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Dehumidification

Principles of dehumidifying - cooling, adsorption or absorption

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 alumina.

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.