| Features and Benefits Refrigeration Cycle
Cooling Cycle Overview
The absorbent/refrigerant combination is a traditional lithium bromide/water solution. The dilute solution is first pumped
from the absorber to the low temperature generator
where it is partially concentrated. A heat exchanger transfers heat from the generator
and preheats the incoming solution.
Part of the solution is then pumped to the high temperature generator where it is further concentrated, while the rest of
the flow from the low temperature generator is mixed
with the strong, concentrated solution coming back
from the high temperature generator. This mixed solution is then mixed with additional
solution from the absorber to form the absorber spray.
Evaporator/Absorber
Liquid refrigerant, pure water, enters the evaporator from the condenser through
a throttling pipe. As the refrigerant passes to the
lower pressure evaporator flash boiling occurs, cooling the remaining liquid refrigerant to the evaporator saturation temperature.
This chilled refrigerant enters the evaporator pan and
is circulated continuously to the evaporator sprays system by the refrigerant
pump. The transfer of heat from the system water to the
refrigerant causes the refrigerant to vaporize or boil, cooling the system water. This refrigerant vapor flows to the
slightly lower pressure in the absorber.
In the absorber, refrigerant is absorbed by the lithium bromide solution, because
of its high affinity for water vapor. This is the
fundamental principle of the absorption process. The
pressure in the absorber is determined by the temperature and concentration of the solution sprayed over the tubes. A mixed
concentration of the solution from the generators and
the absorber is pumped through the absorber spray
system to thoroughly wet the tubes and provide the opportunity for the refrigerant
vapor from the evaporator to absorb into the lithium
bromide solution and be cooled. As the refrigerant vapor is absorbed by the solution, it transfers the heat acquired
in the evaporator to the cooling water which is pumped
through the absorber tubes. The diluted solution is then pumped through the
heat exchangers by the solution pumps to the generators
to reconcentrate or regenerate the lithium bromide solution.
Low Temperature Generator
The dilute solution is pumped into the low temperature generator after being preheated by the low temperature heat exchanger.
The purpose of this generator is to produce refrigerant
for the cycle. To achieve this, vapor from the high temperature generator is used as the energy source to boil the solution.
This vapor condenses inside the tubes, flows to the
condenser sump, and becomes part of the refrigerant for the cycle.
The intermediate concentrated solution leaving the low temperature generator has two paths; the first is to the generator
pump and on to the high temperature generator, the
second is mixed with strong, concentrated solution coming back from the high temperature generator forming a mixed
concentration for the absorber spray system.
Solution Heat Exchangers
The low temperature heat exchanger recovers heat energy from the mixed concentration and preheats the dilute solution
going to the low temperature generator. Preheating the
dilute solution reduces the heat energy required to induce boiling within the low temperature generator. In turn, the reduction
in mixed solution temperature decreases the load on the
cooling tower.
High Temperature Generator
The high temperature generator uses steam or hot water as an energy source.
The intermediate concentrated solution enters at the
bottom of the generator after being preheated by the
high temperature heat exchanger. Heat from the energy source is used to boil refrigerant from the solution, producing
refrigerant vapor for the low temperature generator.
The refrigerant vapor flows to the low temperature
generator and the concentrated solution returns to the absorber through the
high temperature and low temperature heat exchangers.
Condenser
Refrigerant is introduced into the condenser from two sources; liquid refrigerant from the tube side of the low
temperature generator and refrigerant vapor produced by
the low temperature generator.
All refrigerant vapor is condensed and returns to the evaporator as a liquid through the flow metering device. This device
reduces the pressure, and consequently the temperature,
as the refrigerant enters the evaporator pan.
The heat of condensation is rejected to the cooling water loop. The cooling water within the condenser bundle is the same
water that flows through the absorber. |
