Ways of improving the accuracy of certification for gravimetric standard gas mixtures

A requirement is substantiated for improving the accuracy of certification for gravimetric standard gas mixtures (GSGM). Principles are developed for external quality control of GSGM for working standards of the zero order with application of statistical monitoring methods for quality according to a quantified characteristic. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 33–36, February, 2007.     

Dynamic methods for calibration and verification of the metrological characteristics of instruments intended for gas analysis (generalized approach)

A systematic approach to the metrological provision (MP) of gas-analytical measurements in the range of microconcentrations (trace analysis) using dynamic and static control facilities is described. Results of investigations and development of the methods and facilities for continuous preparation of reference gas mixtures (RGMs) for the MP of commercial chromatographs, chemical sensors, and other instruments and devices for gas analysis are presented, including data on the capacity of adsorbents, parameters of sampling adsorption tubes, regimes of sorption and desorption, creation and maintenance of gas mixtures with preset compositions in testing chambers for toxicological investigations. Methodological and technical problems of MP in the field of trace analysis are considered. The main dynamic methods of preparation of the RGMs by flow mixing, diffusion leak, and exponential dilution of initial gases are described. Examples of the new generation of new “smart” systems of the Mikrogaz-F type intended for the RGM preparation in the range of microconcentrations are presented.     

Wood gas generators for small power (∼ 5 hp) requirements

This paper reports experimental and developmental studies on wood gas generators meant for running 5 hp diesel engines in irrigation water pumping. Critical inputs for the design of small reactors are presented. A prototype of the gas generator based on these inputs has been built and tested along with a diesel engine pumpset. The results of various tests on the system are described along with some critical operational features. The lowest amount of diesel at which the engine could be run with a mixture of diesel and gas is about 15% of the consumption with diesel alone. However, to obtain the same energy, that is the same amount of water at a given height, the best replacement of diesel obtained is about 75%. The paper also comments on the economics of such systems. The results presented here are the outcome of a project ‘Wood gas generators for engines of less than 10 hp’ financed and administered by Karnataka State Council for Science and Technology, Indian Institute of Science, Bangalore.     

The prediction of the viscosity of dense gas mixtures

An extension of an earlier procedure for the evaluation of the viscosity of very dense gas mixtures is proposed. The scheme is based upon the rigid-sphere theory of dense fluids, which is modified to take into account the behavior of real gases in a self-consistent manner. In particular, it is shown that a pseudoradial distribution function for each pure gas constructed from pure component viscosity data is a smooth function of density and is well behaved in limits of both high and low density. The method proposed removes the restrictions on the range of applicability of earlier methods. Comparisons with the limited amount of experimental information available indicate that the procedure allows evaluation of the viscosity of gas mixtures to within a few percent.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Development of a Coulometric Method for Assessing the Concentration of Ambient Levels of CO2/Air in Compressed Gas Mixtures

The coulometric method presented here is a reliable method for the direct analysis of CO₂/air cylinder gas mixtures. It is based on Faraday’s laws of electrolysis and therefore no external standardization is required. A series of CO₂/air cylinder gas mixtures ranging in concentration from 300 to 375 µmol/mol (ppm) were analyzed and the results compared to those results obtained by non-dispersive infrared (NDIR) analysis with traceability to gravimetric standards. The coulometric method is rapid, sensitive, precise, and with the proper experimental controls, will yield accurate results.     

Contribution to the gas chromatographic analysis for both refrigerants composition and cell gas in insulating foams – Part I: Method

In this paper, an easy low cost chromatographic analysis for both refrigerants blend composition and cell gas in insulating foams is presented. This work firstly deals with the measurement protocols for these substances. The presented protocols are simple, likely to be used by non-specialists of chemical analysis (i.e. by refrigeration engineers). Among other methods, gas chromatography was used for separation and detection of halocarbons. For refrigerants extracted from refrigeration plants, the analysis requires a prior oil separation. As for insulating foams, analysis of cell gas composition is processed with the same protocol. Sampling remains of main importance; two possible sampling methods were validated and compared. Finally, the interest in the analysis method is illustrated with the example of a real application: study of the distillation phenomenon of a zeotropic refrigerant in an industrial refrigeration plant with flooded evaporators. The results are discussed for their consequences on the working performances of the refrigerating system. In part II, we propose original results obtained with that method to study the aging of insulating foams.     

