3.2. Chilling with liquid secondary agents

In this case, a chilled secondary agent is used in order to refrigerate the product; the product is sprayed with cold agent or is immersed into the chilling agent [1, 4, 5]. Due to the higher values of the convective coefficients, chilling with cold liquid agents requires less time than air chilling. The procedure is used for chilling poultry, fish, and some vegetable products [4, 5].

Food Chilling Methods and CFD Analysis of a Refrigeration Cabinet as a Case Study http://dx.doi.org/10.5772/intechopen.69136 49

Figure 4. Chilling rooms. 1, discharge duct; 2, intake ports; 3, evaporator and fan.

chilling phase, the air temperature is around �10�C, and its speed is approximately 1 m/s; the products, hanged on the conveyer, travel through section (I) of the tunnel in about 4–5 h. The surface of the products is chilled rapidly in this first section. In the second section of the tunnel (II), air temperature is about 0�C, and its speed is 0.3 m/s; the duration of the chilling process is 10–15 h, until the product reaches a relatively uniform temperature in its entire mass [4]. This system allows the diminishing of the evaporative weight loss compared with the one-phase chilling systems because the surface of the product is quickly cooled in the first phase, and a lower temperature difference between the product and the cooling medium is achieved in the

Figure 3. Two-phase chilling tunnel (horizontal cross-section). 1, evaporator; 2, conveyer; I, II, cooling sections.

Figure 2. Air chilling tunnel, with vertical circulation of the air (vertical cross-section). 1, 3, evaporators; 2, auxiliary fan.

Chilling rooms have a lower capacity than chilling tunnels; because of the lower air speed (0.3 m/s), the duration of the chilling process increases. Figure 4 presents some examples of chilling rooms: the air discharge ducts are placed in the upper side of the room, while the air intake ports are

In this case, a chilled secondary agent is used in order to refrigerate the product; the product is sprayed with cold agent or is immersed into the chilling agent [1, 4, 5]. Due to the higher values of the convective coefficients, chilling with cold liquid agents requires less time than air chilling. The procedure is used for chilling poultry, fish, and some vegetable products [4, 5].

second phase.

48 Refrigeration

placed in the lower part.

3.2. Chilling with liquid secondary agents

Depending on the final temperature of the product and on the type of product, chilling may be achieved with water, salt water (brine), or slurry ice; ice or vapor compression refrigeration systems are used in order to cool the secondary agent [4].

Figure 5 presents the schematics of a device for the immersion chilling of poultry [1]; the carcasses are placed on the conveyor (2) and then immersed into the cold agent. The secondary agent is chilled in the heat exchanger (9) by a vapor compression refrigeration system.

Slurry ice is a phase-changing secondary agent, containing small ice crystals (typically 0.1–1 mm in diameter), suspended within a solution of water and a freezing point depressant. Some

Figure 5. Immersion chilling of poultry. 1, immersion tank; 2, conveyor; 3, fan; 4, filter; 5, pump; 6, compressor; 7, condenser; 8, expansion valve; 9, heat exchanger.

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

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 surface of the metallic shell.
