MOLECULAR PRINCIPLE OF CORRESPONDING STATES FOR VISCOSITY AND THERMAL CONDUCTIVITY OF FLUID MIXTURES

Conformal solution theory is developed for the viscosity and thermal conductivity of fluid mixtures. The procedure involves expanding the transport coefficient for the mixture about the value for an ideal solution, using groupings of the potential parameters and molecular mass as expansion coefficients. The parameters for the ideal solution are chosen so as to annul the first-order term in this expansion, thus encouraging rapid convergence. This yields mixing rules (similar to those of the van der Waals 1 theory for thermodynamic properties) for the potential parameters and molecular mass of the reference fluid. Reference fluid properties are obtained from pure fluid corresponding states correlations

By making calculations for dilute gas mixtures and comparing with Chapman-Enskog theory, it is found that the first-order theory works well for mixtures of quite widely different energy parameters (ε) and molecular masses; it is more sensitive to the size difference of the molecular components, however. For cryogenic liquid mixtures composed of simple liquids good results are obtained using two-parameter corresponding states for the reference fluid. For polyatomic fluids it is necessary to use a three-parameter corresponding states approach for the pure fluids. A method of introducing a third parameter, while retaining the simplicity of having only two independent variables, is used for such fluids. Good results are obtained for a variety of binary mixtures. The method is of particular value for multicomponent fluids. Thus, without fitting any parameters from ternary data the theory predicts viscosities for the system carbon tetrachloride/n-hexane/benzene over the full composition range with a standard deviation of only 1.69%.     

A multifluid corresponding states principle for the thermodynamic properties of fluid mixtures

A generalised multifluid corresponding states principle is presented for the correlation and prediction of the thermodynamic properties of fluid mixtures. The multifluid model is an extension of earlier work which was based on the known properties of two (nonspherical) reference fluids. The new model is tested for the prediction of the orthobaric densities of LNG mixtures using all the pure components as the reference fluids. Comparisons with the two-fluid corresponding states method are shown and the advantages and disadvantages of the two methods are outlined. For simple nonpolar mixtures, such as LNG, both methods can give predictions which are well within the accuracy of the experimental data using, at most, only one adjustable coefficient to characterize each binary system.     

THE CORRELATION AND PREDICTION OF THE VISCOSITIES OF MIXTURES OVER A WIDE RANGE OF PRESSURE AND TEMPERATURE

A generalized corresponding states principle (GCSP) based on the known properties of two reference fluids has been used to correlate the viscosities of fluid mixtures over a wide range of pressure and temperature. It is shown that good predictions of the viscosities for a variety of mixtures can be obtained with this method. Asymmetric mixtures, however, require the use of one adjustable constant. Comparisons with the TRAPP method are shown and the advantages and limitations of the two methods are discussed.     

A generalized corresponding states method for the prediction of the thermal conductivity of liquids and liquid mixtures

We have recently developed an extension of the three parameter corresponding states principle based on the properties of two non-spherical reference fluids for the viscosity of liquids and liquid mixtures. We extend the method here to the thermal conductivity. We have tested the method for a large number of binary liquid mixtures using the two pure components in each case as our reference fluids. Good agreement between predicted and experimental thermal conductivities was obtained using only the data for the pure components. This agreement becomes excellent if a single binary interaction consta independent of temperature and composition, is used in the mixture calculations. If the pure component reference properties are not available, then the may he obtained from the properties of two similar fluids.     

EVALUATION OF THE ORIGINAL AND THE EXTENDED CORRESPONDING STATES PRINCIPLE FOR REFRIGERANTS

The corresponding states and extended corresponding states principles have been evaluated for refrigerants. In the two corresponding states techniques the Riedel and Wagner vapour pressure correlations have been used to express the vapour pressure for the reference fluids. As reference fluids CFC12 and HFC134a have been used. These two fluids cover the acentric factor interval wherein refrigerants are found. Parameters have been estimated for CFC12 and HFC134a according to the Reidel and Wagner vapour pressure correlations used in the extended corresponding states principle. Experimental vapour pressure data for CFC12 and HFC134a have been used to estimate parameters according to Riedel and Wagner used in the hypothetical fluid and deviation function used in the corresponding states principle.

The Riedel and Wagner correlations are of equal accuracy in vapour pressure calculations. The results from the corresponding states and extended corresponding states principle are comparable due to the conformity between the Riedel and Wagner correlation, but improved results are obtained in comparison with the Lee-Kesler vapour pressure correlation in acentric factor interval studied.     

