Rotational Viscometry and viscometers

A rotating body immersed in a liquid experiences a viscous drag or retarding force, and this principle can be applied to viscometry. The chief advantage of rotational viscometry is that continuous measurements at a given shear stress or rate of shear can be made over extended periods of time. Thus time-dependent changes in flow properties can be measured conveniently. Another advantage of rotational viscometry is the ease with which shear rate can be altered. 

But though rotational viscometry seems simple in principle, in practice it turns out there are so many sources of error to consider and corrections to be made that an operating rotational viscometer of good accuracy is a rather complicated apparatus. Many commercial instruments, operating either on the continuous rotation principle or the oscillating principle, are described in the monograph by Van Wazer et al. [2]. To illustrate the application of the principles of rotational viscometry to operating instruments, we shall examine the details of two instruments the first practical rotational viscometer, devised by Couette [9], and the Per ranti-Shirley cone-and-plate viscometer. 

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