Vapor Pressure and Evaporation Rate of Fluids in Vacuum as Determined from Ambient Pressure Measurements

Abstract

A technique has been developed, using a modified version of the ASTM D972 Evaporation Test Cell, to determine the true vapor pressures of fluids using ambient pressure conditions. The molecular weights, as determined per ASTM D2224, required for these vapor pressure determinations also permits accurate prediction of the weight loss rates in vacuum. While only esters were found available of sufficient purities and accurately known vapor pressures for calibration purposes, the test data indicate that the calibration of the modified test cell is independent of molecular species. In addition, the saturation efficiency is shown to be independent of temperature over the range 373 K to 473 K. In this paper are presented the experimental technique, illustrative computational methods, data for several classes of lubricants and a simplified quality control technique based on test cell data. It is also shown that, while the extrapolation of Evaporation Test Cell data could give errors of ±170 percent in predictions ...