Viscosity is perceived as ‘thickness’ or resistance to pouring, but there is more to viscosity than this. All fluids have an internal friction between molecules, which determines how well fluid flows. Due to this internal friction, energy is required to move the liquid and viscosity is the measure of the resistance to flow.
Rotational viscometers are used to determine the viscosity of liquids...
The process of flow through an orifice can often be used as a relative...
Elcometer viscosity dip cups are ideal for the quick testing of the...
Used to check viscosity measurements.
Simple to use instruments that measure the fluidity and flow of coatings,...
Fluids are categorised as Newtonian or non-Newtonian.
- Newtonian fluids, such as water and some oils, are fluids that continue to flow at a given temperature, regardless of the forces acting on it. No matter how fast it is stirred or mixed, Newtonian fluids will always behave in the same manner. Newtonian fluids are generally measured with flow and dip viscosity cups.
- Non-Newtonian fluids, such as paints and ketchup, are fluids which change viscosity when a force is applied. There are several different categories and sub-categories of non-Newtonian fluids, they can be described as the following:
Thixotropic - substances which are gel-like at rest but liquid when agitated, eg: non-drip paints, tomato ketchup and most varieties of honey.
Rheopectic - substances where viscosity increases with duration of stress, eg: some lubricants.
Pseudoplastics - also known as shear thinning - the viscosity decreases with increased shear rate, eg: blood, gelatin and clay.
Dilatant - also known as shear thickening - the viscosity increases with increased shear rate, eg: suspensions of rice, corn starch or concentrated sugar solution.
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