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| Mixing - Stirring - Suspending - Homogenising - Dispersing - Emulsifying - DefinitionsTechnical terms abound in the world of technical stirring. Below, there follows a list of the most commonly used terms with explanations.
Rheology is defined as the flow characteristics of a fluid. Rheology can be subdivided into newtonian, pseudoplastic, dilatancy, thixotropic and rheopectic fluids.
Viscosity is the relationship between the speed and the imposed shear stress.
Viscosity is the property of fluids that determines their speed of flow. Water is an example of a fluid with a low viscosity; glycerine is an example of a fluid with a high viscosity.
Only a limited number of fluids have a constant viscosity. Moreover, in many cases, the viscosity is only constant within a narrow bandwidth.
The fluids that are the easiest to work with are those with a regular and constant viscosity. That means that an increase in shear forces can be easily absorbed. A fluid with this property is known as a newtonian fluid. Water is an example of a newtonian fluid.
In the case of some fluids, the viscosity is reduced in direct relation to increases in the temperature gradient (= becoming less viscous/dense). If the shear forces are increased the flow is increased correspondingly. The following are examples of pseudoplastic fluids: latex suspensions, pigment dispersions and paper pulp.
Fluids in which the viscosity increases at higher speed gradients are known as dilatancy fluids (becoming more viscous/dense). With an increase in the shear force, the flow is irregularly reduced. Examples of these fluids include starch suspensions in water, wet sand and certain ceramic suspensions.
In some fluids, a time-related effect can be observed on the viscosity. As a result of the constant movement of the fluid, the viscosity is reduced (= becomes less viscous/dense). Once there is no further force being applied to the fluid, the original viscosity level is restored after a certain time. Thixotropic fluids include, for example, honey, ketchup, clay suspensions and varnishes.
Rheopectic fluids are known to have a time-related effect on viscosity. As a result of the constant movement of the fluid, the viscosity is increased (= becomes more viscous/dense). Once there is no further force being applied to the fluid, the original viscosity level is restored after a certain time. This rheological effect occurs rarely. Examples include plaster. water suspensions, vanadium oxide in water and soap solutions.
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