Abstract
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 ‰, 15 ‰, 25 ‰ and 35 ‰ to address this lack of data. The experiments were
conducted in a large tank in a cold room with bottom-mounted propellers to
create turbulence. A high-resolution camera system 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, concentration and volume. The size and volume
distributions of particles and flocs at all four salinities were found to
fit log-normal 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 range
between 0.52 and 0.45 mm, with particles sizes in freshwater ∼13 % larger than in saline water. However, qualitative observations
showed that frazil ice particles in saline water tend to be more irregularly
shaped. The overall mean size of flocs in freshwater was 2.57 mm compared to
a mean size of 1.47 mm for flocs in saline water. The average growth rate of
frazil particles was found to be 0.174, 0.070, 0.033, and 0.024 mm min−1 and
the average floc growth rate was 0.408, 0.118, 0.089, and 0.072 mm min−1 for
the 0 ‰, 15 ‰, 25 ‰, and 35 ‰, respectively.
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, 0.8 and
0.75 for 0 ‰, 15 ‰, 25 ‰ and 35 ‰ saline water, respectively.
Subject
Earth-Surface Processes,Water Science and Technology
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