Viscosity of gases and liquids

The book by Reid et al. [9] is an excellent source of information on properties such as thermal conductivities, diffusion coefficients and viscosities of gases and liquids. Not only are there extensive tables of data, but many estimation methods and correlations are critically reviewed. 

VISCOSITIES OF GASES AND LIQUIDS. The viscosity of a newtonian fluid depends primarily on temperature and to a lesser degree on pressure. The viscosity of a gas increases with temperature approximately in accordance with an equation of the type... 

Literature data [117] viscosities of gases and liquids, [118] surface tension data. 

The properties of supercritical fluids fall between those of gases and liquids, as shown in Table 1. Thus the mobile phase in SFC has a viscosity... 

The physical properties of supercritical fluids tend to lie between those of gases and liquids. The increased density relative to a gas, and the decreased viscosity relative to a liquid, allow supercritical fluids to be used as excellent solvents in many laboratory and industrial applications (19-25). Also, some notable solvation peculiarities of supercritical fluids have been discovered. For example, supercritical water can dissolve nonpolar oils because the dielectric constant of supercritical water decreases drastically near the critical point (26). 

Comprehensive data on viscosity, thermal conductivity, and diffusion coefficients of gases and liquids are presented in convenient tabular format. 

Here n is the number of chemical species in a mixture, the mole fraction of species i, p., the viscosity of species i at the system temperature and pressure, and A /, the molecular weight of species i. Mainly, the dependence of viscosities on composition is nonlinear for mixtures of gases. Many additional empirical equations are available for estimating viscosities of gases and gas mixtures at low and high densities (Reid et al., 1987) as well as for liquids, suspensions, and emulsions (Bird et al., 2002). 

The diffusivities of gases and liquids typically have magnitudes that are 10 and 10 cm s, respectively. The diffusivity of gases is proportional to and inversely proportional to P, whereas, the diffusivity of liquids is proportional to T and inversely proportional to viscosity jL (may strongly depend on T). 

Figure 5.6 Effect of the temperature on the viscosity of selected organic compounds. Data in these two figures are from R. C. Reid, J. M. Prausnitz, and B. E. Poling, "The Properties of Gases and Liquids," McGraw-Hill, New York, 4th Ed., 1987.

Values of a and zjks are from J. O. Hirschfelder, C. F. Curtiss, and R. B. Bird, Molecular Theory of Gases and Liquids, pp. 1110-1112, John Wiley Sons, Inc., New York, 1954 (also Addenda and Corrigenda, p. 11). The above values are computed from viscosity data and are applicable for temperatures above 100°K. 

At low and moderate pressures, the viscosity of a gas is nearly independent of pressure and can be correlated for engineering purposes as a function of temperatnre only. Eqnations have been proposed based on kinetic theory and on corresponding-states principles these are reviewed in The Properties of Gases and Liquids [15], which also inclndes methods for extending the calculations to higher pressures. Most methods contain molecular parameters that may be fitted to data where available. If data are not available, the parameters can be estimated from better-known quantities such as the critical parameters, acentric factor, and dipole moment. The predictive accuracy for gas viscosities is typically within 5%, at least for the sorts of small- and medinm-sized, mostly organic, molecules used to develop the correlations. 

Viscosity data for pure components are available in several places [11-14, 60-64], and some collections of mixture data (mostly for binaries) also exist [31, 63, 65]. Some additional data references are cited in The Properties of Gases and Liquids [15]. 

FIGURE 2.4-4 Ratio of eddy to molecular viscosity for the turbulent Bow of gases and liquids in pipes. Reprinted with permission from T. K. Sherwood, R. L. Pigfbrd. and C, R. Wilke. Mass Transfer, McGraw-Hill, New York, 1975. 

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