Frazil flocculation and secondary nucleation in a counter-rotating flume

Abstract

The processes of secondary nucleation and flocculation of frazil ice are complex and as yet relatively poorly understood. In order to better understand the effect that turbulence intensity has on these processes, a series of experiments were undertaken at the Hydraulics Research & Testing Facility in the University of Manitoba using a counter-rotating flume. Five sets of bed plates ranging in roughness from smooth PVC to 20 mm gravel were used to generate the turbulence in the flume. Velocity measurements under ice-free conditions were made using a constant temperature anemometer with a conical hot-film probe. The ability to rotate the flume walls at any given rate enabled the researchers to perform experiments where the average velocity was kept constant, whereas the turbulence intensity increased with increasing bed roughness. Measurements of water temperature, air temperature, and digital images taken during ice formation were analyzed. A multiple linear regression model using turbulence intensity and the minimum water temperature as the two independent variables was found to reasonably model the rate of secondary nucleation, and indicated that higher levels of turbulence and colder temperatures increased the rate of secondary nucleation. Initial analysis of the digital images demonstrates that turbulence intensity also increases the uniformity of the vertical distribution of frazil particles and tends to inhibit frazil flocculation.