Modelling frazil and anchor ice on submerged objects

Abstract

Frazil and anchor ice cause blockage of water intakes and icing of other type of submerged objects. In this paper, the physical mechanisms that control these phenomena are discussed and analyzed. Our conclusions are somewhat different from the views presented earlier. 1) Ice crystals in water may originate from microbubbles and turbulence, so that nucleation may occur regardless of an external source 2) The number concentration of ice crystals may not necessarily increase much during an active frazil ice event, 3) The heat transfer from a frazil ice crystal is controlled by its relative rise velocity, not by water turbulence, 4) The collision efficiency of frazil ice crystals on grid components is so small that frazil typically causes no blockage of submerged water intakes, and 5) Blockage is largely caused by ice platelets that grow in-situ on the structural components. We model frazil and anchor ice formation theoretically and find that the uncertainty about the concentration of ice crystals is the main obstacle to accurate modelling. Within these limits, our model results agree well with the available experimental data.