Viskosimeter

A viscometer, also known as a viscosimeter, is an instrument used to measure viscosity, the resistance of a fluid to flow or deformation under applied stress. Viscosity is a key rheological property influencing pumpability, mixing, filtration, and product stability.

Measurements can yield dynamic (absolute) viscosity, in pascal-seconds (Pa·s), or kinematic viscosity, in square meters per second (m^2/s); the latter equals dynamic viscosity divided by density.

The main types include capillary, rotational, and falling-ball viscometers. Capillary viscometers, such as Ostwald or Ubbelohde, determine viscosity from flow time through a calibrated capillary under gravity. Rotational viscometers measure torque required to rotate a spindle, cone, or cylinder at a set shear rate. Falling-ball viscometers estimate viscosity from the fall time of a ball through a liquid inside a calibrated tube. Some instruments combine methods and offer automated temperature control.

Calibration against reference fluids and strict temperature control are essential, as viscosity is highly temperature dependent. For non-Newtonian fluids, viscosity varies with shear rate, so measurements are performed at defined shear conditions and may require rheological profiling.

Viskosimeters find use across industries such as polymers, paints and coatings, food and beverages, cosmetics, pharmaceuticals, and lubricants, as well as in research and development. They support quality control, formulation, and process monitoring, and are common in rheology laboratories.