Pressure rotational viscosity

Viscosities of liquids mixed with C02 have been measured in a high-pressure rotational viscometer, which works according to a Searle-system. The pressure influence on the viscosity of the pure liquid can be described with known correlations [9]. 

The flow behavior of non-Newtonian fluids is usually described by expressing either shear rate or viscosity as a function of shear stress. Absolute viscometers, either capillary or rotational, are used to perform the necessary measurements. In the capillary viscometer, the flow rate is measured as a function of applied pressure. Apparent viscosities calculated by means of Poiseuille s relation [Eq. (9)], are converted to true viscosities using the Weissen-berg-Rabinowitsch correction... 

If the logarithm of the rotational viscosity at constant pressure is plotted versus the inverse temperature, the curves for higher pressure can be obtained from the curve at atmospheric pressure by shifting along the abscissa. Neither the activation energy nor the absolute value of the viscosity at the... 

Figure 22. Rotational viscosity of MBBA as a function of pressure at 85.2 °C.

Figure 23. Rotational viscosity of MBBA as a function of the difference IT- IT, where T is the temperature of the clearing point at the measurement pressure.

A main problem in evaluating the divergence of the rotational viscosity in the vicinity of a smectic phase is the separation of the non-divergent part. An additional determination of the pressure dependence can be very advantageous. First, the pressure dependence can be studied directly, as the pressure dependence of the non-divergent part is less pronounced than its temperature dependence. Secondly, the above discussed... 

Another type of rotational viscometer is the hehcal-screw rheometer (176). This iastmment is basically a screw-type metering pump that does not pump. The measure of force is the pressure difference resulting from the rotational motion. It is possible to use a bank of pressure transducers of different sensitivities to measure viscosity over a wide range. The iastmment can be used for high temperature rheometry and to foUow polymerkation, shear and heat degradation, and other developments. 

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