Variation Of Gas Concentration Research Articles

Mixed-potential gas sensor with PtAu-8YSZ sensing electrode: Electric potential difference measurements at isothermal and thermo-cyclic operation

A commercial mixed-potential gas sensor comprised of a pair of PtAu-YSZ sensing electrodes and a Pt-reference electrode was investigated at isothermal and thermo-cyclic operation under exposure to H2, CO and C3H6 balanced with synthetic air, separately. The sensor showed logarithmic response behavior to the variation of model gas concentration at isothermal operation and strong dependence on temperature. For the first time temperature dependent dynamic response behavior of the sensor was studied by cyclic triangular variation of the operating temperature at a period of 300s in a temperature range between 410°C and 670°C. The electric potential difference (delta V) measurements at thermo-cyclic condition revealed clearly distinct delta V-temperature profiles (ΔVTPs) depending on gas species and remarkable differences between the thermo-cyclic data and the corresponding delta V-values measured at isothermal conditions. Moreover, it was found out that the stability and reversibility of ΔVTPs depends on sensor operating temperature and is a specific characteristic of the individual gas component as well.

Predicting Long Term Storage of CO2 in Abandoned Jharia Coalfield-A Numerical Approach

The increasing anthropogenic CO2 emissions have challenged the world to find ways to reduce the atmospheric CO2 concentration. Whatever may be the consequences, it nearly impossible to move the energy infrastructure away from fossil fuel in the near future, and the only other way left out is to curb the CO2 concentration in atmosphere through sequestration and storage in geological media. This paper studies the sequestration of the CO2 in coal bearing sandstone typical of Jharia Coal field (mostly produce bituminous coal) and presents the effect of the porosity and pore orientation on the rate and extent of the CO2 that could be stored in the sandstone. Sandstone with higher porosities was found to be more efficient in terms of the rate and extent of sequestration. With Finite Element Method, different parameters like gas concentration, gradient and porosity variation with distance and time have been analyzed. The concentration of gas at the point of injection is calculated to be 1780kg/m 3 after 120 days. The concentration of CO2 and its gradient decreases as the porosity increases and vice versa for gas flux. The concentration has been measured around 100Kg/m 4 for all different porosity. KeywordsCO2 Sequestration; Sandstone; FEM; Porosity

Performance of a Finned Turbine Rim Seal

In gas turbines, rim seals are fitted at the periphery of the wheel-space between the turbine disk and its adjacent casing; their purpose is to reduce the ingress of hot mainstream gases. A superposed sealant flow, bled from the compressor, is used to purge the wheel-space or at least dilute the ingress to an acceptable level. The ingress is caused by the circumferential variation of pressure in the turbine annulus radially outward of the seal. Engine designers often use double-rim seals where the variation in pressure is attenuated in the outer wheel-space between the two seals. This paper describes experimental results from a research facility that models an axial turbine stage with engine-representative rim seals. The radial variation of CO2 gas concentration, swirl, and pressure, in both the inner and outer wheel-space, are presented over a range of purge flow rates. The data are used to assess the performance of two seals: a datum double-rim seal and a derivative with a series of radial fins. The concept behind the finned seal is that the radial fins increase the swirl in the outer wheel-space; measurements of swirl show the captive fluid between the fins rotate with near solid body rotation. The improved attenuation of the pressure asymmetry, which governs the ingress, results in an improved performance of the inner geometry of the seal. The fins also increased the pressure in the outer wheel-space and reduced the ingress though the outer geometry of the seal.

Filtration combustion of a porous structure in a multicomponent gas environment

A mathematical model for describing the quasi-isobaric filtration combustion of porous materials with the formation of condensed reaction products in a multicomponent gas is developed. Two-stage combustion waves (control modes) at the counter filtration of gas mixture are examined. The effect of inert gas component on the structure of a two-stage filtration combustion wave is studied, and the critical conditions of the changeover between filtration combustion modes caused by inert gas concentration variation are determined. It is demonstrated the characteristics of the two-stage combustion front propagating in the control mode in a multicomponent gas flow depends on the porosity of the heterogeneous system.

