Suspension

There are various objectives when using an agitator for suspending tasks. In washing processes, for example, or for dissolving solids, off-bottom suspension can be sufficient, while in a process with continuous operation and several vessels arranged in series stringent specifications can be made for the homogeneity of the suspension.

The physical properties of the substances taken into account when designing suspension agitators all impact on the hindered settling velocity wss [m/s] of the solid particles.

Classification of suspension duties
Because of the differing characteristics of particle hindered settling velocities suspension duties can be divided into the following categories:
 
I. Simple suspension duties
If the hindered settling velocities are such that there is laminar flow around the descending particles, this is classified as a simple suspension problem.
 
II. Demanding suspension duties
The largest proportion of all suspension task designs are classified in the category, as confirmed by the extensive investigations carried out by Einenkel.
 
II. ”Difficult” suspension duties
In order to avoid overdesigning the agitator and determine the appropriate scale-up rule for commercial-scale equipment, it is recommended that tests be performed.
 
IV. ”Uniform” suspension no longer attainable
In this range the best that can be achieved is the off-bottom suspension of the solids, i.e. it is no longer possible to suspend the solids right up to the liquid surface. This means that only dissolving or washing processes can be accomplished for this category.