Effect of Pressure on Viscosity of Higher Hydrocarbons and Their Mixtures

Abstract

Using the rolling-ball method the viscosity of seven pure hydrocarbons, having 25 or 26 carbon atoms, and three binary mixtures of them has been measured to 3450 bars at 37.8°, 60.0°, 98.8°, and 135°C. The compounds included isoparaffinic, cycloparaffinic, and aromatic types. The increase in viscosity with pressure was found to be strongly dependent on molecular structure. The viscosity-temperature coefficient 1/η(∂η/∂T)p increased with increased pressure while the viscosity-pressure coefficient 1/η(∂η/∂P)T decreased with increased temperature. The behavior of the binary mixtures corresponded within 5% over a range of 50–100 fold change in viscosity to that of the pure compounds equivalent to them in molecular weight and average molecular structure. This remarkable agreement is interpreted to mean that the viscosity of these compounds is some additive function of their constituent groups whether these groups are combined in the same or different molecules as long as the basic molecular symmetry is unchanged. The values of the Eyring theory ΔF±, ΔH±i, ΔS±, and ΔV± for these data are discussed. For the saturated compounds at constant temperature, an approximately linear relation was found between log η and [(v/v0)4—(v/v0)2] where v is the specific volume and η the absolute viscosity.

Some Remarks on the Navier-Stokes Equations with a Pressure-Dependent Viscosity.

“…Such data suggest that it is reasonable to consider a pressure dependence of the viscosity, even in fluids that can, to a good approximation, be regarded as incompressible. The results of [3] indicate that the dependence of viscosity on pressure becomes stronger as the pressure increases and that it is stronger in fluids that already have a high viscosity at atmospheric pressure. We note that the viscosities of polymer melts are several orders * of magnitude higher than that of any of the fluids studied in [3].…”

“…More recent experiments at very high pressures, however, have shown considerable changes in viscosity. In [3], for example, various organic liquids were studied at pressures of up to several thousand atmospheres. It was found that for some of these liquids the viscosity increased by two orders of magnitude compared to its value at atmospheric pressure, while compression was only of the order of 10% [2].…”

Revisiting plane Couette–Poiseuille flows of a piezo-viscous fluid

“…fluids whose viscosity depends strongly on the pressure) form a very interesting rheological class. The possibility of the existence of such fluids in nature has been discussed by various authors for centuries [2][3][4]. More recently, the fluids exhibiting noticeable dependence of their viscosity on the pressure were found in technological applications such as polymer processing [5] and journal bearing lubrication [6,7].…”

On Fully Developed Flows of Fluids with a Pressure Dependent Viscosity in a Pipe

“…There is a considerable body of experimental literature that indicates without a shadow of doubt the dependence of the viscosity on pressure (see Cutler et al [4], Griest et al [5], Johnson and Cameron [6], Johnson and Tevaarwerk [7], Greenwood [8], Bair and Winer [9]). It has been found that the variation of the viscosity with pressure could even be exponential, with the viscosity varying by several orders of magnitude (see also Szeri [10] for a discussion of the variation of viscosity with pressure in elastohydrodynamics).…”