  We consider evaporation of pure liquid drops on a thermally conductive
substrate. Two evaporative models are considered: one that concentrates on the
liquid phase in determining evaporative flux, and the other one that centers on
the gas/vapor phase. A single governing equation for the evolution of drop
thickness, including both models, is developed. Experiments are used to
estimate relevant parameters. We show how the derived governing equation can be
used to predict which evaporation model is appropriate under considered
experimental conditions.
