A1000 – Agitators, Blenders & Mixers
Agitation is a means whereby mixing of phases can be accomplished and by which mass and heat transfer can be enhanced between phases or with external surfaces. In its most general sense, the process of mixing is concerned with all combinations of phases of which the most frequently occurring ones are:
1. Gases with gases.
2. Gases into liquids: dispersion.
3. Gases with granular solids: fluidization, pneumatic
4. Liquids into gases: spraying and atomization.
5. Liquids with liquids: dissolution, emulsification, dispersion
6. Liquids with granular solids: suspension.
7. Pastes with each other and with solids.
8. Solids with solids: mixing of powders.
Interaction of gases, liquids, and solids also may take place, as in hydrogenation of liquids in the presence of a slurried solid catalyst where the gas must be dispersed as bubbles and the solid particles must be kept in suspension.
Three of the processes involving liquids, numbers 2, 5, and 6, employ the same kind of equipment; namely, tanks in which the liquid is circulated and subjected to a certain amount of shear. This kind of equipment has been studied most extensively. Although some unusual cases of liquid mixing may require pilot plant testing, general rules have been developed with which mixing equipment can be designed somewhat satisfactorily.
The other mixing operations of the list require individual kinds of equipment whose design in some cases is less quantified and is based largely on experience and pilot plant work.
The terms “mixing” and “blending” are often used interchangeably, but technically they are slightly different. Blending is a process of combining materials, but blending is a relatively gentle process compared to mixing.In terms of the phase of material, blending is the process of solid-solid mixing or mixing of bulk solids with small quantity of liquid. The terminology mixing is more closely associated with liquid-liquid, gas-liquid, and viscous materials.