Small Volumes Of Gas Research Articles

Direct determination of sodium, potassium, chromium and vanadium in biodiesel fuel by tungsten coil atomic emission spectrometry

High levels of sodium and potassium can be present in biodiesel fuel and contribute to corrosion, reduced performance and shorter engine lifetime. On the other hand, trace amounts of chromium and vanadium can increase the emission of pollutants during biodiesel combustion. Sample viscosity, immiscibility with aqueous solutions and high carbon content can compromise biodiesel analyzes. In this work, tungsten filaments extracted from microscope light bulbs are used to successively decompose biodiesel's organic matrix, and atomize and excite the analytes to determine sodium, potassium, chromium and vanadium by tungsten coil atomic emission spectrometry (WCAES). No sample preparation other than simple dilution in methanol or ethanol is required. Direct analysis of 10-μL sample aliquots using heating cycles with less than 150s results in limits of detection (LOD) as low as 20, 70, 70 and 90μgkg−1 for Na, K, Cr and V, respectively. The procedure's accuracy is checked by determining Na and K in a biodiesel reference sample and carrying out spike experiments for Cr and V. No statistically significant differences were observed between reference and determined values for all analytes at a 95% confidence level. The procedure was applied to three different biodiesel samples and concentrations between 6.08 and 95.6mgkg−1 for Na and K, and between 0.22 and 0.43mgkg−1 for V were obtained. The procedure is simple, fast and environmentally friendly. Small volumes of reagents, samples and gases are used and no residues are generated. Powers of detection are comparable to other traditional methods.

Calculation of the purification process of carbon dioxide industrial gases

Mathematical model of absorber for small volumes of cleared gases is proposed. There are made calculations of the basic dimensions for the pilot facility, calculation of the basic sizes of absorber for industrial installation, which showed the operability of the mathematical model for large-tonnage production.

Focused fluid flow in the Baiyun Sag, northern South China Sea: implications for the source of gas in hydrate reservoirs

The origin and migration of natural gas and the accumulation of gas hydrates within the Pearl River Mouth Basin of the northern South China Sea are poorly understood. Based on high-resolution 2D/3D seismic data, three environments of focused fluid flow: gas chimneys, mud diapirs and active faults have been identified. Widespread gas chimneys that act as important conduits for fluid flow are located below bottom simulating reflections and above basal uplifts. The occurrence and evolution of gas chimneys can be divided into a violent eruptive stage and a quiet seepage stage. For most gas chimneys, the strong eruptions are deduced to have happened during the Dongsha Movement in the latest Miocene, which are observed below Pliocene strata and few active faults develop above the top of the Miocene. The formation pressures of the Baiyun Sag currently are considered to be normal, based on these terms: 1) Borehole pressure tests with pressure coefficients of 1.043–1.047; 2) The distribution of gas chimneys is limited to strata older than the Pliocene; 3) Disseminated methane hydrates, rather than fractured hydrates, are found in the hydrate samples; 4) The gas hydrate is mainly charged with biogenic gas rather than thermogenic gas based on the chemical tests from gas hydrates cores. However, periods of quiet focused fluid flow also enable the establishment of good conduits for the migration of abundant biogenic gas and lesser volumes of thermogenic gas. A geological model governing fluid flow has been proposed to interpret the release of overpressure, the migration of fluids and the formation of gas hydrates, in an integrated manner. This model suggests that gas chimneys positioned above basal uplifts were caused by the Dongsha Movement at about 5.5 Ma. Biogenic gas occupies the strata above the base of the middle Miocene and migrates slowly into the gas chimney columns. Some of the biogenic gas and small volumes of thermogenic gas eventually contribute to the formation of the gas hydrates.

CT appearance of the pelvis after Cesarean delivery—what is considered normal?

