Regenerative absorption cycles with multiple stage absorber

An improved regenerative absorption refrigeration cycle having a high COP and a commercially practicable pumping system. In the basic cycle, an ammonia/water solution is boiled in an externally-heated generator (11). The boiled-off ammonia vapor is cooled (14) in a regenerator (16), condensed (28), expanded to low pressure (32), and boiled in an evaporator (34) to extract heat from fluid circulating to and from a cooling load (41). The low-pressure liquid ammonia returns (46) to the regenerator (16) and is absorbed back into the low-pressure water from the generator. The solution is then cooled in a low-pressure absorber (50), pumped (53) to a high-pressure conduit (57) which is heated by the regenerator heat before going back to the generator 11. The improved cycle uses at least one intermediate absorber stage 60 to absorb more ammonia vapor (69, 71) into the solution coming from the lower pressure absorber (50) to produce a cooled solution of higher ammonia concentration. This higher concentration can be used to precool (87) the liquid refrigerant prior to expansion (32). Liquid is injected (106) into the ammonia vapor returning (46) to the regenerator to boil and transport heat from the cold end to the hot end of the regenerator. The ammonia vapor is injected into the water in the regenerator at distributed points (101, 102, 103, 19) along the flow path of the water for better heat balance.

This invention relates to absorption refrigeration cycles using high 
temperature heat as the driving source, and more particularly to improved 
regenerative absorption cycles having high coefficients of performance 
(COP) under broad ranges of operating temperatures. 
Absorption cycles can be roughly classified into three categories: the 
basic single-effect cycle, multiple-effect cycles and 
regenerative-absorption cycles. 
The basic single-effect absorption cycle has been used for decades. In such 
a cycle a working fluid pair, e.g. ammonia/water is heated in a generator, 
at high pressure to a temperature sufficient to boil off the ammonia 
(NH.sub.3) as a vapor. The high-pressure ammonia vapor is next cooled in a 
condenser to liquify the ammonia. The pressure of the liquid ammonia is 
then reduced so that it may boil at a low, refrigerating temperature in an 
evaporator. As the ammonia vaporizes, it absorbs heat from the cooling 
load. The ammonia vapor then goes to an absorber where it is absorbed back 
into low pressure water coming from the generator, with the heat of 
absorption being rejected to a heat sink. The absorbed NH.sub.3 /water 
solution is then pumped back to the generator to complete the cycle. 
The basic single-effect cycle has a low COP. It is not successful in 
applications where energy cost is an important consideration. 
Multiple-effect cycles are essentially arrangements of multiple 
single-effect cycles in such a way that heat couplings are provided 
between either the condenser of one single-effect cycle to the generator 
of another single effect cycle (condenser-coupled double-effect cycle) or 
the absorber of one single-effect cycle is heat coupled to the generator 
of another cycle (absorber coupled double-effect cycle) or both the 
condenser and the absorber of one single-effect cycle are heat coupled to 
the generator of another cycle (triple-effect cycle). 
Since the heat couplings in multiple-effect cycles are constrained by the 
tight matching of temperatures between the heat rejecting components (i.e. 
the condenser and absorber) and the heat receiving component (i.e. 
generator or boiler), a change in the heat sink temperature requires a 
readjustment of the temperature of the refrigerated medium or a 
readjustment of the temperature of the heat source. The latter is not 
always possible because the heat source is already at its highest 
temperature to achieve the highest COP possible. 
The undesirable cut-off characteristics of multiple-effect cycles narrows 
their applications to those where the temperatures of the heat sink and of 
the refrigerated medium are relatively constant, such as air-conditioning 
systems using water cooling towers as heat sinks. 
Under optimum operating conditions the COP of multiple-effect cycles can be 
60% (for double-effect cycles) or 85% (for triple-effect cycles) higher 
than that of the single-effect cycle. 
Regenerative-absorption cycles are those in which heat produced by the 
absorption of the low pressure refrigerant vapor back into the low 
pressure absorbing fluid is used to heat the fluid after it has been 
pumped up to high pressure. 
The generator-absorber heat exchange (GAX) can be considered as the 
simplest of the regenerative-absorption cycles. The GAX cycle is 
essentially a single-effect cycle in which internal heat regeneration (or 
recouperation) is attempted between the generator and absorber when 
temperature overlaps permit. The optimum COP of a GAX cycle is about the 
same as that of a double-effect cycle. 
