Measurement of Factors Involved in the Mass Transfer of Water by Molecular Diffusion

The objective of the study is to develop the instrumentation needed to measure the vapor pressure gradient above a water surface, with a view to predicting the rate of evaporation from that surface. This study demonstrated the practicality of a copper constantan thermocouple psychrometer for measuring the vapor pressure or relative humidity at a point, under still atmospheric conditions. Observations indicated that the vapor pressure increased linearly for approximately 0.3 inches above the water surface in a still atmosphere. Evaporation from a free water surface under these conditions appeared to be a process of molecular diffusion only and could be described by Steffan’s molecular diffusion equation. Advisor: L. W. Hurlbu