## Eddy diffusivity of heat transfer

A quantity characterizing the intensity of turbulent heat transfer, defined by the identity

*q*

_{turb}=

*ρc*

_{p}

*w*

_{y}'

*T'*is the turbulent heat flux density (i.e., the heat flux due to turbulent transfer) over a certain unit area in the flow;

*ρ*is the density;

*w*

_{y}' is the fluctuation of the transverse (with respect to the area element) component of the velocity vector;

*T'*is the fluctuation temperature;

*c*

_{p}is the heat capacity of the fluid at constant pressure; ∂

*T*/∂

*y*is the derivative with respect to the normal to the area element of the (time) averaged value of the temperature.

*Comment.*The term is defined by assuming that fluctuations of the physical properties can be neglected.