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Highlights • Estimation of gas mixing/dispersion parameter ( D g , Pe , σ D 2 ) for catalyst bed. • At low liquid flow rate, the bed is in packed bed and it expands for increasing flow. • Gas mixing/dispersion is higher in packed bed state. • For all flow conditions, the gas flow is not deviating much from plug flow. • Scaled down flow condition is good in terms of mixing and catalyst utilization. Abstract Gas dispersion studies has been executed for the catalyst bed section of a representative geometry of scaled-down industrial Moving Bed Hydrotreater Reactor (MBR). The catalyst bed of MBR is modeled using Axial Dispersion Model (ADM) and its parameters gas dispersion coefficient ( D g ) and Peclet number (Pe) are estimated using Residence Time Distribution (RTD) and implementing a methodology based on convolution and regression. Additionally, dimensionless variance ( σ D 2 ) for the catalyst bed is also measured using RTDs first and second moments to compare with those findings of ADM model. This study is conducted at the varying flow rates of gas and liquid including scaled down operating conditions. The results of D g , Pe , and σ D 2 indicate that bed behaves as a packed bed for low liquid flow rate and moves towards three-phase fluidized bed for increasing liquid flow rate. Overall the gas phase behavior is seen to be in plug flow for all the operating conditions, with relatively high dispersion/mixing in packed bed state. Scaled down flow conditions is seen to be best in terms of gas dispersion/mixing and catalyst utilization. [ABSTRACT FROM AUTHOR]

An advanced gaseous tracer technique and procedures were developed and executed to study for the first time the axial dispersion of the gas phase in a slurry bubble column reactor (SBCR) using air-C9C11-FT catalyst. Residence time distribution (RTD) curves were obtained by measuring the pulse-input's response of the gaseous tracer. The gas phase axial dispersion coefficient (Dg) was obtained from minimum square error fit of the one-dimensional axial dispersion model to the measured tracer response data. The effects of solids loading on the axial dispersion of gas phase and the overall gas holdup have been studied. It was demonstrated that increasing solids loading improves the gas axial dispersion while decreasing the overall gas holdup. This work suggests that gas phase axial dispersion is significant in reactor performance evaluation of bubble columns or slurry bubble columns. [ABSTRACT FROM AUTHOR]

The Friends of Friends algorithm identifies groups of objects with similar spatial and kinematic properties, and has recently been used extensively to quantify the distributions of gas and stars in young star-forming regions. We apply the Friends of Friends algorithm to N -body simulations of the dynamical evolution of subvirial (collapsing) and supervirial (expanding) star-forming regions. We find that the algorithm picks out a wide range of groups (1–25) for statistically identical initial conditions, and cannot distinguish between subvirial and supervirial regions in that we obtain similar mode and median values for the number of groups it identifies. We find no correlation between the number of groups identified initially and either the initial or subsequent spatial and kinematic tracers of the regions' evolution, such as the amount of spatial substructure, dynamical mass segregation, or velocity dispersion. We therefore urge caution in using the Friends of Friends algorithm to quantify the initial conditions of star formation. [ABSTRACT FROM AUTHOR]

Eight short-range, open-terrain SF6 tracer tests in low wind speeds were conducted during Phase 2 of Project Sagebrush using continuous releases. Four tests were made during very unstable conditions in July and August 2016, and four during very stable conditions in October 2016. All tests featured 10-min averaging and 1-Hz sampling of tracer concentrations together with an extensive suite of meteorological measurements. We find that the uncertainty in well-mixed daytime measurements of tracer concentrations, using the absolute value of the relative percentage difference in collocated duplicate samplers, approaches a downwind limit of about 7-8%. Concentration variability in collocated sampling, due to stochastic factors and independent of measurement uncertainty, increases the total observational uncertainty closer to the source from about 20% (daytime) to 40% (very stable conditions). Longer averaging periods moderately reduce the concentration variability. The data indicate that the large increase in concentration variability is linked with the suppression of turbulent mixing, small eddy length scales, and meandering in very stable conditions. These results should be considered when comparing observations with model predictions in evaluations. [ABSTRACT FROM AUTHOR]

Empirical evidence of planets in gas-rich circumstellar discs is required to constrain giant planet formation theories. Here we study the kinematic patterns which arise from planet–disc interactions and their observability in CO rotational emission lines. We perform 3D hydrodynamical simulations of single giant planets and predict the emergent intensity field with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes, and vortices bear strong kinematic counterparts. The isovelocity contours in the CO(2-1) line centroids |$v$| ○ reveal large-scale perturbations, corresponding to abrupt transitions from below sub -Keplerian to super -Keplerian rotation along with radial and vertical flows. The increase in line optical depth at the edge of the gap also modulates |$v$| ○, but this is a mild effect compared to the dynamical imprint of the planet–disc interaction. The large-scale deviations from the Keplerian rotation thus allow the planets to be indirectly detected via the first moment maps of molecular gas tracers, at Atacama Large Millimetre/submillimetre Array angular resolutions. The strength of these deviations depends on the mass of the perturber. This initial study paves the way to eventually determine the mass of the planet by comparison with more detailed models. [ABSTRACT FROM AUTHOR]

The use of thermal modulation techniques provides powerful tools to enhance and influence the selectivity and sensitivity of metal oxide based functional layers in gas sensing applications. However, when using micromachined, low-power consuming, so-called hotplate devices, the determination of the absolute temperature of the sensitive layer still presents a challenge. In this contribution, a novel method based on a phase transition in thermally sensitive materials is applied to determine the absolute temperature with high accuracy. The technique relies on depositing small, well-defined amounts of various materials with high spatial resolution using an inkjet printer and then establishing the relation between the heater’s resistivity and the absolute temperature when the phase transition occurs. With this approach, the spatial distribution of the absolute temperature of microelectromechanical systems can be achieved. Due to the flexibility of inkjet printing, the presented method may be applied to a wide range of scenarios. [2018–0021] [ABSTRACT FROM AUTHOR]

The microheater is an important part of a semiconducting metal oxide gas sensor, as its primary function is to heat up the sensitive layer to a desired temperature. The operating temperature of the sensor depends on the sensitive material used and the species of the target gases. Therefore, an accurate extraction of the sensor active area temperature as a function of the applied power is critical for device characterization. These measurements are experimentally challenging due to the extremely small sensing surface area, down to a few tens of $\mu \text{m}^{2}$ , resulting in the need to develop new measurement approaches. In this paper, quantitative testing methods based on platinum and chrome silicon (CrSi) resistance thermometry, as well as a qualitative testing method (light glow) have been carried out to measure the power consumption of two different devices. CrSi has been used as a temperature sensor due to its ability to detect temperatures above 450 °C by acting as a phase-change material. For accurate measurements of temperature distribution, the presented gas sensors are equipped with three configurations of resistive temperature detectors at different locations. To further analyze a sample closed-membrane sensor, finite-element simulations were performed and an analytical model was designed and compared with experimentals. [2017–0228] [ABSTRACT FROM AUTHOR]

Polycrystalline SrTiO 3- δ powders with cubic perovskite phase were prepared by solid-state reaction method followed by the creation of oxygen vacancies δ- thermal activated. The Raman spectroscopic investigation was carried out in a frequency range of 100–2000 cm −1 , and the second-order Raman modes were observed at room temperature. The Electron Paramagnetic Resonance (EPR) results revealed that SrTiO 3- δ samples had evident EPR signals that increased significantly with oxygen-vacancy concentrations. The incorporation of oxygen vacancies was found to decrease the thermal resistivity. Besides, the electrical sensing measurements showed that sensors based on SrTiO 2.925 (STO1) and SrTiO 2.875 (STO2) exhibited semiconductor behavior, while SrTiO 2.75 -based sensor (STO3) revealed the introduction of a metallic behavior at low temperature. Furthermore, these measurements confirmed that the resistivity increased after the introduction of the ethanol gas, which indicates that our samples can be considered as sensors for ethanol gas detection. The formation of oxygen vacancies under ethanol exposure at the surface of SrTiO 3- δ sensors was evaluated by photoluminescence. [ABSTRACT FROM AUTHOR]

It is well known that the performance of monolithic catalysts is limited by gas transport resistance in the washcoat layer. Gases are transported via two types of pores within the washcoat layer: primary pores, which exist inside the particle of catalyst support material (e.g., Al 2 O 3 ), and secondary pores, which are voids among particles of the catalyst support material. Primary pores play an important role in the effectiveness of catalytically active components such as Pt, Rh, and Pd, while secondary pores facilitate gas transport in the washcoat layer. This paper reports the characterization of secondary pores and their effect on gas transport. In order to evaluate the gas transport properties of a washcoat layer, effective gas permeability was measured. Four samples with different pore morphologies were prepared, and their secondary pore properties were characterized with scanning electron microscopy, mercury porosimetry and synchrotron X-ray computed tomography. The obtained pore properties were correlated with the effective gas permeability, and based on the obtained correlation, we formulated a model for the gas permeability of the pores. This new model was compared to the conventional Kozeny-Carman equation. [ABSTRACT FROM AUTHOR]

Partition (or distribution) coefficients determine the relative equilibrium concentrations of chemical constituents (or chemical tracers) in each of the phases of a multi-phase system under dilute conditions. The various fluid phases in a reservoir have differing transport properties (e.g. varying relative permeability) and to correctly interpret the behaviour of injected chemical tracers it is essential that accurate partition coefficients are known. In the context of carbon geosequestration or long-term storage of CO 2 , chemical tracers will be predominantly exposed to an environment consisting of supercritical CO 2 and formation water as the main fluid phases. To estimate/simulate the reservoir properties relevant to injected CO 2 tagged with chemical tracers, it is therefore necessary to incorporate high pressure/temperature CO 2 /water partition coefficients into any model/simulation. In this paper, we present a method to determine these partition coefficients for gaseous chemical tracers using a variation of the widely used EPICS (or equilibrium partitioning in a closed system) method. With this method, only the concentration in one phase (in this case, CO 2 ) needs to be measured. We then report these values for a series of representative chemical tracers (i.e. krypton, xenon, sulfur hexafluoride, perdeuterated methane and R134a) at pressure/temperature conditions that have been previously used at the CO2CRC's Otway CCS demonstration project in Victoria, Australia. These values were generally lower than the corresponding Henry's Law coefficients at comparable temperatures. Experiments also examined the impact of adding CH 4 to the system to mimic feedstock gas at the CO2CRC Otway project and provide data pertinent to scenarios where CO 2 is injected into depleted CH 4 gas fields. These values are compared with Henry's Law coefficients and another recently published set of high pressure/temperature partition coefficients. With computational simulations, we have shown that these differences are potentially significant and demonstrate their impact in three typical CO 2 geo-sequestration scenarios (i.e. injection into two types of aquifers and injection into a depleted reservoir with a gas cap). [ABSTRACT FROM AUTHOR]

The diffusion dynamics of particles in heterogeneous media is studied using particle-based simulation techniques. A special focus is placed on systems where the transport of particles at long times exhibits anomalies such as subdiffusive or superdiffusive behavior. First, a two-dimensional model system is considered containing gas particles (tracers) that diffuse through a random arrangement of pinned, disk-shaped particles. This system is similar to a classical Lorentz gas. However, different from the original Lorentz model, soft instead of hard interactions are considered and we also discuss the case where the tracer particles interact with each other. We show that the modification from hard to soft interactions strongly affects anomalous-diffusive transport at high obstacle densities. Second, non-linear active micro-rheology in a glass-forming binary Yukawa mixture is investigated, pulling single particles through a deeply supercooled state by applying a constant force. Here, we observe superdiffusion in force direction and analyze its origin. Finally, we consider the Brownian dynamics of a particle which is pulled through a two-dimensional random force field. We discuss the similarities of this model with the Lorentz gas as well as active micro-rheology in glass-forming systems. [ABSTRACT FROM AUTHOR]

