Contact quick freezing device
The contact type quick freezing device puts the food between each layer of flat plates, and then the flat plates are pressed tightly. Because the refrigerant in the hollow flat plate evaporates, it directly contacts the quick freezing. This kind of device can use salt water or the like as a refrigerant. Contact quick-freezing device has the advantages of large heat transfer coefficient, short quick-freezing time, operation at room temperature, small area, convenient installation and operation, and easy to move. However, its structure is more complicated and continuous production cannot be carried out. The thickness is limited. The contact quick freezing device is suitable for batch freezing of surimi, meat, fruit puree, shellfish and other foods, and can be used on ships.
Direct freezing device
The direct freezing device directly contacts the food and the low-temperature refrigerant to exchange heat, so that the food is quickly cooled and frozen. The commonly used refrigerants include liquid nitrogen, liquid carbon dioxide, brine, and propylene glycol. According to the contact method, the direct freezing device can be divided into spray type, immersion type, or a combination of the two methods. The direct freezing device has the advantages of fast freezing speed and low dry food consumption, but it has disadvantages such as difficulty in refrigerant recovery, large loss, and high cost. And there are certain restrictions on the refrigerant, especially when it comes in contact with unpackaged food, the refrigerant must be pure, free of peculiar smell and gas, no foreign color and bleaching agent, non-flammable, non-explosive, etc.