OVERVIEW

Many operations in the chemical process industries (CPI) are dependent to a great extent on effective mixing of fluids. While mixing refers to any operation used to change a non-uniform system into a uniform one (i.e., the random distribution into and through one another, of two or more initially separated phases), agitation implies forcing a fluid by mechanical means to flow in a circulatory or other pattern inside a vessel. Mixing is an integral part of a chemical or physical process such as blending, dissolving, dispersion, suspension, emulsification, heat transfer, and chemical reactions. Mixing of fluids is necessary in many chemical processes. It may include mixing of liquid with liquid, gas with liquid, or solids with liquid. Agitation of these fluid masses does not necessarily imply any significant amount of actual intimate and homogeneous distribution of the fluids or particles, and for this reason mixing requires a definition of degree and/or purpose to properly define the desired state of the system. Table 7.1 summarizes the principal purposes for agitating fluids.

In order for the mixing operation to accomplish the overall process requirement, it is necessary to establish the factors which are significant for a mixing device that provides the required end result for the industrial application. It is impractical for the design engineer to completely design a mixer, that is, define its type, diameter, operating speed, shape, and impeller type. Rather, it is reasonable for the engineer to understand the mechanical and processing essentials, and anticipated performance when dealing...