Conditions for continuous ice slurry generation in a nylon helical coiled heat exchanger

Current commercial methods of ice slurry production adopt low refrigeration fluid temperatures and mechanical scraping. This work explores an alternative method requiring neither, reducing the energy required and simplifying the ice maker. Helically coiled tubes are cooled, internal fluid is supercooled until ice nucleates, the flow of the fluid removes ice formed on the tube. Low surface energy and surface roughness nylon pipe was used to reduce ice adhesion and blocking while also slowing the transfer of heat and ice growth rate. Reduced heat transfer through the pipe was offset by an increasing the pipe length. Ice slurry was successfully produced from three different concentrations of sodium chloride water solutions (8, 5 and 3.5 wt% NaCl), at a range of different flow rates and temperatures. Ice slurry mass fractions up to 12–18% were achieved. Operation graphs for each concentration were created and compared showing where ice production, blockages or no ice nucleation occurred. Increasing NaCl concentration appeared to expand the operation region but also reduced the refrigeration fluid temperature required. The operation regions produced would change for different pumps used. Plots of ice production rate and ice fraction showed that the highest ice fractions were produced with 5 wt% brine. Refrigeration temperatures and crystal sizes were compared to that of a scraped surface generator. Improved efficiency was only achievable for low ice fraction production, though more experiments are required to prove this. This method could be utilised to make ice slurry hygienically for use in food processing or medical applications.