Gas Concentration Distribution Research Articles

The detection of carbon dioxide leaks using quasi-tomographic laser absorption spectroscopy measurements in variable wind.

Laser absorption spectroscopy (LAS) has been used over the last several decades for the measurement of trace gasses in the atmosphere. For over a decade, LAS measurements from multiple sources and tens of retroreflectors have been combined with sparse-sample tomography methods to estimate the 2-D distribution of trace gas concentrations and underlying fluxes from point-like sources. In this work, we consider the ability of such a system to detect and estimate the position and rate of a single point leak which may arise as a failure mode for carbon dioxide storage. The leak is assumed to be at a constant rate giving rise to a plume with a concentration and distribution that depend on the wind velocity. We demonstrate the ability of our approach to detect a leak using numerical simulation and also present a preliminary measurement.

An integrated emergency response model for toxic gas release accidents based on cellular automata

An integrated emergency response model based on cellular automata (CA) is proposed for the toxic gas release accidents that happen in the energy and chemical industry. This integrated emergency response model consists of three sub-models: a toxic gas dispersion model, a dynamic evaluation model for accident consequences, and an evacuation route selection model. When a toxic gas release accident happens, the dispersion model predicts the distribution of toxic gas concentration, the evaluation model estimates the consequences in terms of probability of death, expected fatalities and impact scope caused by the accident, and the route selection model provides the safest evacuation route for evacuees. The three sub-models run simultaneously and present real-time results. The proposed model is applied to an ammonia gas release accident in an energy and chemical enterprise, and the corresponding model results are discussed. The efficiency of emergency response for toxic gas release accidents can be further improved through the proposed integrated emergency response model based on CA.

Dynamic characteristics of a solid oxide fuel cell with direct internal reforming of methane

An analysis of a solid oxide fuel cell (SOFC) working with direct internal reforming of methane when subjected to unsteady conditions is presented in this paper. A cell of planar type with the anode-supported structure and the co-flow configuration is investigated. Owing to the reforming and the water–gas shift reactions, it has been known that the steady operation of a cell working with natural gas is different from that with hydrogen. Moreover, since these chemical reactions are strongly temperature-dependent, the former is expected to become much more complex than the latter under unsteady states. It is necessary in the viewpoints of degradation and performance efficiency to understand the evolution of the thermal gradient/stress, the fuel concentration, etc. when the cell is subjected to changes such as load demand. In this work, a three-dimensional numerical model is employed and step changes of the output voltage are introduced to the cell. Results for the temporal profiles of the temperature, the current density, the activation overpotential and the gas concentration distributions in the cell are presented and discussed. It is found that the overshoot in the activation does not appear throughout the cell, but only in the exit region when the voltage jumps from 0.7V to 0.6V.

Research on Path Planning Method of Coal Mine Robot to Avoid Obstacle in Gas Distribution Area

As the explosion-proof safety level of a coal mine robot has not yet reached the level of intrinsic safety “ia” and it cannot work in a dangerous gas distribution area, therefore, path planning methods for coal mine robot to avoid the dangerous area of gas are necessary. In this paper, to avoid a secondary explosion when the coal mine robot passes through gas hazard zones, a path planning method is proposed with consideration of gas concentration distributions. First, with consideration of gas distribution area and obstacles, MAKLINK method is adopted to describe the working environment network diagram of the coal mine robot. Second, the initial working paths for the coal mine robot are obtained based on Dijkstra algorithm, and then the global optimal working path for the coal mine robot is obtained based on ant colony algorithm. Lastly, experiments are conducted in a roadway after an accident, and results by different path planning methods are compared, which verified the effectiveness of the proposed path planning method.

Effect of 220Rn gas concentration distribution on its transmission from a delay chamber: evolving a CFD-based uniformity index.

(220)Rn mitigation can be achieved by delay chamber technique, which relies on the advantage of its short half-life. However, flow rate as well as inlet-outlet position for the delay chamber can have a significant impact on (220)Rn concentration distribution patterns and hence transmission factor. In the present study, computational fluid dynamics simulations to estimate the concentration distribution has been carried out in a chamber of 0.5 m(3) for the combination of six different inlet-outlet positions and five different flow rates. Subsequently, the transmission factor (TF) for the chamber was evaluated and found to be highly dependent on the flow rate and inlet-outlet positions. For ease of scale up, the dependency of TF on the flow rate and the inlet-outlet positions is best summarised by relative transmission factor (RTF), which is the ratio of the TFs for the case of inlet and outlet on different faces to that on the same face.

