Author(s): K. P. Tyshko; N. V. Cherepanov
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Abstract: Laboratory experiments on the supercooling of sea and fresh water and the formation of frazil ice were carried out to clarify the main aspects of these processes under natural conditions. For this purpose, a thermally insulated annular basin with water flow induced by a propeller was used. The water was cooled by a mixture of small pieces of ice and sodium chloride, placed in the central separated part of the basin. The results obtained show that the extent of supercooling and the time until the onset of crystal formation are strongly dependent on the cooling rate. The probable causes of this dependence are discussed. In a different set of experiments, the formation mechanisms of "active" frazil and anchor ice were investigated Such ice types were observed when the total mass of water remained in a supercooled state after crystallization. In these cases, the amount of supercooling did not exceed several hundredths degree centigrade, which also explains ice formation on the propeller and other objects placed in the flow. Measurements of water temperature in the thin contact layer on the surface of these objects showed oscillatory temperature fluctuations in the range of several thousandths degree centigrade. This phenomenon is caused by the dissipation of kinetic energy and its transformation into thermal energy. Thus during these rapid temperature oscillations, the cooling phase and the rate of cooling play an important role for the onset of crystal formation and may be one of the mechanisms of anchor ice formation, as this first set of experiments on supercooled water has shown.
Year: 1998