The Cause of Overestimation of the Natural Gas Volume by Measuring Systems with Converging Devices and How to Eliminate Those Causes

The paper shows that Russian gas distribution organizations use approximate formulas to calculate the dynamic viscosity factor and adiabatic exponent of natural gas as a function of just the operating temperature and pressure of the gas and not its composition. Corrections specific to the accounting period must thus be introduced into the results of measurements. The error of the natural gas accounting unit under real conditions can be determined only by performing a metrological evaluation based on the data about the ranges of variation of the absolute pressure, temperatures and density under standard conditions and of errors in the measurements by the supplier.     

Reasons for the Understatement of the Volume of Natural Gas under Standard Conditions from the Readings of Meters and the Possibility of Eliminating Them

It is proved that it is necessary to introduce corrections into the readings of meters for measuring the volume of natural gas in a fixed time interval to reflect the change in the values of the absolute pressure, temperature, and composition of the gas (the density under standard conditions). The error in the meter for calculating the amount of natural gas under actual measurement conditions can only be determined by carrying out an expert metrological examination based on data on the ranges of variation of the absolute pressure, temperature and density under standard vendor conditions and errors in measuring them.     

Viscosity Prediction for Natural Gas Mixtures

The viscosity of multicomponent natural gas-mixtures containing hydrocarbons (C1 through C7) is predicted by modifying a previously published dilute-gas viscosity model and extending its applicability to a wide range of temperature and pressure conditions including liquid and gas states. Nitrogen, oxygen, carbon dioxide, and helium are also included among components of mixtures for which published viscosity data are available. The approach takes advantage of currently available formulations and models for the density and viscosity of pure fluid constituents of natural gases. The predicted viscosity is compared with available data in both gas and liquid regions. Comparisons of calculated values to the available measurements of viscosity of natural gas mixtures and of binary, ternary, and quaternary mixtures of constituent fluids are summarized to illustrate the accuracy of the predicted values.     

An Improved Algorithm of Measurements of the Volume of Natural Gas in Gas Supply Using Measuring Systems with a Calculator

An algorithm for the measurement and calculation of the mean daily and average monthly volume of natural gas in a measuring system with a constricting device and a calculator, which takes into account the need to combine in time the channels for measuring the excess and barometric pressures, the gas temperature and density under standard conditions is proposed, which eliminates the systematic error inherent in existing methods of making measurements.     

输气管道泄漏音波产生机理研究

为研究输气管道音波法泄漏检测技术的基本原理和应用方法,对输气管道中泄漏音波的产生机理进行了研究。首先从理论上确定输气管道气动噪声的产生机理;其次将仿真模拟得到四极子声源和偶极子声源产生的泄漏音波进行分析并总结规律;再次将音波传感器测得泄漏音波与仿真模拟得到的泄漏音波进行对比验证;然后对比分析多工况条件下仿真模拟和实验方法得到的泄漏音波;最后通过分析仿真模拟中泄漏音波产生机理和实验中所用的音波传感器的工作机理总结输气管道音波法泄漏检测技术的基本原理。研究结果表明：输气管道泄漏音波产生的根本原因是气体泄漏时产生的湍流脉动导致的四极子声源和偶极子声源;实验中音波传感器测得的压力波动主要成分为声源产生的音波波动;仿真模拟和实验的方法可以研究输气管道泄漏音波的产生机理。     

A Capillary Tube Viscometer Designed for Measurements of Hydrogen Gas Viscosity at High Pressure and High Temperature

A capillary tube viscometer was developed to measure the dynamic viscosity of gases for high pressure and high temperature. The apparatus is simple and designed for safe-handling operation. The gas was supplied to the capillary tube from a high-pressure reservoir tank through a pressure regulator unit to maintain a steady state flow. The measurements of a pressure drop across the capillary tube with high accuracy under extreme conditions are the main challenge for this method. A differential pressure sensor for high pressures up to 100 MPa is not available commercially. Therefore, a pair of accurate absolute pressure transducers was used as a differential pressure sensor. Then the pressure drop was calculated by subtracting the outlet pressure from the inlet one with a resolution of 100 Pa at 100 MPa. The accuracy of the present measurement system is confirmed by measuring the viscosity of nitrogen as a reference gas. The apparatus provided viscosities of nitrogen from ambient temperature to 500 K and hydrogen from ambient temperature to 400 K and for pressures up to 100 MPa with a maximum deviation of 2.2 % compared with a correlation developed by the present authors and with REFPROP (NIST).     

The Importance of an Air Pressure Seal on Standard Cell Enclosures with High Temperature Stability

The use of a pressure seal on standard cell still-air enclosures having high-temperature stability is discussed. The seal eliminates the effect of air pressdre variations on the temperature of the cells and the temperature monitor. It is calculated that a pressure change of 1 percent for air at normal temperature and pressure will change the air temperature 0.85 K under adiabatic conditions. While the conditions in a still-air enclosure are far from adiabatic, a measurement made on an oven under development gave an air inner chamber temperature change of 0.8 mK for this pressure change.     

