Diffusion in Laminar vs Turbulent flows

I am modeling a falling film which absorbs a gas. I am interested in how the solute travels normal to the flow. The Laminar flow is a simple solution. However, I am investigating conditions which will likely make the falling film turbulent. I expect that the turbulence will increase the solute transport normal to the bulk flow field, but am not seeing that in my solutions. Can anyone point me to resources about or describe how COMSOL handles the enhancement of diffusion by turbulence?

Any help is much appreciated.

Regards, Mark

(I am using 4.2a, Transport of Diluted species, and the k-epsilon model for turbulence.)