The Ratio of Heat Losses by Conduction and by Evaporation from any Water Surface

Abstract

It is shown that the process of evaporation and diffusion of water vapor from any water surface into the body of air above it is exactly similar to that of the conduction or "diffusion" of specific heat energy from the water surface into the same body of air. Because of this similarity it is possible to represent the ratio $R$ of the heat loss by conduction to that by evaporation by the formula $R=.46\left(\frac{{T}_{w}\ensuremath{-}{T}_{a}}{{P}_{w}\ensuremath{-}{P}_{a}}\right)\frac{P}{760}$ where ${T}_{a}$ and ${P}_{a}$ are the original temperature and vapor pressure of the air passing over the lake, and ${T}_{w}$ and ${P}_{w}$ are the corresponding quantities for the layer of air in contact with the water surface. The substitution of $R$ times the evaporation loss for the value of the conduction heat loss in the Cummings equation for evaporation makes it an exact equation for the determination of evaporation from any water surface in terms of the net radiant energy absorbed by the water and the heat stored in the water.