When an accidental release of indoor airborne pollutants occurs, it is critical to promptly identify the pollutant sources. Current inverse models concentrate on the identification of a single pollutant source or multiple pollutant sources in a simplified puff or constant release scenarios. This investigation proposes an inverse model to precisely determine the locations and temporal release rate profiles of multiple sources releasing the same tracer gaseous pollutant. The model first constitutes a number of candidate group sources by assuming known release positions. Then Tikhonov-based matrix inversion is implemented to solve for the release rate profiles of each candidate group of sources. The concentrations provided by the sensors in the same number of the isolated sources are the known inputs for the matrix inversion. As for the multiple candidate group sources, the occurrence probability of each group is determined by the Bayesian model after matching the concentration with one additional sensor. The above strategy was applied to identify the same pollutant accidentally released by two passengers in a three-dimensional aircraft cabin. The pollutant was from the exhalation points and discharged in an intermittent sinusoidal wave and a square wave of ten seconds, respectively. The results show that the proposed method can correctly determine the locations of multiple temporally released sources. The relative errors between the inversely identified release rates and the CFD-simulated actual rates are generally less than 15%. [ABSTRACT FROM AUTHOR]

Products of secondary organic aerosol (SOA) from aromatic volatile organic compounds (VOCs) - 2,3-dihydroxy-4-oxopentanoic acid, dicarboxylic acids, nitromonoaromatics, and furandiones - were evaluated for their potential to serve as anthropogenic SOA tracers with respect to their (1) ambient concentrations and detectability in PM2.5 in Iowa City, IA, USA; (2) gas-particle partitioning behaviour; and (3) source specificity by way of correlations with primary and secondary source tracers and literature review. A widely used tracer for toluene-derived SOA, 2,3-dihydroxy-4-oxopentanoic acid was only detected in the particle phase (Fp = 1) at low but consistently measurable ambient concentrations (averaging 0.3 ng m-3). Four aromatic dicarboxylic acids were detected at relatively higher concentrations (9.1-34.5 ng m-3), of which phthalic acid was the most abundant. Phthalic acid had a low particle-phase fraction (Fp = 0.26) likely due to quantitation interferences from phthalic anhydride, while 4-methylphthalic acid was predominantly in the particle phase (Fp = 0.82). Phthalic acid and 4-methylphthalic acid were both highly correlated with 2,3-dihydroxy-4-oxopentanoic acid (rs = 0.73, p = 0.003; rs = 0.80, p < 0.001, respectively), suggesting that they were derived from aromatic VOCs. Isophthalic and terephthalic acids, however, were detected only in the particle phase (Fp = 1), and correlations suggested association with primary emission sources. Nitromonoaromatics were dominated by particle-phase concentrations of 4-nitrocatechol (1.6 ng m-3) and 4-methyl-5-nitrocatechol (1.6 ng m-3) that were associated with biomass burning. Meanwhile, 4-hydroxy-3-nitrobenzyl alcohol was detected in a lower concentration (0.06 ng m-3) in the particle phase only (Fp = 1) and is known as a product of toluene photooxidation. Furandiones in the atmosphere have only been attributed to the photooxidation of aromatic hydrocarbons; however the substantial partitioning toward the gas phase (Fp ≤ 0.16) and their water sensitivity limit their application as tracers. The outcome of this study is the demonstration that 2,3-dihydroxy-4-oxopentanoic acid, phthalic acid, 4-methylphthalic acid, and 4-hydroxy-3-nitrobenzyl alcohol are good candidates for tracing SOA from aromatic VOCs. [ABSTRACT FROM AUTHOR]

We develop several critical concepts that should be considered when interpreting, modelling and designing future experiments for flows over sloping terrain. Vertical buoyancy fluxes in katabatic flows can be positive and a source of turbulent kinetic energy (TKE) despite the statically stable, thermal stratification that drives these flows. This phenomenon occurs when the ratio of along-slope to slope-normal kinematic heat fluxes is greater than the cotangent of the slope angle, suggesting a critical value of slope-angle steepness found in earlier studies. We provide field-data-based evidence that the along-slope heat flux may dominate the variables in this inequality, and therefore in generating buoyant TKE production or suppression over a steep slope. These data show the along-slope heat flux can be more variable and significantly larger in magnitude than the slope-normal component. The gradient Richardson number does not include the effects of the along-slope buoyancy; furthermore, none of the canonical stability parameters can properly reflect the TKE redistribution from turbulent transport divergence and the sink of TKE in cases of counter-gradient momentum fluxes, which we frequently observe near the peak of the katabatic jet. In such cases, canonical stability parameters inadequately represent the physical mechanisms associated with stability. These results have broad implications related to accurately modelling turbulence and surface exchanges over sloping terrain and illustrate the need to more thoroughly investigate the along-slope heat flux and its drivers, the meaning and definitions of stability, and the effects of non-local turbulent transport. [ABSTRACT FROM AUTHOR]

The Quick Urban & Industrial Complex (QUIC) atmospheric transport, and dispersion modelling, system was evaluated against the Joint Urban 2003 tracer-gas measurements. This was done using the wind and turbulence fields computed by the Weather Research and Forecasting (WRF) model. We compare the simulated and observed plume transport when using WRF-model-simulated wind fields, and local on-site wind measurements. Degradation of the WRF-model-based plume simulations was cased by errors in the simulated wind direction, and limitations in reproducing the small-scale wind-field variability. We explore two methods for importing turbulence from the WRF model simulations into the QUIC system. The first method uses parametrized turbulence profiles computed from WRF-model-computed boundary-layer similarity parameters; and the second method directly imports turbulent kinetic energy from the WRF model. Using the WRF model's Mellor-Yamada-Janjic boundary-layer scheme, the parametrized turbulence profiles and the direct import of turbulent kinetic energy were found to overpredict and underpredict the observed turbulence quantities, respectively. Near-source building effects were found to propagate several km downwind. These building effects and the temporal/spatial variations in the observed wind field were often found to have a stronger influence over the lateral and vertical plume spread than the intensity of turbulence. Correcting the WRF model wind directions using a single observational location improved the performance of the WRF-model-based simulations, but using the spatially-varying flow fields generated from multiple observation profiles generally provided the best performance. [ABSTRACT FROM AUTHOR]