Numerical modeling of two‐phase bubbly flow mixing with mass transport in an effective microorganism odor removing system

AbstractBACKGROUNDIndustrial odor removers are two‐phase flow systems that use effective microorganisms to capture malodor‐producing gases from the surroundings. The potency of such systems depends on the interaction of gas with the microorganisms. Therefore, the flow and mass transport properties are key to defining the phenomenon more clearly.RESULTSAn efficient mechanism for mixing the two‐phase flow is required to enhance the interaction between the gas and microorganisms. Gas flow must also be controlled to obtain a large residence time in the water basin and facilitate the microorganisms to maximize the usage of malodor‐producing gases. One method of improving the gas residence time is by installing baffles in the water basin. However, the installation of baffles also limits the gas concentration distribution in the water basin. Placing a rotating drum in addition to the baffles may overcome the limitations on gas distribution in the water basin. Gas volume fractions, interfacial area per volume, and gas concentration are evaluated to observe the mixing and gas dissolution phenomenon.CONCLUSIONBefore practical implementation, a numerical study on the subject is required for various designs to investigate their effectiveness. Therefore, the present study uses the Euler–Euler numerical scheme to model the gas–liquid flow with mass transport for various designs of water basin. Results show that gas concentration is the most critical parameter in the case of two‐phase bubbly flow. © 2015 Society of Chemical Industry

Diffuse Helium and Hydrogen Degassing to Reveal Hidden Geothermal Resources in Oceanic Volcanic Islands: The Canarian Archipelago Case Study

We report herein the results of soil gas geochemistry studies, focused mainly on nonreactive and/or highly mobile gases such as He and H2, in five mining licenses at Tenerife and Gran Canaria, Canary Islands, Spain, during 2011–2014. The primary objective was to sort the possible geothermal potential of these five mining licenses, thus reducing the uncertainty inherent to the selection of the areas with highest geothermal potential for future exploration works. By combining the overall information obtained by the statistical–graphical analysis of the soil He and H2 data, the spatial distribution of soil gas concentrations and the analysis of selected chemical ratios of the soil gas to evaluate the influence of deep-seating degassing, two of the five mining licenses (Garehagua and Abeque, both located in Tenerife Island) seemed to show the highest geothermal potential. These results will be useful for future implementation and development of geothermal energy in the Canaries, the only Spanish territory with potential high-enthalpy geothermal resources, thus the most promising area for high-enthalpy geothermal installations.

Global mapping of greenhouse gases retrieved from GOSAT Level 2 products by using a kriging method

Because a synoptic overview facilitates understanding of the temporal and spatial changes in the global distribution of greenhouse gases, we developed a statistical spatial estimation method using kriging. Level 3 (L3) data products for the Greenhouse Gases Observing Satellite (GOSAT) Thermal And Near infrared Sensor for Carbon Observation (TANSO) Fourier Transform Spectrometer (FTS) Short Wave Infrared (SWIR) were generated from column-averaged, dry-air mole fractions of carbon dioxide (XCO2) and methane (XCH4) TANSO-FTS SWIR Level 2 (L2) products using this method. Although there have been some reports on the use of kriging for analysing GOSAT products, the kriging method used in this research was specifically adapted to the statistical characteristics of GOSAT L2 products. In the context of using data for atmospheric research, spatially interpolated data (GOSAT L3 products) cannot be more accurate than model-simulated global distributions of gas concentrations (GOSAT Level 4B (L4B) products), which are generated using an atmospheric tracer transport model. However, the L3 product takes much less time to generate than the L4B. It would take about a year to produce the L4B after generation of an L2 product. The great advantage of the L3 product is that it gives a comprehensive and reasonable monthly global distribution of gas concentrations with little delay. The L3 product using the kriging method can be generated on a monthly basis by estimating global semi-variogram curves from the L2 products for each month and interpolating spatially within a region with a radius of 1000 km from existing L2 data locations. The main purpose of this paper is to describe the methodology and characteristics of kriging used to generate the GOSAT L3 product, not for strictly scientific use of the estimated values, but for a reasonable global map of gas concentrations derived statistically from the sparsely observed L2 products within a short time frame. The characteristics of this method are compared to XCO2 products simulated with an atmospheric tracer transport model. The results show that the method proposed in this study is of practical use for generating L3 products from L2 products.