Thermal conductivity of multicomponent polyatomic dilute gas mixtures

A new expression for the thermal conductivity of anN-component polyatomic gas mixture in the dilute-gas limit has been derived, based on the Thijsse approximation. The results are presented in terms of experimentally accessible quantities to allow for easier calculation of the thermal conductivity and easier interpretation of the experimentally available data. The resulting expression are much simpler than other formulae hitherto available. An additional new expression for the thermal conductivity of anN-component polyatomic gas mixture has been derived by replacing the effective cross-section by their spherical limits. These results are cast in a form which is analogous with, and no more complicated than, the corresponding expressions for purely monatomic mixtures. Paper dedicated to Professor Edward A. Mason.     

New dynamic approach to preparation of vapor and gas mixtures

A new method for verifying the efficiency of gas analyzers based on the use of generators with a linear increase in the tested substance concentration in time is proposed. The controlled parameter is time of increase of gas analyzer data from one preset value to another. The generator structure is described and its application is shown for verification of the efficiency of photoionization gas analyzers.     

Forced modes of dilute binary gas mixtures

Anomalous forced sound dispersion in dilute binary gas mixtures is studied as a function of the mass ratio of the two components, using one- and two-temperature theories as well as different interparticle potentials. For a disparatemass mixture, such as He-Xe, the results are compared with previous work due to Johnson et al. It is suggested that even for nondisparate-mass mixtures, a one-temperature treatment is not appropriate.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

燃气用具连接用不锈钢波纹软管长度测量方法

针对CJ/T 197-2010《燃气用具连接用不锈钢波纹软管》标准中软管长度无相关测量方法,通过对燃气软管相关标准的比对及软管相关标准调查研究,比对长度测量方法的异同,及测量方法对长度测量结果的影响等因素,及对目前常见接头类型的收集和分析,及燃气用具连接用不锈钢波纹软管等燃气软管应用环境的分析,提出燃气用具连接用不锈钢波纹软管等燃气软管统一的长度的测量建议,为相关燃气标准的长度测量提供参考。     

Low-pressure gas atomization of aluminum through a Venturi nozzle

A new concept of powder atomization based on the venturi phenomenon is presented in the current work. In the proposed method, the working gas speeds-up while flowing into the venturi nozzle. Under the low static pressure developing at the narrow part of the venturi, liquid metal is sucked and mixed perfectly with the gas. By controlling the operating parameters, metal powder of different sizes and shapes can be produced. Carbon dioxide and pure aluminum were mixed in the nozzle and the effect of different operating gas pressures on the produced particle size and shape were thoroughly investigated. Most of the particles were found to average to almost 150 μm, however, even sub-micron aluminum particles were produced at low mass fractions. With the increase of the gas pressure from 0.5 bar to 4 bar, finer aluminum particles are produced. One of the most attractive features of the proposed method is the low gas pressure required to cause melt atomization, which in certain cases may be up to 30 times lower compared to current industrial atomization methods.     

Mixture Working Gases in Thermoacoustic Engines for Different Applications

For working gases in thermoacoustic engines, the most important characteristics are low Prandtl number and high ratio of specific heats. These properties change a lot with pressure for some gases, which makes selecting a working gas under high pressure different from that under normal pressure. This article presents optimization calculations for gas mixtures under different pressures. Results show that binary mixtures of helium and xenon can reach the lowest Prandtl number and highest ratio of specific heats when the pressure is lower than 4.5MPa. When the pressure is higher than 4.5MPa, however, the lowest Prandtl number is obtained with a mixture of helium and krypton. It is found that ternary mixtures may be better working gases than binary mixtures in thermoacoustic engines, especially under high pressure. For example, a helium–argon–xenon ternary mixture can be used to obtain a relatively low Prandtl number and high ratio of specific heats. In addition, this article shows that mixtures containing carbon dioxide and other gases can also result in useful working gases. This suggests that it is possible to replace the expensive xenon gas with cheap carbon dioxide for some applications. Finally, the effect of temperature on the Prandtl number, the ratio of specific heats, and the thermal penetration depth is also studied, and a more reasonable construction of the thermoacoutic couple is presented. The results of this study should be useful for helping select working gases in thermoacoustic engines for different applications and design goals.     

