Prediction of isothermal evaporation rates of pure volatile organic compounds in occupational environments—A theoretical approach based on laminar boundary layer theory

Abstract

A model for the prediction of isothermal evaporation rates of pure volatile organic compounds in occupational environments is proposed. The model is based on laminar boundary layer theory and validated by comparing model predictions with experimental data obtained in a test duct. Factorial experiments were conducted with various air velocities in the range usually met in occupational environments, and different lengths of the evaporating surface in the direction of the air flow. The tests were carried out for five organic compounds of widely different volatility. Predicted and measured evaporation rates were in close agreement and the effects on evaporation rate of air velocity and evaporation surface length predicted by the model were confirmed. A critical examination revealed that previous evaporation models suggested for occupational hygiene purposes are usually derived from experiments at air velocities higher than those typically encountered in occupational environments and seem to be restricted to situations with turbulent boundary layer flow, by contrast with the assumptions implicitly or explicitly made by the authors. Compared with the theoretically based model proposed in this work, these models generally tend to overestimate the influence of air velocity and to underestimate the influence of evaporation surface length, when extrapolated to laminar boundary layer conditions.