Methane gas in lake bottom sediments quantified using acoustic backscatter strength

Freshwater lakes and reservoirs can produce substantial quantities of methane (CH4) within bottom sediments. Due to its low solubility in water, CH4 forms bubbles that accumulate within bottom sediments and are released from sediments when buoyant forces exceed viscous, frictional, and inertial forces. Methane ebullition can enhance internal loading of nutrients and hasten release of other sediment-associated contaminants while also exporting a significant amount of C out of the lake basin and delivering a potent greenhouse gas to the atmosphere. The purpose of this study was to evaluate use of hydroacoustic measurements to remotely sense the CH4 content of sediments in lakes. The acoustic signatures of bottom sediments measured using a BioSonics DT-X echosounder at 38, 201, and 430 kHz were compared with gas volumes of surficial sediments determined using a displacement method. Measurements were made on three lakes in southern California, USA that varied in depth, productivity, and other features. The maximum volume backscatter strength of bottom echoes at 201 kHz was highly correlated with gas content (r 2 = 0.93) and, with suitable ground-truthing, can quantify the concentration and spatial distribution of CH4 gas in soft cohesive sediments of lakes and reservoirs. As an application of this technique, the spatial distribution of CH4 within bottom sediments of Lake Elsinore was determined from a hydroacoustic survey conducted in June 2010. Results are also presented from a transect on Lake Hodges demonstrating high levels of CH4 in this eutrophic lake. Hydroacoustic measurements of the maximum volume backscatter strength of soft organic sediments at 201 kHz provide a way to remotely estimate the volume of methane and other gases present in bottom sediments of lakes and reservoirs.

210 クラスタードマイクロフレーム近傍の壁面の位置がガス濃度分布に及ぼす影響

210 クラスタードマイクロフレーム近傍の壁面の位置がガス濃度分布に及ぼす影響

Consequence modelling of the population risk exposure resulting from airborne toxic material released from rail cars within Toronto, Ontario

Rail transportation is commonly used to move toxic-by-inhalation chemicals throughout Canada, passing in close proximity to urban areas. These trains are vulnerable to accidents, sabotage and terrorism, with each scenario resulting in formidable consequences for nearby residents. Modelling of the airborne concentration distribution of chlorine gas released from a railcar in Toronto reveals that in a 'worst case' scenario, approximately 261,590 residents would be expected to experience severely irreversible and life-threatening health effects, including death. An event of this magnitude, stemming from a 10 cm diameter puncture hole in the side of the railcar - accidentally or intentionally caused - would cripple the response capacity of nearby hospitals, and unleash a cascading series of effects. Further, models of anhydrous ammonia and chlorine releases reveal that weather conditions and the incident timing can lead to multiple populations being affected, while the chemical characteristics play an important mitigation role in population risk exposure.

Research on Gas Emission Distribution in Coalface Based on Trend Surface Polynomial Analysis

In this paper, gas intensity data collected from coal mine with wireless gas sensor network has been analyzed for the understanding of gas distribution at mining work place. The concentration parameters acquired at different position were dealt with polynomial equation surface fitting based on trend surface analysis, and we built the trend face analysis model with calculation results. Diagram of gas distribution trend and the isocline chart of gas concentration were achieved with the model. The diagram and chart present the distribution of gas concentration in different direction at coal working place and the gas accumulation at top corner from the ventilate eddy. Then, we discussed the effects of airflow and cutting coal to gas distribution. The research results are significant for monitoring and controlling of gas to avoid explosion accident the coal mining.

