tunnel with gaseous detonation driver is fit for simulating test gas with high total temperature and pressure, since the sound speed of the driving gas is comparatively high. Decreasing the sound speed of the driving gas can lead to initial detonation difficulties and is therefore deficient in low total temperature and high total pressure gas simulations. In this study, a new high-energy detonation initiation method, the closed-type ignition tube, is proposed, in which initial detonation is achieved in high-concentration nitrogen-diluted hydrogen-oxygen mixed gas and a low-sound speed driving gas is successfully obtained. By experiment, the dominant factors of igniter tube initiation energy are defined, and the design principles of closed igniter tube are given. Through experiments and calculation, the influence mechanism of the new method on the flow process of shock tubes/tunnels is clarified, and the principle of using the new initiation tube is identified. Using this new method, low total temperature and high total pressure test gas could be obtained, which provides a feasible method for expanding the ground test capability of hypersonic flight conditions.

Ethanol and Hydrogen Gas-Sensing Properties of CuO–CuFe2O4 Nanostructured Thin Films

Nanocrystalline CuO-CuFe2O4 composite thin films were developed from CuFeO2 ceramic target using a radio frequency sputtering method followed by a thermal oxidation process. This fabrication process helps to develop porous sensing layers which are highly desirable for solid state resistive gas sensors. Their sensing properties towards ethanol and hydrogen gas in dry air were examined at the operating temperatures ranging from 250 deg C to 500 deg C. The electrical transients during adsorption and desorption of the test gases were fitted with the Langmuir single site gas adsorption model. A composite thin film with a total thickness of 25 nm showed highest response (79%) towards hydrogen (500 ppm) at the operating temperature of 400 deg C. The shortest response time (tres) was found to be ~60 and ~90 seconds for hydrogen and ethanol respectively. The dependence of the response of the sensor on gas concentration (10-500 ppm) was also studied.

Varying growth stress to study how H2O affect chromia scaling in high pO2 gas at 900 °C

Thin and thick specimens were isothermally oxidized. The use of different thick specimen allowed the change of the intrinsic defect structure in thermally grown chromia scales independently from the test gas. Oxidation kinetics and micro-structure of scales formed were followed. Oxide cross-sections were analysed to determine oxide thickness and grain width. Chromia scales formed on the various substrates grew at different rates and oxide microstructures differed in grain shape and size. The chromia growth kinetics was found to be depending on the thickness of the specimens used, the gas H2O content, and the Ni alloy content.

Ag-LaFeO3 nanoparticles using molecular imprinting technique for selective detection of xylene

Xylene is a hazardous volatile organic compound, however, the selective detection of ppm-level xylene using oxide semiconductor gas sensor remains a challenging issue. In this study, Ag-LaFeO3 was modified with molecular imprinting technique, in which methacrylic acid and hydroxyethyl methylacrylate are used as functional monomers, respectively. Based on XRD, EDS, XPS, SEM, TEM, BET nitrogen adsorption observations, the structure and morphology of the samples are characterized. The as-prepared molecularly imprinted nanoparticles with methacrylic acid as functional monomer exhibit high selectivity and response to xylene gas, and the response is dependent on the type and content of the functional monomer. To 5 ppm xylene, the optimal response is 36.2 at the operating temperature of 99 °C. In addition, low cross-responses to the other test gases were observed. The remarkable enhancement in the gas-sensing properties of the samples is attributed to their high specific surface area and molecular imprinting structure.

Numerical investigation of oxygen thermochemical nonequilibrium on high-enthalpy double-cone flows

Hypersonic thermochemical nonequilibrium flows over a double-cone configuration are numerically investigated. Simulations with oxygen as the test gas are performed using different coupling models of vibrational excitation and dissociation, including a conventional two-temperature model as the baseline and an improved model established on elementary kinetics and validated against existing shock tube experimental data. For the condition with the highest total enthalpy, the improved model predicts a larger separation region and greater peak heat flux with relative differences of 20.3% and 29.2%, respectively, compared with the baseline two-temperature model. The differences are attributed to inaccurate modeling of the vibration–dissociation coupling effects by the conventional two-temperature model, which overestimates the post-shock degree of dissociation and underestimates the post-shock temperature. The size of the separation bubble is therefore altered due to the change in its density. These findings may help to explain the large discrepancies found between numerical results and experimental data for high-enthalpy double-cone flows in hypersonic studies.

