The number of decks and the design and quantity of heat exhangers to be mounted on each deck depends on the desired moisture content of the product when entering and exiting the machine. First, the air is heated by the heat exchanger and steam on the upper deck, which decreases the moisture in the product. To reach the desired moisture content, the product is exposed to hot air on each deck. On the lower deck, the product is dried at ambient temperature. Here, the product is dried only on the lowest level.
In some situations, the air passing through the exchanger is taken from the outside whereas in others, the hot air is passed through the exchanger after the cooling process. As a result, warm air is heated up by the exchanger. The aim here is to make use of the hot air.