Ice Slurry: Applications
The use of ice for prolonging the storage life of food dates back many millennia. Up until the middle of the 19th century all ice used for cooling was obtained from natural sources such as winter snow/ice or imported arctic ice. Sometimes the natural snow was mixed with salt in order to reach lower temperatures. The first ice cream was produced using this “technology” some two thousand years ago in ancient Rome.
With the introduction of mechanical refrigeration, ice could be produced in different forms such as block, cube, tube or flake ice. Most of these forms of ice require a certain degree of manual operation for transportation from one place to another, and have rather sharp edges that may damage a product’s surface when used for direct contact chilling. Furthermore, they are usually quite coarse and have poor heat transfer performance when releasing their latent heat of fusion.
Ice slurry refers to a homogenous mixture of small ice particles and carrier liquid. The liquid can be either pure freshwater or a binary solution consisting of water and a freezing point depressant. Sodium chloride, ethanol, ethylene glycol and propylene glycol are four most commonly used freezing point depressants in industry. Over the last four decades interest in using phase-change ice slurry coolants has grown significantly.
Ice slurry has a high energy storage density because of the latent heat of fusion of its ice crystals. It also has a fast cooling rate due to the large heat transfer surface area created by its numerous particles. The slurry maintains a constant low temperature level during the cooling process, and provides a higher heat transfer coefficient than water or other single phase liquids. These features of ice slurry make it beneficial in many applications.
For example, the ice slurry based thermal storage system produces and stores cold in the form of a dense ice slurry during nighttime hours when electricity is cheap, and the cold energy can then be quickly released by melting the ice slurry for air-conditioning of buildings during daytime hours when electricity might be several times more expensive.
In some applications ice slurry can be made during periods of no demand and be stored for later use. Both the high energy storage density and the pumpable delivery of ice slurry to the cooling loads make it possible to achieve significant reductions in the size of tanks, pumps, piping, and chillers. The reliable pumping of high ice fraction slurry also referred to as high “ice concentration” out of a tank and through a distribution system without plugging up has only become feasible recently. Studies have shown that ice slurry must be engineered to have the correct ice particle characteristics (size, globular shape and smoothness) in order to achieve its full potential as a coolant. The use of ice slurry has the potential to greatly improve the effectiveness of District Energy Systems and to protectively cool patients experiencing medical emergencies such as cardiac arrest or during planned surgeries. Ice slurry can also be used as a cold storage medium in various vessels without built-in refrigeration systems such as ice slurry cooled trolleys, trucks or fishing boats.
This paper discusses the latest developments in ice slurry as a secondary refrigerant and direct contact cooling technology used in bakery, produce packing, fishery, as well as its new emerging application for protectively cooling organs during medical emergencies and surgery. Market demands and challenges are also discussed for each industry, as well as a detailed description of the state-of-the-art solutions being used.