Author(s): Lars Bengtsson
Linked Author(s): Lars Bengtsson
Keywords: No Keywords
Abstract: The heat loss from water to the atmosphere prior to freeze-over and the growth of an ice-cover during mid winter is discussed. It is found that in northern Scandinavia lakes freeze over after about the same number of negative degree-days every year, and that the maximum ice thickness for a specific lake is very much the same from year to year. Also heat losses from open river stretches at very low air temperatures are discussed. A formula for thermal equilibrium ice thickness is presented. The equilibrium thickness depends strongly on air and water temperature and on flow velocity. In ice covered lakes a pronounced thermocline usually develops. In the course of the winter the bottom water gains heat from the sediments. Measurements show that the heat transfer rate is about 1 Watt/m. Different methods for keeping a water surface ice-free are discussed. Examples of air bubbler systems and heated discharges are given. It is shown that when complete mixing of the heated water and the resident water can be obtained, the heat required for keeping limited areas ice-free is rather small. Ice may be produced by man for energy utilization purposes, e. g. heating, or for the purpose of creating winter roads or ice platforms. Since a thick ice cover reduces the heat loss to the atmosphere, the normal static growth of ice is reduced, and the total ice thickness is not very much in excess of that under natural conditions.
Year: 1981