An experimental study of freezing of supercooled water droplet on solid surface

Abstract

Results of experimental investigations of the freezing of immobile water droplet on an aluminum plate are presented. The process was studied with the aid of a high-speed photo camera. The freezing of supercooled water contained in the surface droplet proceeds in a few stages: (i) preliminary heating of water and nucleation of ice microcrystals, (ii) relatively fast formation of the ice-liquid system with a transition to the state of thermodynamic equilibrium near the freezing temperature, and (iii) slow process of complete freezing. The rate and duration of each stage and the time of delay between the moment of action upon the supercooled droplet and the onset of freezing are estimated. Processes of supercooled and nonsupercooled water solidification are compared.Icing of flying vehicles during flight is commonly recognized to be a serious safety problem that is still important because, despite numerous investigations, accidents caused by icing are still taking place. It is reliably established that icing proceeds predominantly via collision of flying vehicles with supercooled water droplets occurring in the atmosphere. To ensure safe aviation, a system of anti-icing measures is developed for each particular aircraft and it is certified with respect to flight under icing conditions. In solving these tasks, an important research tool, in addition to test flights and on-ground experiments in cooled high-speed wind tunnels (both having a number of disadvantages and restrictions), is offered by numerical simulations, which have become very effective due to rapid development of computational technologies.In most cases, well-known mathematical models describing the process of ice growth [1][2][3][4][5] are based on the Messinger hypothesis [6], according to which the spreading of liquid over the surface is described without taking into account its physical state, collision of supercooled water droplets with the ice-water interface, and their subsequent spraying. Results of mathematical modeling based on existing methods agree well only with the experimental data for rime ice (in which the incident supercooled droplets freeze almost immediately upon collision) and agree satisfactorily for some regimes with glaze ice formation. Discrepancies take place because this setting of the problem does not take into account peculiarities of the interaction of supercooled water droplets with streamlined surfaces, the fact that droplets colliding with, recoiled from, and residing on the surface can possess different geometric shapes with involved surfaces, and that water contained in droplets can occur in various physical states.The mechanism of freezing of a supercooled liquid and the processes of ice nucleation and formation of dendrites and ice structures were studied in [7,8]. More recently, it was established [9, 10] that freezing of a droplet occurring on a surface possessing a negative centigrade temperature proceeds from the surface side and involves the formation of a phase transition front. Since the volume of ice is great...

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