Author(s): K. Johnson; E. P. Lozowski
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Abstract: Icicles are a common occurrence in northern climates, whenever a supply of water near the freezing point drips under gravity into air with a temperature below 0°C. They can occur with snowmelt, freezing rain, and freezing spray. Although attractive to look at, their shape and mass can make them a hazard. In freezing spray in particular, they not only allow the accumulation of additional mass which might otherwise be lost to the airstream, but they increase the cross-sectional area of the accretion, thereby permitting the build-up of still larger ice masses. Recent experimental work on icicles by Maeno and Takahashi (1984), prompted us to devise a simple numerical model to predict the growth rate of icicles. In the process of doing this, we also found it necessary to conduct our own icicle growth experiments, under controlled temperatures and wind speeds, in the refrigerated FROST wind tunnel at the University of Alberta. The results of our theoretical and experimental investigations have led to a computer model which yields a reasonable estimate of the maximum icicle growth rate for given environmental conditions. We have also gained some insight into the icicle growth mechanism. The physics of the processes, and in particular, liquid incorporation at the tip, are seen to be very important in determining the length growth rate and final shape of the icicle. By comparison, the growth in diameter seems to be much more straightforward. We have succeeded in modelling both of these in the limit as the drip rate tends to zero. The experiments also show the importance of the drip rate for growth in length, although so far, we have been unable to successfully model this aspect of the process. However, a recent model developed simultaneously with ours but independently by Makkonen (1988) does hold out some hope for modelling drip rate effects. This paper presents the highlights of both our experimental and modelling work, along with recommendations for future work to improve our insight into icicle development and our ability to simulate it.
Year: 1988