Viscosity pure species

The ordinary multicomponent diffusion coefficients D j and the viscosity and thermal conductivity are computed from appropriate kinetic theory expressions. First, pure species properties are computed from the standard kinetic theory expressions. For example, the binary diffusion coefficients are given in terms of pressure and temperature as... 

As illustrated in the low-density limit of Fig. 3.3, the viscosity of gases increases with increasing temperature. Moreover, for pressures well below the critical pressure, there is very little pressure dependence. The kinetic theory of dilute gases provides the theoretical basis for the temperature dependence. The Chapman-Enskog theory provides an expression for dilute pure-species viscosities as... 

Using appropriate kinetic theory expressions, evaluate and plot the pure-species viscosities and thermal conductivities in the range 1000 K < T < 2000 K. 

Rule 1. Fit experimentally measured viscosities as a function of temperature for the pure species to Eq. 12.100 (presented later), using e and a as the adjustable parameters. Measured viscosities are generally more reliable than thermal conductivities for extracting these parameters. 

Pure species viscosities are given by the standard kinetic theory expression [178]... 

To expedite the evaluation of transport properties, one could fit the temperature dependent parts of the pure species viscosities, thermal conductivities, and pairs of binary diffusion coefficients. Then, rather than using the complex expressions for the properties, only comparatively simpler polynomials would be evaluated. The fitting procedure must be carried out for the particular system of gases that is present in a given problem. Therefore the fitting cannot be done once and for all but must be done once at the beginning of each new problem. 

In these equations, T is the temperature, p is the pressure, X is the mole fraction of species k, m is the molecular mass, R is the universal gas constant, and / is the pure species viscosity. The T>jk are first order (in the Chapman-Enskog theory) binary diffusion coefficients, given by Eq. 12.113. It is actually inappropriate [103] to use a second-order or higher approximation [265] to the binary diffusion coefficients here. For this reason the Dixon-Lewis paper used the notation to emphasize that the first-order approxima-... 

Here x, and Mi are the mole fraction and molecular weight of species i in the gas mixture of n species and /x, is the viscosity of pure species i at the system temperature and pressure. 

Table 1 reports the kinematic viscosities for the selected pure species at 19 temperatures in the range -10 to +80°C. As one can see, this table lacks some v values where phase separation occurred. 

Sub-problem 3 554 alternatives remained after screening the target properties of the blends obtained from sub-problem 2 using the linear mixing rules. Dynamic viscosity and lethal concentration are the influencing factors that determined the blend formulations. Nevertheless, the RON value cannot be predicted for all blends because the RON of the pure species is not available. So these compounds were also removed... 

The method for predicting the thermal conductivity of a dense-gas mixmre (Mason et al. 1978 Kestin Wakeham 1980 Vesovic Wakeham 1991) is analogous to that for the viscosity, so that only its main features need be described here. The pseudo-radial distribution function for the thermal conductivity of the pure species is obtained by solving equation (5.60) for g,- at each temperature and the mixture molar density... 

Experimental data are represented by the SUPERTRAPP procedure (STRAPP) of Ely Hanley (1983 Ely Huber 1990), which predicts the density, viscosity and thermal conductivity of pure species and mixtures (see Chapter 12 for details). 

Pure, low temperature organic Hquid viscosities can be estimated by a group contribution method (7) and a method combining aspects of group contribution and coimectivity indexes theories (222). Caution is recommended in the use of these methods because the calculated absolute errors are as high as 100% for individual species in a 150-compound, 10-family test set (223). A new method based on a second-order fit of Benson-type groups with numerous steric correctors is suggested as an alternative. Lower errors are claimed for the same test set. 

In a very dilute solution, between the co-spheres of the ions the interstitial solvent is unmodified and has the same properties as in the pure. solvent,. The co-sphere of each positive ion and the co-sphere of each negative ion, however, may contribute toward a change in the viscosity. We should expect to find, in a very dilute solution, for each species of ion present, a total contribution proportional to the number of ions of that species present in unit volume. At the same time, we may anticipate that the electrostatic forces between the positively and the negatively charged ions must be taken into account. 

In a centrifugal field, dissolved molecules or suspended particles either sediment (if their density exceeds that of the pure solvent), or flotate for the opposite case (negative or inverse sedimentation). Under otherwise identical experimental conditions, the velocity of the molecules or particles depends on the viscosity of the solution or suspension and - very importantly - on the mass and shape of the dissolved species. Sedimentation and flotation are antagonized by the diffusion. Depending on the rotor speed and the molar mass of the dissolved/dis-... 

---