Tests of hygrolog WSX-160 moist gas generators

We present the results of tests of five Hygrolog WSX-160 moist gas generators. We note that the generators reproduce five (out of six according to the documentation) values of the dew point (frost point) with the error indicated in the documentation. We consider methods for elimanation of the uncertainty arising at an operating pressure different from normal atmospheric pressure. We indicate additional operating conditions for the generators which assure the claimed technical and metrological characteristics. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 65–66, November, 1997.     

Flammability of gas mixtures. Part 2: influence of inert gases

Ternary systems, which contain flammable gas, inert gas and air, were studied in order to give the user an evaluation of the ISO 10156 calculation method for the flammability of gas mixtures. While in Part 1 of this article the fire potential of flammable gases was the focal point, the influence of inert gases on the flammability of gas mixtures was studied in Part 2. The inerting capacity of an inert gas is expressed by the dimensionless K value, the so-called "coefficient of nitrogen equivalency". The experimental determination of K values is demonstrated by using explosion diagrams. The objective of this study was to compare the estimated results, given by ISO 10156, with measurements of explosion ranges based on the German standard DIN 51649-1, given by CERN and CHEMSAFE. The comparison shows that ISO 10156, Table 1, supplies conservative K values, which can be regarded as safe in all cases. Nevertheless, in a number of cases ISO underestimates the inerting capacity, so that non-flammable gas mixtures are considered flammable.     

Measurement and parametrisation of the gas gain in proportional counters

Two parameter formulae for gas gain in proportional counters have been verified for different mixtures based on Ar, Kr and Xe with organic and inorganic quench gases.A new formula for gas gain is also proposed by means of which good agreement with the experimental results is obtained.     

Nonlinear inverse dynamic models of gas sensing systems based onchemical sensor arrays for quantitative measurements

Gas sensing systems based on low-cost chemical sensor arrays are gaining interest for the analysis of multicomponent gas mixtures. These sensors show different problems, e.g., nonlinearities and slow time-response, which can be partially solved by digital signal processing. Our approach is based on building a nonlinear inverse dynamic system. Results for different identification techniques, including artificial neural networks and Wiener series, are compared in terms of measurement accuracy     

Thermogravimetry-evolved gas analysis-mass spectrometry system for materials research

Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA-MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA-EGA-MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for (i) temperature programmed decomposition (TPD), (ii) synthesis of nanocrystalline materials, (iii) gas-solid interactions and (iv) analysis of gas mixtures. The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA-MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas-solid interactions are also described.     

Heat transfer coefficient measurements for mixed gas working fluids at cryogenic temperatures

The use of mixed gas working fluids has become common in Joule-Thomson type cryocoolers for a variety of applications. However, there is very little data or theory currently available regarding the heat transfer coefficient associated with these multi-component, multi-phase mixtures at cryogenic temperatures. This paper describes an experimental test facility and procedure that has been used to make careful measurements of the horizontal, flow boiling heat transfer coefficient for several hydrocarbon mixtures that are nominally optimal for small, Joule-Thomson cryocoolers in the 80 K to 120 K operating range. Data are presented over a range of temperatures from 100 K to room temperature and for several pressures and mass flow rates. The results indicate that quality and mass flux are the most important parameters governing the heat transfer coefficient among those that were varied. The experiment is verified by carrying out tests using single-phase, pure nitrogen gas and comparing the results with the Dittus-Boelter equation. The experimental uncertainty of the measurements is estimated from 1st principles; additionally, the repeatability of the experimental measurements was investigated by replicating tests at a nominal set of operating conditions and composition on separate days. The measurements presented here are intended to aid in the design of small, mixed-gas Joule-Thomson cryocoolers.     

A dynamic simulation of the conforming shell gas journal bearing

A time-dependent mathematical model for the conforming shell gas journal bearing is presented. A numerical scheme is devised to solve this mathematical model. The results of a dynamic simulation of the bearing are exhibited for a specific design.