Drying- /Heating Cabinets

A drying cupboard is used for the dehumidification of an object. This takes place as a rule via the dehumidification of the air by applying hygroscopic substances that are called sorbents.

Areas of application - drying cupboard

Dry cupboards are used in libraries and archives for the protection of media, such as microfilms and recording media. In the electrical industry, components that are sensitive to humidity, like ceramic capacitors, are stored by means of dry cupboards. Dry cupboards are also used in forensics for the recovery of DNA which was destroyed by humidity. In chemical laboratories, dry cupboards are applied for the execution of experiments, for the drying of sensitive instruments and for the storage of certain substances. In the production of microlenses and microscope lenses, the optical industry as well uses dry cupboards. Another important operational area for dry cupboards is the solar technology industry.

Drying methods

Drying cupboards are usually made like common electric ovens. Simple types only allow to control temperature. When drying electronic components, the wettability of the connections considerably lessens after baking. Another disadvantage for the components is thermal stress. In adsorption drying, either a rotor or a chamber system is used. Chamber dehumidification dehumidifies periodically, not continuously, resulting in lower power consumption and lower moisture ratio. The process air is conducted first through a container which is filled with zeolite. There the water molecules are filtered by adsorption from the process air and are saved in zeolite A. However, the hygroscopic properties of zeolite A decrease with increasing saturation. Therefore this zeolite A must be regenerated. That is accomplished by removing it from the process air and releasing it to the ambient air. There, the humidity is reduced in contact with air that is heated up to 200 °C, and it is vented to the environment. Now the zeolite A can be refluxed. In the nitrogen process, nitrogen is used to displace the humid air by purging. However, this method requires a considerable amount of nitrogen.

Drying process of a drying cupboard

If humidity is reduced below 5 %, the vapour pressure difference rises so much that the water molecules in the objects to be dried overcome the adhesive forces and therefore are released into the process air. This dries the object.

Literature

• http://de.wikipedia.org/w/index.php?title=Trockenschrank&oldid=78739425 (called: 31.03.11).