We analyse the rotation curves and gravitational stability of a sample of six bulgeless galaxies for which detailed images reveal no evidence for strong bars. We explore two scenarios: Newtonian dark matter models and MOdified Newtonian Dynamics (MOND). By adjusting the stellar mass-to-light ratio, dark matter models can match simultaneously both the rotation curve and bar-stability requirements in these galaxies. To be consistent with stability constraints, in two of these galaxies, the stellar mass-to-light ratio is a factor of ∼1.5–2 lower than the values suggested from galaxy colours. In contrast, MOND fits to the rotation curves are poor in three galaxies, perhaps because the gas tracer contains non-circular motions. The bar stability analysis provides a new observational test to MOND. We find that most of the galaxies under study require abnormally high levels of random stellar motions to be bar stable in MOND. In particular, for the only galaxy in the sample for which the line-of-sight stellar velocity dispersion has been measured (NGC 6503), the observed velocity dispersion is not consistent with MOND predictions because it is far below the required value to guarantee bar stability. Precise measurements of mass-weighted velocity dispersions in (unbarred and bulgeless) spiral galaxies are crucial to test the consistency of MOND. [ABSTRACT FROM AUTHOR]

A practical and feasible solution to reduce the global impacts from fossil fuels is represented by the locally distributed micro-cogeneration systems with high temperature solid oxide fuel cells (SOFC) fed by biogenous fuel coupled in an energy distributed system. One of the main drawback is the low tolerability towards certain fuel impurities, mostly sulfur, chlorine and siloxane compounds. The opportunity to predict the breakthrough time of a gas cleaning section with a high precision level is mandatory to meet SOFC requirements. The reaction kinetic equation called the Wheeler-Jonas equation is adopted to estimate this breakthrough time. Two different commercial activated carbons were studied estimating the breakthrough time varying the operating temperature, the pollutant concentration (single and multiple effects) and the relative humidity. Results showed how relative humidity content affects inversely the removal performance for both sorbents. The Carbox sample, below RH 20% showed interesting results due to its metals content and microstructure. Here, relative humidity promoted the best condition to remove organic vapors from the biogas stream. Multiple contaminant conditions for both sorbent materials decreased the removal performance (t b ). This decreasing for the Carbox sample ranged from a minimum of 44% to a maximum of 50% for H 2 S, and 70% for HCl with wet and dry conditions respectively. [ABSTRACT FROM AUTHOR]

The long-term performance and flux inhibition of a 10 μm-thick Pd 77 Ag 23 membrane under the exposure to varying concentrations of NH 3 ranging from 10 to 500 ppm at a temperature between 300 and 450 °C was investigated. At 450 °C no H 2 flux inhibition was found in the presence of 200–500 ppm NH 3 . However, an inhibition of the H 2 flux was observed at lower operating temperatures in the presence of 200 ppm NH 3 . In addition, a further gradual H 2 flux decline is observed giving evidence for NH 3 adsorption on the membrane surface. A H 2 flux reduction of ~ 36% was observed after 20 h of exposure at 300 °C compared to the H 2 flux obtained at this temperature in the absence of any NH 3 . The subsequent increase in operating temperature back to 450 °C, however, quickly recovered the H 2 flux back to its original H 2 flux value obtained prior to any NH 3 exposure at 450 °C. First-principles calculations, however, indicated that H 2 flux decrease upon NH 3 exposure could not be accounted for by a simple lowering of the hydrogen surface coverage due to the competitive adsorption of NH 3 related species under the experimental conditions. The role of NH 3 therefore seems more complex, for instance related to hydrogen dissociation kinetics and incorporation or changes in the Pd-alloy membrane due to surface segregation, but this remains uncertain at this stage. [ABSTRACT FROM AUTHOR]

Methane emissions from streams and rivers have recently been recognized as an important component of global greenhouse budgets. Stream methane is lost as evasion to the atmosphere or in-stream methane oxidation. Previous studies have quantified evasion and oxidation with point-scale measurements. In this study, dissolved gases (methane, krypton) were injected into a coastal plain stream in North Carolina to quantify stream CH4 losses at the watershed scale. Stream-reach modeling yielded gas transfer and oxidation rate constants of 3.2 ± 0.5 and 0.5 ± 1.5 d-1, respectively, indicating a ratio of about 6:1. The resulting evasion and oxidation rates of 2.9 mmol m-2 d-1 and 1,140 nmol L-1 d-1, respectively, lie within ranges of published values. Similarly, the gas transfer velocity (K600) of 2.1 m d-1 is consistent with other gas tracer studies. This study illustrates the utility of dissolved-gas tracers for evaluating stream methane fluxes. In contrast to point measurements, this approach provides a larger watershed-scale perspective. Further work is needed to quantify the magnitude of these fluxes under varying conditions (e.g., stream temperature, nutrient load, gradient, flow rate) at regional and global scales before reliable bottom-up estimates of methane evasion can be determined at global scales. [ABSTRACT FROM AUTHOR]

A shallow CO 2 injection experiment was performed on a pilot site near Bordeaux, France, in February 2015. A gas mixture composed of approximatively 90% CO 2 and 5% of each He and Kr as gas tracers was injected through a vertical well, with low injection rate, at 1.80 m depth and into the carbonate vadose zone. A set of geochemical monitoring tools was installed in order to monitor the developing gas plume and to allow comparison between this experiment and a former release experiment which used a higher flow injection was made. Measurement showed a heterogeneous spatial and temporal variation of the gas plume. Difference in time arrival of peak concentration of He, Kr and CO 2 confirmed that diffusion alone did not occur in the porous media. Former studies mentioned advective flow drove through preferential paths. Both advection and diffusion flow may have been observed in the experiment. It also shows that the difference in molecular weights and the heterogeneity of the limestone could lead He to be used as a temporal tracer, and Kr as a spatial tracer as it allows us to estimate the extent of CO 2 plume. The ratios between the various gas components also indicate that a sizeable amount of CO 2 could be consumed before it reaches the subsurface, meaning that the vadose zone could be a buffering zone to CO 2 leakage. The comparison between this experiment and a former one with different injection condition revealed that the presence of advection is dependent of the heterogeneity of the limestone. However, the injection rate induces the amount of gas diffusing or/and advecting. Observations from both, our recent and a previous leakage experiment and future laboratory experiment could improve our understandings of the buffering zone and help to foresee CO 2 leakage for future storage site. [ABSTRACT FROM AUTHOR]

