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Viscosity measurement

Viscosity measurement for oil monitoring and process reliability

Viscosity is the internal resistance to deformation offered by a fluid and describes how fluids behave under operating conditions. It is essential for oil condition monitoring and process reliability. Accurate viscosity measurement helps detect wear, contamination and performance changes at an early stage.

WIKA solutions reliably measure viscosity, including dynamic and kinematic viscosity and the temperature dependence of viscosity. Using robust viscometers and viscosity sensors, precise results are ensured even under changing temperature conditions.

Why measure viscosity?

Viscosity is a fundamental physicochemical property that characterises a fluid’s internal resistance to flow. In industrial processes, it is monitored as an indicator of product quality, formulation consistency, contamination, degradation and process stability. Deviations in viscosity may reveal changes in composition, temperature control, ageing or operating conditions, making it a critical parameter for quality assurance, process optimisation and equipment protection.

What are typical applications for viscosity measurement?

Viscosity measurement is widely used in applications where liquid flow behaviour, formulation stability and product performance must be controlled. Typical examples include lubricating oils, fuels, chemical intermediates, additives, solvents, polymers, coatings and other industrial process liquids. Continuous viscosity monitoring supports consistent product quality, repeatable production conditions and robust process control.

How can viscosity be measured?

Viscosity can be determined using laboratory techniques such as rotational, capillary, falling-ball, or oscillating viscometers. For process applications, in-line viscosity sensors enable continuous measurement directly in the production line. When combined with density and temperature measurement, in-line technologies provide real-time insight into fluid condition, composition changes and process stability.

At what temperature is viscosity measured?

Viscosity must always be specified at a defined temperature, as it is highly temperature-dependent. Common reference temperatures include 20 °C, 40 °C and 100 °C, depending on the application, liquid type, and applicable standard. A viscosity value reported without its corresponding temperature is incomplete and may be misleading.

How is viscosity linked to temperature?

For most liquids, viscosity decreases as temperature increases because molecular mobility rises and internal resistance to flow is reduced. Conversely, decreasing temperature increases viscosity and may significantly affect pumpability, flow rate and process performance. Accurate viscosity measurement therefore requires either stable temperature control or temperature compensation.

What is the difference between dynamic and kinematic viscosity?

Dynamic viscosity quantifies a fluid’s internal resistance to shear-induced flow. Kinematic viscosity, expressed as ν\nuν, describes the ratio between dynamic viscosity and density. Dynamic viscosity is directly related to shear stress, while kinematic viscosity is commonly used when gravitational flow behaviour is relevant, for example in oils and fuels.

What is a Newtonian fluid?

A Newtonian fluid exhibits a constant viscosity at a given temperature, independent of the applied shear rate. Its shear stress is linearly proportional to shear rate, resulting in predictable flow behaviour during pumping, mixing or circulation. Fluids whose viscosity changes with shear rate are classified as non-Newtonian and may show shear-thinning, shear-thickening or time-dependent behaviour.