ObjectiveTo describe the normal computed tomography (CT) appearance of the pelvis after uncomplicated Cesarean section (C-section). Patients and methodsPelvic CT examinations of 31 patients after uncomplicated C-section were reviewed. ResultsHigher postoperative day (POD) correlated well with decreases in the uterine long axis and endometrial width but did not correlate to scar width. Full thickness defect of the uterine wall was revealed in 48% of patients. Small volumes of intrauterine gas presented in half of patients at POD 1–26. Free pelvic fluid appeared in 74%. Pelvic collections were rare and small. ConclusionThere is wide variability in pelvic CT appearance following uncomplicated C-section.

Pressure, O2, and CO2, in aquatic Closed Ecological Systems

Pressure increased during net photosynthetic O2 production in the light and decreased during respiratory O2 uptake during the dark in aquatic Closed Ecological Systems (CESs) with small head gas volumes. Because most CO2 will be in the liquid phase as bicarbonate and carbonate anions, and CO2 is more soluble than O2, volumes of gaseous CO2 and gaseous O2 will not change in a compensatory manner, leading to the development of pressure. Pressure increases were greatest with nutrient rich medium with NaHCO3 as the carbon source. With more dilute media, pressure was greatest with NaHCO3, and less with cellulose or no-added carbon. Without adequate turbulence, pressure measurements lagged dissolved O2 concentrations by several hours and dark respiration would have been especially underestimated in our systems (250–1000ml). With adequate turbulence (rotary shaker), pressure measurements and dissolved O2 concentrations generally agreed during lights on/off cycles, but O2 measurements provided more detail. At 20°C, 29.9 times as much O2 will distribute into the gas phase as in the liquid, per unit volume, as a result of the limited solubility of O2 in water and according to Henry’s Law. Thus even a small head gas volume can contain more O2 than a larger volume of water. When both dissolved and gaseous O2 and CO2 are summed, the changes in Total O2 and CO2 are in relatively close agreement when NaHCO3 is the carbon source. These findings disprove an assumption made in some of Taub’s earlier research that aquatic CESs would remain at approximately atmospheric pressure because approximately equal molar quantities of O2 and CO2 would exchange during photosynthesis and respiration; this assumption neglected the distribution of O2 between water and gas phases. High pressures can occur when NaHCO3 is the carbon source in nutrient rich media and if head-gas volumes are small relative to the liquid volume; e.g., one “worse case” condition developed 800mmHg above atmospheric pressure and broke the glass container. Plastic screw cap closures are likely to leak at high pressures and should not be assumed to seal unless tested at appropriate pressures. Pressure can be reduced by having larger head-gas volumes and using less concentrated nutrient solutions. It is important that pressure changes be considered for both safety and closure, and if total O2 is used as the measure of net photosynthesis and respiration, the O2 in the gas phase must be added to the dissolved O2.

An experimental study of secondary oil migration in a three-dimensional tilted porous medium

A three-dimensional physical experiment was conducted to study secondary oil migration under an impermeable inclined cap. Light-colored oil was released continuously at a slow rate of about 0.1 mL/min from a point at the base of an initially water-saturated porous model. With buoyancy as a primary driving force, a vertical cylindrical shape of an oil migration pathway was observed first, and then a layer-shaped lateral migration pathway was observed beneath the top inclined sealing plate once the oil cluster had reached the top cap. Magnetic resonance imaging was used to observe the migration processesmdashfor example, morphology of the migration pathway, intermittency of oil bubbles, and variation of oil saturation within the migration paths. Results show that the snap-off phenomenon (related to fast local imbibition processes) occurred more commonly during vertical migration than it did during lateral migration. The lateral migration pathway that parallels to the top inclined cap has a typical vertical thickness of 2 to 4 cm (0.8ndash1.6 in.) (i.e., roughly 40ndash80 pores). This thickness is consistent with the prediction derived from scaling laws related to pore size and Bond number. Along the lateral migration direction, the sectional area and the horizontal width of the migration pathway fluctuate significantly, although the average oil saturation along the pathway remains almost the same. After stopping the initial oil injection, the sectional area of the migration pathway shrinks significantly. Therefore, we believe that this significant shrinking of the migration pathway is the main reason why only a relatively small volume of oil and gas has been lost during secondary migration.

