Basic tasks of mixing
This applies to both the selection of a suitable stirring rotor and required performance of the stirrer drive.
Viscosity describes the thickness or fluidity of liquids and/or fluids. In viscous liquids particles are bound together more strongly and thus less movable which is referred to as internal friction.
Dynamic viscosity is measured in pascal seconds (Pa·s) or millipascal seconds (mPa·s) (obsolete expression poise ‘P’ or centipoise ‘cP’).
Kinematic viscosity is expressed in m²/s. It describes the inner friction of a liquid and is calculated by dividing the dynamic viscosity by the density of a liquid.
Dynamic viscosity is measured in pascal seconds (Pa·s) or millipascal seconds (mPa·s) (obsolete expression poise ‘P’ or centipoise ‘cP’).
Kinematic viscosity is expressed in m²/s. It describes the inner friction of a liquid and is calculated by dividing the dynamic viscosity by the density of a liquid.
| Millipascal second mPa·s (centipoise cP) | Example |
|---|---|
| 0,3 | acetone |
| 1 | water |
| 2 | milk |
| 80 | olive oil |
| 200 | maple syrup |
| 3.000 | honey |
| 5.000 - 10.000 | molasses |
| 50.000 - 70.000 | ketchup |
| 150.000 - 250.000 | tomato puree |
Homogenising
Mixing liquids which are soluble in each other to balance differences of concentration and temperature. The liquids which are to be mixed may vary in concentration, colour or temperature.
Suitable stirring rotors low to medium viscosity
Heat exchange
To intensify the heat exchange in stirring vessels especially with viscous liquids. Transfer of liquid to and away from the heat exchanger (e.g. heating jacket) by means of suitable flows.
Suitable stirring rotors low to medium viscosity
Gas injection
The purpose of treating a liquid with gas is to increase the phase boundary between liquid and gas that can, for example, shorten chemical reaction times.
The stirring rotor needs to divide the gas flow into small bubbles and distribute them evenly in the liquid.
Dispersing
Dispersing describes the mixture of two compounds which are not or hardly soluble in each other, e.g. to intensify the exchange of components. Dispersions (heterogeneous mixture) are instable and segregate without energy supply.
Suspending
Suspending distributes or disperses solid particles homogeneously throughout the liquid. The stirrer shall prevent sedimentation of the solid particles.