In any externally heated heat engine, whether producing work or 
refrigeration, a working fluid is circulated between the heat source and 
the heat sink. The temperature of the working fluid should approach the 
temperature of the heat source during the heat input process and should 
approach the temperature of the heat sink during the heat rejection 
process. The better the temperature approaches, the higher the COP (or 
efficiency). 
Internal heat regeneration is necessary to obtain good temperature 
approaches. The working fluid travelling from the heat source to the heat 
sink must be cooled internally as much as possible before it reaches the 
heat sink. Conversely, the working fluid pumped up from the heat sink to 
the heat source must be heated by internal heat exchange as much as 
possible before the fluid reaches the heat source. 
In order to increase the COP of regenerative-absorption cycles, 
regenerative flow paths and loops must satisfy three criteria: 
(1) The amount of heat to be regenerated must be small to reduce the 
physical size of the regenerator and to minimize losses due to the 
difference in heat exchange temperatures; 
(2) The temperature approaches to the heat input and to the heat rejection 
processes must be close for high COP; 
(3) For commercial practicability, the number of pumps, their operating 
temperatures and their pumping rates must be minimized to reduce cost and 
increase reliability. 
U.S. Pat. No. 4,442,677 to K.W. Kauffman in 1984 discloses a variable 
effect absorption cycle that has internal regeneration, but the amount of 
heat regenerated is too large and the pumping rates are high. 
U.S. Pat. No. 4,921,515 to K. Dao in 1990 discloses an advanced 
regenerative-absorption cycle which can have a COP of the 130% higher than 
that of a single-effect cycle. However, this cycle does not satisfy the 
third criterion above, in that the circulation pump of the topping cycle 
is subjected to high temperatures and must operate at a high flow rate. 
The high temperatures could be avoided by subcooling the solution through 
the regenerator and pumping it back through the regenerator but doing so 
would increase the amount of heat needed to be regenerated and would 
degrade the COP. 
SUMMARY OF THE INVENTION 
It is the principal object of the present invention to provide an improved 
regenerative-absorption cycle that has a high COP and is commercially 
practicable. 
To achieve the foregoing and other objects, a regenerative-absorption cycle 
is provided having a multiple stage absorber for increasing the 
temperature approach to the heat sink and in which part of the solution 
from a lower-pressure externally-cooled absorber is pumped up to the 
liquid inlet of a higher-pressure externally-cooled absorber, in which 
another part of the solution from the lower pressure absorber is pumped up 
to a boiling conduit in the regenerator and heated so that a portion of 
the refrigerant in the solution is boiled off, with the boiled off 
refrigerant vapor being then introduced into the higher pressure absorber 
to be absorbed into the solution therein, thereby resulting in a cooled 
solution from the higher pressure absorber at the heat sink temperature 
and with a greater concentration of refrigerant than from the lower 
pressure absorber. 
Another aspect of the invention is that the higher concentration liquid 
from the higher-pressure absorber can be expanded and boiled to provide 
precooling of the high-pressure liquid refrigerant coming from the 
condenser and prior to its expansion into the evaporator of the cycle. 
A further aspect of the invention is the injection of solution that is 
relatively weak in refrigerant into the refrigerant vapor returning from 
the evaporator to the regenerator for absorption into the liquid absorbent 
flowing through the regenerator. The injected solution is boiled by heat 
from the regenerator and mixes with the refrigerant vapor to produce a 
vapor of higher concentration of absorbent vapor before being released 
from absorption in the regenerator. This injection essentially uses the 
low temperature heat readily available at the cold end of the regenerator 
to boil the injected fluid, with heat being transported in the form of 
absorbent vapor, to the hot end of the regenerator where heat is in short 
supply. 
Yet another aspect of the invention is that means are provided for the 
distributed release of vapor into the regenerator for absorption into the 
liquid absorbent over the length of the flow path of the absorbent through 
the regenerator such that at the hot end of the regenerator only a minimal 
amount of vapor is released into the absorbent liquid for absorption. The 
mixing of a small amount of vapor into the absorbent at the hot end of the 
regenerator will conserve the high temperature of the mixture that 
otherwise might be cooled down, by an introduction of a large amount of 
vapor, too much to be useful. 
