PREDICTION OF ISOTHERMAL EVAPORATION RATES OF PURE VOLATILE ORGANIC-COMPOUNDS IN OCCUPATIONAL ENVIRONMENTS - A THEORETICAL APPROACH BASED ON LAMINAR BOUNDARY-LAYER THEORY

A model for the prediction of isothermal evaporation rates of pure vol atile organic compounds in occupational environments is proposed. The model is based on laminar boundary layer theory and validated by compa ring model predictions with experimental data obtained in a test duct. Factorial experiments were conducted with various air velocities in t he range usually met in occupational environments, and different lengt hs of the evaporating surface in the direction of the air flow. The te sts were carried out for five organic compounds of widely different vo latility. Predicted and measured evaporation rates were in close agree ment, and the effects on evaporation rate of air velocity and evaporat ion surface length predicted by the model were confirmed. A critical e xamination revealed that previous evaporation models suggested for occ upational hygiene purposes are usually derived from experiments at air velocities higher than those typically encountered in occupational en vironments and seem to be restricted to situations with turbulent boun dary layer flow, by contrast with the assumptions implicitly or explic itly 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 evapo ration surface length, when extrapolated to laminar boundary layer con ditions.