System Components

Figure 1 shows basic components of a simple vacuum freeze dryer: a vacuum chamber containing a set of parallel

Heating medium

Heater heating plates, between which is a tray holding the frozen food to be dried; a vacuum pump for evacuating the chamber and removing inleaking air; a condenser where water vapor generated during drying condenses as ice; refrigeration for cooling the condenser; and a system that supplies hot heat-transfer fluid to the plates. Other elements not shown include a pressure-tight door that permits insertion and removal of loads; instruments for sensing plate, condenser and drying food temperatures, and for sensing pressure in the chamber; and the controller that regulates plate temperatures.

Figure 1 shows a single pair of heating plates and one tray of frozen food. Plant-scale freeze dryers contain many plates and many rows of trays holding many tray-loads of product. Large-scale freeze dryers are described later in this article. Reference 5 provides design details about such dryers.

Small-scale freeze dryers may contain up to five heating plates. They can process up to four rows of product, have a transparent plastic door that permits products to be observed during drying, and may be fitted with a balance or load cells that weigh food loads as they dry. Drying rates and temperatures measured in suitably instrumented small freeze dryers are used to help select operating conditions used in production-scale drying.

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