During high load operation, some abnormal conditions can
cause the lithium bromide concentration to increase above
normal, with the strong solution concentration close to crys-
tallization (see Equilibrium Diagram and Chiller Solution
Cycle.) If, for some reason, the machine controls do not pre-
vent strong solution crystallization during abnormal operat-
ing conditions and flow blockage does occur, the strong-
solution overflow pipe will reverse or limit the crystallization
until the cause can be corrected. The overflow pipe is lo-
cated between the low-temperature generator discharge box
and the absorber, bypassing the heat exchanger, as shown in
Fig. 5.
If crystallization occurs, it generally takes place in the shell
side of the low-temperature heat exchanger, blocking the flow
of strong solution from the generator. The strong solution
then backs up in the discharge box and spills over into the
overflow pipe, which returns it directly to the absorber sump.
The solution pump then returns the hot solution through the
heat exchanger tubes, automatically heating and decrystal-
lizing the shell side.
Equilibrium Diagram and Chiller Solution
Cycle —
The solution cycle can be illustrated by plotting
it on a basic equilibrium diagram for lithium bromide in so-
lution with water (Fig. 7). The diagram is also used for per-
formance analyses and troubleshooting.
The left scale on the diagram indicates solution and water
vapor pressures at equilibrium conditions. The right scale
indicates the corresponding saturation (boiling or condens-
ing) temperatures for both the refrigerant (water) and the
solution.
The bottom scale represents solution concentration, ex-
pressed as percentage of lithium bromide by weight in so-
lution with water. For example, a lithium bromide concen-
tration of 60% means 60% lithium bromide and 40% water
by weight.
The curved lines running diagonally left to right are so-
lution temperature lines (not to be confused with the hori-
zontal saturation temperature lines). The single curved line
beginning at the lower right represents the crystallization line.
The solution becomes saturated at any combination of tem-
perature and concentration to the right of this line, and it
will begin to crystallize (solidify) and restrict flow.
The slightly sloped lines extending from the bottom of the
diagram are solution-specific gravity lines. The concentra-
tion of a lithium bromide solution sample can be determined
by measuring its specific gravity with a hydrometer and read-
ing its solution temperature. Then, plot the intersection point
for these 2 values and read straight down to the percent lithium
bromide scale. The corresponding vapor pressure can also
be determined by reading the scale straight to the left of the
point, and its saturation temperature can be read on the scale
to the right.
PLOTTING THE SOLUTION CYCLE — An absorption so-
lution cycle at typical full load conditions is plotted in
Fig. 7 from Points 1 through 13. The corresponding values
for these typical points are listed in Table 2. Note that
these values will vary with different loads and operating
conditions.
Point 1 represents the strong solution in the absorber, as it
begins to absorb water vapor after being sprayed from the
absorber nozzles. This condition is internal and cannot be
measured.
Point 2 represents the diluted (weak) solution after it leaves
the absorber and before it enters the low-temperature heat
exchanger. This includes its flow through the solution pump.
This point can be measured with a solution sample from the
pump discharge.
Point 3 represents the weak solution leaving the low-
temperature heat exchanger. It is at the same concentration
as Point 2, but at a higher temperature after gaining
heat from the strong solution. This temperature can be
measured.
Point 4 represents the weak solution leaving the drain heat
exchanger. It is at the same concentration as Point 3, but at
a higher temperature after gaining heat from the steam con-
densate. This temperature can be measured. At this point the
weak solution first flows through the level control device (LCD)
valve and then it is split, with approximately half going to
the low-stage generator, and the rest going on to the high-
temperature heat exchanger.
Point 5 represents the weak solution in the low-stage gen-
erator after being preheated to the boiling temperature. The
solution will boil at temperatures and concentrations corre-
sponding to a saturation temperature established by the va-
por condensing temperature in the condenser. This condition
is internal and cannot be measured.
Point 6 represents the weak solution leaving the high-
temperature heat exchanger and entering the high-stage gen-
erator. It is at the same concentration as Point 4 but at a higher
temperature after gaining heat from the strong solution. This
temperature can be measured.
Point 7 represents the weak solution in the high-stage gen-
erator after being preheated to the boiling temperature. The
solution will boil at temperatures and concentrations corre-
sponding to a saturation temperature established by the va-
por condensing temperature in the low-stage generator tubes.
This condition is internal and cannot be measured.
Point 8 represents the strong solution leaving the high-stage
generator and entering the high-temperature heat exchanger
after being reconcentrated by boiling out refrigerant. It can
be plotted approximately by measuring the temperatures of
the leaving strong solution and the condensed vapor leaving
the low-stage generator tubes (saturation temperature). This
condition cannot be measured accurately.
Point 9 represents the strong solution from the high-temperature
heat exchanger as it flows between the two heat exchangers.
It is the same concentration as Point 8 but at a cooler tem-
perature after giving up heat to the weak solution. The tem-
perature can be measured on those models which have sepa-
rate solution heat exchangers.
LCD — Level Control Device
TC
— Temperature Control (Capacity Control)
Fig. 6 — Typical Flow Circuits, (Simplified)
Arrangement Shown for 16JT810-880
7
Summary of Contents for 16JT Series
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