High pressure rheometer for in situ formation and characterization of methane hydrates

We present a novel setup for a high pressure rheometer operating with concentric cylinders geometry for in situ studies of hydrate formation and rheological characterization. The apparatus uses an external high pressure mixing cell to saturate water-in-oil emulsions with methane gas. The capability of mixing combined with a true rheometer design make this apparatus unique in terms of setup and sample formation. We have used the apparatus to form gas hydrates in situ from water-in-oil emulsions and characterize suspension rheological properties such as yield stress and shear-thinning behavior.     

A highly modular beamline electrostatic levitation facility, optimized for in situ high-energy x-ray scattering studies of equilibrium and supercooled liquids

High-energy x-ray diffraction studies of metallic liquids provide valuable information about structural evolution on the atomic length scale, leading to insights into the origin of the nucleation barrier and the processes of supercooling and glass formation. The containerless processing of the beamline electrostatic levitation (BESL) facility allows coordinated thermophysical and structural studies of equilibrium and supercooled liquids to be made in a contamination-free, high-vacuum (～10(-8) Torr) environment. To date, the incorporation of electrostatic levitation facilities into synchrotron beamlines has been difficult due to the large footprint of the apparatus and the difficulties associated with its transportation and implementation. Here, we describe a modular levitation facility that is optimized for diffraction studies of high-temperature liquids at high-energy synchrotron beamlines. The modular approach used in the apparatus design allows it to be easily transported and quickly setup. Unlike most previous electrostatic levitation facilities, BESL can be operated by a single user instead of a user team.     

Fiber optic sensing technology for detecting gas hydrate formation and decomposition

A fiber optic-based distributed sensing system (DSS) has been integrated with a large volume (72 l) pressure vessel providing high spatial resolution, time-resolved, 3D measurement of hybrid temperature-strain (TS) values within experimental sediment-gas hydrate systems. Areas of gas hydrate formation (exothermic) and decomposition (endothermic) can be characterized through this proxy by time series analysis of discrete data points collected along the length of optical fibers placed within a sediment system. Data are visualized as an animation of TS values along the length of each fiber over time. Experiments conducted in the Seafloor Process Simulator at Oak Ridge National Laboratory clearly indicate hydrate formation and dissociation events at expected pressure-temperature conditions given the thermodynamics of the CH(4)-H(2)O system. The high spatial resolution achieved with fiber optic technology makes the DSS a useful tool for visualizing time-resolved formation and dissociation of gas hydrates in large-scale sediment experiments.     

A high-pressure cell for kinetic studies on gas hydrates by powder x-ray diffraction

A new high-pressure-low-temperature cell was developed for in situ observations of gas hydrates by powder x-ray diffraction. The experimental setup allows investigating hydrate formation and dissociation as well as transformation processes between different hydrate crystal structures as a function of pressure, temperature, and feed gas composition. Due to a continuous gas flow, the composition of the gas phase is kept constant during the whole experiment. This is crucial for the formation of mixed hydrates formed from feed gas mixtures that contain one or more components in low concentrations. The pressure cell can be used in a pressure range between 0.1 and 4.0 MPa and a temperature range between 248 and 298 K. First results of time-resolved measurements of a mixed structure II CH(4) + iso-C(4)H(10) hydrate and a structure I CO(2) hydrate are presented.     

Study on gas hydrates for the solid transportation of natural gas

Natural gas hydrate typically contains 85 wt.% water and 15 wt.% natural gas, and commonly belongs to cubic structure I and II. When referred to standard conditions, 1 m³ solid hydrate contains up to 200 m³ of natural gas depending on pressure and temperature. Such the large volume of natural gas hydrate can be utilized to store and transport a large quantity of natural gas in a stable condition. In the present investigation, experiments were carried out for the formation of natural gas hydrate governed by pressure, temperature, gas compositions, etc. The results show that the equilibrium pressure of structure II is approximately 65% lower and the solubility is approximately 3 times higher than structure I. It is also found that for the sub-cooling of structure I and II of more than 9 and 11 K respectively, the hydrates are rapidly being formed. It is noted that utilizing nozzles for spraying water in the form of droplets into the natural gas dramatically reduces the hydrate formation time and increases its solubility at the same time.     

Gas loading apparatus for the Paris-Edinburgh press

We describe the design and operation of an apparatus for loading gases into the sample volume of the Paris-Edinburgh press at room temperature and high pressure. The system can be used for studies of samples loaded as pure or mixed gases as well as for loading gases as pressure-transmitting media in neutron-scattering experiments. The apparatus consists of a high-pressure vessel and an anvil holder with a clamp mechanism. The vessel, designed to operate at gas pressures of up to 150 MPa, is used for applying the load onto the anvils located inside the clamp. This initial load is sufficient for sealing the pressurized gas inside the sample containing gasket. The clamp containing the anvils and the sample is then transferred into the Paris-Edinburgh press by which further load can be applied to the sample. The clamp has apertures for scattered neutron beams and remains in the press for the duration of the experiment. The performance of the gas loading system is illustrated with the results of neutron-diffraction experiments on compressed nitrogen.     

