# Use of Phase Change Materials for Food Applications--State of the Art in 2022
## 2 Food Applications of PCM
### Food Storage and Transport
#### 2.2.8 \"Just\" Ice  
At the transition of the discussion of storage and transport of food it is necessary to discuss also just ice. Historically [58; 59], natural ice, harvested in winter from the surface of lakes and rivers, has been stored and transported to places where it was used for many cooling applications, specifically for cooling foods like meat, fish, vegetables, and fruits. Natural ice allowed to keep food refrigerated or frozen, by keeping it together with the food for example for storage in rooms, cellars, cupboards (predecessors of today's household refrigerators), boxes, which are also useful for transport, as well as for transport in compartments on trucks, trains, ships etc. The use of natural ice was replaced starting with the 20 th century by mechanically driven cooling, allowing cooling where and when needed, including also the production of artificial ice in industrial plants for applications where ice is still used. Because of its simplicity, using just water/ice without an encapsulation and maybe heat exchanger, its application is often forgotten. However, despite that natural ice is practically completely replaced, the use of artificial ice is still widespread, and a big market. Actually, the technology of using artificial ice for cooling has even significantly developed: today, ice is not only used in blocks of different sizes. Today smaller ones vary in shape, like cube or flake ice, are mixed with some water to be able to flow, even pumped, called slush ice and ice slurries. According [60], the amount of manufactured can or block ice in the US in 1997 was 345,000 t, that of cube, crushed, or other processed ice about 2,211,000 t. This was 25 years ago; numbers should have been rising a lot since. Nevertheless, these numbers are for any application. Artificial ice to cool food is still seen on buffets, display/retail coolers in marketplaces and supermarkets, specifically for fish, used on fishing boats etc. Specifically regarding food, the fish industry is interesting, has data available, and is active also in R&D. Ref. [61] has some interesting information on the use of ice for fish handling: advantages of ice, compared to other cooling methods, as its large cooling capacity and self-contained temperature control by melting (characteristic of PCM), its convenience regarding its storage, transport, and even production from water (mentioning even the use of clean seawater), that it is a safe food-grade substance if produced properly and utilizing drinking water, and depending on the type of ice can be distributed around fish. And specific to the application, cooling is very critical to produce safe fresh fish of acceptable quality. The Norwegian fish industry, to take as example, is dominated by fish farming and the export of salmon. Every week between some 10,000 and 25,000 t of salmon (fresh, chilled, or frozen) are exported [62]. For export, these are put on ice for transport. Ice accounts for about 30% of the weight of a shipment while 70% is fish (according personal communication), roughly a ratio of 1:2. This means, every week some 5000 to 12,000 t of ice; and this only for the export of salmon. According [63], storing fish in ice boxes, as was done historically, causes complex handling at today's common large catch volumes. It is today only applicable for smaller boats. In larger ones, harvested fish caught far away from the shore is stored in tanks until delivery for onshore processing. Tanks equipped with mechanical refrigeration are calledrefrigerated sea water (RSW) systems. If ice is added they are called chilled seawater (CSW) systems. It is crucial to prepare the tanks for the fish input in a way to have a minimum temperature. The paper numerically investigates four different scenarios: ice added in various amounts, and the use of a PCM with 4 \({}^{\circ}\)C phase change temperature in the tank's outer shell, within tank's tubes, and in a separate tank integrated in the return line of the RSW system.