TABLE OF CONTENTS Mixing the movement of fluids and solids to enhance a process result is accomplished by means of an agitation source. For example, the sun is the agitation source for mixing in the earth's atmosphere. Similarly, an air compressor and/or a mechanical mixer is the agitation source in any municipal wastewater treatment plant to enhance the process results of (1) solids suspension and (2) oxygen absorption from sparged or entrained air.
In its most general sense, the process of mixing is concerned with all combinations of phases, of which the most frequently occurring are
Gases with gases
Gases into liquids: gas dispersion
Gases with granular solids: fluidization, pneumatic conveying, drying
Liquids into gases: spraying and atomization
Liquids into liquids: dissolution, emulsification, dispersion
Liquids with granular solids: solids suspension, mass transfer, and dissolution
Pastes with each other and with solids
Solids with solids: mixing of powders
Interaction of three phases gases, liquids, and solids-may also occur, as in the hydrogenation of a vegetable oil in the presence of a suspended solid nickel catalyst in a hydrogen-sparged, mechanically agitated reactor.
Three of the processes involving liquids numbers 2, 5, and 6 in the preceding list employ the same equipment; namely, tanks in which the liquid is circulated and subjected to a desired level of shear. Mixing involving liquids has been most extensively studied and is most important in practice; thus, fluid mixing will be given most coverage here. Many mixing process results can be designed a priori, by using the mixing literature without resorting to experimental studies.