Livestock production is a source of numerous environmental problems caused by pollutant gas emissions. In naturally ventilated buildings, estimating air flow rate is complicated due to changing climatic conditions and the difficulties in identifying inlets and outlets. To date no undisputed reference measurement method has been identified. The objective of this paper was to compare CO 2 - and SF 6 -based tracer gas methods for the estimation of ventilation rates ( V R C O 2 vs. V R S F 6 ) in naturally ventilated dairy barns both under conventional and very open ventilation situations with different spatial sampling strategies. Measurements were carried out in a commercial dairy barn, equipped with an injection system for the controlled release of SF 6 , and measurement points for the monitoring of SF 6 and CO 2 concentrations to consider both horizontal and vertical variability. Methods were compared by analysing daily mean V R C O 2 / V R S F 6 ratios. Using the average gas concentration over the barn length led to more accurate ventilation rates than using one single point in the middle of the barn. For conventional ventilation situations, measurements in the ridge seem to be more representative of the barn average than in the middle axis. For more open situations, both V R C O 2 and V R S F 6 were increased, V R C O 2 / V R S F 6 ratios being also more variable. Generally, both methods for the estimation of ventilation rates gave similar results, being 10–12% lower with the CO 2 mass balance method compared to SF 6 based measurements. The difference might be attributed to potential bias in both methods. [ABSTRACT FROM AUTHOR]

Perfluoromethylcyclohexane (PMCH) was released in a Midwestern underground longwall mine in the United States using a PMCH permeation plug release vessel (PPRV). The operators of this mine graciously allowed full access to an active longwall panel at two points in time to perform the test. This paper presents a study designed to determine the feasibility of using a PPRV in an underground mine environment for tracer gas studies. The results of this study showed that the PPRV is a feasible tracer delivery system for releasing PMCH at mine scale. Some of the advantages afforded by the PPRV over traditional release techniques are also highlighted. [ABSTRACT FROM AUTHOR]

Airborne transmission is a main spread mode of respiratory infectious diseases, whose frequent epidemic has brought serious social burden. Identifying possible routes of the airborne transmission and predicting the potential infection risk are meaningful for infectious disease control. In the present study, an internal spread route between horizontal adjacent flats induced by air infiltration was investigated. On-site measurements were conducted, and tracer gas technique was employed. Two measurement scenarios, closed window mode and open window mode, were compared. Using the calculated air change rate and mass fraction, the cross-infection risk was estimated using the Wells–Riley model. It found that tracer gas concentrations in receptor rooms are one order lower than the source room, and the infection risks are also one order lower. Opening windows results in larger air change rate on the one hand, but higher mass fraction on the other hand. Higher mass fraction not necessarily results in higher infection risk as the pathogen concentration in the source room is reduced by the higher air change rate. In the present study, opening windows could significantly reduce the infection risk of the index room but slightly reduce the risks in receptor rooms. The mass fraction of air originated from the index room to the receptor units could be 0.28 and the relative cross-infection risk through the internal transmission route could be 9%, which are higher than the external spread through single-sided window flush. The study implicates that the horizontal transmission route induced by air infiltration should not be underestimated. [ABSTRACT FROM AUTHOR]

Qualitative measurements of leaks in air flows are frequently conducted in engineering. However, an environmentally friendly leak rate measurement technique which yields quantitative results and is applicable to hot, large-scale circular air flows (≈10 kg/s; ≈ 700 °C) with high leak rates has not been presented yet. This paper describes the development, test and validation of a stationary and a dynamic, helium based tracer gas method on a lab-scale model of a solar air receiver with partial air recirculation. Helium is chosen as tracer gas since it is environmentally friendly, stable under high temperatures and is also cheap for large-scale air flows. The tracer gas is injected either continuously or intermittently into the model system, its concentration is measured using a mass spectrometer and the static or dynamic concentration response of the system is used to determine the leak rate. The stationary method needs two measurement points upstream and downstream the leak, the dynamic method only one measurement point if applied to a circular air flow system. Since the dynamic method is time dependent the transfer function of the measurement setup was determined and the dynamic measurement error was considered. An extensive uncertainty analysis is presented for both the stationary and the dynamic method. Exemplary measurements were conducted at the model system with very good results. Both dynamic and static measurements yield the same result within their confidence intervals. The leak rate of the solar receiver model with a mass flow rate of m ̇ in = ( 0.247 ± 0.008 ) / kg s was measured to be l stat = ( 36.1 ± 2.3 ) % and l dyn = ( 34.5 ± 3.6 ) % with the static and the dynamic method respectively. [ABSTRACT FROM AUTHOR]

An innovative surface plasmon resonance (SPR) approach for the detection of 2,4,6-trinitrotoluene (TNT) gas traces, obtained using an engineered molecular imprinted sol–gel film as recognition layer onto a plasmonic gold grating, is here proposed. The SPR substrate combined with the sol–gel matrix is able to trap gas phase TNT molecules from a TNT-saturated environment (4.9 ppb). Taking advantage of the azimuthally-controlled grating-coupled SPR, this sensing platform demonstrates the potentiality to detect TNT traces <1 ppb with a sensitivity of 0.47°/ppb. [ABSTRACT FROM AUTHOR]

Tracer gases are an effective method for assessing mine ventilation systems, especially when other techniques are impractical. Based on previously completed laboratory and field experiments, this paper discusses some common and challenging issues encountered when using tracer gases in underground mines. The discussion includes tracer release methods, sampling and analysis techniques. Additionally, the use of CFD to optimize the design of tracer gas experiments is also presented. Finally, guidelines and recommendations are provided on the use of tracer gases in the characterization of underground mine ventilation networks. This work has informed the practical use of tracer gases in mines, and this body of knowledge is expected to contribute to more efficient and more common use of tracer gases by mine engineers, which will allow for better characterization of mine ventilation system and improved safety. The findings can also be used when using the tracer gas technique in the evaluation of atmospheric environment and air quality investigation in buildings. [ABSTRACT FROM AUTHOR]