SF_6气体密度继电器校验系统的设计

文章根据电力系统中SF6气体密度继电器现场校验工作的需要,提出了以SM89516A单片机为核心的密度校准系统。系统通过采集SF6气体的压力和温度值,然后依据气体密度状态方程,采用卡丹公式对这些数据进行处理,最终完成SF6密度继电器在标准条件下的报警、闭锁动作压力值的测量。工程实践证明,该系统可以方便、准确地对任意环境下的各种SF6密度继电器进行额定压力、闭锁压力及报警压力的校验。     

天然气水合物试样制备及力学性质研究进展

天然气水合物是天然气与水在低温高压条件下形成的笼形物。天然气水合物储量丰富,是人类理想的潜在替代能源,被认为是21世纪具有商业开发前景的战略资源。分析了国内外水合物实验装置设计及相应的实验研究内容,重点介绍了我国天然气水合物试样制备研究现状及取得的成果。     

变模温与型腔气体反压辅助微孔发泡注塑技术及其产品内外泡孔结构演变

建立了一种变模温和型腔气体反压协同控制的微孔发泡注塑技术,研制了相应的变模温控制系统与型腔气体反压控制系统,构建了变模温与型腔气体反压辅助微孔发泡注塑试验线,并对变模温与型腔气体反压作用下的产品内外泡孔结构演变进行了研究。结果表明,变模温与型腔气体反压辅助工艺单独施加于微孔发泡注塑技术时,对其产品内外泡孔结构均具有双重影响:变模温可以改善产品大部分的表面形貌,但其对填充过程中的熔体发泡影响不大;型腔气体反压可以基本抑制填充过程中的熔体发泡,但却对产品内部泡孔密度有比较明显的降低影响。通过变模温与型腔气体反压的协同控制,可以实现微孔发泡注塑产品表面气泡形貌和内部泡孔结构的良好调控。     

Some Metrological Characteristics of Flow Meters in Which the Coriolis Force Is Used

The effect of the viscosity of the medium being measured is investigated. It is proved that the readings of a flow meter based on the use of the Coriolis force depend on the viscosity of the medium (the velocity profile) and the measurement error may reach 30%. The effect of a change in the parameters of the gas flow on the readings of such flow meters as a function of the location of the instrument (the longitudinal coordinate) is also considered and a conversion formula is derived.     

The effect of the pattern of gas/surface interaction on the relation for Knudsen layer under conditions of strong subsonic condensation

The moments method is used within the model of diffuse reflection to investigate the effect of the temperature accommodation coefficient α_T on the flow behind the Knudsen layer under conditions of strong subsonic condensation. An explicit expression is obtained for dimensionless pressure as a function of temperature and Mach number M, as well as of the coefficients of evaporation, condensation, and temperature accommodation. It is demonstrated that the difference of α_T from unity may have a significant effect on the flow parameters and, in particular, on the value of Mach number that is the maximal value attainable under conditions of subsonic condensation. It is further demonstrated that this effect increases in the case of mirror reflection of molecules from the surface. The adiabatic exponent is investigated as well.     

基于Unisim动态模拟的高压缓冲罐内气体状态的分析

根据高压缓冲罐的实际应用情况,结合Unisim的动态模拟功能,从充压、泄压和备用三个工况对缓冲罐内的气体状态进行了研究,得出了各个工况下的温度压力随时间变化的特点,辨析出各种工况下存在的潜在风险,并提出了预防措施,以便在日常工作中能多一个考量维度,设计出更加完善的后备系统.     

Reliability of Measurements of the Natural Gas Flow Rate and Volume in Gas Distribution Organizations

The proposed new approach to the procedure for measuring the flow rate and volume of gas under standard conditions in gas distribution organizations increases the reliability of the measurements. It is based on identical transformations of the Clapeyron-Mendeveleev equation, with modifications, and takes into account the composition of the natural gas and the recommendations of Federal Law No. 69-FZ (article 19) of March 31, 1999, about natural gas certification by Gosstandart of the Russian Federation. Use of the modified Clapeyron–Mendeleev equation is shown to changes the form of the transformation functions of various primary measuring transducers (turbine, rotary, vortex, ultrasonic, etc.) under the conditions of actual measurements.     

Modelling of Gas Streams Taking Account of Viscosity

It is shown that in some cases in studying the interaction of a technical device with a gas stream among similarity criteria it is possible to introduce a dimensionless value as the ratio of a new dimensional complex (the product of dynamic viscosity and kinematic viscosity having a dimension of force) into the reaction force of a mechanical device under a hydrogas-dynamic influence. Then the choice of model gases and their ranking is facilitated; it is also possible to vary the gas stream by changes in pressure and temperature making it possible to embrace the field of corrosive and toxic gas operation. The method may be extended to liquid streams.__________Translated from Izmeritelnaya Tekhnika, No. 2, pp. 46–48, February, 2005.     

