Compressed gases transport properties

Quasi-nondestmctive techniques include several transport measurements that are used to test specific membrane properties. They require sample mounting by compression sealing or glass solders that rarely leave the dehcate membrane surface intact. Gas transport properties of dense and microporous membranes are tested by measuring single gas ji as a function of and and by obtainmg fluxes and a/,from the stationary composition and flow rate of gas mixtures at the membrane feed and permeate side. To use the results of these measurements for comparison and optimized membrane designs, substantial... 

Wlrile quaternary layers and stmctures can be exactly lattice matched to tire InP substrate, strain is often used to alter tire gap or carrier transport properties. In Ga In s or Ga In Asj grown on InP, strain can be introduced by moving away from tire lattice-matched composition. In sufficiently tliin layers, strain is accommodated elastically, witliout any change in the in-plane lattice constant. In tliis material, strain can be eitlier compressive, witli tire lattice constant of tire layer trying to be larger tlian tliat of tire substrate, or tensile. 

The physics of the problem under study is assumed to be governed by the compressible form of the Favre-filtered Navier-Stokes energy and species equations for an ideal gas mixture with constant specific heats, temperature-dependent transport properties, and equal diffusion coefficients. The molecular Schmidt, Prandtl, and Lewis numbers are set equal to 1.0, 0.7, and 1.43, respectively [17]. 

A gaseous pure component can be defined as supercritical when its state is determined by values of temperature T and pressure P that are above its critical parameters (Tc and Pc). In the proximity of its critical point, a pure supercritical fluid (or a dense gas as it is alternatively known) has a very high isothermal compressibility, and this makes possible to change significantly the density of the fluid with relatively limited modifications of T and P. On the other hand, it has been shown that the thermodynamic and transport properties of supercritical fluids can be tuned simply by changing the density of the medium. This is particularly interesting for... 

Fluids are highly compressible along near-critical isotherms (L01-1.2 Tc) and display properties ranging from gas-like to Liquid-Like with relatively small pressure variations around the critical pressure. The liquid-like densities and better-than-liquid transport properties of supercritical fluids (SCFs) have been exploited for the in situ extraction of coke-forming compounds from porous catalysts [1-6], For i-hexene reaction on a low activity, macroporous a catalyst, Tiltschcr el al. [1] demonstrated that reactor operation at supercritical... 

Applications of ultrasonic techniques to solid-gas systems rely on the fact that velocity and attenuation of US-waves in porous materials is closely related to pore size, porosity, tortuosity, permeability and flux resistivity. Thus, the flux resistivity of acoustic absorbents oan be related to US attenuation [118,119], while the velocity of slow longitudinal US is related to pore tortuosity and diffusion, and transport properties, of other porous materials [120]. Ultrasound attenuation is very sensitive to the presence of an external agent suoh as moisture in the pore space [121] and has been used to monitor wetting and drying prooesses [122] on the other hand, US velocity has been used to measure the elastic coefficients of different types of paper and correlate them with properties such as tensile breaking strength, compressive strength, etc. [123]. 

Supercritical fluids exhibit liquid-like solvent properties and gas-like transport properties. The combination of these properties makes supercritical fluids suitable for the various applications mentioned above. Carbon dioxide is the supercritical fluid of choice due to its mild critical temperature, nontoxicity, nonflammability, and low cost. Carbon dioxide becomes a supercritical fluid when it is heated above 31.1°C and simultaneously compressed above 73.8 bar. 

Currently there are more than 200 different substances commonly shipped in compressed gas containers that can be considered compressed gases. The Department of Transportation (DOT) defines these materials based on their properties such as vapor pressure, flammability, toxicity, and physical state in the container. The specific definitions in this handbook according to DOT classification are in three Class 2 compressed gas divisions 2.1... 

The focus of this book concerns the properties and the accepted means of transportation, storage, and handling of compressed gases. This handbook is simultaneously intended as an overview of the subject and a source of supplementary information. It is also intended to serve as a guide to pertinent federal regulatory requirements and published standards of the Compressed Gas Association and other standards-developing organizations. 

The physical and solvent properties of water depend strongly on temperature and pressure. " Near the critical point T = 647.1 K, = 22.06 MPa), the isothermal compressibility of water may be 10" times higher than that of the saturated liquid at 25 °C, and isobaric specific heat capacity may increase to 1X10 kJ K kg whereas thermal conductivity can be as high as 0.8 W m K . The transport properties of hot compressed water fall between those of a gas and a liquid. At densities of ca. 700 kgm and lower, the diffusion coefficient D is proportional to the inverse of the density, like in gases. A change in transport properties has consequent effect on radical reactions, which are diffusion-controlled or partially diffusion-controlled (see section 15.4). 

To apply the above scheme, accurate experimental measurements for the transport properties of the monatomic fluids were collected. In Table 10.1 the experimental measurements of diffusion, viscosity and thermal conductivity used for the correlation scheme are shown. This table also includes a note of the experimental method used, the quoted accuracy, the temperature range, the maximum pressure and the number of data sets. The data cover the range of compressed gas and the liquid range but not the critical region, where there is an enhancement (Chapter 6) which cannot be accounted for in terms of this simple molecular model. 

USSR National Standard Reference Data Service (NSRDS). The system was developed in 1976-1980 in the All-Union Research Center of NSRDS (now Russian Research Center on standardization, information and certification of raw materials, materials and substances) in Moscow. It provides specialists with attested databases, formed on the basis of standard and recommended reference data. The data of the lUPAC Commission on Thermodynamics, the International Association for the Properties of Steam, the U.S. National Bureau of Standards and other authenticated foreign data are used in the system as well. The informadon blocks of the system are sets of program modules, being the mathemadcal models of substances, and the blocks of numerical data for each substance. The basis for the model of a substance is a unified equadon of state for gas and liquid in the form of a double power expansion of the compressibility with respect to density and temperature. The principles of the molecular-kinetic theory and the dependence of the excess viscosity and thermal conductivity on density and temperature are used for the calculation of the transport properties. 

The ability to store a desired chemical substance is a typical property of porous materials. Methane (CH4) is the main component of natural gas, which is an important candidate for clean transportation fuels. The storage of CH4 by adsorbents has been pursued vigorously as an alternative to compressed gas storage at high pressure. However, the conventional adsorbents have afforded insufficient capacity... 

A transport property is the capacity of a substance to transport or transfer matter, momentum, energy, heat, electric charge, and so on, such transport being accomplished, in part, via collisions. Diffusion, viscosity, and thermal conductivity are among the many transport properties of a substance. The speed of sound is determined by the ability of a substance to transmit a compression wave. Without giving the derivation, we state that the speed of sound in a gas or a liquid is... 

The correction for the pressure dependence of transport properties of gases can be piade by use of various correlations. These include the gas density which in turn is calculated from the compressibility factor. For viscosity the method proposed by Dean, Stiel [9] can be used, and for the thermal conductivity the method proposed by Stiel, Thodos [54] can be used. For the bulk diffusion coefficient it is normally assumed that it is inversely proportional to the density. 

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