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42 TRG-TRC011-EN
notes
period three
Capacity Control
As a second line of defense, most absorption water chillers include devices that
allow the chiller to recover in the event that crystallization does occur. Some of
these devices simply sense impending crystallization, put the chiller through a
dilution cycle, and shut the chiller down. Other devices keep the chiller
operating while regaining control of the solution temperature and
concentration.
The device shown in the figure above is a heat exchanger bypass that allows
the chiller to de-crystallize and continue to operate. If crystallization does occur,
the heat exchanger begins to be blocked, and the flow of concentrated solution
from the generator to the absorber is reduced. Dilute solution, however,
continues to flow from the absorber to the generator, resulting in concentrated
solution backing up inside the generator.
This backed-up solution will eventually rise enough that the concentrated
solution spills over into the bypass pipe and returns directly to the absorber,
bypassing the heat exchanger. As a result, the temperature of the solution in the
absorber is increased, approaching the temperature in the generator. As this
warmer solution flows from the absorber, through the heat exchanger, to the
generator, it raises the temperature of the heat exchanger and de-crystallization
occurs.
heat
heat
exchanger
exchanger
evaporator
evaporator
absorber
absorber
generator
generator
heat exchanger
heat exchanger
bypass
bypass
Figure 50