Additional objects, advantages and novel features of the invention will be 
set forth in the description which follows, and in part will become 
apparent to those skilled in the art upon examination of the following, or 
may be learned by practice of the invention. The objects and advantages of 
the invention may be realized by the instrumentalities and combinations 
pointed out in the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein preferred embodiments are shown, and 
in particular to FIG. 1 wherein a first embodiment is shown, the 
multiple-stage-absorber regenerative-absorption cycle 10 includes a basic 
regenerative-absorption cycle comprising a high-pressure generator 11 
externally heated, as by a burner 12. The cycle preferably uses 
ammonia/water or ammonia/brine as the refrigerant-absorbent working fluid 
pair, but other refrigerant-absorbent fluid pairs may be used. The 
description below relates to the use of an ammonia/water pair. Although 
specific temperatures, pressures and concentrations are set forth, it is 
to be understood that these parameters are set forth merely to illustrate 
the operation and that the use of the invention is not limited thereto. It 
will be appreciated that different temperatures, pressure and 
concentrations would be expected for optimum results with different fluid 
pairs. 
The ammonia/water solution in the interior 13 of generator 11 is at a 
pressure of about 250 psig and will be heated to a temperature of about 
380.degree. F. to boil off ammonia and water vapors. These vapors pass out 
of the generator to the conduit 14 extending through the regenerator 16. 
The regenerator 16 comprises a heat exchanger with an external shell 17, a 
liquid inlet 18, a vapor inlet 19, and internal baffles 21 which form a 
plurality of serially-connected sections within the shell to channel fluid 
entering through the inlets in an elongated serpentine flow path through 
the interior of the shell to the liquid outlet 22. Liquid from the liquid 
outlet 23 of generator 11, at a concentration of about 5% NH.sub.3, passes 
through expansion valve 24, to reduce its pressure to about 70 psig, and 
enters the liquid inlet 18 of the regenerator. Ammonia and water vapors 
will enter the regenerator, as at vapor inlet 19, and the vapor will 
absorb into the liquid to release heat. The temperature in the regenerator 
will decrease in a downstream direction from the inlets to the outlet 22 
thereof. 
As the vapors from the generator pass through conduit 14 they will be 
cooled and rectified, with the condensate from the water vapor draining by 
gravity back into the generator. The vapor in conduit 14 leaving the 
regenerator 16 is about 100% NH.sub.3 and enters the inlet 26 of tube 27 
of condenser 28. As the ammonia vapor passes through the condenser, cool 
heat-sink water passing through shell 29 will cause the vapor to condense. 
The liquid ammonia leaving the condenser outlet 30 will flow through line 
31 to the expansion valve 32 where the pressure is reduced from 250 psig 
to about 70 psig. The low pressure fluid enters inlet 33 of the evaporator 
34 and the heat from the refrigerating fluid circulating through the 
evaporator shell 36 will cause the liquid ammonia to boil. As the ammonia 
boils it absorbs heat from the refrigerating fluid in the shell so that 
the fluid leaving the shell is colder than when it entered. The cooled 
refrigerating liquid is then used in the conventional cooling coils (now 
shown) of the cooling load 41, i.e. the space which is to be refrigerated 
by the cycle 10. The temperature of the fluid leaving the shell 36 will be 
in the order of 38.degree. F. 
The low-pressure ammonia vapor will now leave the outlet 42 of evaporator 
34 and pass through line 43 to the inlet 44 of the low-pressure conduit 46 
extending into regenerator 16, with the vapor then being injected into the 
low-pressure liquid coming down from the generator outlet 23 and expansion 
valve 24. 
The solution of ammonia and water leaving the outlet 22 of the regenerator 
16 will flow through line 47 to the liquid inlet 48 of tube 49 in the low 
pressure absorber 50. Although absorber 50 is shown as separate from 
condenser 28, they will preferably have the same shell 29, with the tubes 
27 and 49 being cooled by the same heat-sink fluid flowing through the 
shell 29. 
