Terminology of Chemical Transport

There is some terminology of chemical transport that needs to be defined. Some terminology has already been implied, and some may seem obvious, but these are so important to this text that we need to define them in one place and at one time. 

Diffusion - In this text, we will dehne diffusion (and most other processes) from an engineering perspective, in that we will go to the level of detail that suits our objective. Diffusion can then be defined as the mixing of chemicals by random molecular motion. Diffusion coefficients in dilute solutions will be discussed in detail in Chapter 3. 

Convection (or advection) - The transport of a chemical or other quantity by an imposed flow. 

Turbulent diffusion - The mixing of chemicals by turbulence, such that a turbulent diffusion coefficient can be defined separately from the temporal mean convection. 

Dilution - The mixing of a more concentrated solution with one that is less concentrated. The adage The solution to pollution is dilution is still used, sometimes appropriately, for many pollution and mitigation processes. 

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