Viscosity — Definitions and measurement devices

Accurate data on fluid viscosity is fundamental to science and industry. Indeed, viscosity plays an important role in many industrial processes involving fluid flow or the transfer of quantities of motion; for example, viscosity is a parameter involved in flow measurement, in the calculation of heat transfer coefficients and in the control of chemical processes. As experimental viscosity data are limited or non-existent for many fluids and fluid mixtures, particularly under extreme conditions of temperature and pressure and in the critical region, it is important to develop experimental and theoretical methods of viscosity evaluation for industrial applications. As it is impossible to measure the viscosity of all systems as a function of temperature, pressure and composition, the use of databases must be accompanied by the development of theoretical models based on accurate experimental data of characteristic fluids.

This article can therefore serve as a guide for engineers considering undertaking viscosity measurements, or be useful to those seeking to evaluate the viscosities of gases and liquids as a function of temperature at atmospheric pressure.