The cooled ammonia/water solution leaving the outlet 52 of absorber 50 is 
pumped by pump 53 to the high 250 psig pressure of the cycle and flows 
through line 54 to the inlet 56 of the high-pressure boiling conduit 57 
extending through regenerator 16. The outlet 58 of conduit 57 is in 
communication with the interior 13 of generator 11. As the ammonia/water 
solution passes through the conduit 57, it is heated by the absorption of 
the ammonia into the fluid circulating through the regenerator 16 and will 
boil, with vapors going off to conduit 14 and with the remaining liquid 
draining into the generator 11 for further heating. 
The PTX diagram, FIG. 1A shows the pressure, temperatures and NH.sub.3 
concentrations of the fluids at various points in the above described 
cycle. In this PTX diagram liquids are represented by solid lines, while 
vapors are shown by dotted lines. All liquid and vapor lines upstream of 
expansion valve 32 and in direct communication with the interior of 
generator 11 will be at the 250 psig high-pressure side of the cycle, 
while all liquid and vapor lines upstream of pump 53 and in direct 
communication with the interior of the regenerator 16 will be at the 70 
psig low-pressure side of the cycle. 
The present invention improves on the basic regenerative absorption cycle 
described above in a number of interdependent ways. 
First of all, multiple-stage absorption is provided to increase the heating 
of the working fluid prior to the time it reaches the externally-heated 
generator 11. As shown in FIG. 1, a single intermediate-pressure absorber 
60 may be used for this purpose, absorber 60 having a tube 61 with liquid 
and vapor inlets 62 and 63 and an outlet 64, the tube 61 extending through 
the same shell 29 as absorber 50 and condenser 28 for cooling by the 
heat-sink fluid circulating through the shell. 
Part of the liquid pumped by pump 53 from the low-pressure absorber 50 is 
pumped through line 66 to the inlet 62 of the intermediate-pressure 
absorber 60 and part is pumped through line 67 to the inlet 68 of the 
intermediate-pressure boiling conduit 69. Heat from the regenerator first 
sensibly heats the liquid solution, and then causes it to boil, with the 
vapors passing into conduit 71 for cooling and rectification. The 
condensed water drains back into the hottest part of the conduit 69 while 
the ammonia vapor leaves conduit 71 and goes to the vapor inlet 63 of the 
absorber 60. 
As absorber tube 61 is cooled, the ammonia vapor will reabsorb into the 
solution so that the solution leaving outlet 64 will have a greater 
ammonia concentration than that leaving absorber 50. This richer solution 
is then pumped by pump 73 through line 74 to another 250 psig high-pumped 
pressure boiling conduit 76. As the solution passes through this conduit 
it too will be heated and will boil. The vapors mingle with those coming 
from generator 11 and pass to conduit 14 for cooling and rectification 
while the remaining solution drains into the generator 11 for further 
heating. 
The solution remaining in the intermediate-pressure conduit 69 will flow 
into the conduit 77 and be cooled therein as it goes towards pump 78. 
From there, the relatively low concentration solution is pumped up through 
line 79 to the inlet of yet another high-pressure boiling conduit 81. As 
with conduit 57 and 76, conduit 81 has its outlet in communication with 
conduits 14 and the interior of generator 11 so that vapor boiled off in 
conduit 81 will go to conduit 14 while the remaining solution goes to the 
generator 11. 
Flow restrictors 82, 83 and 84 are provided in lines 54, 66 and 67 to set 
the distribution of flow from pump 53. Typically, the flows through 
restrictors 82, 83 and 84 will be 35%, 20% and 45% of the liquid from the 
low-pressure absorber 50. 
A further aspect of the invention is that the rich solution from the 
absorber 60 is used to precool the high-pressure liquid ammonia in line 31 
from the condenser 28 so as to minimize undesirable flashing of the liquid 
as its pressure is reduced by expansion valve 32. For this purpose, the 
high-pressure liquid ammonia passes through tube 86 of precooler 87, while 
the low-pressure ammonia vapor from evaporator 34 passes through the shell 
88 of the precooler. Part of the solution from outlet 64 of the 
intermediate-pressure absorber 60, rich in ammonia, goes through line 91 
and conduit 92 in the precooler to expansion valve 93 for pressure 
reduction. The expanded liquid exits at 94 into the interior of shell 88 
and is heated by the liquid refrigerant in tube 86 to boil and absorb heat 
from the refrigerant in tube 86. The ammonia and water vapors from the 
boiling and the remaining solution will mix with the ammonia vapor from 
evaporator 34 and will pass through line 43 to the low-pressure conduit 
46. 
