- The adsorption chiller uses
water as it's cooling agent.
Water evaporates in a vacuum at room temperature and thereby
extracts heat from it's surroundings (evaporation-energy). Through
this process, a cooling takes place in the circuit.
- Compared to open systems, the
evaporated water is not released as steam into the surroundings,
but recondensed within the machine.
- The adsorption chiller is a
closed system.
- For thermodynamical reasons,
a direct condensation of the evaporated water is energetically
not feasible.
- Therefore, the water is first
adsorbed by a solid carrier material. This material consists
of silica-gel, a material related to quartz or sand.
- In refrigeration engineering
the principle of adsorption - the collection of water vapour
in the air by a hydroscopic material (silica-gel, zeolithe) -
is commonly used to dehumidify the air. Utilizing the warm waste
air in such systems, the material used is constantly regenerated
(disc wheels).
The same process takes place in the packaged chiller.
- With the use of hot water, the
adsorbed water on the carrier material (silica-gel) is again
evaporated and thereby the carrier material is regen-erated.
- Condensation of the secondary
evaporated water (off the carrier material) is, opposed to the
primary evaporated water (out of the cooling circuit), now easy.
The following factors are essential for the process:
- Silica-gel can easily take up
water (adsorb), without causing a structural change or volume
expansion.
- Silica-gel can easily release
the stored water through a temperature increase.
This process is reversible and unlimitedly repeatable.
The evaporation process is temperature and pressure dependent.
Under normal atmospheric pressure (760 mm Hg), water evaporates
at 100°C. If the surrounding pressure drops, the evaporating
temperature of the water also decreases.
- With the achievement of a high
enough vacuum, the water evaporates at a lower temperature.
- For the purpose used in the
adsorp-tion chiller, a vacuum in the area of 10-20 mm Hg, is
sufficient.
If water is sprayed or injected into a vessel under vacuum, it
evaporates spontaneously and extracts energy from it's surroundings.
- The adsorption chiller utilizes
the following properties:
- the reversible adsorption and
de-sorption process of water on silica-gel
the spontaneous evaporation of water on silica-gel
the easy condensation of water on a high energy level.
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