The evolution of the flow structure of thermal gravity-capillary convection in thin cylindrical water layers with a free surface, heated from below, was numerically studied. The layer diameter ranges from 10 mm to 40 mm, and the height ranges from 0.1 mm to 5 mm. The influence of the layer height and temperature difference on heat transfer was investigated, and the boundaries for the transition to nonstationary flow regimes were determined. The relative contributions of buoyancy and thermocapillary effects were examined, and analytical dependencies for heat dissipation from the free surface as a function of temperature difference and layer height were constructed. The dimensions of the ordered Rayleigh-Bénard convective cells were determined to be approximately 0.42 mm for a diameter of 40 mm and a layer height of 400 μm, which is comparable to the size of monolayer levitating microdroplets above an evaporating liquid layer in the atmosphere.