Epprecht viscometer

Figure 9. Intermediate shear rate viscosity characteristics of formulations I, II, and III from Table II (Epprecht viscometer)...

Rotation Viscometers. In rotation viscometers, a rotor moves against a stator (see Figure 9-23). The Epprecht viscometer is particularly suitable for measurements on highly viscous solutions. Here, the angle of rotation of a torsion wire on which the stator is suspended is a measure of the torque produced by the rotating rotor on the liquid. Since all the other quantities (cylinder radius, width of the slit, gap between rotor and stator, number of rotations in unit time) are kept constant, the viscosity is easily calculated. 

The Brookfield viscometer is of simpler construction than the Epprecht viscometer. In this case, a rotating metal plate or cylinder is immersed in the liquid and the frictional braking forces that act on it are measured. 

Table III shows the viscosity characteristics of these systems as obtained from the Epprecht rotational viscometer. With this instrument, shear rate can be obtained in units of reciprocal seconds (sec-1). These data are plotted in Figure 9. Under these shearing rates (19.2 to 125 sec"1), all three formulations are pseudoplastic.

Shear stress versus shear rate data for concentric cylinder viscometer (Epprecht, Model RM-15), K = 0.794. Uncorrected shear rate (eq. 5.3.11) is compared to true shear rate (eq. 5.3.24) and with n evaluated graphically versus y for a 1% carboxymethylcellulose solution From Mi leman (1968, p. 25). 

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