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Dairy processing: Heat exchangers

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The following provides recommended practices for free-standing heat exchangers that are not part of the pasteurization system and that are used to heat or cool dairy products.

Heat exchangers are widely used in the dairy processing industry for fore-warming or cooling the milk product and for cooling cheese brine. They are designed to transfer heat from a hot liquid to a cold liquid. Heat exchangers can cause the final product to become contaminated if they are not properly controlled.

Types of heat exchangers

Most heat exchangers are one of the following types.

Spiral type: These are tubular type preheaters which are fully enclosed inside the tube chests or inside milk vapour areas. These systems are impossible to inspect inside, therefore a cleaning program is essential.

Surface cooler type: In this system milk is distributed over the cooling coils by means of a distributor pipe or trough and the milk drops from the lower coil into a collecting trough. Product is exposed to air in this system therefore, subjecting the product to air-borne contamination.

Tubular type: These heat exchangers consist of a small tube mounted concentrically within a larger tube. Product is pumped through the inner tubes, entering at the low point and leaving at the high point while the heating or cooling medium enters the larger tube at the high point and flows through the space between tubes, leaving at the bottom. The system is designed to keep the two mediums separate.

Plate type: These heat exchangers consist of a number of stainless steel plates, sealed at the edges with gaskets, and are clamped tightly within a press. The spaces between the plates are occupied alternatively by milk and the heating or cooling medium. The system is designed to keep the two mediums separate.

Additional controls for pasteurized products

If the product passing through the heat exchanger is pasteurized finished product, an automated mechanism is an effective means of achieving the correct pressure relationship in the cooling section during forward flow, divert and shutdown conditions, so that the pressure on the cooling media side is not greater than that of the pasteurized product at all times.

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