At present, China's quick-freezing equipment can be roughly divided into strong blowing continuous quick-freezing device, tunnel freezing device, contact freezing device, and direct freezing device.
(1) The strong ventilation quick-freezing device uses a finned tube evaporator, the blower adopts a centrifugal fan or axial fan with a high head, and the refrigerant is forcedly circulated by an ammonia pump, so it has the characteristics of high heat transfer efficiency and small footprint. In general, the speed of air passing through the frozen objects is 3-6m / s, and the temperature is 40-40-30 ℃, so the quick freezing speed is 2 to 4 times faster than that of the pipe rack quick freezing. , Can use mechanical intermittent in or out or continuous in and out, the production capacity is larger.
(2) The tunnel-type freezing device is equipped with an air cooler and a blower. The frozen objects are mounted on the cart, and when passing through the tunnel, the cold wind is blown into it to quickly freeze. The tunnel-type freezing device, because it is not restricted by the shape of the food, the food is transmitted on the hanging rail, and the labor intensity is small. Most of the devices use axial fans, which have large wind speed and fast freezing speed (but the food consumption is large). The defrosting of the evaporator uses hot ammonia and water at the same time, so the defrosting time is short, which is characterized by large air volume and fast freezing speed. .
(3) Contact quick-freezing device is also called flat-plate quick-freezing device. Its working procedure is to put food between each layer of flat-plate and press the plate tightly with oil. Because the refrigerant in the hollow plate evaporates and directly contacts quick-freezing, the heat transfer coefficient is large Quick freezing time is short, and it can be operated at room temperature. This device can use Freon, brine, etc. as the refrigerant, but the disadvantage is that the structure is complex, continuous production is not possible, and the thickness of quick-frozen food is limited.
(4) Direct freezing device This method requires food (packaged or unpackaged) to be in direct contact with the unfrozen liquid. After the food exchanges heat with the unfrozen liquid, the temperature is quickly cooled and frozen. The direct contact freezing method requires that the food be in direct contact with the unfrozen liquid, so there are certain restrictions on the unfrozen liquid, especially when it comes into contact with unpackaged food. These restrictions include non-toxic, pure, no peculiar smell and gas, no foreign color and bleach, non-flammable and non-explosive. In addition, after the antifreeze comes into contact with food, the original composition and nature of the food should not be changed.
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