CT‐based estimation of intracavitary gas volumes using threshold‐based segmentation: In vitro study to determine the optimal threshold range

This study investigated the optimal Hounsfield unit (HU) threshold range when using threshold-based segmentation to estimate volumes of contained gas (i.e. intestinal gas) on CT. A water-filled cylindrical acrylic imaging phantom containing two saline bags modified to allow injection of known volumes of gas (room air) was constructed. The phantom was imaged with CT following injection of known gas volumes. Images were analysed using standard threshold-based 3D region growing with human-entered seed points. The lower threshold was -1024 HU, and upper thresholds between -700 HU and -200 HU were tested for each volume. Appropriate statistical analysis was performed. Measurements were normally distributed. There was excellent correlation between measured and injected volumes for all thresholds (Pearson's r > 0.99). The optimal upper threshold for small gas volumes (1-6 mL) was -550 HU with 0.1% ± 3.9% (mean ± standard deviation) error. The optimal upper threshold for large gas volumes (10-50 mL) was -350 HU with 0.7 ± 3.6% (mean ± standard deviation) error with Pearson correlations of r > 0.99 for both. Accurate estimation of gas volumes on CT is possible using threshold-based segmentation software with a wide range of upper thresholds. The optimal upper threshold for estimation of small volumes (1-6 mL) was -550 HU and -350 HU for volumes of 10-50 mL.

Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces, and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β→1; albeit at low βS (< 0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however, some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency-dependent force coefficients. The equivalent damping decreases above and below βS ∼ 0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.

Flare Reduction Options and Simulation for the Qatari Oil and Gas Industry

Flaring and venting are two activities associated with oil and gas production. Qatar is a world leader in the production and exporting of liquid natural gas (LNG). Flaring is a combusting process used to dispose of natural gas (sweet, sour acid gas or otherwise other hydrocarbon vapors) through a vertical stack. Facilities in the oil and gas industry may routinely flare small volumes of natural gas that are technically difficult and uneconomic to conserve. It is estimated that flaring of gas associated with these industries is around 100 billion cubic meters per year worldwide; emitting around 400 million tones of CO2 and wasting 1600 Trillion Btu of energy each year. The reduction of flaring is gaining momentum globally and the Qatari industries are paying increased attention to this international focus on energy conservation and global climate change mitigation measures. The reduction of the volume of gas flared each year is an important issue for the gas industry for health, safety and environmental impacts, as well as conservation of energy resources. Qatar Ministry of Environment (MoE) cap targets flaring rate to 0.3% of inlet feed gas, which is usually met in QG from the existing trains in operation today. However, sustaining the overall flaring rate within the 0.3% governmental target value will pose a new challenge with the commissioning and operation of the new “Mega Trains” which will produce the world largest amount of LNG in a one given facility. This paper will present an initial engineering feasibility study to explore the minimization of routine and non-routine flaring in the Qatari Gas industries by carrying out a flare reduction assessment study and simulation using FlareNet.

Reversible Hydrogen Electrode Application as Indicator Electrode for Real Time Kinetic Study of Microbial H2 Production

The Reversible Hydrogen Electrode (RHE) potential depends on the pH and the H2 pressure which determines the disolved hydrogen concentration according to the Henry law. RHE was applied as hydrogen sensor for real time bacterial hydrogen production rate evaluation employing the photosynthetic Rodobacter Capsulatus strain IR3 in 10 ml reactor containing RCV medium. The reliable determination of the produced H2 volume for determination of the process rate requires big reactor volumes since the H2 production rate is small, measured in mL/hour and the precise measurements of small gas volumes is very complicated. The RHE potential monitoring however allows real time determination of the generated H2 and hence the process rate without consumption of great reagent amounts.

