The excess enthalpies of (carbon dioxide + cyclohexane) at 390.15, 413.15, 438.15, 498.15, and 508.15 K from 7.50 to 14.39 MPa

Excess enthalpies of binary mixtures with endothermic–exothermic changes in mixing processes: empirical correlations

“…This possibility will not be taken into account in this present work, i.e., we shall study the fit with only a single model. An alternative to using equation (2) together with a simple linear model is to modify the Redlich + Kister model by using two polynomial expressions weighted with negative exponential functions, as was done by Ott et al [16] and Cordray et al [11]:…”

“…Even when the model is appropriate for other ranges and deviations for each experimental point, and also the mean deviation, are small, the denominator can be zero for some values of x, thus leading to a discontinuity. In some cases [11][12][13][14], equation (2) has been used together with other simple models for certain ranges of the mole fraction. This possibility will not be taken into account in this present work, i.e., we shall study the fit with only a single model.…”

“…The selected models are: (i) the classical Redlich + Kister model [15]; (ii) the extended version of the Redlich + Kister expression used by Christensen et al [12][13][14], which is a Padé type expression; (iii) the expression used by Ott et al [16] and Cordray et al [11], containing an exponential term; and (iv) the expression given by Gruszkiewicz et al [17], and recently used by Ochi et al [6]. As far as we know, the validity of all these four models has not been studied.…”

“…Nevertheless, there is no fixed criterion to decide which type of correlation must be used for each thermodynamic range or for each type of mixture. With only a few exceptions (see for example [9,11]), the published data have been fitted by using only a single analytical expression. The correlation models commonly used by the experimentalist are based on different analytical expressions and contain a variable number of adjustable coefficients which are different for each thermodynamic state and must be found by trial-and-error.…”

Calorimetry in the near-critical and supercritical regions. Nitrous oxide + hydrocarbon mixtures

“…Simultaneously, Christensen et al [4,5] were setting up a new highpressure flow calorimeter able to detect both exothermic and endothermic processes which was quickly applied to determine the excess enthalpies of CO 2 þ hydrocarbon mixtures in the critical region. From 1983 to his early dead, James J. Christensen published data of mixtures such as CO 2 þ ethane [6], þ pentane [7,8], þ hexane [9,10], þ cyclohexane [11][12][13][14], þ decane [15,16], þ toluene [17][18][19][20] and þ pyridine [21,22]. Figure 1 shows the experimental P,T conditions at which data are available for three of these systems.…”