Evaporation of a Volatile Chemical from a Multicomponent Liquid Spill.

Abstract

The evaporation of volatile species from an otherwise non- volatile liquid spill is considered to assess the effects of initial composition and liquid phase resistance to mass transfer on evaporation rate. An idealized but resaonable general model is developed for the liquid phase. At the surface, vapor-liquid equilibria and mass transfer by wind convection are incorporated into a non-linear, third type, jump boundary condition. The resulting moving boundary value problem is solved numerically and the dimensionless surface flux and cumulative fraction evaporated are found to depend upon a modified Biot No., molecular weight ratio and initial mass fraction of volatile. Limiting case models are developed for the extremes of infinitely dilute versus pure fluid, and surface convection limited versus liquid phase diffusion limited behavior. Their range of applicability is determined by comparing their predictions with those of the general model. By estimating the range of Biot No. that might be encountered, it is shown that liquid phase resistance is important even for shallow spills and that detailed knowledge of vapor-liquid equilibria is often not required. Application of the models to real spills is discussed.