A quantity characterizing the intensity of turbulent mass transfer of a particular component in a mixture defined by the identity
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; wy'
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
is the derivative with respect to the normal to the area of the (time-) averaged value of the mass fraction of the given component.