A tunnel freezer is a long cryogenic tunnel where cold air is passed over food products and they are frozen quickly. This is used in industrial food processing to increase yield by freezing the product faster and also reduces dehydration costs. The tunnel freezer can be cooled by liquid nitrogen (at -196°C), carbon dioxide, or some other refrigerant.

A typical tunnel freezer consists of an insulated enclosure where the products and the cryogenic liquid are kept at temperature, a conveyor belt by which the products travel through the tunnel-shaped freezing area, an injection system for the gas, a ventilation system that ensures cold air is available to reach the products, and an exhaust system for excess gases.

The most common type of tunnel freezer is the straight belt tunnel. This takes advantage of the latent heat of vaporization of liquid nitrogen (86 BTUs per lb) by blowing cold nitrogen vapor over the products and then forcing the vapor back towards the entrance of the tunnel to maximize the refrigeration value of the vapor.

Another variation is a flat belt tunnel freezer. This uses the same principle as the straight belt tunnel but uses a flat stainless steel conveyor belt instead of a curved one. This allows the cooling, chilling, and freezing to be done on a wider variety of food products that might be a little too large for straight belt freezers.

Both flat belt tunnel freezers and straight belt tunnel freezers are often cooled using either liquid nitrogen or carbon dioxide, depending on the type of product to be cooled. While both nitrogens are able to cool the product and inhibit microbial growth, research has shown that liquid nitrogen is superior for this purpose, since it does not affect the flavor or aroma of the product.

A more advanced variation of the tunnel freezer is a IQF (Individual Quick Frozen) freezer. This provides a more controlled, individualized freezing process by placing the products on staggered conveyor belts. This prevents the products from freezing together and increases the surface exposure to the refrigerant. This allows the IQF tunnel to control the amount of water content, weight, shape, and fragility that the product is exposed to in order to achieve the best results. This type of tunnel freezer is often found in food processing facilities that focus on a specific product or brand. The IQF tunnels can be custom designed to meet the precise requirements of a particular project. This is a cost-effective way to increase productivity while keeping the product quality consistent. This can result in higher sales, a better brand image, and improved customer loyalty.

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