Another aspect of the invention is that a portion of the ammonia/water 
solution flowing through the regenerator 16 is recirculated back to the 
generator 11 to increase the amount of refrigerant vapor produced by the 
generator. For this purpose, pump 96 pumps liquid from a desired point 97 
along the flow path through the regenerator and through line 98 to a 
suitable high pressure point in communication with the interior of 
generator 11, such as tube 99 projecting into high-pressure boiling 
conduit 81. 
Further aspects of the invention are that the ammonia vapors coming from 
the evaporator 34 and the precooler 87 are injected into the liquid within 
the regenerator 16 at a number of points along the flow path of the liquid 
and that the ammonia concentration of the injected vapors are matched to 
the ammonia concentration of the solution into which the vapors are 
injected. 
This is accomplished by providing conduit 46 with orifices 101, 102 and 
103, which together with outlet 19 allows vapor 46 to be injected into 
each section of regenerator 16. 
Ideally, the absorption of vapor into the liquid within regenerator 16 
should be counterflow, with the liquid becoming gradually richer in 
refrigerant, while the vapor should become gradually richer in water 
vapor. Also, the flow rate of the liquid should gradually larger while the 
flow rate of the vapor become smaller. Such counterflow would best be 
achieved by using gravity to induce the liquid flow. However, since 
gravity is preferably used in the cycle to provide the counterflow 
rectification and mass transfer in the conduits 14, 57, 76, 81 and 69, 
then counterflow of the liquid and vapor in the regenerator must be best 
approximated by disposing the low-pressure conduit 46 in the bottom of the 
regenerator shell and letting the vapor bubble upwardly into the liquid as 
it travels through its up-and-down serpentine path. The orifices 101 102, 
103 and 19 are sized so that the rate of injection into the liquid 
decreases towards the downstream end of conduit 46. 
To provide for concentration matching, liquid of relatively low refrigerant 
concentration is injected through tube 106 into the upstream end of 
conduit 46, with the amount of injection being about 10% of the mass flow 
rate into conduit 46. The injected liquid boils in conduit 46 to produce a 
vapor that is rich in water, so that through orifice 101 is richer in 
refrigerant than the vapor at orifice 102, which in turn is richer in 
refrigerant than that of orifice 103. The vapors at orifices 103 and 19 
are superheated and have the same concentration. If any excess liquid in 
conduit 46 remains, it is stopped at collecting ring 107 and drains 
through orifice 108 into the shell of the regenerator. For best COP, the 
amount of liquid injected into conduit 46 should be such that there is a 
minimal excess flow from orifice 108. With the abovedescribed injection, 
the COP can be increased by as much as 10%. 
The fluid injected into conduit 46 can come from any source within the cold 
side of the regenerator. Preferably, it is picked up from the outlet of 
conduit 77 and expanded to low pressure by valve 109. However, if the 
liquid in line 43 from the precooler is sufficient, it may not be 
necessary to inject liquid through line 106. 
In addition, vapor at the upstream end of conduit 46, wherein the ammonia 
concentration is highest, is injected through line 111 into the vapor 
inlet 112 of the absorber 29. Flow restrictor 113 maintains a slightly 
higher pressure in conduit 46 as compared to the pressure at the outlet 22 
of the regenerator 16. The vapor injected into absorber 50 is absorbed by 
the solution coming from the regenerator to increase its concentration of 
refrigerant. 
The primary heat produced in the regenerator for boiling the fluids in 
conduits 57, 76, 81, 69 and 46 comes from the absorption of the ammonia 
vapors into the liquid coming down from the generator 11. However, the 
rectifications in conduit 14 and 71 and the sensible cooling of the liquid 
is conduit 77 also contributes to the heating of the other conduits. 
The fluids flowing though pumps 53 and 73 are cooled by absorber 50 and 60 
to about 110.degree. F., while the fluid flowing through pump 78 is at 
about the low-side temperature of the regenerator 16, i.e. about 
150.degree. F. As a consequence, high-temperature pumps are not needed in 
this cycle, thus reducing both the cost of the initial installation and 
the subsequent maintenance of the pumps 
FIGS. 2 and 2A are schematic and PTX diagrams of another preferred 
embodiment using only a single pump 53. The operation of the cycle is 
substantially the same as previously described in connection with FIGS. 1 
and IA except that the following components of FIG. 1 are not used: pumps 
73 and 78, lines 74 and 79, and boiling conduits 76 and 81. Also, it may 
be necessary to dump some of the liquid from conduit 77 through flow 
restrictor 121 and line 122 into line 47 to avoid excessive flow of liquid 
through tube 106 into conduit 46 and out through orifice 108. 