A corresponding states model for the thermal conductivity of gases and liquids

A new model for the prediction of the thermal conductivity of pure fluids and mixtures is presented. The model is based on the corresponding states theory, and to use the model only well-known, pure component parameters plus the transport properties of a reference substance (here methane) are required. No P—V—T information is needed. The model is applied to the lower hydrocarbons (up to pentane), nitrogen, carbon dioxide, and mixtures of these at reduced temperatures between 0.6 and 3.0 and reduced densities between 0.0 and 2.7. For over 600 data points, the deviation between experimental and predicted values is typically between 2 and 5%.     

CRITICAL POINT PREDICTION USING A MULTI-FLUID GENERALIZED CORRESPONDING STATES PRINCIPLE

The Generalized Corresponding States Principle (GCSP), based on the properties of two non-spherical reference fluids, offers flexibility and ease of computation for the prediction of thermodynamic and transport properties of pure fluids and fluid mixtures. In this work, the multi-fluid GCSP is used for the calculation of the critical properties of mixtures. Classes of mixtures studied include those containing: (1) simple spherical molecules; (2) large quasi-spherical molecules such as the cyclosiloxanes; (3) both spherical and large nonspherical molecules such as those important in supercritical extraction and hydrocarbon processing; and (4) molecules exhibiting strong dipole moments. The advantages of the GCSP method are outlined, particularly for fluids not usually amenable to conventional corresponding states treatments.     

CRITICAL POINT PREDICTION USING A MULTI-FLUID GENERALIZED CORRESPONDING STATES PRINCIPLE

The Generalized Corresponding States Principle (GCSP), based on the properties of two non-spherical reference fluids, offers flexibility and ease of computation for the prediction of thermodynamic and transport properties of pure fluids and fluid mixtures. In this work, the multi-fluid GCSP is used for the calculation of the critical properties of mixtures. Classes of mixtures studied include those containing: (1) simple spherical molecules; (2) large quasi-spherical molecules such as the cyclosiloxanes; (3) both spherical and large nonspherical molecules such as those important in supercritical extraction and hydrocarbon processing; and (4) molecules exhibiting strong dipole moments. The advantages of the GCSP method are outlined, particularly for fluids not usually amenable to conventional corresponding states treatments.     

COMPARISON OF PREDICTIVE CORRELATIONS FOR THE NORMAL BOILING DENSITY OF NONPOLAR FLUIDS

Seven empirical correlations for the calculation of the normal boiling density of non polar pure fluids are studied for their accuracy and applicability. One of the correlations is specific only for the normal boiling density, five are based on the corresponding states method (these need the critical parameters and acentric factor as inputs), and the other is a new kind of correlation that uses the Lennard-Jones molecular parameters and the acentric factor as input data. As reference, we take the value for the normal boiling density given by the specific correlation functions proposed in the DIPPR project for 252 nonpolar fluids, grouped into 17 families. In view of the results, we recommend the use of the Yamada-Gunn expression because of its simplicity and because other, less simple, models represent no clear improvement over its accuracy. We also recommend the use of the molecular-parameter model because it gives very good results for some families of fluids.     

COMPARISON OF PREDICTIVE CORRELATIONS FOR THE NORMAL BOILING DENSITY OF NONPOLAR FLUIDS

Seven empirical correlations for the calculation of the normal boiling density of non polar pure fluids are studied for their accuracy and applicability. One of the correlations is specific only for the normal boiling density, five are based on the corresponding states method (these need the critical parameters and acentric factor as inputs), and the other is a new kind of correlation that uses the Lennard-Jones molecular parameters and the acentric factor as input data. As reference, we take the value for the normal boiling density given by the specific correlation functions proposed in the DIPPR project for 252 nonpolar fluids, grouped into 17 families. In view of the results, we recommend the use of the Yamada-Gunn expression because of its simplicity and because other, less simple, models represent no clear improvement over its accuracy. We also recommend the use of the molecular-parameter model because it gives very good results for some families of fluids.     

EQUATION OF STATE FOR POLAR AND NONPOLAR SUBSTANCES FROM CORRELATIONS OF PURE COMPONENT PROPERTIES

A cubic equation of state of the van der Waals type is presented which is suitable for polar and nonpolar fluids and fluid mixtures. The form is based on the three-parameter equation of lwai, Margerum and Lu. Problems in parameter generalization are avoided by calculating the parameters directly from existing pure component vapor pressure and saturated liquid molar volume correlations. The proposed approach yields excellent representation of pure component saturated and single-phase region properties. Excellent results are also obtained for mixtures.     