Comparison of two on-line tar-monitoring devices with off-line liquid sample tar-analysis operated on a test gas generation system applying ethene pyrolysis

Two on-line tar monitoring devices were operated in parallel on a test gas generation system. The test gas generator applied in this work, is an adaptation of a system introduced by VTT/Finland. Typical aromatic ‘tar’- species are produced by decomposing ethane in a nitrogen atmosphere at 900 °C. By adding steam and toluene to the nitrogen/ethene flow prior to the reactor, the resulting ‘tar’-spectrum can be modified.The analytical systems applied were the flame ionization detection based ‘FID online - Total Tar Analyzer 300’ from University of Stuttgart and Ratfisch Analysensysteme GmbH, and the tar monitoring system based on UV-fluorescence induced by LEDs developed at Technische Universität Berlin (TUB). The Liquid Quench (LQ) Sampling System, from Paul Scherrer Institute (PSI) was in operation for connecting an on-line micro-GC for continuous monitoring of the permanent gases. Liquid samples for results comparison were taken with the easy to handle ‘compact trapping system’ (CTS) and were analyzed according to standard methods.The results of this collaborative work proved the applicability of both measurement devices for tar monitoring. Both can follow changes in tar load of the gas immediately. There are differences in response to different ‘tar’-species distributions which are attributed to the two different basic underlying physical detection principles and the instrument configurations.Applying a simple thermo-chemical reaction system for test gas generation fills a gap between dosing individual tar species into a sample gas and the desired operation of on-line measurement tools at laboratory and industrial scale gasifiers.

Supersonic Combustion of a Scramjet Engine Using Hydrogen Fuel in Shock Tunnel

Experiments were carried out on a scaled model of scramjet engine with gaseous hydrogen as a fuel in a 1 m combustion-driven shock tunnel. The simulated enthalpy was , at a freestream Mach number of 6.8 with varying stagnation pressures (110–190 bar), dynamic pressures (72–130 kPa), and equivalence ratio (0.24–1.16). Detailed studies were carried out to tailor the shock tunnel. Experiments were carried out with air and as the test gases with hydrogen () injection to bring out the difference between reactive and nonreactive cases. Pressure measurement along the centerline of the engine and heat flux (through temperature measurements) inside the combustor was carried. The occurrence of supersonic combustion was ascertained through pressure measurements where no upstream influence was seen ahead of the strut injector and the same was corroborated by heat flux measurements. The pressure rise due to supersonic combustion downstream of the fuel injection was nearly three times as compared with nonreactive case. For the current case, when the combustor inlet pressure () exceeds 1 bar, a sharp rise in the pressure signature was observed downstream of fuel injection, whereas no such marked trace was seen when is below 1 bar.

Electro-Plasmonic Gas Sensing Based on Reduced Graphene Oxide/Ag Nanoparticle Heterostructure

Graphene has been entitled as a promising candidate for gas sensing applications, however suffers from low selectivity, as a limit for commercialization. We propose a gas sensor based on reduced graphene oxide (rGO)/Ag nanoparticles (Ag NPs), which can overcome this limitation by benefiting from both localized surface plasmon resonance of Ag NPs, and chemisorption capability of gas molecules on rGO sheets. These simultaneous gas detection mechanisms help to reveal both physical and chemical aspects of gas molecules. We show that gas-induced plasmonic shift is enhanced in rGO/Ag NPs (Δλ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LSPR</sub> ≈ 5 nm), comparing with Ag NPs (Δλ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LSPR</sub> ≈ 1.4 nm) versus 250 ppm of nitrogen concentration. Furthermore, electrical measurements prove that gas-induced variation in the conductivity response is higher in rGO/Ag NPs (ΔG/G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ≈ 3.6%), in comparison with Ag NPs (ΔG/G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ≈ 1.5%). Finally, we have utilized electro-plasmonic measurement in the proposed structure, leading to about 47% enhancement in the measured sensitivity, when λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">incident</sub> = 440 nm is illuminated during nitrogen exposure. The proposed structure allows both electrical sensing and electro-plasmonic sensing by means of a simple measurement configuration, revealing both chemisorption and physisorption finger prints of the test gas.

An Electrical Measuring System Integrated with a Linear-arrayed Probing Device and an Optical Registration System for Gas Sensors

The electrical measurement is necessary for quality assurance and classification for all chips during manufacturing processes. Linear-arrayed probing device with capability of simultaneously measuring 10 chips of gas sensors is developed considering the compromise of performance, cost and registration for wafer-based electrical measurement system. An optical registration system, consists of 2 optical imaging devices, is designed and integrated with a linear-arrayed probing device and motion stage platform for probes alignment and wafer positioning. A small gas chamber is required to provide homogenous concentration of testing gas at probing area above wafer. Proposed measuring system has the features that homogeneous concentration of gas in chamber can be achieved quickly in 1 minute, and probing efficiency is good that probing a 6”-wafer with chip size of 1x1 mm (about 17600 chip/wafer) can be finished in 30 minutes. Detail design of electrical measuring system and implementation of all of devices, subsystems, gas chambers, a chuck table with heater and the motion stage platform are completed. And system I&amp;T is being conducted at the moment.