Gas Concentration Distribution Law in the Roadway after Coal and Gas Outburst

Gas emission happens after coal and gas outburst, and it could cause secondary disasters in the roadway. Therefore it is necessary to research gas concentration distribution law in the roadway after coal and gas outburst, and theoretical basis for avoiding the occurrence of secondary disasters could be provided. Based on the above, Fluent is used to simulate gas concentration distribution law in the roadway during outburst. The research results show that gas velocity of the initial stage is larger in the whole process of gas outburst and gas emission impacts opposite walls in the form of jet in the roadway intersection. The flow changes direction and moves along the main airway and return airway. It produces countercurrent along the main airway. Because the pressure in the main airway is high, gas migration velocity becomes zero after a certain distance and is "back" to return airway. The higher the outburst velocity is, the longer the flow length is. Gas concentration variation with two kinds of different outburst intensities and position are regressed and it shows that correlation coefficients of power function are the highest. The research results have a certain theoretical value to prevent the occurrence of secondary disasters after coal and gas outburst.

Reconstruction of Axisymmetric Temperature and Gas Concentration Distributions by Combining Fan-Beam TDLAS With Onion-Peeling Deconvolution

Fan-beam tunable diode laser absorption spectroscopy (TDLAS) system was combined with onion-peeling deconvolution to reconstruct axisymmetric temperature and gas concentration distributions. The fan-beam TDLAS system consists of two tunable distributed feedback diode lasers at 7185.597 and 7444.36 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , a cylindrical lens and multiple photodiode detectors in a linear detector array. When a well-collimated laser beam penetrates through a cylindrical lens, a fan-beam laser was formed. Then, the fan-beam laser penetrates through the target region and is detected by the photodiode detectors in the detector array. After transforming the fan-beam geometry to equivalent parallel-beam geometry, axisymmetric temperature and gas concentration distributions can be reconstructed using the onion-peeling deconvolution. To obtain the reconstruction results with higher accuracy, a revised Tikhonov regularization method was adopted in the onion-peeling deconvolution. In this paper, numerical simulation and experimental verification were carried out to validate the feasibility of the proposed methods. The results show that the proposed methods can be used to on-line monitor the axisymmetric temperature and gas concentration distributions with higher accuracy and robustness in combustion diagnosis.

A SCR Model Calibration Approach with Spatially Resolved Measurements and NH3 Storage Distributions

The selective catalytic reduction (SCR) is a technology used for reducing NO x emissions in the heavy-duty diesel (HDD) engine exhaust. In this study, the spatially resolved capillary inlet infrared spectroscopy (Spaci-IR) technique was used to study the gas concentration and NH3 storage distributions in a SCR catalyst, and to provide data for developing a SCR model to analyze the axial gaseous concentration and axial distributions of NH3 storage. A two-site SCR model is described for simulating the reaction mechanisms. The model equations and a calculation method was developed using the Spaci-IR measurements to determine the NH3 storage capacity and the relationships between certain kinetic parameters of the model. A calibration approach was then applied for tuning the kinetic parameters using the spatial gaseous measurements and calculated NH3 storage as a function of axial position instead of inlet and outlet gaseous concentrations of NO, NO2, and NH3. The equations and the approach for determining the NH3 storage capacity of the catalyst and a method of dividing the NH3 storage capacity between the two storage sites are presented. It was determined that the kinetic parameters of the adsorption and desorption reactions have to follow certain relationships for the model to simulate the experimental data. The modeling results served as a basis for developing full model calibrations to SCR lab reactor and engine data and state estimator development as described in the references (Song et al. 2013a, b; Surenahalli et al. 2013).

Study on Distribution of Gas Concentration on the Upper Corner by Thermal Imaging Equipment and Swirling Jet

The gas accumulation is often mine hidden danger and has become a hotspot recently. in order to analysis the coal gas distribution law, the paper determines the heat transfer and temperature distribution using infrared thermograph and swirling jet device. Based on similarity theory, it can simulate the gas concentration distribution and gas migration. Based on an experiment result, the gas accumulation can be dissipated effectively and the distribution of gas concentration becomes uniform as the time, it can be provided as a reference of rotation fan design.