Baseline variability in onshore near surface gases and implications for monitoring at CO2 storage sites

The measurement of gas concentrations and fluxes in the soil and atmosphere is a powerful tool for monitoring geological carbon capture and storage (CCS) sites because the analyses are made directly in the biosphere in which we live. These methods can be used to both find and accurately quantifying leaks, and are visible and tangible data for public and ecosystem safety. To be most reliable and accurate, however, the measurements must be interpreted in the context of natural variations in gas concentration and flux. Such baseline data vary both spatially and temporally due to natural processes, and a clear understanding of their values and distributions is critical for interpreting near-surface gas monitoring techniques. The best example is CO2 itself, as the production of this gas via soil respiration can create a wide range of concentrations and fluxes that must be separated from, and not confused with, CO2 that may leak towards the surface from a storage reservoir. The present article summarizes baseline studies performed by the authors at various sites having different climates and geological settings from both Europe and North America, with focus given to the range of values that can result from near surface processes and how different techniques or data processing approaches can be used to help distinguish a leakage signal from an anomalous, shallow biogenic signal.

Transport properties in AlInSb/InAsSb heterostructures

Based on theoretical studies of transport properties in InAsSb-based quantum well heterostructures, we propose a material design for InAsSb quantum well with AlInSb barrier. Variation of electron mobility and two-dimensional electron gas concentration in AlyIn1−ySb/InAs1−xSbx heterostructures over the compositional range of which InAsSb is fully strained to AlInSb are investigated, where impact from dislocation scattering could be minimized. In comparison with InAs and InSb based quantum well heterostructures, InAsSb is advantageous in achieving the highest electron mobility despite of alloy disorder scattering. The maximum mobility of 37 000 cm2/V s is attainable in 15 nm InAs0.2Sb0.8 quantum well with Al0.24In0.76Sb barrier and there is great potential for further improvement. Our InAsSb based quantum well heterostructure is proved to be a robust structure for high-speed applications.

Studies on Respiration Rate Model of Mung Bean Sprout in Modified Atmosphere Packaging

This study took mung bean sprout as test materials to measure the variation of gas concentration in the film over time. This study measured the permeability coefficient of the selected LDPE film under 8°C,13°C,18°C,23°C and 28°C and calculated the respiratory rate of mung bean sprout under temperature ranges from 8°C to 28°C by the method of Osmosis system using C language. The chemical kinetics model equation was fitted to the respiration rate of bean sprouts. Experimental results: 1. Permeability coefficient of film increased with the temperature, the relationship between the permeability coefficient of the film and the temperature fitted with the Arrhenius equation. 2. With the temperature increasing, the respiratory rate of mung bean sprouts increased. By fitting chemical kinetics equation of model to the respiration rate, the results showed that the variation of respiration rate conformed to the chemical kinetics equations. The relationship between temperature and the respiration rate constantkof the chemical kinetics equations were found following of Arrhenius equation.

Shockwave tensile phase transmission depends on the gas concentration of the coupling medium

Previous research shows that a shockwave’s tensile phase can be strongly attenuated as a function of gas concentration in the coupling medium. Here, we seek to elucidate the relationship between tensile attenuation and gas concentration via pressure measurements at the focus and highspeed imaging. By performing in vitro experiments with water of varying gas concentrations (2.05 mg/L, 4.30 mg/L, and 6.50 mg/L), the negative impulsive pressure is correlated to the density of the bubble cloud that occurs in the beampath. It is found that for gas contents below 4 mg/L the bubble cloud remains sparse and the shockwave’s tensile phase is successfully transmitted with no loss in impulsive pressure. For gas contents 4 mg/L and above the bubble cloud becomes highly dense and prevents transmission with up to a 75% loss in impulsive pressure. Corresponding stone comminution experiments show that the treatment efficiency sharply decreases with increasing gas concentration. These results underlie the importance of degassing the water used in the coupling medium before treatment.

Phosphine Induced Anode Performance Degradation in a Planer SOFC: A Numerical Study

A mathematical model which was validated using button cells is used to predict the phosphine induced performance degradation in relatively large planar cells operating on hydrogen fuel. The empirical model parameters are calibrated using button cell experiments as guide. These parameters are then used to perform simulations to predict fuel contaminant performance degradation of planar cells. The results from the three dimensional model show that the contaminant coverage of Nickel and fuel distribution inside the anode is highly non-uniform. These non-uniform distributions are caused by the geometrical alignment of gas channels and current collectors, as well as the variation of gas concentration along the flow direction. The non uniform deactivation of anode gave raise to altering of current distribution inside the planar cell such that the cell can still produce current even when some regions of the anode are partially inactive. This is in stark contrast with what is observed in button cells where all the distributions are essentially one-dimensional. It is thus observed that the life time for planar cells could be much longer than that for similar button cells.

