Viscosity, SecondpVT-Virial Coefficient, and Diffusion of Pure and Mixed Small Alkanes CH4, C2H6, C3H8,n-C4H10,i-C4H10,n-C5H12,i-C5H12, and C(CH3)4 Calculated by Means of an Isotropic Temperature-Dependent Potential. I. Pure Alkanes

Abstract

Reference tables of second pVT-virial coefficients B(T), viscosity η(T), and self-diffusion ρD(T) are given for all neat alkanes CnH2n+2, n<6, for temperatures T⩽1200 K starting at 100 K for CH4, 150 K for C2H6, and 180 K for C3H8, n-C4H10, i-C4H10, n-C5H12, i-C5H12, and C(CH3)4. Restricting ourselves to low densities the thermophysical properties are calculated by means of an isotropic (n-6) Lennard-Jones temperature dependent potential (LJTDP). In this model the potential well depth εeff(T) and the separation at minimum energy Rm(eff)(T) are explicitly temperature dependent, whereas the repulsive term n>12 is independent of T. The LJTDP has been used before in order to construct reference tables of thermophysical properties of neat gases [Zarkova and Hohm, J. Phys. Chem. Ref. Data 31, 183 (2002)] and binary mixtures [Zarkova, Hohm, and Damyanova, J. Phys. Chem. Ref. Data 32, 1591 (2003)]. However, those studies were restricted to atoms and globularly shaped nondipolar molecules. Here the approach is extended to elongated, not necessarily spherically symmetric, and in part slightly dipolar molecules. As in previous works the potential parameters εeff(T), Rm(eff)(T), and n are determined by minimizing the root-mean-square deviation between calculated and experimentally obtained thermophysical properties B(T), η(T), ρD(T), and the second acoustic virial coefficient β(T) normalized to their experimental error. In extension of our previous efforts we present a thorough statistical analysis of the experimental input data which gives us the possibility to select primary data which could be used to build up a database.

Calculation of the transport and relaxation properties of methane. I. Shear viscosity, viscomagnetic effects, and self-diffusion

“…Finally, Fig. 2 also shows a comparison with values recommended as reference data by Zarkova et al 63 These values were calculated via an isotropic three-parameter Lennard-Jones ͑n − 6͒ potential obtained from a multiproperty fit to experimental data for the second pressure and acoustic virial coefficients, as well as for viscosity and selfdiffusion at low density. They agree neither with the calculated values nor with the experimental data and hence cannot be considered as standard viscosity values for methane.…”

Ab initio intermolecular potential energy surface and second pressure virial coefficients of methane

“…On the contrary, the data of Douslin et al 32 show virtually no differences to the EOS, because they were used to determine the equation. Figure 5 also shows a comparison with values recommended as reference data by Zarkova et al 46 In the case of methane the basis for these values is an isotropic threeparameter Lennard-Jones-͑n −6͒ potential obtained from a multiproperty fit to experimental data for the second pressure and acoustic virial coefficients as well as for viscosity and self-diffusion at low density. Figure 5 also shows a comparison with values recommended as reference data by Zarkova et al 46 In the case of methane the basis for these values is an isotropic threeparameter Lennard-Jones-͑n −6͒ potential obtained from a multiproperty fit to experimental data for the second pressure and acoustic virial coefficients as well as for viscosity and self-diffusion at low density.…”

A critical review of statistical calibration/prediction models handling data inconsistency and model inadequacy

“…Model inadequacy can sometimes be seen as a consequence of the use of a unique parameter set in different experimental conditions: a "better" model can indeed be obtained by using different values of the parameters along the control space. This can be achieved by modeling the dependence of the physical parameters on the control variable, [75][76][77] or by splitting the data in series along the control space and using a hierarchical model identical to the one in Section 3.2.2.2 for inference of the hyperparameters describing the model's parameters distribution (model M H2 in Wu et al 9 ). To differentiate both hierarchical schemes, the present one is named HierC.…”