Commonly encountered pre-packaged desiccants are solids, and work through absorption or adsorption of water, or a combination of the two. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules.
Pre-packaged desiccant is most commonly used to remove excessive humidity that would normally degrade or even destroy products sensitive to moisture. Some commonly used desiccants are: silica gel, activated charcoal, calcium sulfate, calcium chloride, montmorillonite clay, and molecular sieves.
A specific usage of a desiccant would be in insulated windows where it is placed inside the spacer between the air space and window edge. This prevents moisture condensation between the panes.
Chemical reactivity of Desiccant
Because of their common use in preservation, it is usually desirable for a desiccant to be substantially chemically stable or chemically inert, and a number of useful desiccants with this property have been identified and are in common use, such as silica gel, chalk and clay-based desiccants.
Performance efficiency
One measure of desiccant efficiency is the ratio (or percentage) of water storable in the desiccant, relative to the mass of desiccant.
Another measure is the residual relative humidity of the air or other fluid being dried.
The performance of any desiccant varies with temperature and both relative humidity and absolute humidity. To some extent, desiccant performance can be precisely described, but most commonly, the final choice of which desiccant best suits a given situation, how much of it to use, and in what form, is made based on testing and practical experience.
Read more: Dry Desiccant
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