Chlorine and hydrogen cyanide gas interactions with human skin: In vitro studies to inform skin permeation and decontamination in HAZMAT incidents

Accidental or intentional toxic gas releases may result in significant public health and psychological consequences. Management of exposed individuals during HAZMAT incidents should be risk-based and supported by a suitable scientific evidence base. There appear to be large evidence gaps in relation to dermal absorption of gases, as well as management advice for potentially exposed individuals. Chlorine and hydrogen cyanide are two common HAZMAT gases and this paper addresses the need for experimental data tailored to HAZMAT scenarios and first responders. In addition to time variations of gas concentration, the modifying effects of clothing, temperature, and oil-based sunscreen on epidermal absorption and penetration are assessed. Results for chlorine show little penetration up to 500ppm but with small enhancing effects due to heavy cotton and oil-based sunscreen. Hydrogen cyanide up to 800ppm shows minor penetration consistent with previous studies, with little variability in the presence of sunscreen and clothing. Practical guidelines to support the decision-making of emergency responders with regard to personal decontamination have been derived.

Co3O4—A systematic investigation of catalytic and gas sensing performance under variation of temperature, humidity, test gas and test gas concentration

A “new” gas sensing material; Co3O4, which is mainly known as a good catalyst for CO combustion, was investigated by means of resistance and catalytic conversion measurements. A systematic screen of sensors with sensitive layers of undoped, 0.2wt% Pd- and Pt-doped Co3O4 was done by variation in temperature, humidity, test gas, and test gas concentration. It was found that all three kinds of materials show best response to EtOH (sensor signals up to 28,000 @ 100°C, 0% r.h., 90ppm), good response to CO (sensor signals up to 100 @ 100°C, 0% r.h., 50ppm), but only a marginal response to CH4 exposure, in particular at 50% r.h. The occurrence of maxima in sensor signals at 50% r.h. indicates a change in the surface reaction mechanism for both EtOH (175–200°C) and CO exposure (125–150°C). The 0.2wt% Pt-doped sensors display superior gas sensing properties concerning recovery times and sensor signal height as well as a higher overall catalytic conversion. Additionally, at 0% r.h. and under exposure to CO a comparison with the benchmark material SnO2 @ 300°C reveals even higher sensor signals for Co3O4 @ 100°C.

Relationships Between Radon Anomalies and Seismic Activities In Tuzla Fault Zone In Western Turkey

Seismic activities around the world requires one to investigate and develop new methods for the prediction of earthquakes. The seismic studies provide evidence which indicate that significant variations of radon concentration may occur in association with major geophysical events. In these studies, some predictions have been done using many methods and techniques. One of these methods is to observe variations of radon gas concentration in soil and groundwaters. The Aegean region has allway suffers from several tectonic activities. Izmir and its surrounding located in this region have been frequently effected by earthquakes through historical and antique periods. In this study, possible relationships has been investigated between seismic data and the radiation of radon concentration as a precursor for earthquakes in Doganbey fault zone that has high risk level for Izmir. In this fault zone, radon concentrations in waters and soils have been measured using collector method and nuclear track detectors, respectively. Data given by Bogazici University Kandilli Observatory and Earthquake research Institute was considered in order to correlate with experimental results. The annual radon concentrations measured using collector method in four stations of thermal waters during one year varied from 0.28 Bq L -1 to 11.01 Bq L -1 . The radon concentrations found using nuclear track detectors (LR115) in soils of thermal water fields varied from 50 track cm -2 week -1 to 750 track cm -2 week -1 . Comparing the radon data obtained using both methods with earthquake magnitudes, it could be said that there is a positive correlation between radon emanation rate and seismic activities in the area under investigation.

Prediction of Mine Gas Emission Based on Time Series Analysis

Because the variation of mine gas concentration is influenced by various factors, so it’s impossible for traditional prediction methods of mine gas emission to include all the factors. To solve the problem, the paper proposed a prediction method of mine gas emission based on AR model of time series analysis. The experiment results indicated that the method can predict mine gas emission accurately.

Current Excitation Method for $\Delta{R}$ Measurement in Piezo-Resistive Sensors With a 0.3-ppm Resolution

This paper presents a new highly sensitive (10 μV/ppm) bidirectional current excitation method for piezo-resistive sensor measurements, through excitation of two half bridges for ΔR measurement. The proposed circuit is insensitive to thermoelectric and stray noise effects since it measures the peak-to-peak value of the generated voltage. Measurement results using resistors show that variations as low as 0.3 ppm are measurable from 15°C to 80°C with resistors. As an experimental application, 40 parts per billion variation in gas concentration using piezo-resistive SU-8 microcantilevers is measured by the proposed circuit at room temperature.

