Disruption of thin (0.3-0.7 mm) horizontal layers of liquid (ethanol) was experimentally investigated during local heating with the substrate side at a heater diameter of 1.6 mm. The influence of the liquid layer thickness and the heating intensity on rupture dynamics was investigated. Visualization and inspection of the liquid layer were realized using the schlieren and shadow methods. General steps of the disruption are determined and the average formation rate of the dry spot is measured, which is 0.2-4 mm/s and increases with increasing of both the layer thickness and the heat flux. It is shown that one of the general factors that affect the rupture dynamics of the liquid layer and the formation of the dry spot in the area of local heating apart from the thermocapillary effect is evaporation.

The needs of microelectronics for heat removal are growing and have already exceeded the value of 1 kW/cm2. To assess the ability of jet impingement cooling to meet the growing requirements, a review of experimental studies was conducted. The review demonstrated both the lack of progress in increasing critical heat flux value over the past 30 years, and the fact that this technique is still considered effective and promising. The review showed that the movement to intensify heat transfer is in the same direction as in other promising cooling technologies. It is noted that the most productive heat transfer occurs in the region of the thinnest liquid film spreading from a free impingement liquid jet. New fundamental studies are discussed that note the significance of heat transfer values in a very thin liquid film, and this is important for the development of cooling technologies. Problems are formulated for the required detailed studies of highly dynamic processes in the boiling region of an ultrafine liquid film at the micro level, aimed at intensifying heat transfer.

Abstract. Experimental study of liquid layers breakdown when heated locally from the substrate side was made. Water and ethanol were used as working liquids with a layer thickness of 300 μm. Basic steps of the breakdown process were found and mean velocities of the dry spot formation were determined; the values are 0.06 mm/sec for ethanol and 5.15 mm/sec for water. The formation of residual layer over the hot-spot before the breakdown has been found for both liquids. The creation of a droplet cluster near the heating region is observed when using water as a working fluid. It was shown that evaporation is one of the general factors influencing the process of layer breakdown and dry spot formation as well as thermocapillary effect.

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