Figure 6: Condenser
This completes the cooling cycle.
Crystallization
All absorption chiller-heaters that use LiBr and water as the solution/refrigerant pair are subject
to crystallization. This is due to the fact that some areas of the unit operate with solution liquid
concentration levels that are solely possible at higher than the normal ambient temperature
surrounding the unit. For example, the solution concentration in the generator of a single effect
absorption unit is usually 64.3% LiBr by weight. LiBr begins to crystallize at 110°F (43.4°C).
Crystallization is the result of the LiBr solution temperature going too low or the concentration too
high. The LiBr solution becomes like slush. At this point the LiBr solution cannot absorb any more
water and starts to solidify (crystallize).
Crystallization occurs in the solution heat exchanger and sometimes even in the generator. It also
happens in pipes that are not well insulated, where room temperature can affect the solution
moving through the pipes.
You can prevent crystallization by making sure you keep the solution temperature high and the
concentration at the optimum percentage (64%).
As the solution temperature in the generator is normally high enough in most load conditions, no
crystallization occurs as long as the higher solution temperatures are maintained. Special measures
do have to be taken before the unit is shut down so that the solution is sufficiently diluted in
all areas of the unit to prevent crystallization during the off cycle, as the solution temperature
eventually equals the surrounding ambient temperature.
All units employ some sort of dilution cycle that fulfills this requirement. As long as the unit
is allowed to dilute itself during an orderly shutdown sequence, the unit should be able to sit
idle at fairly low plant room ambient temperatures for extended periods of time without any
threat of crystallization. Typically, after a dilution cycle, the average solution concentration in the
chiller-heater is below 45% LiBr by weight and has no tendency to crystallize at normal ambient
temperatures.
Model YHAU-CGN/H-CXR(M)Double Effect Direct Fired Small Absorption Chiller-Heater
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