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Absorption Anti-Crystallization & De-Crystallization Devices
Major absorption chiller manufacturers now incorporate devices that minimize
the possibility of crystallization. These devices sense impending
crystallization and shut the machine down after going through a dilution
cycle. These devices also prevent crystallization in the event of power
failure. A typical anti-crystallization device consists of two primary
components:
- A sensor in the concentrated solution
line at a point between the concentrator and the heat exchanger, and
- A normally open, two-position valve
located in a line connecting the concentrated solution line and the line
supplying refrigerant to the evaporator sprays.
If crystallization occurs, the liquid level
rises in the concentrated solution line as resistance to flow within the
heat exchanger increases. This increase in level is sensed which, in turn,
opens the valve permitting refrigerant (water) to flow into the concentrated
solution, thereby reducing the solution concentration. When flow is
re-established, the machine is placed in a dilution cycle and shut down.
If a power failure occurs, the valve is
already open and the pressure of the refrigerant in the evaporator spray
piping forces enough water into the concentrated solution line to dilute the
solution and prevent crystallization. Restoring power closes the valve and
the machine returns to normal operation.
Some chillers are also equipped with heat
exchanger bypass lines that facilitate de-crystallization. When
crystallized, concentrated solution cannot flow from the concentrator to the
absorption chiller. Diluted solution, however, does flow from the absorption
chiller to the concentrator, building up to the point that it spills over
into the bypass line and returns directly to the absorption chiller. This
causes the absorption chiller to heat up until its temperature approaches
that of the concentrator. The hot solution returning from the absorption
chiller through the heat exchanger de-crystallizes the machine.
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