Viscosity Measurements and Predictions for Natural Gas

A vibrating-wire viscometer of very high precision was used to measure the viscosity of methane and of two natural gases. The experimental data were, in general, taken at temperatures of 260, 280, 300, and 320 K and at pressures up to 20 MPa, and additionally in the case of methane at temperatures of 340 and 360 K and at pressures up to 29 MPa. The estimated uncertainty is ±0.3 and ±0.5% for methane and the natural gases, respectively. The new experimental data for methane were used together with zero-density or low-density viscosity values from this study and from the literature to develop a viscosity equation for natural gas composed of two contributions. The mixing rule of Wilke [J. Chem. Phys. 18: 517 1950] was applied for the zero-density viscosity part which is based on zero-density correlations for twelve components (methane, nitrogen, carbon dioxide, ethane, propane, n- and isobutane, n- and isopentane, n-hexane, n-heptane, and n-octane) and agrees with the values derived from experiment within ±0.3%. The density dependence of the residual viscosity part was correlated with methane data only, neglecting any temperature dependence, whereas the composition dependence is characterized by a pseudo-critical viscosity value. For methane the agreement between the correlated and experimental data is within ±0.5 %. The values predicted with the correlation and the experimental data agree within ±1 % for both the high calorific, H, natural gas and the low calorific, L, natural gas.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Two-dimensional laminar boundary layer in flow of thermodynamically equilibrated water vapor

This paper examines the boundary problem of a laminar boundary layer in flow of thermodynamically equilibrated water vapor. An approximate method of solution is proposed, based on an approximation for the density and the coefficient of dynamic viscosity across the layer.Notation u and v longitudinal and transverse velocity components - x and y longitudinal and transverse coordinates - density - p pressure - T temperature - h enthalpy - V specific volume - Pr Prandtl number - z dryness level - adiabatic exponent of the heated vapor - , ,gu coefficients of thermal conductivity, dynamic and kinematic viscosity Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 789–795, November, 1978.     

Molecular-dynamic simulation of the thermophysical properties of liquid uranium

The procedure for the calculation of the embedded atom model (EAM) potential, which involves the use of data on the structure of liquid metal in the vicinity of the melting temperature and of the results of impact tests, is applied to uranium. The use of the method of molecular dynamics and of the EAM potential produces good agreement with experiment as regards the structure, density, and potential energy of liquid metal at temperatures up to 5000 K, as well as along the shock adiabat up to pressures of ≈360 GPa. The thermodynamic properties of solid (bcc) and liquid uranium are determined at pressures up to 470 GPa and temperatures up to 12 000 K. The predicted value of bulk modulus of liquid at 1406 K is close to the actual value. The self-diffusion coefficient under isobaric heating increases with temperature by the power law with exponent of ≈2.103. The Stokes—Einstein relation is used to determine the dynamic viscosity at temperatures up to 6000 K. The obtained potential is not quite adequate for describing crystalline uranium under normal conditions. The melting temperature of uranium with EAM potential is equal to 1455 ± 2 K and somewhat higher than real. The melting temperature monotonically increases with pressure and reaches the value of 7342 K at 444 GPa. For obtaining agreement with experimental data for energy of uranium along the p = 0 isobar, it is assumed that an additional contribution to energy emerges at elevated temperatures, which is due to excitation of atomic electrons and leads to a high heat capacity: it may be as high as almost 100 kJ/mol at 5000 K. This contribution further causes a high heat capacity of highly compressed states of uranium.     

A Procedure for Measuring Mass Flow Rate Using Critical Nozzles

A new approach to measuring mass flow rate using critical nozzles is proposed. The novelty of the approach lies in the fact that the laws of conservation (of mass, energy and momentum) in the one-dimensional gas flow are matched and the dependence of the thermal characteristics of an actual gas (the adiabatic exponent and the compressibility) on the static pressure and the temperature in the gas flow is taken into account. The VNIIMS procedure and algorithm are presented and are illustrated using a specific example.     

A Proposed Dynamic Pressure and Temperature Primary Standard

Diatomic gas molecules have a fundamental vibrational motion whose frequency is affected by pressure in a simple way. In addition, these molecules have well defined rotational energy levels whose populations provide a reliable measure of the thermodynamic temperature. Since information concerning the frequency of vibration and the relative populations can be determined by laser spectroscopy, the gas molecules themselves can serve as sensors of pressure and temperature. Through measurements under static conditions, the pressure and temperature dependence of the spectra of selected molecules is now understood. As the time required for the spectroscopic measurement can be reduced to nanoseconds, the diatomic gas molecule is an excellent candidate for a dynamic pressure/temperature primary standard. The temporal response in this case will be limited by the equilibration time for the molecules to respond to changes in local thermodynamic variables. Preliminary feasibility studies suggest that by using coherent anti-Stokes Raman spectroscopy we will be able to measure dynamic pressure up to 10⁸ Pa and dynamic temperature up to 1500 K with an uncertainty of 5%.