EDDY DIFFUSION AND EVAPORATION IN FLOW OVER AERODYNAMICALLY SMOOTH AND ROUGH SURFACES: A TREATMENT BASED ON LABORATORY LAWS OF TURBULENT FLOW WITh SPECIAL REFERENCE TO CONDITIONS IN THE LOWER ATMOSPHERE
A theoretical treatment of the problems of eddy diffusion and evaporation is developed, based on the use of well-established laboratory data for the laws of turbulent flow. Expressions which are free from adjustable constants and involve only directly measurable quantities are derived for the two-dimensional diffusion of matter and evaporation of liquid in flow over aerodynamically smooth and rough surfaces. For aerodynamically smooth surfaces the evaporation formulae obtained are identical with those found previously by O. G. Sutton using a different treatment. The latter results, which have been shown to be in good agreement with laboratory experiments, may be derived independently as a special case by a more direct method involving fewer assumptions. The formulae obtained for aerodynamically rough surfaces are in excellent agreement with observational data on the diffusion of smoke in the lower atmosphere under adiabatic conditions, and on the evaporation of liquid from the ground surface. The treatment may also be applied to the transfer of heat from aerodynamically smooth and rough surfaces provided the temperature differences are not too large.