chapter one the estimation of physical properties

THE ESTIMATION OF PHYSICAL PROPERTIES
1.8 CHAPTER ONE
thalpy of vaporization, and pressure corrections to ideal-gas enthalpies and entropies.
The substance is, of course, a well-known refrigerant, and its known properties
are shown by the solid curves. While environmental concerns no longer permit use
of CCl 2 F 2 , it nevertheless serves as a good example of building a full description
from very little information.
For a standard refrigeration cycle operating between 48.9 and 6.7C, the evaporator
and condenser pressures are estimated to be 2.4 and 12.4 bar, vs. the known
values 2.4 and 11.9 bar. The estimate of the heat absorption in the evaporator checks
closely, and the estimated volumetric vapor rate to the compressor also shows good
agreement: 2.39 versus 2.45 m 3 /hr per kW of refrigeration. (This number indicates
the size of the compressor.) Constant-entropy lines are not shown in Fig. 1-2, but
it is found that the constant-entropy line through the point for the low-pressure
vapor essentially coincides with the saturated vapor curve. The estimated coefficient
of performance (ratio of refrigeration rate to isentropic compression power) is estimated
to be 3.8; the value obtained from the data is 3.5. This is not a very good
check, but it is nevertheless remarkable because the only data used for the estimate
were the normal boiling point and the chemical formula.
Most estimation methods require parameters that are characteristic of single pure
components or of constituents of a mixture of interest. The more important of these
are considered in Chap. 2.
The thermodynamic properties of ideal gases, such as enthalpies and Gibbs energies
of formation and heat capacities, are covered in Chap. 3. Chapter 4 describes
the PVT properties of pure fluids with the corresponding-states principle, equations
of state, and methods restricted to liquids. Chapter 5 extends the methods of Chap.
4 to mixtures with the introduction of mixing and combining rules as well as the
special effects of interactions between different components. Chapter 6 covers other
thermodynamic properties such as enthalpy, entropy, free energies and heat capacities
of real fluids from equations of state and correlations for liquids. It also introduces
partial properties and discusses the estimation of true vapor-liquid critical
points.
Chapter 7 discusses vapor pressures and enthalpies of vaporization of pure substances.
Chapter 8 presents techniques for estimation and correlation of phase equilibria
in mixtures. Chapters 9 to 11 describe estimation methods for viscosity, thermal
conductivity, and diffusion coefficients. Surface tension is considered briefly in
Chap. 12.
The literature searched was voluminous, and the lists of references following
each chapter represent but a fraction of the material examined. Of the many estimation
methods available, in most cases only a few were selected for detailed
discussion. These were selected on the basis of their generality, accuracy, and availability
of required input data. Tests of all methods were often more extensive than
those suggested by the abbreviated tables comparing experimental with estimated
values. However, no comparison is adequate to indicate expected errors for new
compounds. The average errors given in the comparison tables represent but a crude
overall evaluation; the inapplicability of a method for a few compounds may so
increase the average error as to distort judgment of the method’s merit, although
efforts have been made to minimize such distortion.
Many estimation methods are of such complexity that a computer is required.
This is less of a handicap than it once was, since computers and efficient computer
programs have become widely available. Electronic desk computers, which have
become so popular in recent years, have made the more complex correlations practical.
However, accuracy is not necessarily enhanced by greater complexity.
The scope of the book is inevitably limited. The properties discussed were selected
arbitrarily because they are believed to be of wide interest, especially to
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