By using an adsorber, the incoming moisture is adsorbed and the system to be ventilated is protected from contamination by water. The
process of dehumidification by an adsorbent, such as silica gel or molecular sieve, is based on the physical process of adsorption. The silica gel attracts the water molecules into the pores by Van der Waals forces. The color indicator contained on the surface changes color with increasing polarity. With GIEBEL adsorbers it is from orange to green. The absorption capacity and attraction of silica gel to water is based on the isotherm. This isotherm represents the graphical course of the absorption capacity as a function of the ambient humidity.

The isotherm of silica gel rises constantly with increasing humidity until it reaches a plateau at approx. 60% RH. The maximum absorption capacity is then approx. 37-40 wt.% at 100% RH. Based on this isotherm, the application criterion of min. 50-60% RH results for the use of an adsorber.

Since the isotherm depends on the temperature, it changes. As the temperature rises, the curve becomes flatter, which means that the silica gel can absorb less water. Above a temperature of 80°C, the process changes from adsorption to regeneration and thus becomes unusable for air drying. This results in a maximum air temperature of 80°C for the use of an adsorber.

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