Dehumidification

The fundamental principles of dehumidifying - cooling, adsorption or absorption

Air may be dehumidified by

1. Cooling the air - condensation of vapor in the air
2. Adsorption of water vapor in the air
3. Absorption of water vapor in the air

1. Cooling the air - vapor condensation

In a cooling system the humidity is reduced by cooling the air below dew point. A part of the moisture in the air is condensed and drained out.

2. Adsorption

In an adsorption system the humidity is reduced with an adsorbent material as silica gel or activated aluminia.

Adsorption is a physical process in where moisture is condensed and held on the surface of the material without any change of in the physical or chemical structure of the material. The adsorbent material can be reactivated by heat.

• Temperature for reactivation: 160 - 170 ^oC.
• Heat required for reactivation: 4800 - 4800 kJ/kg water removed.

Silica gel - SiO₂

Silica gel - SiO₂ - is a hard, adsorbent, crystalline substance and very porous. Voids are about 50 - 70% by volume and adsorbs water up to 40% of its own mass. The bulk density of silica gel is 480 - 720 kg/m³. The specific heat capacity is 1.13 kJ/kgK.

Activated alumina

Activated alumina is about 90% aluminum oxide Al₂O₃ and very porous. Voids are about 50 - 70% by volume and adsorbs water up to 60% of its own mass. The bulk density is 800 - 870 kg/m³. The specific heat capacity is 1.0 kJ/kgK.

3. Absorption

In an absorption system the humidity is reduced with an absorbent material such as a calcium chloride solution. Absorption involves a change in the physical or chemical structure of the material and it is in general not easy to reactivate the material.

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