Optimizing [13N]N2 radiochemistry for nitrogen‐fixation in root nodules of legumes

AbstractHere we explored the conditions for synthesizing [13N]N2 in a state that is suitable for the administration to plant root nodules enabling studies of nitrogen fixation. [13N]N2 was prepared batchwise, starting with [13N]NO from the 16O(p,α)13N nuclear reaction on a liquid water target. [13N]NO was first reduced to [13N]NH3 using Devarda's alloy, and then the [13N]NH3 was oxidized to [13N]N2 by hypobromite using carrier‐added NH4Cl. The amounts of carrier NH4Cl and hypobromite were varied to determine the effects these parameters had on the radiochemical yield, and on the radiotracer specific activity. As expected, increasing the amount of carrier NH4Cl improved the radiochemical yield. Unexpectedly, increasing the amount of excess hypobromite from 1.6‐fold to 6‐fold molar equivalents (relative to NH4Cl) improved the radiochemical yield and radiotracer specific activity under all conditions of carrier NH4Cl. As a comparison, we measured [13N]N2 specific activity derived from in‐target production based on a 50 µA min irradiation driving the 14N(p,pn)13N reaction on a gaseous N2 target. The ‘wet’ radiochemistry approach afforded two advantages over the in‐target approach with a ∼600‐fold improvement in specific activity, and the ability to collect the tracer in a small volume of gas (∼20 mL at STP). Copyright © 2010 John Wiley & Sons, Ltd.

Evaluation of a glow discharge chamber coupled to time of flight mass spectrometry for the analysis of small gas volumes and bubbles in glass

Glow discharge time-of-flight mass spectrometry (GD-TOFMS) is becoming a powerful tool not only for simultaneous elemental determinations but also for possible molecular analysis of solid and gaseous samples. In this work, a modified in-house GD ion source, operated with radiofrequency (rf) power and coupled to an orthogonal TOFMS, is investigated for the analysis of small volumes of gaseous samples. Moreover, the results are compared with those obtained using a previous GD source design containing an internal flow tube. The modified in-house GD ion source has a reduced internal volume and no flow tube built in, allowing the use of lower gas flow rates. Additionally, this design allows the GD source to be placed closer to the sampler cone of the MS, resulting in improved ion transport efficiency. Limits of detection obtained for the analysis of small volumes of gas, turned out to be more than one order of magnitude better when using this modified in-house GD ion source. Furthermore, the pulsed mode of the rf-GD system (both, in millisecond and microsecond regimes) has been investigated to further improve the analytical performance of the technique for small gas volumes analysis. Calibration curves are obtained for the selected molecular compounds including nitrogen, oxygen and carbon dioxide. The results show that the limits of detection can be further improved by using a 100 μs-pulsed-rf-GD-TOFMS system, where limits of detection observed were below nanolitre for molecular nitrogen and oxygen, and below picolitre for carbon dioxide.

The measurement of compositions and the isotopic distribution of released fission gas in the fuel rods of pressurized water reactors (PWR) of Korea

In this work the analysis procedures of fission gas compositions and their isotopic distributions using a gas chromatography (GC) system and/or a quadrupole mass spectrometer (QMS) system were established, and their analysis results were reviewed in order to evaluate their analytical performance. Also, the accumulated data, up to now, regarding fission gas measurement were reviewed to discern any irradiation histories of the punctured fuel rods. A simple gas injection apparatus was designed and fabricated for the quantitative injection of a small volume of fission gas into the GC and the QMS system. With an appropriate temperature controlling of a molecular sieve 5A column, nitrogen, krypton and xenon of a mixture gas was clearly separated within 7 min. According to the analysis results, the relative standard deviation in the determination of fission gas compositions, krypton and xenon, by the GC analysis or by the QMS analysis was about 1%. Based on the review results of the isotopic ratios of krypton and xenon of the released fission gas, it is likely that no abnormally irradiated rods, i.e. defected rods, were included among the punctured rods.

