Powder Mixing
Mixing is one of the basic processes commonly used in various industries. The process of mixing may proceed in a forced manner – due to applying external energy, e.g. with agitators or by rotating a tank filled in with the substances to be mixed.
Mixing is aimed at achieving mutually uniform distribution of the ingredients involved. It consists in changing the configuration of different particles of the medium in order to make it homogenous in a single- or multiphase environment as regards the concentration, thickness, temperature and other properties of the mixture. It is also a way to intensify the processes of heat transfer and mass transfer, as well as to hasten a reaction. Optimization of mixing is aimed at obtaining the required degree of blending in a short time and with the smallest possible input of energy.
What reflects the quality of blending is the distribution of concentration of particular ingredients, i.e. the homogenity of the mixture. In the event of mixing two components characterized by similar physical properties (thickness and particle diameter), the process may theoretically result in a number of states of blending:
- the state of complete segregation – two separate agglomerations can be distinguished within the mixture
- the state of partial blending
- perfect disorder
- the state of partial order
- ideal blending, which is a state of order characterized by an appropriate configuration of particular elements.
Heterogeneous mixtures (consisting of particles of varied diameters) easily get segregated and hence they never reach the state of the so-called perfect disorder. During the process of mixing, segregation nearly always takes place when the components significantly differ in their physical properties. The mechanism involved is that finer grains, which are initially at the top, go to the bottom during the mixing process and stay there, even though the process has not been stopped. Similar behaviour may be observed while mixing ingredients of significantly different thicknesses.
Devices for mixing loose substances find application in the following industries: