New method and fluidized water system for intensive chilling and freezing of fish

The physical and thermophysical properties of several kinds of fish have been explored — brook trout, scad (Trachurus mediterraneus ponticus) and sat (Sprattus phalericus). The average statistical dimensions, correlation between mass and surface, shape coefficient, density, specific heat capacity, heat conductivity and thermal diffusivity have been determined. It was established experimentally that among the conventional methods for water chilling and freezing of fish (immersion, sprinkling and bubbling through) the most intensive thermal transfer is achieved by bubbling through for which the surface heat transfer coefficient h is ∼ 350 W m−2 K−1. A new method and an industrial system have been created for intensive chilling and freezing of fish on the basis of a high degree of turbulence of the refrigeration medium. All other conditions being equal (physical and thermophysical characteristics, shape and dimensions of the fish, and temperature conditions), the heat transfer is very high: h is 720–760 W m−2 K−1. Within a temperature range of the freezing mixture from −15 to −17°C, the time at which the temperature at the centre is lowered from 25 to −8°C is: 18–23 min for brook trout (180–200 g), 8–12 min for scad (15–30 g), 3–4 min for sprat (10–15 g). The system has various sizes depending on the place of installation and use (on board a fishing vessel or ashore) and has a throughput of 650–1500 kg of fish per hour. The process is continuous. The cooled or frozen fish emerges individually, which facilitates its placement into suitable packagings, its distribution, sale and consumption. The high intensity of the process provides good conservation of muscle tissue morphology. The method and system can be used for refrigerating other marine and fresh water products (mussels, oysters, whelks, etc.) and some kinds of vegetables, preserving their high quality for a long time.