Guide to Heat Exchangers

Plate and frame designs include a series of corrugated parallel plates separated from each other by gaskets. Gaskets control the flow of hot and cold fluids over the plate surfaces, allowing heat to transfer from hot to cold fluids of low to medium viscosity.

Gasket plate and frame heat exchangers are among the most efficient designs so are also among the most common designs in processing systems. Gaskets between plates guide the flow of product and heating/cooling fluids through alternating channels. As hot fluids pass over the plates, heat transfers from the hot to the cold side, decreasing the temperature of the hot side and raising the temperature of the cold side.

Key to efficient operations, heat exchangers must maintain sufficient fluid velocity across plates to transfer heat while also controlling pressure drops that can disrupt operation. Systems typically employ plate and frame heat exchangers for pasteurization, raw milk cooling, and CIP heating. Given their suitability for products with low to mid viscosity and few to no particulates, plate heat exchangers are commonly used for beverage, beer, wort, eggs, sauces, and most dairy processing.

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Regenerative heating and cooling

In milk processing, chilled milk is heated from, for example, 4 °C to a pasteurization temperature of 72 °C and held at that temperature for 15 seconds and then chilled to 4 °C again.

Heat always transfers from warmer substances to colder ones, so during pasteurization, heat exchangers use heat from the pasteurized milk to warm the cold milk, which saves heating and refrigeration energy. The process is called regenerative heat exchange or heat recovery, typically reaching 90% and achieving up to 95% heat recovery from pasteurized milk. Recovery is lower for higher-fat products such as cream and ice cream mix.

Regeneration has a positive impact on energy savings, capital costs, and efficient operation. Heat transfer occurs rapidly when the temperature differential is high. As temperature difference decreases, the rate of transfer slows down and stops altogether when temperatures equalize.