Marangoni instability of bi-component droplet gasification

Simplified analyses using a linear stability approach are developed to predict influences of thermal and solutal Marangoni effects on hydrodynamic stability of bi-component droplets evaporating in a spherically-symmetrical manner in hot environments. It is predicted that with zeotropic mixtures and for partial derivative sigma/partial derivative T<0 and partial derivative sigma/partial derivative gamma<0 (where sigma is surface tension, T temperature, and gamma the surface mass fraction of the more volatile droplet component), the thermal and solutal Marangoni effects oppose each other in that the thermal effect is stabilizing and the concentration effect is destabilizing. The model is applied to alkane/alkane and alcohol/water mixture droplets. The alkane mixture droplets were predicted to be hydrodynamically stable. For alcohol/water mixtures, the results suggest that critical radii for marginal stability exist; when a droplet is initially pure methanol which subsequently absorbs water from the ambient, the critical radius is predicted to depend upon the relative humidity of the environment. (C) 1996 American Institute of Physics.