Estimating respiration and photosynthesis rates in streams usually requires good knowledge of reaeration at the given locations. For this purpose, gas-tracer tests can be conducted, and reaeration rate coefficients are determined from the decrease in gas concentration along the river stretch. The typical procedure for analysis of such tests is based on simplifying assumptions, as it neglects dispersion altogether and does not consider possible fluctuations and trends in the input signal. We mathematically derive the influence of these non-idealities on estimated reaeration rates and how they are propagated onto the evaluation of aerobic respiration and photosynthesis rates from oxygen monitoring. We apply the approach to field data obtained from a gas-tracer test using propane in a second-order stream in Southwest Germany. We calculate the reaeration rate coefficients accounting for dispersion as well as trends and uncertainty in the input signals and compare them to the standard approach. We show that neglecting dispersion significantly underestimates reaeration, and results between sections cannot be compared if trends in the input signal of the gas tracer are disregarded. Using time series of dissolved oxygen and the various estimates of reaeration, we infer respiration and photosynthesis rates for the same stream section, demonstrating that the bias and uncertainty of reaeration using the different approaches significantly affects the calculation of metabolic rates. [ABSTRACT FROM AUTHOR]

A new in situ method for directly measuring the gas collection efficiency in the region around a gas extraction well was developed. Thirteen tests were conducted by injecting a small volume of gas tracer sequentially at different locations in the landfill cell, and the gas tracer mass collected from each test was used to assess the collection efficiency at each injection point. For 11 tests the gas collection was excellent, always exceeding 70% with seven tests showing a collection efficiency exceeding 90%. For one test the gas collection efficiency was 8 ± 6%. Here, the poor efficiency was associated with a water-laden refuse or remnant daily cover soil located between the point of tracer injection and the extraction well. The utility of in situ gas tracer tests for quantifying landfill gas capture at particular locations within a landfill cell was demonstrated. While there are certainly limitations to this technology, this method may be a valuable tool to help answer questions related to landfill gas collection efficiency and gas flow within landfills. Quantitative data from tracer tests may help assess the utility and cost-effectiveness of alternative cover systems, well designs and landfill gas collection management practices. [ABSTRACT FROM AUTHOR]

The authors give the results of experiments investigations into the intercassette interaction of the coolant in the WWER-reactor mixed core consisting of TVSA-T and TVSA-12 PLUS. The investigations were carried out on an aerodynamic stand by the method of gas tracer diffusion. An analysis of the spatial distribution of projections of the absolute flow velocity and of the propagation of the tracer concentrations enabled the authors to particularize the pattern of coolant flow past the spacer and mixing grids of the fuel assemblies. [ABSTRACT FROM AUTHOR]

Global quantitative estimations of ecosystem functions are vital. Among those, ecosystem respiration and photosynthesis contribute to carbon cycling and energy flow to food webs. These can be estimated in streams with the open channel diel oxygen method (single or two stations) essentially relying on a mass balance of oxygen over a defined reach. The method is generally perceived as low cost and easy to apply with new drift free optic sensors. Yet, it remains challenging on several key issues reviewed here: measurements of gas transfer at the air-water interface, appropriate mixing of tracers, uncertainty propagation in the calculations, spatial heterogeneity in oxygen concentrations, the derivation of net primary production (NPP) or autotrophic respiration, and the temperature dependence of photosynthesis and respiration. An extremely simple modeling tool is presented in an Excel workbook recommended for teaching the basic principles of the method. The only method able to deal with stream spatial heterogeneity is the method by Demars et al. Example data, Excel workbook, and R script are provided to run stream metabolism calculations. Direct gas exchange determination is essential in shallow turbulent streams, but modeling may be more accurate in large (deep) rivers. Lateral inflows should be avoided or well characterized. New methods have recently been developed to estimate NPP using multiple diel oxygen curves. The metabolic estimates should not be systematically temperature corrected to compare streams. Other recent advances have improved significantly the open channel diel oxygen method, notably the estimation of respiration during daylight hours. [ABSTRACT FROM AUTHOR]

The tracer gas ratio method, using CO2 as natural tracer, has been suggested as a pragmatic option to measure emissions from naturally ventilated (NV) barns without the need to directly estimate the ventilation rate. The aim of this research was to assess the performance of a low-cost Non-Dispersive Infra-Red (NDIR) sensor for intensive spatial field monitoring of CO2 concentrations in a NV dairy cow house. This was achieved by comparing NDIR sensors with two commonly applied methods, a Photo-Acoustic Spectroscope (PAS) Gas Monitor and an Open-Path laser (OP-laser). First, calibrations for the NDIR sensors were obtained in the laboratory. Then, the NDIR sensors were placed in a dairy cow barn for comparison with the PAS and OP-laser methods. The main conclusions were: (a) in order to represent the overall barn CO 2 concentration of the dairy cow barn, the number of NDIR sensors to be accounted for average concentration calculation was dependent on barn length and on barn area occupation; and (b) the NDIR CO2 sensors are suitable for multi-point monitoring of CO2 concentrations in NV livestock barns, being a feasible alternative for the PAS and the OP-laser methods to monitor single-point or averaged spatial CO2 concentrations in livestock barns. [ABSTRACT FROM AUTHOR]

The objective of this study was to measure enteric CH4 emissions using a new portable automated open-circuit gas quantification system (GQS) and the sulfur hexafluoride tracer technique (SF6) in midlactation Holstein cows housed in a tiestall barn. Sixteen cows averaging 176 ± 34 d in milk, 40.7 ± 6.1 kg of milk yield, and 685 ± 49 kg of body weight were randomly assigned to 1 out of 2 treatments according to a crossover design. Treatments were (1) ad libitum (adjusted daily to yield 10% orts) and (2) restricted feed intake [set to restrict feed by 10% of baseline dry matter intake (DMI)]. Each experimental period lasted 22 d, with 14 d for treatment adaptation and 8 d for data and sample collection. A common diet was fed to the cows as a total mixed ration and contained 40.4% corn silage, 11.2% grass-legume haylage, and 48.4% concentrate on a dry matter basis. Spot 5-min measurements using the GQS were taken twice daily with a 12-h interval between sampling and sampling times advanced 2 h daily to account for diurnal variation in CH4 emissions. Canisters for the SF6 method were sampled twice daily before milking with 4 local background gas canisters inside the barn analyzed for background gas concentrations. Enteric CH4 emissions were not affected by treatments and averaged 472 and 458 g/d (standard error of the mean = 18 g/d) for ad libitum and restricted intake treatments, respectively (data not shown). The GQS appears to be a reliable method because of the relatively low coefficients of variation (ranging from 14.1 to 22.4%) for CH4 emissions and a moderate relationship (coefficient of determination = 0.42) between CH4 emissions and DMI. The SF6 resulted in large coefficients of variation (ranging from 16.0 to 111%) for CH4 emissions and a poor relationship (coefficient of determination = 0.17) between CH4 emissions and DMI, likely because of limited barn ventilation and high background gas concentration. Research with improved barn ventilation systems or outdoors is warranted to further assess the GQS and SF6 methodologies. [ABSTRACT FROM AUTHOR]

