What is air drying?

Air drying is a process of decreasing the amount of steam in the air using appropriate methods.

The humidity can be directly removed from the air by:

Lowering the air temperature below the dew point, which makes the water condense. That’s why this is called the condensation method. This phenomenon can be observed, when removing a chilled drink from a fridge, so the packaging quickly covers with dew. This happens because the air temperature around the packaging begins falling below the dew point. This method is used in air dryers with a refrigeration system.

Water steam desiccation using hygroscopic substances is a sorption method. It is widely used in the form of bags filled with sorbent crystals or balls that are put into PC cases or humidity-sensitive product packaging.

The following methods of air drying are used in practice:

heating and ventilation
is the most common method, but it is inefficient and uneconomical.

condensation drying
makes the steam in the air condense. It is more efficient and economical than heating and ventilation.

sorption drying (adsorption and absorptions)
removes the water from the air by absorbing it. This method is the most efficient.

Depending on the operating method, there are two types of drying:

closed circuit
when there is no exchange between the dried air and the outside air,
e.g. when drying rooms with a condensation dryer,

open circuit
when there is a partial or total exchange between the dried air and the outside air,
used mostly in air-conditioning systems.

Important terms

Dew point - a temperature at which water drops condense in the air at specified initial temperature and humidity. When the air is 100% saturated, it is not able to absorb any more water, and further lowering of the temperature will make the water condense on surfaces that have a temperature close to the one causing 100% saturation.

Steam condensation - a transformation of water steam in the air from the gaseous to the liquid state (condensation) or solid state (freezing, sublimation).

A hygroscopic substance - may be a water solution of calcium chloride and magnesium chloride, a solution of lithium chloride, a silica gel, potassium chloride, activated aluminium, calcium chloride, salts of lithium chloride and lithium bromide.