Laboratory Measurements of the Properties of Frazil Ice Particles and Flocs in Saline Water

Abstract

Measurements of the size and shape of frazil ice particles and flocs in saline water and of frazil ice flocs in freshwater are limited. This study consisted of a series of laboratory experiments producing frazil ice at salinities of 0 â°, 15 â°, 25 â°, and 35 â° to address this lack of data. The laboratory set-up consisted of a large tank in a cold room with bottom mounted propellers to create turbulence. A high resolution camera set-up was used to capture images of frazil ice particles and flocs passing through cross polarizing lenses. The high resolution images of the frazil ice were processed using a computer algorithm to differentiate particles from flocs and determine key properties including size, shape, and volume.The size and volume distributions of particles and flocs at all four salinities were found to fit lognormal distributions closely. The concentration, mean size, and standard deviation of flocs and particles were assessed at different times during the supercooling process to determine how these properties evolve with time. Comparisons were made to determine the effect of salinity on the properties of frazil ice particles and flocs. The overall mean size of frazil ice particles in saline water and freshwater was found to be similar, however qualitative observations showed that frazil ice particles in saline water tend to be more irregularly shaped. The overall mean size of frazil ice flocs in freshwater was significantly larger than in saline water. This resulted in frazil ice flocs in freshwater having a tendency to rise to the surface during the experiments whereas the saline water flocs tended toiiistay suspended in the flow until the end of the experiment. Estimates for the porosity of frazil ice flocs were made by equating the estimated volume of ice produced based on thermodynamic conditions to the estimated volume of ice determined from the digital images. The estimated porosities of frazil ice flocs were determined to be 0.86, 0.82, 0.80, and 0.75 for 0 â°, 15 â°, 25 â°, 35 â° saline water, respectively.