Drop Evaporation Under Unsteady Conditions

In the previous two chapters we have investigated models of drop evaporation under steady-state conditions, an assumption widely used, although clearly unphysical: a mass source inside the drop is needed to maintain the drop shape unchanged during evaporation. To relieve this assumption a time dependent problem must be set and solved, increasing the complexity of analytical approaches. In particular, even for a spherical drop shrinking by evaporation, a moving boundary problem must be solved, which is known to be a challenging task, even for the simplest geometries. In this chapter we will see how it is possible to account for unsteadiness of the heat and mass transfer processes and still approach the modelling by analytical methods.