Lee-Kesler method

Calculations were made with the Grayson-Streed modification of the Chao-Seader method for K values and the Lee-Kesler method for enthalpy departures. Initial estimates for stage temperatures and flow rates were as follows, where numbers in parentheses are consistent with specifications ... 

In Figure 10 are shown comparisons of the equation of state methods with the experimental data. The Lee-Kesler methods represent the data the best. Again, if the water acentric factor determined to best represent the pure steam enthalpy data is applied to the mixtures, further improvement is noted for the predictions by the Lee-Kesler method. Use of interaction constants within the Lee-Kesler, or other models, would undoubtedly provide even better representation of the data. 

The value obtained from the Ambrose-Walton-Lee-Kesler method compares favorably with the value of 0.2499 recommended in the DIPPR 801 database (obtained from the vapor pressure correlation). 

For higher gas densities, the Lee-Kesler method described below provides excellent predictions for nonpolar and slightly polar fluids. Extended four-parameter corresponding-states methods are available for polar and slightly associating compounds. 

Applicability Nonpolar and moderately polar compounds. An extended Lee-Kesler method, not described here, may be used for polar and slightly associating compounds [Wilding, W. V, and R. L. Rowley, Inf. J. Thermophys., 8 (1986) 525]. 

TABLE 2-353 Constants for the Two Reference Fluids Used in Lee-Kesler Method ... 

Hence, the computation of Z is split in two parts Z°- term for an ideal spherical molecule, and Z - deviation function accounting for non-sphericity. A large number of generalised predictive methods for physical properties exploit this formulation, as for example the Lee-Kesler method (see later the section 5.4). 

Lee-Kesler method has been extended to oil and petrochemical type mixtures, as for example hydrocarbons and alcohols with COj, H2, CH4 and HjS, and it is known as Lee-Kesler-Ploecker (LKP). Special mixing rules are designed to describe both symmetric (non-polar) and symmetric (polar) molecules. More details can be found in Poling et al. (2001). 

Lee-Kesler method is considered more accurate for enthalpy and entropy than those based on cubic EOS. It is preferred in cryogenics or gas processing. 

Problem 5.9 n-Octane is compressed reversibly at constant temperature along the critical isotherm until the critical point is reached. The initial pressure is 1 bar. The pressure takes place in a closed system. Use the Lee-Kesler method to calculate the following ... 

The Lee-Kesler method for correlating gas phase properties (reference equation and corresponding states approach) has been extended to vapor-liquid equilibria calculations. The calculation of accurate phase equilibria results is more difficult than for the properties of single phase fluids. 

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