viscometri

Viscometri, commonly called viscometers in English, are instruments that measure viscosity, the resistance of a fluid to flow. Viscosity is a key property in lubrication, foods, cosmetics, paints, and many manufacturing processes. In practice, viscosity measurements rely on flow time, torque, or drag under controlled shear.

Common types include capillary viscometers, which determine flow time through a narrow tube by gravity; rotational viscometers, which measure torque required to rotate a spindle; falling-ball viscometers, which time a ball's descent through the liquid; and oscillatory viscometers, which apply small-amplitude shear to obtain complex viscosity. Each type covers different ranges and temperatures.

Dynamic viscosity is expressed in pascal-seconds (Pa·s), with many measurements given in millipascal-seconds (mPa·s) or centipoise (cP). Viscosity depends strongly on temperature, so measurements are performed at a defined temperature using temperature-controlled baths and calibrated standards to ensure accuracy.

Viscometri support quality control, formulation, and process design across industries such as petrochemicals, foods, cosmetics, coatings, and pharmaceuticals. Standards issued by ISO and ASTM specify apparatus, procedures, and data interpretation for consistent results.

Historically, capillary viscometers based on Poiseuille's law laid the groundwork for practical devices. Notable designs include Ubbelohde and Cannon-Fenske capillary viscometers, while modern laboratories frequently employ rotational viscometers for broader ranges and complex fluids.