At the Cooperative Research Centre for Greenhouse Gas Technology's (CO2CRC) field site in the Otway Basin of Victoria, Australia, investigations into the storage of CO 2 -rich gas in a depleted hydrocarbon gas field have been conducted in the Waarre C reservoir. The injected gas from the nearby Buttress field contained 75 mol% CO 2 , 21 mol% CH 4 with the remaining balance being a mixture of wet hydrocarbons, condensate and nitrogen. Chemical tracers (sulphur hexafluoride, SF 6 ; krypton, Kr; perdeuterated methane, CD 4 ) were added on the basis of literature surveys and small volume trials at the Frio II Brine experiment in Texas. The aim of the project was to measure, monitor and verify the presence of injected CO 2 in a depleted gas field and that the arrival of tracers was a major component of demonstrating breakthrough of CO 2 at the monitoring well, Naylor-1. The paper focuses on methods developed for the injection, recovery and analysis of samples collected at the Naylor-1 well. Results of tracer analysis compare well with other data collected (including pH and density measurements) to demonstrate breakthrough. A slip-stream injection system was designed to deliver the tracers mixed with the CO 2 -rich gas into the subsurface at the CRC-1 well. The tracers were added to the gas stream 17 days after the start of injection (CO 2 injection commenced 18th March, 2008) into the depleted natural gas field at Naylor. A U-tube system was used to retrieve the samples from the Naylor-1 monitoring well. Collected gas and formation water samples were analysed in detail for gas composition, tracers, isotopes ( 13 C CO 2 mainly) and inorganic geochemistry for the broader project. The tracer results confirm that CO 2 breakthrough at the monitoring well occurred within the predicted times. However the interval between samples taken from the U-tubes was too coarse to resolve detailed differences in arrival times between the CO 2 and tracers. Of the three tracers used, SF 6 provided the clearest evidence of breakthrough at U-tube 2. Kr, because of its abundance in air, and its potential to be present in the subsurface, was more prone to contamination and had higher background levels prior to breakthrough. CD 4 was expected to provide some more unique data based on the presence of abundant CH 4 in the reservoir interval. With hindsight, larger volumes should have been injected to facilitate comparisons with the other tracers and add value to the data set. The test of CD 4 however acted as a suitable proof of concept that CD 4 could be used in such a high background of CH 4 . Further work is ongoing to generate data for partition coefficients between supercritical CO 2 , CH 4 and water under the injection conditions. [ABSTRACT FROM AUTHOR]

The optically thin critical densities and the effective excitation densities to produce a 1 K km/s (or 0:818 Jy km/s (νjk/100 GHz)²(beam/10″)²) spectral line are tabulated for 12 commonly observed dense gas molecular tracers. The dependence of the critical density and effective excitation density on physical assumptions (i.e., gas kinetic temperature and molecular column density) is analyzed. Critical densities for commonly observed dense gas transitions in molecular clouds (i.e., HCN 1-0, HCO+ 1-0, N2H+ 1-0) are typically 1-2 orders of magnitude larger than effective excitation densities because the standard definitions of critical density do not account for radiative trapping and 1 Kkm=s lines are typically produced when radiative rates out of the upper energy level of the transition are faster than collisional depopulation. The use of effective excitation density has a distinct advantage over the use of critical density in characterizing the differences in density traced by species such as NH3, HCO+, N2H+, and HCN, as well as their isotopologues; but, the effective excitation density has the disadvantage that it is undefined for transitions when Eu/k » Tk, for low molecular column densities, and for heavy molecules with complex spectra (i.e., CH3CHO). [ABSTRACT FROM AUTHOR]

The measure of air change rate (ACR) in building is a difficult and usually expensive task. The tracer gas method is the reference technique but its implementation is difficult and the interpretation of results is not straightforward. In the present work, the concentration decay method by multiple CO 2 transmitters is experimentally validated in the case of cross-ventilation. It is observed that in-situ CO 2 transmitters lead to ACR values in good agreement with reference measurements obtained from mechanically controlled values. Whereas multiple transmitters in different sampling positions show the imperfect mixing, a sensor located at the outlet or an averaged value of all sensors can provide an accurate measure of the ACR. Moreover, the spatial variation of CO 2 concentration can be used to assess the ventilation efficiency in the test chamber. Different measures and calculation methods are discussed, and the uncertainty analysis of each method is carried out. [ABSTRACT FROM AUTHOR]

Whole-site methane emissions from 15 Danish landfills were assessed using a mobile tracer dispersion method with either Fourier transform infrared spectroscopy (FTIR), using nitrous oxide as a tracer gas, or cavity ring-down spectrometry (CRDS), using acetylene as a tracer gas. The landfills were chosen to represent the different stages of the lifetime of a landfill, including open, active, and closed covered landfills, as well as those with and without gas extraction for utilisation or flaring. Measurements also included landfills with biocover for oxidizing any fugitive methane. Methane emission rates ranged from 2.6 to 60.8 kg h −1 , corresponding to 0.7–13.2 g m −2 d −1 , with the largest emission rates per area coming from landfills with malfunctioning gas extraction systems installed, and the smallest emission rates from landfills closed decades ago and landfills with an engineered biocover installed. Landfills with gas collection and recovery systems had a recovery efficiency of 41–81%. Landfills where shredder waste was deposited showed significant methane emissions, with the largest emission from newly deposited shredder waste. The average methane emission from the landfills was 154 tons y −1 . This average was obtained from a few measurement campaigns conducted at each of the 15 landfills and extrapolating to annual emissions requires more measurements. Assuming that these landfills are representative of the average Danish landfill, the total emission from Danish landfills were calculated at 20,600 tons y −1 , which is significantly lower than the 33,300 tons y −1 estimated for the national greenhouse gas inventory for 2011. [ABSTRACT FROM AUTHOR]

