The paper presents the vaporization process of a water droplet on a flat surface with initial temperature much lower than the maximum heat flux temperature in nucleate boiling. Water droplet vaporization is different from the process of a liquid vaporization with low boiling temperature described by . As the character of wetting the surface is decisive for the whole process, it is proposed to divide the process into three following stages: initial, fundamental and final. In the initial stage, the dropiet spreads and forms on the surface. In the fundamental stage, the already formed droplet evaporates preserving its constant wetting surface. Characteristic lines appear in the droplet water -air interface in irregular intervals. The lines are called here dividing lines. The dividing line delimits two flow regions: the first with the cellular motion, and the second with intensive natural convection currents. Probably, formation and disappearance of successive dividing lines are connected with change of the surface tension caused by the change of droplet geometry. The time between formation and disappearance of a dividing line can be the criterion for further division of the fundamental stage into substages. It should be underlined that the phenomenon observed in the fundamental stage helps understand the droplet vaporization process better and, so far, has not been found in literature. In the final stage, successive processes occur fast one after another: the "old" droplet shrinks rapidly, the "new" one, with smaller wetting surface, forms and evaporates, then it shrinks and the next "new" one forms.
The succession goes on until the liquid evaporates completely.