Correlation and Estimation of Transport Properties

Although transport properties are, strictly speaking, not part of chemical thermodynamics, the most common correlation and estimation methods are briefly introduced here, as they are needed for process simulation steps that are determined by mass transfer (e.g., absorption columns) and for the design of the equipment (e.g., heat transfer). It was decided to present the methods for calculating diffusion coefficients here as well, although they refer to mixtures and not to pure compounds. 

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This present volume, which is complementary to the previous publication, discusses the present state of theory with regard to the dilute-gas state, the initial density dependence, the critical region and the very dense gas and liquid states for pure components and mixtures. In all cases, the intention is to present the theory in usable form and examples are given of its application to nonelectrolyte systems. This will be of particular use to chemical and mechanical engineers. The subtitle of this volume Their correlation, prediction and estimation reflects the preferred order of rqrplication to obtain accurate values of transport properties. Careful correlation of accurate experimental data gives reliable values at interpolated temperatures and pressures (densities), and at different compositions when the measurements are for mixtures. Unfortunately, there are only a limited number of systems where data of such accuracy are available. In other cases, sound theoretical methods are necessary to predict the required values. Where information is lacking - for intermolecular forces, for example - estimation methcxls have to be used. These are of lower accuracy, but usually have more general tq)plicability. 

When the above methods fail, estimation methods become important. Schemes based on the Corresponding-States Principle which are particularly important in this respect are described. In order to demonstrate clearly just when the methods of correlation, the theoretical expressions and estimation techniques are applicable, examples are given of transport-property data representation for systems of different complexity simple monatomic fluids, diatomic fluids, polyatomic fluids (specifically, water and refrigerant R134a), nonreacting mixtures and (dilute) alkali-metal vapors as an example of a reacting mixture. 

It should be clear from the preceding classiflcation of methods of correlation, prediction and estimation of the transport properties of fluids that the list has been presented in the preferred order of application. That is, whenever a correlation of critically evaluated data is available it should be used. Examples of the development of some of these correlations are given in later chapters for different classes of fluids. Wide-ranging correlations of this type are available for only a small subset of the fluids of interest, and the next best means of obtaining the properties is either directly from theory (in rare cases) or from a representation of the results of an exact theory supported by experimental data. This would, in fact, always be the preferred choice of method for the evaluation of the properties of mixtures where wide-ranging correlations in temperature, density and composition are not practicable. This approach is viable at present only for the dilute state of gases and gas mixtures. 

In this expression, V is the polymer specific volume, and Vq is the so-called occupied volume of the polymer, which is commonly estimated by group contribution methods (20), For correlations of transport properties with free volume, the FFV defined in equation 6 is used in place of (v ) in equation 5, and the parameters A and yw are treated as empirical adjustable constants. The chapter by Laciak et al, in this book describes a new methodology for estimating permeability coefficients a priori. Their approach does not rely explicitly on correlations between transport properties and... 

Transport properties and coefficients have been presented in this chapter, including theories, correlations, and experimental methods. While correlations are useful for estimating the transport properties and coefficients, it is desirable for any detailed study of a reactor to determine these properties experimentally using the methods presented in this chapter. 

The transport properties of the supercritical fluids fall somewhat in between the gas and the liquid and also depend on how removed one is from the critical point. Dense gasses have the solubilizing power of liquids and the mobility of gasses as depicted in Table 20.1.3. There are quite a few empirical correlations and theoretical models, which are primarily extensions of corresponding low-pressure liquid and gas counter parts. Similarly, some of the classical experimental methods can be used for measurement of transport properties of supercritical fluids. A rather brief overview of the methods applicable for supercritical fluids will be presented since specialized reviews in the area give a good account of the state of the art. " " For engineering purposes, one can use applicable property estimation methods available in flowsheet simulators such as ASPEN PLUS, PROll, G-PROMS, and CHEMCAD. These methods are discussed in a text classical in the field." ... 

C. Hoheisel, in Transport Properties of Fluids Their Correlation, Prediction and Estimation, J. Millat, J.H. Dymond, C.A. Nieto de Castro, eds., Cambridge University Press, N.Y., 1996. 

These possible steric effects have been evaluated by an approach involving partition coefficients. In this way, an estimate of comparative lipophilicity can be made since this property is felt to influence the ease of membrane transport and thus eventual availability to the site of action. A number of psychotomimetic phenylisopropylamines have been studied in an octanol-water partition system, and the correlation of the resulting values, with central activity has provided a relationship that suggests an optimum lipophilicity for maximum biological activity (Barfknecht et al. 1975). These partition values have been correlated to serotonin receptor stimulation capability (Nichols and Dyer 1977) and have recently been extended to a number of phenethylamine compounds (Nichols et al. 1977). 

The thermal conductivity k is a transport property whose value for a variety of gases, liquids, and solids is tabulated in Sec. 2. Section 2 also provides methods Tor predicting and correlating vapor and liquid thermal conductivities. The thermi conductivity is a function of temperature, but the use of constant or averaged values is frequently sufficient. Room temperature values for air, water, concrete, and copper are 0.026, 0.61, 1.4, and 400 W/(m K). Methods for estimating contact resistances and the thermal conductivities of composites and insulation are summarized by Gebhart, Heat Conduction and Mass Diffiision, McGraw-Hill, 1993, p. 399. 

Millat J, Dymond JH, Nieto de Castro CA (1996) Transport properties of fluids, their correlation, prediction and estimation. Cambridge University Press. Cambridge, UK... 

In Great Britain, the National Engineering Laboratory (NEL, formerly a government agency but now privatized) has prodnced a database for thermodynamic and transport properties. PPDS contains correlations for properties of a large number of pure components these are based on evaluated experimental data where possible but also include some estimated properties. For mixtures, the database contains binary interaction parameters fitted to data for use with common equation-of-state and liqnid-activity methods for calculating phase eqnilibria. Information is available at their Web site [14]. 

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