Viscosity of pure liquids

Capillary viscometers are ideal for measuring the viscosity of Newtonian fluids. However, they are unsuitable for non-Newtonian fluids since variations in hydrostatic pressure during sample efflux results in variations in shear rate and thus viscosity. This unit contains protocols for measuring the viscosity of pure liquids and solutions (see Basic Protocol) and serums from fruit juices and pastes (see Alternate Protocol). 

This protocol describes a method for measuring the viscosity of pure liquids and solutions by capillary viscometry. The sample is loaded into a Cannon-Fenske viscometer. The time required for the sample to flow between two time points on the viscometer is used to calculate the kinematic viscosity or viscosity. 

This method is an adaptation of the Basic Protocol for measuring the viscosity of pure liquids and solutions. The °brix (unithi.4) of the sample is adjusted to a desired value by dilution. In many protocols, a nominal value of 5 °brix is the accepted target value for dilution. The sample is then filtered to remove particles that would plug the capillary tube of the viscometer, and the serum viscosity is measured in a Cannon-Fenske viscometer. 

The discussion here has been directed to the viscosity of pure liquids. When an electrolyte or other solute is added, the viscosity changes. Many data exist in the literature for the viscosity of solutions. This subject is of special importance to engineers interested in the flow properties of solutions. The discussion here is meant to be only a brief introduction to the basic concepts. In the following sections, attention is turned to the transport of solute species in solutions. 

All diffusivity correlations require values of the corresponding viscosities. Hence, we first estimate the viscosities of pure liquids by the group eontributions method of Van Velzen (1972a,b). The values at 85 °C are ... 

Under the conditions prescribed, the methods outlined above always give identical values for the coefficients of viscosity of pure liquids assuming that turbulence does not exist and that Newton s law connecting velocity gradient and shear stress truly represents the conditions. This is actually the case, as is known from experience, for the majority of pure liquids, but there are exceptions, which appear important for our purpose because they concern liquids made up of long chain substances as we shall see later, these play an important part in the realm of high polymer solutions. It has been proved impossible in many cases to describe the me-... 

After this brief discussion of the viscosity of pure liquids, it is time to pass to the question Is it possible to draw deductions from measurements of the viscosity of solutions, regarding the magnitude, form and internal mobility of the dissolved or dispersed particles and the energy interactions between them ... 

Van der Wyk has advanced a theory of viscosity of binary mixtures based on Andrado s theory of the viscosity of pure liquids referred to above. He tried to find an explanation first for the processes in normal binary mixtures. The formulas current for these mixtures, which represent viscosity as dependent on the concentration of the constituents, arc, however, without exception, empirical laws. Attempts have certainly been made to give theoretical support to the laws but they usually turn out to be not quite successful. 

Kinematic viscosity of pure liquid water at different temperatures up to 100 °C is listed in Table 1.6. 

Table 1.6. Kinematic Viscosity of Pure Liquid Water at Different Temperatures and 1.0 atm Pressure ...

As there is no theoretically based model for liquid viscosity, there is considerable variation in the types of models that have been developed, and the limited amount of data and their accuracy makes it difficult to discriminate among the models that have been proposed. Most viscosity correlations are essentially empirical in nature and generally require at least one parameter fit to experimental data for accurate estimates of the viscosities of pure liquids. Some of these models have been generalized for certain types of liquid hydrocarbons and provide reasonably accurate predictions, but only for those groups of substances. 

Barrer, R. M. (1943). The viscosity of pure liquids. 11. Polymerised ionic melts.. Ghent Soc. 

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