Application of the group contribution concept to Kihara potential for estimating thermodynamic and transport properties: Part VI. Heavy globular molecules (SF6, MoF6, WF6, UF6, C(CH3)4, Si(CH3)4)

The group contribution concept using spherically symmetric Kihara intermolecular potential is applied to calculate second virial coefficient, dilute gas viscosity and diffusion coefficient for heavy globular molecules: sulfur hexafluoride SF6, molybdenum hexafluoride MoF6, tungsten hexafluoride WF6, uranium hexafluoride UF6, tetramethyl methane C(CH3)4, and tetramethyl silane Si(CH3)4. Kihara potential parameters are determined when second virial coefficient and viscosity data are satisfactorily fitted within experimental uncertainties. In the minimization procedure, each individual molecules itself is treated as a single functional group, namely molecular group, whereas functional groups (CH0, Si0, CH3) are assigned to tetramethyl molecules (C(CH3)4, Si(CH3)4). Kihara potential parameters for molecular or functional groups (reduced core radius a*, fit parameters of the potential well depth α and β) are next used to estimate mixture properties: second cross virial coefficient, mixture viscosity, and binary diffusion coefficient. Mixture property predictions are notably improved by adding group binary interaction coefficient kij,gc, which are determined by regressing second cross virial coefficient data.Application of the present method indicates that second virial coefficient data are represented with better results than those of the Tsonopoulos correlation, the correlation of Dymond's group, and the Zarkova and Hohm correlation. Feasibility of the present model to calculate dilute gas viscosity is proved by comparison with the Lucas method and the Zarkova and Hohm correlation. Prediction results of binary diffusion coefficient are in significant agreement with experimental data and are compared well with values obtained by means of the Fuller method.