Although recirculation pump 96 is not shown in FIG. 2, such a pump may be 
used in this cycle, if desired, to pump a portion of the fluid flowing 
through the regenerator 16 from a selected point along the flow path back 
to the interior of generator 11. The same is true in connection with the 
cycles of FIGS. 3 and 4. 
FIGS. 3 and 3A are schematic and PTX diagrams of another preferred 
embodiment also using three pumps as in the cycle of FIG. 1, but with the 
addition of a second intermediate-pressure absorber stage 130 to produce a 
solution having a higher NH.sub.3 concentration. 
This embodiment again operates substantially as described in connection 
with FIG. 1 except that the output of pump 73 is now split into three 
streams, with one stream going through line 74 to the high-pressure 
boiling conduit, another stream going through line 131 to the liquid inlet 
132 of the tube 133 extending through the shell 29 of absorber 130, and 
the other stream going through line 134 to the inlet 136 of the second 
intermediate-pressure boiling conduit 137. Flow restrictors 141, 142 and 
143 are sized to provide proper distribution of the flow from pump 73 to 
line 74, 131 and 134. The working pressure of the second 
intermediate-pressure conduit 137 and absorber 130 is higher than that of 
the intermediate-pressure conduit 69 and absorber 60 but less than that of 
the high-pressure portion of the cycle. 
As before, the solution entering boiling conduit 137 will first be heated 
and then boil, with the vapors going through conduit 144 for cooling and 
rectification. The ammonia vapor will then go through line 146 to the 
vapor inlet 147 of the absorber tube 133. In the absorber 130, again 
cooled by the same heat-sink fluid as the other absorbers, the ammonia 
vapor will absorb into the liquid therein to produce a solution of higher 
NH.sub.3 concentration than that produced by absorber 50 or 60. In this 
embodiment, line 91 from the conduit 92 in precooler 87 is connected to 
the outlet of absorber 130, rather than the to the outlet of absorber 60, 
so that a fluid richer in refrigerant will be sent to the precooler. This 
richer fluid will boil more readily in the shell of the precooler 87 and 
will cool the liquid ammonia in precooler conduit 86 to a greater degree. 
Such cooling further decreases the tendency of the liquid ammonia to flash 
as it goes through expansion valve 32. 
The remaining liquid in boiling conduit 137 which flows into conduit 148 
for cooling may be expanded to any convenient location. Preferably, it is 
expanded through valve 149 and conveyed by line 151 to the liquid inlet of 
the first intermediate-pressure absorber 60. 
For best COP, the length that the boiling conduit 137 extends into 
regenerator 16 is such that the concentration of the liquid leaving 
conduit 148 matches that of the liquid going to absorber 60 from absorber 
50. Generally, the length of conduit 137 is less than that of conduit 69 
for this to occur. 
FIGS. 4 and 4A are schematic and PTX diagrams of yet another preferred 
embodiment. This cycle is essentially an extension of the cycle of FIG. 3 
and uses five pumps. Pump 160 pumps part of the liquid output of absorber 
130 through line 161 to the high-pressure boiling conduit 162. Instead of 
being expanded down to the inlet of absorber 60, the liquid output of the 
second intermediate-pressure conduit 148 is now pumped up by pump 163 
through line 164 to another high-pressure boiling conduit 165. Conduits 
162 and 165, like the other high-pressure boiling conduits 57, 76 and 81, 
have outlets in communication with the interior of generator 11. 
In this embodiment the extension of the second intermediate-pressure 
boiling conduit 137 into the regenerator matches that of the first 
intermediate-pressure boiling conduit 69. 
