3650 -- A Novel Method for Measuring Water Evaporation Into Still Air PDF

The available correlations for the rate of evaporation of water into still air appear to be mainly from investigations conducted during the 1930s and 1940s. The experimental techniques employed in that era required considerable manual data collection by the experimenter. Consequently, experiments were generally conducted over short time periods and on a small scale. The present study of evaporation rate measurement takes advantage of the many advances in experimental methods made since the publication of earlier work by conducting experiments on a larger scale and over longer time periods. With the assistance of personal computers, digital electronic balances, and electronic data acquisition systems, the ability to control and monitor water evaporation experiments has been greatly improved over manual measurements methods. Evaporation rates were measured for water at temperatures ranging from 25 deg C to 50 deg C in air at 20 deg C and 50% and 70% relative humidity. The evaporation surface area was 1.2 square meters. The water evaporation rates into still air found close agreement with the results of Boelter et al. (1946), thus confirming previous work. However, it was found that the equation recommended by ASHRAE (ASHRAE 1991) for predicting water evaporation overestimates evaporation rates into still air.

KEYWORDS: measuring, water, evaporation, experiment, microcomputers, monitoring, temperature, relative humidity, accuracy.