Design and construction of a magnetic resonance compatible multi-injector gas jet delivery system

We present the design, construction, and performance of a novel multi-injector gas jet delivery capable of operating in a magnetic resonance imaging environment. This apparatus is computer controlled and built with two separate pneumatic circuits enabling gas jet applications at variable sites through four independently activated injectors. Gas jet delivery is fully controllable in terms of pressure, flow rate, gas temperature, application time, and duration of interstimulus interval. We characterized these parameters, considering effects such as pressure drop by flow transport, transient effects, and delays in activation. The system offers new possibilities for use in various biomedical contexts such as, e.g., quantitative sensory testing or dental hypersensitivity assessment.     

A compact setup to study homogeneous nucleation and condensation

An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.     

Automatic 300-4 K temperature cycling apparatus

The apparatus described here automatically cycles small samples between 300 and 4 K by alternately raising and lowering the sample through the neck of a commercial liquid helium storage Dewar. A bellows, which is pressurized by the helium boil-off gas, provides all of the required mechanical motion. By utilizing the cooling available from the boil-off gas, liquid helium helium consumption is limited to 0.03 l/cyc for a 12-g sample. Cycle times can be as short as 5 min.     

Optimized acquisition parameters and statistical detection limit in quantitative EELS

Optimizing the acquisition parameters for EELS recording has to be accomplished simultaneously from the physical and the statistical points of view; the statistical aspect of the question is covered here. Approximate probability density functions of the variables of interest are derived, which provide a global measure of signal-to-noise ratio taking into account every step of the EELS edge area estimation process. Qualitative and quantitative advice is given regarding the critical choice of the estimation and integration energy regions. The notion of visual contrast is presented; it permits the introduction of the concept of statistical detection limit. It is found that for typical experimental conditions, when other factors are equal, the required analysis time for the sample varies approximately as the inverse square of the concentration.     

微机测控高压气瓶疲劳试验装置研制

疲劳试验是气瓶出厂时的强制抽检项目 ,对于保证高压气瓶反复充装 ,长期可靠使用具有重要意义。本文开发研制的疲劳试验装置采用先进的计算机数据采集和控制技术 ,能够根据设定参数实现可控压力循环 ,实时显示并记录循环压力波形 ,同时自动存储压力循环次数 ,并给出标准规定的试验记录和报告。     

Creating a high temperature environment at high pressure in a gas piston cylinder apparatus

An internal heater capable of 1400 K has been developed for use with a gas piston cylinder apparatus capable of achieving in excess of 3 GPa with an argon pressure medium. The heated gas piston cylinder produces a truly hydrostatic environment for samples up to 3 mm in diameter and 8 mm in length. The apparatus can be used to study systems that are sensitive to stress or samples that cannot withstand shear tractions. The gas piston cylinder apparatus was developed in an effort to reduce experimental uncertainty in the pressure scale and has been used to improve understanding of the Bi I-II transition at 298 K. We estimate that the pressure during a high temperature soak in the gas piston cylinder can be known to within ±0.01 GPa.     

Online monitoring method of hydrate agglomeration in natural gas pipelines based on acoustic active excitation

Natural gas hydrate, which forms and agglomerates under the condition of low temperature and high pressure, can easily affect production or even lead to serious accidents. In order to prevent hydrate agglomeration in a pipeline, the industries generally add seriously excess inhibitor with experience, which causes serious environmental pollution and huge costs. However, due to the uncontrollable production and environmental conditions, hydrate plugging in a pipeline still occurs. According to the issues above, the method, for hydrate agglomeration online monitoring in a natural gas pipeline based on acoustic active excitation, has been presented in this paper. The method is to monitor and locate the hydrate agglomeration in a pipeline in order to take measures in time. Both the modeling and the experimental results show that the method can monitor and locate the hydrate agglomeration online at different locations with good accuracy.     

原子荧光法测定环境水样中的锑

利用氢化物发生-原子荧光分析技术(HG-AFS)对环境水样包括地表水、地下水、废水中的锑进行分析方法探究。通过一系列正交实验,优化出AFS-830原子荧光光度仪分析测定锑的最佳实验条件,方法的精密度为1.2%～8.6%、回收率为88%～112%、检出限为0.2μg/L、线性关系r大于0.999。实验结果表明:应用优化的仪器条件测定锑能够满足环境水样的分析要求。     

Development of a nuclear magnetic resonance system for in situ analysis of hydrogen storage materials under high pressures and temperatures

A NMR system for in situ analysis of hydrogen storage materials under high pressure and temperature conditions was developed. The system consists of a gas pressure and flow rate controlling unit, a temperature controller, a high temperature NMR probe tunable for both (1)H and other nuclei, and a sample tube holder. Sample temperature can be controlled up to 623 K by heated N(2) gas flow. Sample tube atmosphere can be substituted by either H(2) or Ar and can be pressurized up to 1 MPa under constant flow rate up to 100 ml/min. During the NMR measurement, the pressure can be adjusted easily by just handle a back pressure valve. On the blank NMR measurement, (1)H background noise was confirmed to be very low. (1)H and (11)B NMR spectrum of LiBH(4) were successfully observed at high temperature for the demonstration of the system. The intensity of the (1)H NMR spectra of H(2) gas was also confirmed to be proportional to the applied pressure.     

