Ficks Law Analogy for Turbulent Diffusion

An alternative to Equation 2.8 for chemical transport in the presence of turbulent fluid mixing is the following empirical expression. By analogy with Tick s first law 

This is the defining equation for the turbulent diffusivity in m /s, called the eddy diffusivity. Within a single fluid, it is highly variable and depends on position, direction, and the nature of the flow field. Nevertheless, by selecting appropriate, average numerical values, it enjoys some use in chemodynamic model dispersion applications such as horizontal dispersion of chemicals in surface waters, vertical dispersion in the water column, dispersion in the atmosphere and in groundwater and biodiffusions in soils and sediment (see Chapters 13, 15, and 20). 

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