E-M-HG2-S-V1_04
Rotronic AG
Bassersdorf, Switzerland
Document code
Unit
HygroGen2 humidity and temperature
generator: Instruction Manual
Instruction Manual
Document Type
Page
16
of 46
Document title
© 2009-2010; Rotronic AG
16
E-M-HG2-S-V1_04
Desiccant Cell
5a – Cell cap
5b – Retaining clip
5c – Cell body
Caution: Do not use dusty
desiccants as the dust
may be passed into the
chamber.
2.5 Choice of Desiccant
The HygroGen is supplied from the factory with the desiccant cell packed with molecular sieve. A variety
of desiccant materials may be used in the HygroGen desiccant cell. Some of these are outlined below,
including their effectiveness and health and safety implications. Dusty desiccants should be avoided as
the dust may be passed in to the HygroGen chamber. Material Safety sheets for the desiccants supplied
by ROTRONIC are available on request.
2.6 Molecular Sieve Desiccant (Factory Standard)
Molecular sieves have the appearance of small opaque tan beads. Molecular sieves are synthetically
produced, highly porous crystalline metal-alumina silicates. They have many internal cavities that are
linked by window openings of precise diameters. It is these diameters (measured in Angstroms) that
classify molecular sieves. Adsorption occurs only for molecules with smaller diameters than these cavity
openings. Larger molecules will be excluded from adsorption. Preferentially adsorbed are molecules of
greater polarity. This makes molecular sieves ideal for adsorption of water from air and liquids, as water
molecules are both polar and very small.
Molecular sieves will absorb water molecules and other contaminants from liquids and gases down to
very low levels - often just 1 part per million. Molecular sieve’s desiccant properties differ from silica gel
in a number of ways. They absorb water vapour more rapidly and they will reduce water vapour to
much lower levels than silica gel, making their use essential when a very dry atmosphere is required.
They perform more effectively as moisture absorbers at higher temperatures (greater than 25°C) than
silica gel does. Molecular sieve desiccant contains less than 1% quartz, classed as a carcinogen in the EU.
