Viscosity-density correlation of Newtonian liquids

The viscosity of monatomic liquids was modeled by an equation derived from the kinetic theory of gases. Viscosities may be calculated from data on density and molecular weight of the liquid. In adapting this relationship to polyatomic liquids, a single correction factor was developed for each of five series of homologues; n-paraffins, n-1 -alkenes, n-alkylcyclohexanes, n-alkylbenzenes and n-alcohols, to account for the deviations of the calculated viscosities from those reported, extending over a one- to three-hundred degree range. The factor is a function of reduced temperature relative to the normal boiling point, TrB. A single equation for each of the series of homologues, n-paraffins to n-alcohols, was thus used as a predictor for the viscosities with an average error of 6.8, 4.9, 7.9, 4.9 and 29.5 per cent, respectively. The correction factors for the hydrocarbon series, excluding the alcohols were sufficiently similar so that they were estimated to be identical. A combined correction factor for two series, n-paraffins and n-l-alkenes, was employed to extrapolate to the alkylbenzenes and alkylcyclohexanes with an accuracy in predicted viscosity of 10. 1 and 18.4 per cent, respectively. The maximum error in both series was only 37.9 per cent. Thus predictions of liquid viscosity were performed over extended temperature ranges, with good accuracy without requiring viscosity data. A further refinement of the correction factor for each of the five series of homologues was introduced by correlation with two parameters; TrB and with the number of carbon atoms in the alkyl group, C. The use of the carbon parameter decreased the average error in predicted viscosity to 1.78, 1.95, 2.39, 3.46 and 14.5 per cent for the n-paraffins, n-l-alkenes, n-alkylcyclohexanes, n-alkylbenzenes and the n-alcohols, respectively. The idealized liquid state model which is the basis of the present development does not adequately predict the viscous behavior of real liquids. It is significant, however, that the deviations from the model are relatively consistent, and may be taken into account by a relatively simple empirical function, applicable to a wide variety of liquids. This study also describes the experimental determination of density and kinematic viscosity over wide ranges of temperature and of molecular weight for the n-alcohols. A density apparatus based on the hydrostatic weighing method was constructed and used for the measurement of n-alcohol densities from room temperature to near their normal boiling points. The apparatus permitted a density measurement every 30 minutes on 5 ml of liquid sample with an average accuracy of 1.4 x 10-4 g/ml, and a reproducibility of 1-4 x 10-4 g/ml