Research on Working Face of Residual Coal Self-Ignition Characteristics and Early Warning Technology

Development of air leakage in goaf and residual coal self-ignition Characteristics Study on the spontaneous combustion of residual coal in goaf in the early prediction, prevention and control management has very important significance. Based on the mining coal working surface pressure energy distribution and Sign gas detection of Nanzhuang coal mine working face within the airtight air leakage condition and the O2, CO, CO2, C2H6, C2H4, C3H8 and other Sign gas concentration variation, identified 4601, 8808 lane closed walls within Coal body broken belt of spontaneous combustion danger area and its morphology. According to the spontaneous combustion of residual coal in goaf features from strengthening ventilation management, strengthening the gas and temperature detection, perfusion of three-phase foam developed a comprehensive system for the prevention and control of coal spontaneous combustion

Methane emission from naturally ventilated livestock buildings can be determined from gas concentration measurements

Determination of emission of contaminant gases as ammonia, methane, or laughing gas from natural ventilated livestock buildings with large opening is a challenge due to the large variations in gas concentration and air velocity in the openings. The close relation between calculated animal heat production and the carbon dioxide production from the animals have in several cases been utilized for estimation of the ventilation air exchange rate for the estimation of ammonia and greenhouse gas emissions. Using this method, the problem of the complicated air velocity and concentration distribution in the openings is avoided; however, there are still some important issues remained unanswered: (1) the precision of the estimations, (2) the requirement for the length of measuring periods, and (3) the required measuring point number and location. The purpose of this work was to investigate how estimated average gas emission and the precision of the estimation are influenced by different calculation procedures, measuring period length, measure point locations, measure point numbers, and criteria for excluding measuring data. The analyses were based on existing data from a 6-day measuring period in a naturally ventilated, 150 milking cow building. The results showed that the methane emission can be determined with much higher precision than ammonia or laughing gas emissions, and, for methane, relatively precise estimations can be based on measure periods as short as 3 h. This result makes it feasible to investigate the influence of feed composition on methane emission in a relative large number of operating cattle buildings and consequently it can support a development towards reduced greenhouse gas emission from cattle production.

The last deglaciation: timing the bipolar seesaw

Abstract. Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

Performance improvement for chemical absorption of CO2 by global field synergy optimization

Chemical absorption of CO2 is deemed as an effectively controllable way to accomplish large reduction of greenhouse gas emission. A two dimensional (2-D) model for two-phase flows is established for chemical absorption of CO2 in the packed column. A good agreement has been reached between the simulated temperature and fluid flow profiles and experimental results. The field synergy equations are deduced to optimize the fluid flow, mass transfer, heat transfer and chemical reaction by an established Lagrange function. The synergy angle is an index to express the synergy degree among the physical phenomena. The global field synergy optimized velocity field, temperature distribution and gas concentration variation trend are obtained, contributing to improvement of 9% CO2 removal efficiency. Meanwhile, the entropy generation rate was well applied to quantify the overall improvement from the perspective of exergy. The results indicated that the entropy generation rate induced by mass transfer and reaction composes the most part of the irreversibility. The exergy loss is reduced by 12.8% after global field synergy optimization mainly for the two resistances reduction. The results showed that the field synergy optimization could be an intensification method for CO2 capture, whose improvement effect could be assessed by entropy generation analysis.

Design and Fabrication of MOSFET Type Hydrogen Gas Sensor Using MEMS Process

In this study, MOSFET type micro hydrogen gas sensors with platinum catalytic metal gates were designed, fabricated, and their electrical characteristics were analyzed. The devised MOSFET Hydrogen Sensors, called MHS-1 and -2, were designed with a platinum gate for hydrogen gas adsorption, and an additional sensing part for higher gas sensitivity and with a micro heater for operation temperature control. In the electrical characterization of the fabricated Pt-gate MOSFET (MHS-1), the saturated drain current was 3.07 mA at 3.0 V of gate voltage, which value in calculation was most similar to measurement data. The amount of threshold voltage shift and saturated drain current increase to variation of hydrogen gas concentration were calculated and the hydrogen gas sensing properties were anticipated and analyzed. (Received October 14, 2010)

Formation of Single-Crystal Spherical Particle Architectures by Plasma-Induced Low-Temperature Coalescence of Silicon Nanocrystals Synthesized by Laser Ablation in Water

We report that the synthesis of silicon nanocrystals (SiNCs) by laser ablation in water produces unique surface characteristics and, in particular, hydroxyl-terminated surfaces, which can induce coalescence and formation of micrometer-sized single-crystal Si spherical particles under a low-temperature (∼550 °C) plasma process. We demonstrate that the spherical particles can be self-organized into aggregates that extend with varying gas concentrations. At the same time, SiNCs that were sufficiently apart not to coalesce have shown peculiar photoluminescence properties, which suggest an increased tunneling probability from self-trapped excitonic surface states.