Drying ovens remove moisture from foods and other items using evaporation. Some common items dried in these ovens include raisins, jerky and even flowers. The evaporation process preserves the color of the items, making them more appealing to the eye.
Drying ovens use convection heating. The object is heated using air currents, which makes the water inside evaporate. The humidity level in the oven rises, which causes the inner semi-solid membrane to absorb the water. The end result is a product with little, if any, moisture left inside.
These ovens use fans to create the air current and to insure that it keeps circulating around the food. Some models also have an adjustable ventilation system that insures the oven has an adequate supply of air. For example, a built-in convection drying oven has less air circulating around it than a free-standing one. In an industrial setting, free-standing models are preferred.
In the scientific world, drying ovens are also used to sterilize medical equipment. A similar version, called a gravity convection oven, is used to dry materials that can't handle strong air flows, like delicate powders. Clean-room drying ovens are used when it's critical to keep contaminants out of a product, such as in research or forensic labs.