Test Gas Composition Research Articles

Nd3+ added Mg– Cd ferrite material study the thick film gas sensing properties

The general formula Mg1-x Cd x Fe2O4 (x = 0.0,0.1,0.3, 0.5, 0.7) was used to prepare 5 wt % Nd3+ nano crystallite ferrite samples using the oxalate co-precipitation method. XRD, SEM, and FT-IR were used to characterize the samples. The cubic spinel structure was confirmed by XRD, which revealed an orthoferrite (NdFeO3) secondary phase. In the range of 350–800 cm−1, Mg–Cd ferrites show two distinct bands of absorption. In Mg–Cd ferrites, the surface morphology SEM study shows that grain size increases with Cd2+ concentration and decreases with Nd3+ presence. The response of Mg–Cd ferrites with Nd3+ is higher than that of Mg–Cd ferrites without Nd3+. With an increase in Cd2+ concentration, the response and recovery times of Nd3+ added Mg–Cd ferrites are speed up. Cd ferrite sensors combined with Nd3+ have faster response and recovery times than other samples. These differences are dependent on the test gas's composition as well as the material's grain size.

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.

Scaling Kinetics and Scale Microstructure of Chromia Scales Formed on Ni-25%Cr Model Alloy during Oxidation in H2o-Containing High and Low pO2 Test Gas at 1000°C

The isothermal oxidation behaviour of a Ni25Cr model alloy was studied employing the JuSie-methodology, i.e. using specimens of different thickness for each specific test gas composition at 1000°C in dry and wet N2-1%O2 as well as in Ar-7%H2O. The oxidation mechanisms were evaluated using thermo-gravimetry and SEM/EBSD analyses of oxide scale cross sections. The ion beam polished oxide cross-sections were analysed in terms of oxide grain growth and nucleation rates of new oxide at the oxide-gas interface. The findings can be explained by considering the effect of H-defects and in-scale stress state on point defect concentrations in the chromium sub-lattice.

Experimental and Modeling Study of Methyl trans-3-Hexenoate Autoignition

This work presents the results of an experimental and computational study of methyl trans-3-hexenoate autoignition. Experimental autoignition studies were conducted using the University of Michigan rapid compression facility. Pressure time histories were used to determine ignition delay times as a function of test gas composition and experimental conditions. The fuel/oxygen equivalence ratio and dilution level were ϕ = 0.3 and inert/O2 = 3.76 (mole basis). End of compression conditions targeted an average pressure of 10.5 atm and temperatures ranging from 884 to 1085 K. A correlation in Arrhenius form was developed by regression analysis of the experimental data, where the ignition delay time is τign (ms) = 1.4 × 10–6 exp[30 100/(R(cal mol–1 K–1)T)] with a R2 value of 0.99. Gas-sampling experiments were also conducted to measure stable intermediates formed during autoignition. A detailed reaction mechanism was developed and model predictions were compared to the experimental data. While ignition delay ti...

Composition of the test gas in the test section of a high-enthalpy wind tunnel

A method and system for sampling a chemically active gas from a hypersonic flow with high stagnation parameters are developed. Results of an experimental study of the test gas composition at the nozzle exit of the IT-302M hotshot wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences are presented. As the air in the settling chamber is heated up to 3000 K by an electric arc only, the volume fraction of oxygen in the test section decreases from 21 to 18%, which may require supplying an additional amount of oxygen into the settling chamber as a compensation for its reduction in some tests of gas-dynamic models with combustion. In the case with hydrogen used together with the electric arc for increasing the energy of the facility, the degree of completeness of the reaction of hydrogen combustion in air in the settling chamber is determined. For the minimum possible supply of electric energy for the IT-302M wind tunnel (based on conditions of arc combustion stability), the hydrogen combustion efficiency is ≈0.9 for extremely lean hydrogen-air mixtures with the hydrogen concentration much lower than the flammability limits under standard conditions. The combustion efficiency rapidly approaches unity as the hydrogen concentration in the settling chamber and the electric energy supply are increased.

Detonation interaction with an interface

Detonation interaction with an interface was investigated, where the interface separated a combustible from an oxidizing or inert mixture. The ethylene-oxygen combustible mixture had a fuel-rich composition to promote secondary combustion with the oxidizer in the turbulent mixing zone (TMZ) that resulted from the interaction. Sharp interfaces were created by using a nitro-cellulose membrane to separate the two mixtures. The membrane was mounted on a wood frame and inserted in the experimental test section at a 45° angle to the bulk flow direction. The membrane was destroyed by the detonation wave. The interaction resulted in a transmitted and reflected wave at a node point similar to regular shock refraction. A detonation refraction analysis was carried out to compare with the measured shock angles. It was observed that the measured angle is consistently lower than the predicted value. An uncertainty analysis revealed possible explanations for this systematic variation pointing to factors such as the incident wave curvature and the role of the nitro-cellulose diaphragm. Analysis of the TMZ and Mach stem formed from the reflection of the transmitted shock wave off the solid boundary were carried out and found to justify the size and strength of these features as a function of the test gas composition. The role of secondary combustion in the TMZ was also investigated and found to have a small influence on the wave structure.

Mass spectrometer measurements of test gas composition in a shock tunnel

Shock tunnels afford a means of generating hypersonic flow at high stagnation enthalpies, but they have the disadvantage that thermochemical effects make the composition of the test flow different to that of ambient air. The composition can be predicted by numerical calculations of the nozzle flow expansion, using simplified thermochemical models and, in the absence of experimental measurements, it has been necessary to accept the results given by these calculations. This note reports measurements of test gas composition, at stagnation enthalpies up to 12.5 MJ.kg(exp -1), taken with a time-of-flight mass spectrometer. Limited results have been obtained in previous measurements. These were taken at higher stagnation enthalpies, and used a quadruple mass spectrometer. The time-of-flight method was preferred here because it enabled a number of complete mass spectra to be obtained in each test, and because it gives good mass resolution over the range of interest with air (up to 50 a.m.a.).

A demountable, gas-balanced autoclave with chemically inert reaction vessel

A high-pressure autoclave with several novel design features is described. Test specimens are held in an inner vessel made of a chemically inert material, e.g. silica, thus eliminating the possibility of spurious side reactions that could alter the test-gas composition. This vessel is surrounded by a furnace and an outer steel pressure vessel. A semiautomatic gas-balancing system is used to prevent excessive differential pressures which could rupture the inner vessel. The autoclave has been designed to operate at a pressure of 44*105 Pa (650 p.s.i.) and temperature of 1273K with a uniform temperature zone of about 300 mm in a reaction vessel diameter of 100 mm. Under these conditions the outer autoclave walls reach a temperature of about 450K. The autoclave is completely demountable. The specimen holder is of modular form and can accommodate several hundred small test coupons or, alternatively, a few large ones. Details of heater design, thermal insulation and control systems are given. The performance and long-term temperature stability are discussed.

Frequency Response of Condenser Microphones in Gases other than Air

Performance of scale model fan noise experiments in a unique free-field heavy gas test facility required that a method be developed for determining microphone response in the high molecular weight gas. Using an electrostatic actuator, calibration experiments in air, argon, helium, and freon-12 were conducted at several gas pressures. Results indicated that microphone pressure response is essentially independent of the test gas composition. At diaphragm resonance frequency, where the greatest sensitivity variation was observed, changes due to gas composition were only about 1 dB. Apparently diaphragm damping is governed by pressure rather than gas density. This result obviates the need for microphone calibration in gases other than air.