Analysis of low‐concentration gas samples with continuous‐flow isotope ratio mass spectrometry: eliminating sources of contamination to achieve high precision

Developments in continuous-flow isotope ratio mass spectrometry have made possible the rapid analysis of delta13C in CO2 of small-volume gas samples with precisions of < or = 0.1 per thousand. Prior research has validated the integrity of septum-capped vials for collection and short-term storage of gas samples. However, there has been little investigation into the sources of contamination during the preparation and analysis of low-concentration gas samples. In this study we determined (1) sources of contamination on a Gasbench II, (2) developed an analytical procedure to reduce contamination, and (3) identified an efficient, precise method for introducing sample gas into vials. We investigated three vial-filling procedures: (1) automated flush-fill (AFF), (2) vacuum back-fill (VBF), and (3) hand-fill (HF). Treatments were evaluated based on the time required for preparation, observed contamination, and multi-vial precision. The worst-case observed contamination was 4.5% of sample volume. Our empirical estimate showed that this level of contamination results in an error of 1.7 per thousand for samples with near-ambient CO2 concentrations and isotopic values that followed a high-concentration carbonate reference with an isotope ratio of -47 per thousand (IAEA-CO-9). This carry-over contamination on the Gasbench can be reduced by placing a helium-filled vial between the standard and the succeeding sample or by ignoring the first two of five sample peaks generated by each analysis. High-precision (SD < or = 0.1 per thousand) results with no detectable room-air contamination were observed for AFF and VBF treatments. In contrast, the precision of HF treatments was lower (SD > or = 0.2 per thousand). VBF was optimal for the preparation of gas samples, as it yielded faster throughput at similar precision to AFF.

What is the origin of intravascular gas on postmortem computed tomography?

Purpose Intravascular gas is frequently demonstrated on postmortem computed tomography (PMCT). The purpose of this study is to classify the distribution patterns of intravascular gas and to determine its developmental mechanism. Method and materials The series included 43 cases (mean age, 62 years). All causes of death were non-traumatic (14 cases, sudden death; 29 cases, death caused by known disease). Using a 16-row multi-detector CT, whole body images were obtained with 1.25-mm collimation. Gas in veins, right heart was classified as venous gas. Gas in arteries, left heart was classified as arterial gas. Results PMCT showed intravascular gas in 20 cases. Distribution of gas was divided into 2 patterns; pattern 1 (11 cases): a small volume of venous gas (superior and inferior vena cava, right heart, subclavian veins and brachiocephalic veins) and no arterial gas; pattern 2 (9 cases): both venous (same positions of pattern 1 plus hepatic veins) and arterial gas (left heart, ascending aorta, vertebral arteries and cerebral arteries). Conclusion Since imaging findings of pattern 1 are similar to those frequently demonstrated after intravenous contrast-enhanced CT, this gas is presumed to be of exogenous origin from intravenous catheters. In contrast, the gas in pattern 2 may be of endogenous origin, such as decompression disease. Bubbles should move through the ventral side of vessels in the supine position, and subsequently must be trapped by extruded anatomical structures to the ventral side, for example, right ventricle, vertebral and cerebral arteries, hepatic veins and renal veins.

Mid-Infrared Trace Gas Analysis with Single-Pass Fourier Transform Infrared Hollow Waveguide Gas Sensors

A hollow core optical fiber gas sensor has been developed in combination with a Fourier transform infrared (FT-IR) spectrometer operating in the spectral range of 4000-500 cm(-1), enabling continuous detection of small volume gas-phase analytes such as CH(4), CO(2), C(2)H(5)Cl, or their mixtures at trace levels. Ag/Ag-halide hollow core optical fibers simultaneously serve as an optical waveguide for broad-band mid-infrared radiation and as a miniaturized absorption gas cell. Specifically, carbon dioxide, methane, and ethyl chloride as well as binary mixtures in a carrier gas were analyzed during exponential dilution experiments. In the studies reported here, the integration of an optical gas sensor with FT-IR spectroscopy provides excellent detection limits for small gas volumes ( approximately 1.5 mL) of individual analytes at a few tens of parts per billion (ppb, vol/vol) for carbon dioxide and a few hundreds of ppb (vol/vol) for methane. Furthermore, the broad-band nature of the radiation source and of the hollow core optical waveguide provides the capability of multi-constituent analysis in mixtures.