链状流体的分子热力学模型(Ⅱ)──混合物汽液平衡

实际链状流体混合物的亥氏函数表示为参考流体（硬球链流体混合物）的贡献和由于链节间的方阱位能相互作用的贡献之和．前者直接用作者先前建立的硬球链流体混合物的分子热力学模型计算,不含混合规则;后者采用Alder等人的结果,用vanderWaals单流体理论计算混合物的能量参数.对于不含氢键作用的二元混合物,有一可调相互作用参数,需由实验数据拟合得到．本模型可以满意地关联小分子混合物和高分子溶液的汽液平衡。     

A CUBIC EQUATION OF STATE BASED ON A SIMPLIFIED HARD-CORE MODEL

The Redlich-Kwong (RK) equation of state introduced in 1949 has been considered the most accurate two-constant-parameter cubic equation of state. The other cubic equations which are more accurate than the RK equation contain either three, or more, parameters and/or their parameters are temperature- dependent. A New two-constant-parameter cubic equation of state, $ is introduced using a simplified molecular theory of hard-sphere fluids for its repulsive term. This two-constant-parameter cubic equation of state appreciably increases the accuracy of thermodynamic property predictions and phase equilibria of pure fluids and flluid mixtures over the equations of this category.     

HIGH PRESSURE DENSITIES OF MIXTURES OF COAL CHEMICALS

Densities of seven coal chemicals (benzene, toluene, letralin, quinoline, m-cresol, bicyctohexyl and 1-methylnapthalene) and their binary mixtures at temperatures between 298 K and 338 K and pressures between 0.1 MPa and 34.5 MPa were measured using a high-pressure vibrating tube densitometer and are reported in this paper. The pure component densities were correlated using a modified Tail equation. The pure components were then used as reference fluids in a corresponding stales method for the prediction of the densities of the mixtures. @KEYWORDS High pressure Densities Mixtures Coal chemicals.     

闭式热源下混合工质与纯工质的ORC性能比较

为了全面比较有机朗肯循环(ORC)中混合工质与纯工质的性能优劣，在给定供热量及进出口温度的闭式热源条件下，建立了基本ORC和回热ORC的数值仿真模型，所用工质为R600a/R601a，所用冷源为一定流量范围的冷却水。在模拟中，以最大净输出功为目标，同步优化循环的蒸发及冷凝温度，得到了不同组分工质的性能参数。比较结果表明，混合工质的热力性能不一定优于纯工质。在闭式热源下，相变换热器中具有更好温度匹配的混合工质一般也具有更小的换热损失。针对回热ORC，回热器将影响工质在相变换热器中的温度分布，但对相变换热器中的损失影响较小。     

Unified equation of state based on the lattice fluid theory for phase equilibria of complex mixtures part II. Application to complex mixtures

In part I of the present article [Yoo et al., 1995], new rigorous and simplified lattice-fluid equations of state (EOS) were derived and their characteristic features of the molecular thermodynamic foundation were discussed by applying to pure fluids. In this part II, both EOSs were extended to various phase equilibrium properties of mixtures. Comparison of the models with experimental mixture data ranges from density, to equilibria of vaporliquid, vapor-solid and liquid-liquid phases for nonpolar/nonpolar, nonpolar/polar, polar/polar mixtures. Both models were also applied to supercritical fluid phase equilibria and activities of solvents in polymer solutions. With two temperature dependent parameters for pure compounds and one temperature-independent binary interaction energy parameter for a binary mixtures, results obtained to date illustrated that both EOSs are quantitatively applicable to versatile phase equilibria of mixtures over a wide range of temperatures, pressures and compositions.     

用微扰理论、平均球近似结合统计缔合流体理论建立纯流体的状态方程

分别采用微扰理论和平均球近似（MSA）处理实际流体偶极──偶极间的相互作用,结合统计缔合流体理论（SAFT）处理氢键缔合相互作用,建立了一个纯缔合流体的状态方程．用分子链节微观参数分别关联了37种纯缔合流体（水、醇、酸和胺）的饱和液相密度和饱和蒸汽压．结果表明：采用微扰理论处理偶极──偶极相互作用的关联结果明显优于平均球近似,与分子模拟数据比较,结论一致．     

THE APPLICATIONS OF A GENERALIZED EQUATION OF STATE TO THE CORRELATION AND PREDICTION OF PHASE EQUILIBRIA∗

Two methods of generalizing an equation of state are demonstrated and their limitations are outlined. One method involves the correlation of the equation of state constants and the second method involves a recently proposed Generalized Corresponding States Principle based on the properties of two (nonspherical) reference fluids. The PVT properties of pure fluids are represented by a new cubic equation of slate with four parameters which are obtained from vapor pressure and saturated liquid density data. It is demonstrated how a limited amount of data on key components may be used to obtain phase equilibria in mixtures.     

The measurement and prediction of the densities of the ternary mixture hexane + hexadecane + n-propyl alcohol

The densities of mixtures of hexane, hexadecane and n-propyl alcohol were measured at 298.15 and 323.15°K using a 10 ml pyconometer. The results were correlated using a multifluid corresponding states principle based on using all pure components as reference fluids. For the prediction of the densities of ternary mixtures, only the binary interaction coefficients found for the three binary mixtures are required.