  For a small sessile or pendant droplet it is generally assumed that gravity
does not play any role once the Bond number is small. This is even assumed for
evaporating binary sessile or pendant droplets, in which convective flows can
be driven due to selective evaporation of one component and the resulting
concentration and thus surface tension differences at the air-liquid interface.
However, recent studies have shown that in such droplets gravity indeed can
play a role and that natural convection can be the dominant driving mechanism
for the flow inside evaporating binary droplets (Edwards et al., Phys. Rev.
Lett. 121, 184501 (2018); Li et al., Phys. Rev. Lett. 122, 114501 (2019)). In
this study, we derive and validate a quasi-stationary model for the flow inside
evaporating binary sessile and pendant droplets, which successfully allows to
predict the prevalence and the intriguing interaction of Rayleigh and/or
Marangoni convection on the basis of a phase diagram for the flow field
expressed in terms of the Rayleigh and Marangoni numbers.
