Density gases and

Calculate the scaling law exponent n for low-density gases and indicate any important assumptions that you have invoked to obtain your answer. 

TRANSPORT COEFFICffiNT BEHAVIOR FOR HIGH DENSITY GASES AND MIXTURES OF GASES... 

The principle of corresponding states, extended on the basis of kinetic theory and some knowledge of intermolecular forces, allows the correlation of the transport coefficients of low-density gases and their mixtures over a very wide temperature range. The ability to operate in a predictive mode is especially valuable for mixtures of any number of components, for which accurate experimental data are extremely scanty. 

Graham showed that the rate of diffusion of different gases through a porous diaphragm was inversely proportional to the square roots of their densities this is the basis of a method of separation of gases, and has been applied successfully to the separation of hydrogen and deuterium. 

The z-factor must be determined empirically (i.e. by experiment), but this has been done for many hydrocarbon gases, and correlation charts exist for the approximate determination of the z factor at various conditions of pressure and temperature. (Ref. Standing, M.B. and Katz, D.L., Density of natural gases, Trans. AIME, 1942). 

In the second part of hla memoir Reynolds gave a theoretical account of thermal transpiration, based on the kinetic theory of gases, and was able CO account for Che above "laws", Chough he was not able to calculate Che actual value of the pressure difference required Co prevent flow over Che whole range of densities. ... 

Low Density Gases. A fan may have to operate on low density gas because of temperature, altitude, gas composition (high water vapor content of the gas can be a cause of low density), reduced process pressure, or a combination of such causes. To develop a required pressure, the fan has to operate at a considerably higher speed than it would at atmospheric pressure, and hence it must operate much closer to top wheel speed. Bearing life is shorter, and the fan tends to vibrate more or can be overstressed more easily by a slight wheel unbalance. Abrasion of the blades from dust particles is more severe. Therefore, a sturdier fan is needed for low density gas service. 

Gases and vapors permeate FEP resin at a rate that is considerably lower than that of most plastics. Because FEP resins are melt processed, they are void-free and permeation occurs only by molecular diffusion. Variation in crystallinity and density is limited, except in unusual melt-processing conditions. 

The permeabUity of ceUular polymers to gases and vapors depends on the fraction of open ceUs as weU as the polymer-phase composition and state. The presence of open ceUs in a foam allows gases and vapors to permeate the ceU stmcture by diffusion and convection dow, yielding very large permeation rates. In closed-ceUed foams the permeation of gases or vapors is governed by composition of the polymer phase, gas composition, density, and ceUular stmcture of the foam (194,199,215,218,219). 

Barrier Properties. VinyUdene chloride polymers are more impermeable to a wider variety of gases and Hquids than other polymers. This is a consequence of the combination of high density and high crystallinity in the polymer. An increase in either tends to reduce permeabiUty. A more subtle factor may be the symmetry of the polymer stmcture. It has been shown that both polyisobutylene and PVDC have unusually low permeabiUties to water compared to their monosubstituted counterparts, polypropylene and PVC (88). The values Hsted in Table 8 include estimates for the completely amorphous polymers. The estimated value for highly crystalline PVDC was obtained by extrapolating data for copolymers. 

Riazi-Whitson They presented a generahzed correlation in terms of viscosity and molar density that was apphcable to both gases and liqmds. The average absolute deviation for gases was only about 8 percent, while for liquids it was 15 percent. Their expression relies on the Chapman-Enskog correlation [Eq. (5-194)] for the low-pressure diffusivity and the Stiel-Thodos correlation for low-pressure viscosity ... 

A key limitation of sizing Eq. (8-109) is the limitation to incompressible flmds. For gases and vapors, density is dependent on pressure. For convenience, compressible fluids are often assumed to follow the ideal-gas-law model. Deviations from ideal behavior are corrected for, to first order, with nommity values of compressibihty factor Z. (See Sec. 2, Thvsical and Chemical Data, for definitions and data for common fluids.) For compressible fluids... 

If the density of a vapor is greater than air, as is the case with most gases and vapors encountered in industry, flammable concentrations may collect at low levels, such as at floor level or in basements, and can travel considerable distances to a source of ignition and the flames will then flash back. 

Table 4.1 Densities of some toxic gases and vapours relative to air at 20°C ...

The density of a vapour or gas at eonstant pressure is proportional to its relative moleeular mass and inversely proportional to temperature. Sinee most gases and vapours have relative moleeular masses greater than air (exeeptions inelude hydrogen, methane and ammonia), the vapours slump and spread or aeeumulate at low levels. The greater the vapour density, the greater the tendeney for this to oeeur. Gases or vapours whieh are less dense than air ean, however, spread at low level when eold (e.g. release of ammonia refrigerant). Table 6.1 ineludes vapour density values. 

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