Carrier 16DF013-050 - Manual (Page 9)

Solution Cycle and Equilibrium Diagram — The
solution cycles for cooling and heating operation can be il-
lustrated by plotting them on a basic equilibrium diagram
for lithium bromide in solution with water (Fig. 7 and 8).
The diagram is also used for performance 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 of the refrigerant (water).
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 COOLING SOLUTION CYCLE — An
absorption solution cycle at typical full load conditions is
plotted in Fig. 7 from Points 1 through 12. The correspond-
ing 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. At
this point, the weak solution is split, with approximately half
of it going to the low-stage generator, and the rest of it going
on to the high-temperature heat exchanger.
Point 4 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 5 represents the weak solution leaving the high-
temperature heat exchanger and entering the high-stage gen-
erator. It is at the same concentration as Points 2 and 3, but
at a higher temperature after gaining heat from the strong
solution. This temperature can be measured.
Point 6 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 7 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 8 represents the strong solution from the high-temperature
heat exchanger as it flows between the 2 heat exchangers. It
is the same concentration as Point 7, but at a cooler tem-
perature after giving up heat to the weak solution. It is an
internal condition and cannot be measured.
Point 9 represents the strong solution leaving the low-stage
generator and entering the low-temperature heat exchanger.
It is at a weaker concentration than the solution from the
high-stage generator, and can be plotted approximately by
measuring the temperatures of the leaving strong solution
and vapor condensate (saturation temperature). This condi-
tion cannot be measured accurately.
Point 10 represents the mixture of strong solution from the
high-temperature heat exchanger and strong solution from
the low-stage generator after they both enter the low-
temperature heat exchanger. It is an internal condition and
cannot be measured.
Point 11 represents the combined strong solution before it
leaves the low-temperature heat exchanger after giving up
heat to the weak solution. This condition is internal and can-
not be measured.
Point 12 represents the strong solution leaving the low-
temperature heat exchanger and entering the absorber spray
nozzles, after being mixed with some weak solution in the
heat exchanger. The temperature can be measured but the
concentration cannot be sampled. After leaving the spray
nozzles, the solution is somewhat cooled and concentrated
as it flashes to the lower pressure of the absorber.
9