Technically, drying is a mass transfer process resulting in the removal of water moisture or moisture from another solvent, by evaporation from a solid, semi-solid or liquid (hereafter product) to end in a solid state, provided there is a source of heat, and sink of the vapor thus produced. In the most common case, a gas stream, e.g., air, applies the heat by convection and carries the vapor as humidity. Other possibilities are vacuum drying, where the source of heat may be by conduction or radiation (or microwaves) and the vapor is removed by the vacuum system. Another possibility is drum drying, where a heated surface is used in connection with aspirators to draw the vapor outside the site. In this regard, the mechanical extraction of the solvent, e.g., water, by centrifugation, is not considered "drying". The ubiquitous term dehydration may mean drying of water-containing products as foods, but its meaning is more vague, as it is also applied for water removal by osmotic drive (salt or sugar solution), or else in medicine as the condition whereby a person loses water by respiration and evaporation and does not incorporate, for whatever reason, the "make-up" water to keep the normal physiological behavior of the body. Mass transfer is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of atoms and molecules within physical systems. ... Dew on a spider web Moldy bread Moisture generally refers to the presence of water, often in trace amounts. ... Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. ...

Drying maybe both a natural or an intentional process.

The process of extreme drying is called desiccation. Desiccation is the state of extreme dryness, or the process of extreme drying. ...

There is very extensive technical literature on this subject, including several major textbooks and a dedicated scientific journal (Drying Technology [1]).

Methods of drying

• Application of dry heated air (convective drying). This causes evaporation of the surface water, which is replaced by water from inside the solid until the whole has dried out.
• Indirect or contact drying (heating through a hot wall), similar to above.
• Dielectric drying (radiofrequency or microwaves being absorbed inside the material)
• Freeze drying
• Supercritical drying

This article or section is in need of attention from an expert on the subject. ... Freeze drying (also known as Lyophilization) is a dehydration process typically used to preserve a perishable material, or to make the material more convenient for transport. ... Supercritical drying (red arrow) goes beyond the critical point of the working fluid in order to avoid the direct liquid-gas transition seen in ordinary drying (green arrow). ...

Applications of drying

• Devices commonly called dryers are used for efficient drying of various things: hair after shower, candies at candy factories, semiconductor wafers
• Most processes giving a solid product involve a drying step
• Drying is often used to preserve food
• Desiccation is used to obtain absolute alcohol
• Wood drying is integral part of timber processing