In order to reduce costs, pump 163 and high-pressure boiling conduit 165 
may be eliminated, with the liquid output of conduit 148 being expanded 
down through expansion valve 166 (shown in dotted lines in FIG. 4) to 
merge with the liquid coming from conduit 77 so that both liquids can be 
pumped by pump 78. However, this mixing of two liquids of different 
concentrations may result in a loss of COP that may not justify the 
elimination of pump 163 and its associated elements. To minimize this loss 
of COP, the relative lengths of conduits 137 and 69 may be optimized for 
better concentration matching between the liquids. An example of such 
optimization would be to extend the length of conduit 137 deeper into the 
regenerator 16 until the concentration of the liquid in conduit 148 
matches that in conduit 77. The length of conduit 69 should be extended to 
the location where the liquid starts boiling in the high-pressure boiling 
conduit 57, that is to the intersection of the line of constant 
concentration of the fluid pumped up through line 54 and the line of 
constant condenser pressure (i.e. 250 psig) as shown in the PTX diagram 
FIG. 4A. 
One important aspect of the design of the regenerator 16, common to all 
embodiments, is the proper sizing of the heat transfer areas of the 
various conduits to achieve proper temperature matching of all boiling 
streams, especially the boiling stream in conduit 69. The temperature of 
liquid at a location where the conduit 69 ends should match the 
temperature where the liquid starts boiling in the high-pressure conduit 
57. Such location, for typical space cooling applications, is about a 
little more than half the length of the regenerator 16 because the total 
amount of heat transferred between the conduits and the shell side of the 
regenerator up to the end of conduit 69 is about a little more than the 
total amount of heat transferred in the rest of the regenerator, assuming 
that the heat transfer areas between conduits and the shell side are 
uniformly distributed along the length of the regenerator and assuming 
that the heat transfer coefficients are constant. 
The CO of the cycles shown in FIGS. 1 and 2 depends on the size of the 
regenerator. With the heat-sink fluid adequate for cooling the condenser 
28 and absorbers 50 and 60 to a temperature of 110.degree. F. and an 
evaporator temperature of 38.degree. F., and a 100% heat exchange 
effectiveness in the regenerator, the COP are 1.51 and 1.25 for the cycles 
of FIGS. 1 and 2, respectively. By comparison, the COP for the prior art 
GAX cycle is 1.08.With optimum heat transfer regenerator area, the COP are 
1.33, 1.17 and 1.03 for the cycles of FIGS. 1 and 2 and the GAX cycle. 
Various modifications of the cycles described above may be made. 
For example, the cycles have been specifically described in connection with 
refrigeration systems, i.e. where the work performed by the high pressure 
vapor is the cooling of load 41. However, the high pressure vapor could 
also be used to drive a turbine, by the substitution of a turbine for the 
condenser 28, expansion valve 32 and evaporator 34. In either case, the 
condenser-valve-evaporator system or a turbine would constitute means 
connected between and reducing the pressure from the vapor outlet of the 
generator 11 and a vapor inlet 101, 102, 103 or 19 of the regenerator 16. 
Also, in FIGS. 1-4, the liquid pumped up to the liquid inlet of the 
intermediate boiling tube 69 has been shown as pumped up from the outlet 
52 of the low-pressure absorber stage 50 by pump 53. 
This is the preferred point in the low-pressure side of the cycle, i.e. 
upstream of pump 53 because the liquid at that point has the highest 
concentration of ammonia in the low-pressure side of the cycle. However, 
the liquid going to the intermediate-pressure boiling conduit 69 could be 
taken from another point in the low-pressure side, such as from line 47 to 
the absorber 50 or from a point within the shell of the regenerator 16, as 
long as the liquid at the selected point has a concentration high enough 
to produce the desired amount of ammonia, when boiled in conduit 69, for 
absorption into the liquid flowing through the intermediate-pressure 
absorber stage 60. If a point is selected other than at the outlet of the 
low-pressure absorber stage 50, then another pump would be required to 
pump the low-pressure liquid up to the pressure of the 
intermediate-pressure boiling conduit 69. 
The foregoing description of the preferred embodiments have been presented 
for the purposes of illustration and description. It is not intended to be 
exhaustive or to limit the invention to the precise features described, 
and obviously many other modifications and variations are possible in 
light of the above teaching. The embodiments were shown in order to 
explain most clearly the principles of the invention and the practical 
applications thereby to enable others in the art to utilize most 
effectively the invention in various other modifications as may be suited 
to the particular use contemplated. It is intended that the scope of the 
invention be defined by the claimed appended thereto.