Three dimensional asymmetries in freeze front due to interplay of rotational flow field

The freezing of water is a ubiquitous phase transition process with substantial relevance across cryogenics, aerospace engineering, environmental science, and materials science. Though ice formation in quiescent stratified pool has been studied thoroughly, the complex interplay between ice front and predominant convection current is not described fully. Presence of rotational motion introduces complex physical behaviours like early nucleation, spatial promotion of phase change heat and mass transfer, etc., that changes the freezing process and produces patterns. Understanding how motion and rotation affect freezing is critical for predicting natural phenomena such as ocean ice formation, polar vortices, freezing in rotating planetary bodies.

In this experimental work we have investigated the freezing phenomenon of water kept in a steady rotary flow field in square pool, where the top surface is exposed to freezing temperature. The interaction between the rotationally induced flow and moving ice–water interface reveal that the circulation pattern becomes locked to the square symmetry of the container, forming four-lobed structure. Due to rotation there is mixing near the pool centre and thermal stagnation zones near the corners, where local freezing initially accelerates. As a result, in the early stage of freezing, ice-water interface develops a concave morphology, with ice forming faster near the exposed surface and its corners, while the centre remains water for a longer duration. A fluidic scaling law from rotational inertia and freeze front damping rate is proposed to differentiate the inertial and phase change controlled-domains of the combined convection-freezing physics. An extension of present work may lead to large-scale system understanding under controlled convection.