Effects of Variable Liquid Properties on Multicomponent Droplet Vaporization

Abstract

A multicomponent droplet vaporization model, the Diffusion-Limit Model, is modified to account for the variation of liquid properties due to large temperature gradients as well as considerable concentration gradients within the droplet. The effects on the vaporization behavior are analyzed for an isolated biocomponent droplet consisting of heptane and dodecane. The results are presented for both moderate and high gas temperatures excluding combustion. During the vaporization process the liquid phase properties vary considerably. For example, the Lewis number changes by approximately one order of magnitude. The mass ratio of the liquid components seems to be rather sensitive to the variation of thermophysical property values, especially during the second half of the droplet lifetime, where about 50 percent of the droplet mass will still evaporate. The gas phase behavior is less affected by the use of constant liquid properties. For both gas temperature levels tested it was found that single component models cannot describe satisfactorily the whole vaporization process of multicomponent droplets. With regard to ignition the sharp rise of the vapor concentration in the beginning of the droplet vaporization is important. This behavior is caused by the more volatile component and cannot be achieved by the single component substitute.