Using laboratory experimental techniques, the process of the origin and development of free convection in water cooled from the surface due to heat exchange with the air and evaporation is examined. Application of three different measurement methods (thermographic, visual, and thermovisual) allowed us to enhance the reliability of the results obtained. We found that cellular motion on a millimeter scale originates in a thin (approximately 1 mm thick) surface water layer for a few seconds after the onset of cooling. Subsequently, large inhomogeneities are generated against the background of this motion. An analysis of the results showed that the initial cellular structure might be explained by the mechanism of Marangoni thermocapillary convection, while the subsequent larger scale motion is caused by the Raleigh thermogravitational convection.
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