Abstract
Accurate measurement and determination of liquid viscosity data under high pressure conditions requires knowledge of liquid density data. In this study, a high pressure falling sinker-type viscometer was used to determine the viscosity of n-dodecane at elevated pressures up to 132 MPa without supplementary knowledge of liquid density. The viscometer, which involves the downward movement of a cylindrical sinker under the influence of gravity through the liquid contained within a closed tube, avoided the need for density data by repeating the sinker-timing experiments with two geometrically similar but different-sized sinkers thereby allowing the liquid density in the associated formulae to be eliminated. Furthermore, it was possible to subsequently derive liquid density. Both viscosity and density data were compared to published data for which good correlation was found for viscosity. To minimize errors, it is suggested that the two sinkers for such an approach should be of sufficiently differing densities.
Highlights
The viscosity of liquids is an important property in fluid flow and the estimation of other physical properties such as in the estimation of diffusion in liquid systems [1]
Consisting of a vertically positioned closed tube, a cylindrical sinker is allowed to descend at terminal velocity under the influence of gravity through a liquid under investigation
Under very high pressure conditions, the calculations are not so straightforward as liquids may not be assumed to be incompressible since density data is required to complete the viscosity calculations
Summary
The viscosity of liquids is an important property in fluid flow and the estimation of other physical properties such as in the estimation of diffusion in liquid systems [1]. The viscosity is readily determined from the time for the sinker to descend a known distance and the physical details of the viscometer. Under very high pressure conditions, the calculations are not so straightforward as liquids may not be assumed to be incompressible since density data is required to complete the viscosity calculations. The critical point data can be predicted in some cases, this can lead to complication and mathematical uncertainty which can significantly influence the determined viscosity data. To overcome the need for compressibility data for liquids at high pressure, we examined the use of two geometrically similar sinkers to determine liquid viscosity as a way of overcoming the need for supporting density data
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