Ice nucleation on a cold surface

The mechanism of ice nucleation on a cold scraped surface was investigated. This involved designing and constructing a flowcell that simulated the scraped region of a scraped surface heat exchanger and observing the cold surface by video microscopy. Results indicated that relatively high surface undercoolings were required to initiate nucleation and that the onset of nucleation was characterised by the development of an ice front which grew quickly across the surface. The nucleation and growth processes which were both found to exhibit very fast kinetics, were also characterised by the coalescence of small islands of ice which spread from the points on the metal surface where nuclei had formed. Once they coalesced, the resulting ice layer grew in the vertical direction. The mechanism of ice nucleation was affected by the surface undercooling, by the scraper location within the thermal boundary layer, by the action of scraping and by the scraping frequency.