3.3. Ice chilling

This method is used for chilling fish and vegetables [1, 4].

Figure 6. Schematics of a slurry ice installation. SSHE, scrapped surface heat exchanger.

Food Chilling Methods and CFD Analysis of a Refrigeration Cabinet as a Case Study http://dx.doi.org/10.5772/intechopen.69136 51

commonly used compounds are salt (sodium chloride), ethylene glycol, propylene glycol, various alcohols (isobutyl, ethanol), and sugar (sucrose, glucose) [6]. This type of ice has many advantages in comparison with the traditional ice (flake ice, shell ice, crushed ice, etc.): it can be used in direct contact with the object to be chilled; due to the large contacting area, it has very good cooling performances; slurry ice can be pumped to the point of use (Figure 6), eliminating costly and maintenance intensive rakes, augers, and ice conveying systems [7]; operating at temperatures below the freezing point of water, ice slurry facilitates several efficiency improvements such as lowering the required temperature difference in heat exchangers due to the

Slurry ice is produced in scrapped surface heat exchangers (SSHE); Figure 7 presents the operating principle of the SSHE for slurry ice. The ice slurry generator consists of a cylindrical metal shell (1). The exterior surface is cooled by the evaporating refrigerant passing through the cooling jacket (2), while water freezes in contact with the cold inner surface of the shell. Spring-loaded rotating blades (4) scrap off the ice crystals formed on the inner cylindrical

beneficial thermo-physical properties of ice slurry [6].

This method is used for chilling fish and vegetables [1, 4].

Figure 6. Schematics of a slurry ice installation. SSHE, scrapped surface heat exchanger.

surface of the metallic shell.

3.3. Ice chilling

50 Refrigeration

Figure 7. Schematic diagram of the ice slurry generator. 1, cylindrical metal shell; 2, cooling jacket; 3, rotating shaft; 4, blade.

Ice is often produced in the form of lumps or blocks, of various weights, from 10 to 200 kg. Alternatively, ice may be made in the form of smaller pieces (granular ice). Different types of granular ice exist (flake ice, tube ice, plate ice) [4].

In order to obtain ice blocks, the water to be frozen is filled into large metal molds, which are placed in a tank containing refrigerated brine, for up to 24 h. When the ice blocks are completely frozen, they are removed from the freezing tank and dipped into hot water. This melts the surface of the block so that it can be tipped out of its mold. The molds can then be refilled with water and returned to the freezing tanks. The large ice blocks may then be broken down into smaller pieces in an ice-crushing machine (Figure 8).

Figure 8. Ice-crushing machine. 1, infeed hopper; 2, large ice chunks; 3, blade; 4, rotating drum; 5, crushed ice; 6, discharge chute.

One of the most common types of granular ice is flake ice, which is obtained by freezing water onto the surface of a rotating, refrigerated drum (Figure 9). The water freezes into a 2–3-mmthick layer of ice, which is then scraped off the drum as flakes of ice.

Storing fish in ice is largely used aboard fishing ships; apart from chilling the fish, ice removes heat from the surrounding structure of the box or storage compartments, absorbs the heat input through the structure from the warm air and sea outside, and removes the heat produced by the spoilage process in the fish themselves [8]. It is therefore essential that plenty of ice is properly distributed throughout the catch to ensure efficient cooling. Ideally, each fish should be in contact only with ice; in practice, there are alternating layers of ice and fish (Figure 10). The ice-to-fish ratio is comprised between 1/3 and 1/1; there should be at least 5 cm thick layers of ice (1, 3) between fish and the compartment walls [8]. In order to avoid the lower layers being damaged under the weight of the upper layers, fish must be placed on shelves, in order to keep the depth of the storage compartment (2) lower than 0.5 m [8].

Ice chilling is also used for vegetables and fruits [4]; the products are placed in wooden or cardboard crates, filled with ice. Figure 11 presents the schematics of an ice-filling machine; the ice flakes flow into the machine hopper (2) through the chute (1) and are poured into the crates through the hopper (4).