Isoconversion effective activation energies derived from repetitive injection fast gas chromatography/mass spectrometry

Evolved gas analysis by using fast temperature programmed gas chromatography/mass spectrometry is described. A small volume gas chromatograph oven is used to permit rapid heating and cooling of a capillary gas chromatography column, resulting in short analysis cycle times. This capability permits automated sampling and analysis of a purge gas effluent stream generated during thermal analysis of a solid sample. Species-specific mass spectral information extracted from successively acquired chromatograms can be used to generate concentration profiles for volatile products produced during sample heating. These species-specific profiles can be used for calculation of isoconversion effective activation energies that are useful for characterizing the thermal reaction processes.

High-Frequency Oscillatory Ventilation for Adult Patients With ARDS

High-frequency oscillatory ventilation (HFOV) is characterized by the rapid delivery of small tidal volumes (Vts) of gas and the application of high mean airway pressures (mPaws). These characteristics make HFOV conceptually attractive as an ideal lung-protective ventilatory mode for the management of ARDS, as the high mPaws prevent cyclical derecruitment of the lung and the small Vts limit alveolar overdistension. In this review, we will summarize the literature describing the use of HFOV in adult patients with ARDS. In addition, we will discuss recent experimental studies of HFOV that have advanced our understanding of its mechanical properties. We identified 2 randomized controlled trials (RCTs) and 12 case series evaluating HFOV in adults with ARDS. In these studies, HFOV appears to be safe and consistently improves oxygenation when used as a rescue mode of ventilation in patients with severe ARDS. The two RCTs comparing HFOV to conventional ventilation revealed encouraging results but failed to show a mortality benefit of HFOV over conventional ventilation. Further research is needed to identify optimal patient selection, technique, the actual Vt delivered, and the role of combining HFOV with other interventions, such as recruitment maneuvers, prone positioning, and nitric oxide.

Continuous Measurements of Belowground Nitrous Oxide Concentrations

Nitrous oxide released from soil is a concern since it can act as a potential atmospheric pollutant and it represents a loss of N from the soil. To better understand the factors controlling N2O production and transport, we developed a system to obtain continuous measurements from below the soil surface. The sampling system pulls small volumes of soil gas from buried sample probes through a tunable diode laser trace gas analyzer. The advantage of this system is that it measures concentrations spectroscopically, allowing regular, continuous measurements. This provides it with the distinct advantage of being able to capture short‐term changes in gas concentrations that may be important for nutrient and greenhouse gas budgeting. Furthermore, the system is relatively simple to install and could be integrated into existing field measurements of trace gas flux. Measurements of belowground N2O concentrations were obtained during the spring thaw from buried probes in a conventionally tilled field that was planted in soybean [Glycine max (L.) Merr.] the previous summer. Measurements showed that belowground N2O concentrations at the 25‐cm depth varied between 65 and 85 μmol mol−1 before snowmelt. After melting of the snow and the beginning of the soil thawing, N2O concentrations decreased to a value generally &lt;1 μmol mol−1 During this period when belowground N2O concentrations were near atmospheric values, wind speed influenced concentrations, possibly through a pressure pumping effect.

Composite Reactive Block for Heat Transformer System and Improvement of System Performance

A new process for fabricating composite reactive block composed of the expanded graphite and reactive salt for the heat transformer system is proposed. The suitable condition to expand the graphite is found to be over 700°C for 15 min, and the reactive salt is impregnated by immersing the expanded graphite in the reactive salt solution. The performance of the heat transformer using the composite reactive block is accordingly simulated. It is found that the gas volume has quite important effect on the matching of the reacting rates and consequently it affects the system performance. The system COP is higher in the case of small gas volume, in particular when the driven temperature is high.