A viscometer can be an important component in process and quality control. The technical term to refer to this is extensional viscosity.Ī viscometer is frequently used in laboratories, but it also has practical applications in factories and other industrial environments. However, a fluid's viscosity also may be measured on the basis of stretching.
Rotational viscometers with rotating spindles or rotors, also known as "cup and bob" or Searle viscometers, are the most common tools used to measure the shear viscosity of fluids. The term viscosity typically refers to shear viscosity, i.e., how a material reacts to being sheared. Rotating-cup rheometers are called Couette systems, while rotating-bob rheometers are called Searle systems, as shown in Figure 3 and Figure 4, respectively.A viscometer, viscosity meter or rheometer is a measuring instrument used to determine a fluid's internal flow resistance or viscosity. These rheometers involve an additional design consideration depending on whether the outer cylinder (the cup) or the inner cylinder (the bob) rotates. USP38 Concentric cylinder rotational rheometers are sometimes referred to as cup-and-bob rheometers.
Controlled shear rate rheometers measure the shear stress (from the torque on the rotor axis) resulting from a given shear rate (or rotational speed). Controlled shear stress rheometers measure the shear rates resulting from the application of a given force or torque (the stress). Both controlled-stress and controlled-rate rotational rheometers are available commercially in configurations with absolute geometries (e.g., very small annular gaps between concentric cylinders) that allow calculation of apparent viscosities for non-Newtonian fluids.
Apparatus: In the concentric cylinder rheometer, the apparent viscosity is determined by placing the liquid in the gap between the inner cylinder and the outer cylinder.
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