Transient analysis of gas transport in anode channel of a polymer electrolyte membrane fuel cell with dead-ended anode under pressure swing operation

Further cost reduction is a critical issue for commercialization of fuel-cell electric vehicles (FCEVs) based on polymer electrolyte fuel cells (PEFCs). The cost of the fuel-cell system is driven by the multiple parts required to maximize stack performance and maintain durability and robustness. The fuel-cell system of the FCEV must be simplified while maintaining functionality. The dead-ended anode is considered as a means of simplification in this study. Generally, if hydrogen is supplied under constant pressure during dead-ended operation, stable power generation is impossible because of accumulation of liquid water produced by power generation and of nitrogen via leakage from the cathode through the membrane. Herein, pressure oscillation is applied to address this issue. Empirical and CFD data are employed to elucidate the mechanism of stable power generation using the pressure swing supply. Simultaneous and time-continuous measurements of the current distribution and gas concentration distribution are also conducted. The results demonstrate that the nitrogen concentration in the anode channel under pressure constant operation differs from that under pressure swing supply conditions. The transient two-dimensional CFD results indicate that oscillatory flow is generated by pressure swing supply, which periodically sweeps out nitrogen from the active area, resulting in stable power generation.

Numerical Simulation on the Performance of a Solid Oxide Fuel Cell with Direct Ammonia Internal Decomposition

Electrical performance of a 3D planar solid oxide fuel cell, with ammonia internal decomposition as fuel and yttrium-stabled zirconia as electrolyte, has been simulated numerically, incorporated with the software Comsol Multiphysics. With the help of the software, gas concentration distribution in an anode/cathode channel as well as current density distribution was demonstrated. The poor gas concentration distribution in the cathode channel is mainly responsible for the poor current density distribution. Furthermore, the effect of current density on the solid oxide fuel cell ohmic and activation overpotential was analyzed. The simulation results conform to the data in the experimental literature well.

Unsteady 360 Computational Fluid Dynamics Validation of a Turbine Stage Mainstream/Disk Cavity Interaction

The amount of cooling air assigned to seal high pressure turbine (HPT) rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor–stator forward disk cavity were performed at Arizona State University (ASU). The turbine rig has 22 vanes and 28 blades, while the cavity is composed of a single-tooth lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide) under a range of purge flows from 0.435% (Cw = 1540) to 1.74% (Cw = 6161). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the cavity between the lab seal and the rim seal. The data from the experiments were compared to time-dependent computational fluid dynamics (CFD) simulations using fluent CFD software. The CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. An unsteady Reynolds averaged Navier–Stokes (RANS), 360-deg CFD model of the complete turbine stage was employed in order to increase the understanding of the swirl physics which dominate cavity flows and better predict rim seal ingestion. Although the rotor–stator cavity is geometrically axisymmetric, it was found that the interaction between swirling flows in the cavity and swirling flows in the gas path create nonperiodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 deg full stage unsteady analysis. At low purge flow conditions, the vortices that form inside the cavities are greatly influenced by mainstream ingestion. Conversely at high purge flow conditions the vortices are influenced by the purge flow, therefore ingestion is minimized. The paper also discusses details of meshing, convergence of time-dependent CFD simulations, and recommendations for future simulations in a rotor–stator disk cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.

Evaluation of Geographic Information Systems-Based Spatial Interpolation Methods Using Ohio Indoor Radon Data

This paper evaluates the performance of six different Geographic Information System based interpolation methods: inverse distance weighting (IDW), radial basis function (RBF), global polynomial interpolation, local polyno- mial interpolation, kriging, and cokriging, using the Ohio homes database developed between 1987 and 2011. The best performing interpolation method to be used in the prediction of radon gas concentrations in the unmeasured areas of Ohio, USA was determined by validating the model predictions with operational performance measures. Additionally, this study performed a zip code level-based analysis that provided a complete picture of the radon gas concentration distribution in Ohio. The RBF method was identified to be the best performing method. While the RBF method performed significantly better than the IDW, it was statistically similar to the other interpolation methods. The RBF predicted radon gas concentration results indicated a significant increase in the number of zip codes that exceeded the United States Environmental Protec- tion Agency and the World Health Organization action limits, thereby, indicating the need to mitigate the Ohio radon gas concentrations to safe levels in order to reduce the health effects. The approach demonstrated in this paper can be applied to other radon-affected areas around the world.