Moderne Lecksucher mit Vakuumtechnik

SummaryModern leak detectors in vacuum technologyIn many areas of industrial manufacturing, quantitative leak tightness measurements are required in order to analyze product quality. This article examines three approaches to vacuum leak testing, which utilize different measuring principles and completely different working pressures. The processes are divided into “non‐gas selective”, “single gas selective” and “double gas selective”.The pressure rise method does not work gas‐selectively. In so‐called foil test chambers the pressure rise measurement is used in optimized design and is particularly suitable for leak testing in the food industry.The classic test gas vacuum leak detection is a gas‐selective method. The test gas is selectively detected and the chamber is pumped independently of the type of gas. Major innovations in current device solutions are the extension of the measuring range and improved convenience in use.To achieve a detection limit of less than 10−12 mbar·l/s, a double gas selective operation is used, residual gases from the test chamber are selectively pumped, additionally, the test gas detection is selective.

Corrosion Behavior of Austenitic Stainless Steels in Oxidizing and Reducing Gases Relevant to Oxyfuel Power Plants

The oxidation behavior of three austenitic stainless steels was studied at 650°C up to 1000 h. The selected materials (S304HCu, TP347HFG, and Sanicro 25) were exposed to an atmosphere simulating oxyfuel combustion, and the results compared with the behavior in a test gas with addition of CO, thus simulating locally occurring reducing operating conditions. For the 18% Cr steels (S304HCu and TP347HFG), lower corrosion rates were generally found in reducing than oxidizing gas. As might be expected based on its substantially higher Cr content, Sanicro 25 showed lower oxidation rates than the two 18% Cr steels in the oxyfuel gas. However, the opposite was the case in the reducing gas. The higher Ni content resulted in formation of a mixed sulfide/oxide outer layer, which adversely affected the formation of a protective chromia scale, resulting in a higher corrosion rate than for the 18% Cr steels.

Flow control devices in SAGD completion design: Enhanced heavy oil/ bitumen recovery through improved thermal efficiency

One method of thermal recovery, steam-assisted gravity drainage (SAGD), has proven a commercial success in heavy oil/bitumen production. However, geological and reservoir heterogeneity often complicate this task resulting in uneven production rates, higher operational costs, and stranded heavy oil/bitumen. This work theorizes that SAGD recovery is improved using flow control devices (FCDs) to force conformance in SAGD laterals. To test this theory, a novel protocol and test flow loop was developed to measure pressure drop across an autonomous hybrid FCD while flowing multiphase mixtures containing steam. This laboratory data was used to qualify existing pressure drop correlations and determine if nitrogen gas, a common test gas to describe FCD pressure drop response, creates suitable data for modeling steam systems. Finally, the flow loop was used to induce a steam “flash”, a transition of water at saturation temperature to vapor due to a suddenly decreased pressure environment, within the FCD to determine if steam flashing changes expected pressure drops. Using linear regression, a correlation of expected pressure drop across the autonomous hybrid FCD for mixtures of heavy oil/bitumen, water, and steam was generated. Existing correlations proved inadequate for mixtures containing steam, consistently underestimating pressure drop across the FCD. However, the empirical correlation of this research highly matched laboratory data with an R-squared value of 0.94. A secondary linear model captured modifications in FCD behavior due to steam flashing. This second model also exhibited a strong goodness-of-fit with an R-squared value of 0.96. For both empirical correlations, p-values less than 0.05 were easily obtained, inferring the statistical significance of each correlation. Correlations generated in this research were added to the REVEAL™ reservoir simulation package to accurately forecast FCD impact on SAGD well pair performance. Simulating four-year periods of production for SAGD well pairs in Albertan reservoirs consistently show that FCD usage simultaneous improved bitumen recovery by 50% or more and decreased cumulative steam/oil ratios (cSOR) by 12 m3/m3, largely through improved steam chamber conformance and by eliminating steam breakthrough events in the producer. Net Present Value (NPV) analysis of improvements with the additional cost of FCD completion tools unfailingly showed a strong economic argument for the use of FCDs to improve thermal efficiency.