Scanning mass spectrometer for quantitative reaction studies on catalytically active microstructures

We describe an apparatus for spatially resolving scanning mass spectrometry which is able to measure the gas composition above catalytically active microstructures or arrays of these microstructures with a lateral resolution of better than 100 mum under reaction conditions and which allows us to quantitatively determine reaction rates on individual microstructures. Measurements of the three-dimensional gas composition at different vertical distances and separations between active structures allow the evaluation of gas phase mass transport effects. The system is based on a piezoelectrically driven positioning substage for controlled lateral and vertical positioning of the sample under a rigidly mounted capillary probe connecting to a mass spectrometer. Measurements can be performed at pressures in the range of <10(-2)-10 mbars and temperatures between room temperature and 450 degrees C. The performance of the setup is demonstrated using the CO oxidation reaction on Pt microstructures on Si with sizes between 100 and 300 mum and distances in the same order of magnitude, evaluating CO(2) formation and CO consumption above the microstructures. The rapidly decaying lateral resolution with increasing distance between sample and probe underlines the effects of (lateral) gas transport in the room between sample and probe. The reaction rates and apparent activation energy obtained from such measurements agree with previous data on extended surfaces, demonstrating the feasibility of determining absolute reaction rates on individual microstructures.     

Environmental chamber for in situ dynamic control of temperature and relative humidity during x-ray scattering

We have designed, constructed, and evaluated an environmental chamber that has in situ dynamic control of temperature (25 to 90?°C) and relative humidity (0% to 95%). The compact specimen chamber is designed for x-ray scattering in transmission with an escape angle of 2θ = ±30°. The specimen chamber is compatible with a completely evacuated system such as the Rigaku PSAXS system, in which the specimen chamber is placed inside a larger evacuated chamber (flight path). It is also compatible with x-ray systems consisting of evacuated flight tubes separated by small air gaps for sample placement. When attached to a linear motor (vertical displacement), the environmental chamber can access multiple sample positions. The temperature and relative humidity inside the specimen chamber are controlled by passing a mixture of dry and saturated gas through the chamber and by heating the chamber walls. Alternatively, the chamber can be used to control the gaseous environment without humidity. To illustrate the value of this apparatus, we have probed morphology transformations in Nafion(?) membranes and a polymerized ionic liquid as a function of relative humidity in nitrogen.     

基于Markov特征的油气管道泄漏检测与定位方法

针对传统的基于压力信号的管道泄漏检测方法误报率和漏报率偏高,同时定位误差较大的缺点,设计了一种基于Markov特征的管道泄漏检测与定位方法。首先,将管道压力数据构造为Markov链的形式,并提取其动态特征;然后,将所提取的特征应用于Neyman-Pearson异常检测方法之中,检测全部压力数据样本的状态,并对检测到的异常样本进行同源信号匹配,修正检测结果;最后,将相似性定位方法与连续小波定位方法结合,确定管道首末两端响应压力变化的时间差,并根据管道长度和压力波传输速度等信息,对泄漏源定位。所提方法能应用于小泄漏和缓慢泄漏的检测与定位,易于实现,误报率与漏报率显著降低,定位精度提高。通过对历史数据的分析,验证了所提方法的可行性和有效性。     

A Setup for Studying the Low-Temperature Thermal Conductivity of Powder Samples

A setup for studying the thermal conductivity of powder samples in the temperature range 2–200 K using the stationary heat flow method is described. The design of the cryogenic part of the setup allows a sample to be loaded at low temperatures. The effective thermal conductivities of methane hydrate powder and the ice powder obtained upon methane hydrate decomposition were measured, and the true thermal conductivities were determined. A heat exchange gas (helium) at a lowered pressure was used to reduce the interface thermal resistance between the grains in the powders.__________Translated from Pribory i Tekhnika Eksperimenta, No. 3, 2005, pp. 153–157.Original Russian Text Copyright © 2005 by Krivchikov, Gorodilov, Korolyuk.     

SF6气体检测技术的研究进展及发展趋势

针对高压设备SF_6气体泄漏检测问题,介绍了SF_6气体泄漏产生的危害。根据SF_6气体检漏技术的研究进展,可把SF_6气体泄漏检测技术分为非光学检测和光学检测两大类。对气体浓度监测技术、真空负离子捕获技术、紫外电离技术和负电晕放电技术等非光学检测技术进行简要的概述,同时对激光成像技术、红外吸收光谱技术和光声光谱技术等光学检测技术进行了重点阐述,并对比分析了各种技术的优缺点,提出了SF_6气体检漏仪的未来发展趋势。