A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF) was used as the nonreactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well and analyzed for SF, CH, CO, and VOCs. The travel times determined for SF from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate transport by only gas-phase diffusion. In addition, significant concentrations of CH and CO were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF are caused by advective transport associated with landfill gas generation. The rates of transport varied vertically, which is attributed to multiple factors including spatial variability of water content, refuse mass, refuse permeability, and gas generation. [ABSTRACT FROM AUTHOR]

Summary Quantification of the volume of groundwater discharge to streams, and the source aquifer of that discharge, is required to adequately manage the impacts of groundwater use on stream ecosystems. This has been achieved through longitudinal surveys of gaseous tracers, but their effectiveness can be limited by rapid equilibration between the stream and the atmosphere. Here we develop the use of carbon-14 in dissolved inorganic carbon (DIC) in a stream as a tracer of groundwater discharge. A controlled equilibration experiment was conducted, during which groundwater with an initial 14 C activity of 5.5 pMC was allowed to equilibrate with the atmosphere over 72 days. The effective transfer velocity for 14 C was measured as 0.013 m d −1 . The method was then tested at an artificial groundwater discharge location, where the effective transfer velocity was measured as 0.025 m d −1 . In these simple systems, the ratio of the effective 14 C transfer velocity to the CO 2 gas transfer velocity is a function of pH, and proportional to the fraction of DIC present as CO 2 . The method was then applied along a reach of the Daly River, Australia, where groundwater discharge is known to occur. A decrease of 7 pMC was observed across the major spring discharge zone, with subsequent equilibration with the atmosphere occurring over at least tens of kilometres. This allowed for the effective transfer velocity to be estimated at between 0.09 and 0.15 m d −1 , and for the 14 C activity of groundwater discharge to be estimated at between 60 and 66 pMC. The equilibration of 14 C in stream DIC is in the order of 10 times slower than for gas tracers, which may allow for the detection of smaller groundwater discharge fluxes than is possible with gas tracers. If the total groundwater discharge flux is known, measurements of 14 C in stream DIC can also be used to infer the 14 C activity of discharging groundwater. This method may be a useful alternative to direct groundwater sampling, particularly in remote basins with few groundwater wells. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen isotope exchange experiments are performed in donor doped PbZrxTi1−xO3 (PZT) under field load. A detailed mapping of the oxygen tracer ions and thus indirectly of the oxygen vacancy distribution is enabled by spatially resolved time-of-flight secondary ion mass spectrometry (ToF-SIMS). Hence, knowledge can be gained on the oxygen vacancy redistribution under the influence of high electric fields applied to Cu inner electrodes of a PZT multilayer stack. Upon field load an enhanced oxygen tracer concentration is measured near to the cathode and interpreted in terms of a field-driven oxygen vacancy accumulation at an oxide ion blocking Cu cathode. Oxygen tracer depth profiles in near-anode and near-cathode diffusion zones give quantitative information on local grain and grain boundary diffusion coefficients and their dependence on applied voltages. [Copyright &y& Elsevier]

A miniature dosage meter for toxic gas is developed based on TaS2 nanosheets, which is capable of indicating the toxic dosage of trace level NO at room temperature. The TaS2 film-based chemiresistor shows an irreversible current response against the exposure of NO. The unique non-recovery characteristic makes the TaS2 film-based device an ideal indicator of total dosage of chronicle exposure. [ABSTRACT FROM AUTHOR]

Today, ground-based optical remote sensing (ORS) has become an intensively used method for quantifying pollutant or greenhouse gas emissions from point or area sources, and for the validation of airborne or satellite remote sensing data. In this study, we present the results of a release experiment using acetylene (CH) as a tracer gas, where three ORS techniques were simultaneously tested for two main purposes: (1) the detection of emission sources and (2) the quantification of release rates. Therefore, passive and active open-path Fourier transform infrared spectroscopy (OP-FTIR) and open-path tunable diode laser absorption spectroscopy (TDLAS) were applied and evaluated. The concentration results of the active ORS methods are compared to those estimated by a Lagrangian stochastic atmospheric dispersion model. Our results reveal that passive OP-FTIR is a valuable tool for the rapid detection and imaging of emission sources and the spatial tracer gas distribution; while with active OP-FTIR and TDLAS, CH concentrations in the sub-ppm range could be quantified that correlated well with the concentration data obtained by our modeling approach. [ABSTRACT FROM AUTHOR]

Jilin oilfield is conducting the first large-scale demonstration project on CO2 storage and enhanced oil recovery (EOR) in the northeast of China. A comprehensive monitoring program has been designed and deployed in the target reservoir of block H-59 using a wide range of techniques to monitor the injection and production systems, the CO2 migration fronts, and potential CO2 leakage pathways. Tube fault detection, corrosion inhibitors, anti-CO2 corrosion cement, and production dynamic analysis have been adopted to guarantee the safety at the well site. CO2 movement in the reservoir is detected mainly by gas tracer, electric spontaneous potential measurement, and fluid sampling. Near-surface environmental monitoring is also conducted around the injection site. Field experience has shown that the monitoring targets should be focused on the reservoir, near-surface, and injection and production systems. Applying monitoring techniques to ensure the integrity of wellbores can not only prevent the leakage of CO2, but also avoid the blind expansion of monitoring program scopes. It is reliable and economical to take full advantage of techniques based on wellbores to monitor CO2 movement in oil reservoirs with dense well patterns. Up to April 2013, nearly 21.7 × 104 tons of CO2 has been injected without obvious leakage caused by integrity failure of wells or the geological structure of reservoir. More than 96% of injected CO2 has been safely stored with the rest of injected CO2 normally breakthrough in the production wells. The preliminary monitoring experience obtained can provide valuable guidance for the future enlarged Jilin project and other CO2 EOR and storage operations. [ABSTRACT FROM AUTHOR]

Highlights: [•] A field trial of CO2 ECBM is presented in which 460tonnes of CO2 was injected. [•] A multi-lateral horizontal well of 2.3km in-seam length was used for the injection. [•] Gas migration was monitored in a well 25m from the injection well. [•] The CO2 concentration gradually increased to a maximum of 12%. [•] A tracer gas was injected at the start and towards the end of trial. [Copyright &y& Elsevier]