## Eddy mass diffusivity

A quantity characterizing the intensity of turbulent mass transfer of a particular component in a mixture defined by the identity

*j*=

*ρ*

*w*

_{y}

*'c'*is the mass flux of the particular component over a certain elementary area picked out in the flow, resulting from turbulent transfer;

*ι*is the density of the mixture;

*w*

_{y}

*'*is the fluctuation of the transverse (with respect to the area) component of the velocity vector;

*R'*is the fluctuation of the mass fraction of the given component; ∂

*c*/∂

*y*is the derivative with respect to the normal to the area of the (time-) averaged value of the mass fraction of the given component.