Fluid Dynamics Theoretical Basis of Rotational Viscometer

The rotary drum viscometer is named for its measurement system using a cylindrical drum, which is rotated to make the material under test sheared. This rotational viscometer was first produced in 1890, and after continuous improvement, it was widely used after the 1940s due to its wide application range, accurate measurement results, and convenient operation. It has become the most commonly used rheological measuring instrument.

Commonly used rotary viscometers are divided into three types according to the working conditions of the drum:

1. Inner cylinder rotary coaxial cylinder rotary viscometer
   The measuring system of the viscometer is composed of coaxial inner and outer cylinders, the outer cylinder is fixed, the inner cylinder is rotated by a synchronous motor, and the test material is filled between the inner and outer cylinders. The rheological parameters of the sample are determined by measuring the rotational speed of the inner cylinder and the shear stress on the surface of the inner cylinder. The domestic NXS-II rotational viscometer (Chengdu Instrument Factory) and the German RV rotational dryness meter. The Swiss RMI5 Rotary dryness meter, etc. all belong to this type.
   A schematic diagram of the hook structure of the NXS-11 rotary dryness meter. When the synchronous motor drives the inner cylinder to rotate. The rotor of the motor is subjected to the shearing torque of the material, and the stator is deflected at a certain angle due to the reaction torque. The deflection is balanced by the addressing spring connected with the stator, and the deflection angle is read by the PY dial.
   The NXS-II rotary dryness meter can also be inserted into the sample for portable site survey.
2. Outer cylinder rotating coaxial cylinder rotational viscometer
   Outer cylinder rotary coaxial cylinder rotary viscometer The outer cylinder is driven by a synchronous motor through a speed change gear, and the surface of the inner cylinder is deflected at a certain angle by the shearing moment of the sample. This deflection is balanced by the measuring spring and is determined by the scale. Disk read deflection angle. Domestic ZNN-D and NDJ-2 rotational viscometers belong to this type.
3. Single cylinder rotary viscometer
   The single-cylinder rotary viscometer has no outer cylinder, and the sample is contained in other suitable containers, and the rotating cylinder is directly inserted into the sample for rheological measurement. The dial is driven by the synchronous motor through the transmission gear, and the measuring spring and the drum rotate. The measuring spring is twisted due to the shear moment of the sample acting on the rotating cylinder, the rotating cylinder and the pointer lag behind the dial by an angle, and the deflection angle is read on the dial.