Method and apparatus for the absorption-cooling of a fluid

The invention relates to an apparatus for the absorption cooling of a fluid, in particular air. Two separate mutually independent but interacting absorption cooling devices are provided, the cooling system of one of the two devices being used for cooling the absorbent liquid of the other device, this liquid, after dilution, by the fact of having absorbed steam, being boiled by heat provided by condensing steam resulting from boiling the diluted absorbent liquid of the initially considered absorption device by means of an external burner. The pressure in each component of the absorption device used for directly cooling the air is less than the pressure in the corresponding component of the other device, the absorbent liquid of which is cooled by external cooling fluid. The two devices are provided with heat exchangers cooled with air, such heat exchangers being serially arranged so that the same airflow passes therethrough.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an and apparatus for the 
absorption-cooling of a fluid, in particular air. 
2. Discussion of the Background 
Air cooling, commonly known as air conditioning, is achieved by two 
different systems. 
A first system, widely used for air conditioning in buildings and vehicles, 
uses compressors operating with chlorofluorocarbons and driven by electric 
motors or vehicle engines. 
A second system, known as an absorption system, operating normally with 
saline solutions, is applied in practice only to very large buildings 
because although it consumes very little electric power it requires large 
cooling towers to disperse the heat produced. 
Traditional air conditioners of the compressor type consume considerable 
power, this being very important when used in vehicles. In addition, air 
conditioners of this type are very dependent in operation on the engine 
r.p.m. when installed in motor vehicles. 
It should also be noted that the use of chlorofluorocarbons constitutes a 
serious source of ecological damage, as is now well known throughout the 
world. 
Air conditioning machines of absorption type have many undoubted advantages 
over air conditioners of compressor type, both in terms of electrical 
power consumption, which is very low, and in ecological terms as the 
saline solutions generally used cause no damage if lost to the environment 
external to the apparatus. 
However, absorption air conditioners produce a very large heat quantity to 
be dispersed, this quantity being double that of compressor air 
conditioners of equal capacity. This heat has to be at least partly 
dispersed from an aqueous saline solution, generally of lithium bromide, 
having a temperature of about 42.degree. C., to produce very cold water at 
about 4.degree. C., usable for cooling the air to be conditioned. This 
temperature of 42.degree. C., which is very close to the temperature 
reached during the summer months in many countries, including those of 
temperate climate, is often less than the temperature reached in hot or 
equatorial countries. Thus in no way can the external air be used as a 
cooling medium, and in fact currently known absorption air conditioners 
comprise cooling water circuits for the saline solution, this water then 
being cooled in evaporative cooling towers, making it impossible to apply 
the system to vehicles or small users. 
As is well known to the expert of the art, the saline solution temperature 
of 42.degree. C. is strictly related to the vapor pressure of the very 
cold water and to the solution concentration. An increase in this 
temperature could only be achieved by increasing the salt concentration in 
the solution, but in practice this is not possible under normal working 
conditions because the salt concentration in the water is already very 
close to the crystallization curve, and the formation of crystals within 
the solution circulation circuits is obviously to be totally avoided. 
SUMMARY OF THE INVENTION 
The main object of the present invention is to provide an apparatus for 
absorption air conditioning, which is of low electricity consumption, can 
be cooled directly by the external air, is of small overall size in 
relation to the installed refrigeration power and can hence be easily 
applied to air conditioners both in motor vehicles and in closed 
environments. 
An absorption apparatus for cooling a fluid, in particular air, comprising 
two separate absorption cooling devices, each having a mutually 
communicating evaporator and absorber and a generator, in which a pressure 
substantially less than atmospheric is maintained in the evaporator and in 
the absorber, water being present in the evaporator, from which it is 
withdrawn to be returned to the evaporator after passing through a heat 
exchanger in which the water absorbs heat, a steam absorbent liquid being 
present in the absorber, from which it is withdrawn to be returned to the 
absorber after at least partly passing into said generator in which the 
pressure is higher than that in the corresponding evaporator and absorber 
and in which a heating member is provided to boil said absorbent liquid, 
with the formation of steam which is withdrawn and then condensed in a 
steam condensing heat exchanger after which it is returned to said 
evaporator, and with the formation of a concentrated absorbent liquid 
which is returned to the absorber after passing through a heat exchanger 
in which it transfers heat to the absorbent liquid from the absorber, in 
the absorber there being provided a heat exchanger for cooling the 
absorbent liquid, wherein said water heat exchanger of the first device is 
the heat exchanger through which the air to be cooled passes, whereas in 
the second device it constitutes the heat exchanger for cooling the 
absorbent liquid of the first device, the heat exchanger for cooling the 
absorbent liquid of the second device being a heat exchanger which 
transfers heat to a fluid external to the two devices, the heating member 
for the absorbent liquid in the generator of the first device being the 
heat exchanger for condensing the steam from the generator of the second 
device whereas in the generator of the second device it consists of a 
burner, and the pressure and hence the temperature in the evaporator and 
absorber of the first device being less than those in the corresponding 
components of the second device, characterized in that the heat exchanger 
for cooling the absorbent liquid of the second device is in series with 
the steam condensing heat exchanger of the first device, in that said two 
heat exchangers are cooled with air which is first forced through the heat 
exchanger of the second device and thereafter through the heat exchanger 
of the first device, and in that the pressures and temperatures in the two 
generators are of such value that the saturation temperature of the steam 
in the heat exchanger of the first device enables condensation of such 
steam by the air cooling such exchanger. 
Advantageously, the method and apparatus of the present invention are used 
for the simultaneous generation of heat which can be used to heat water 
usable directly or indirectly. This characteristic enables the apparatus 
to be considered as a true high efficiency heat pump. 
The method and the structure and characteristics of the apparatus according 
to the present invention will be more apparent from the description of a 
simplified embodiment given hereinafter by way of non-limiting example 
with reference to the accompanying drawing, in which the single figure is 
a schematic representation of an apparatus for the absorption cooling of 
air.

The two absorption devices are each of well known conventional structure 
and operation and will therefore not be described in detail, the following 
explanation being sufficient for their understanding. 
The two devices each comprise an evaporator 1, 1A and an absorber 2, 2A 
communicating with each other (and in which a pressure substantially lower 
than atmospheric is maintained), and a generator 3, 3A. 
Water is present in the evaporators 1, 1A and is withdrawn to be returned 
to the top of the evaporators after passing through a line 4, 4A, a pump 
P, a heat exchanger 5, 5A in which the water absorbs heat (i.e. transfers 
cold to the external environment), and a line 6, 6A. 
A liquid (preferably an aqueous solution of lithium bromide) for absorbing 
the steam generated in the adjacent evaporator is present in the absorbers 
2, 2A, this liquid being withdrawn through a line 7, 7A to be recycled to 
the top of the absorber though a recycle line 8, 8A provided with a pump 
P. Part of the liquid withdrawn from each absorber is fed via a line 9, 
9A, a pump P and a heat exchanger 10, 10A to the generator 3, 3A in which 
the pressure is higher than that in the corresponding evaporator and 
absorber. 
The liquid present in the generator is brought to boiling by a heating 
member 11, 11A. In this manner steam is formed, and is withdrawn from the 
top of the generator, passed through a line 12, 12A and then through a 
condensing heat exchanger 13, 11 in which the steam condenses to be then 
returned to the respective evaporator 1, 1A via a return line 14, 14A 
comprising a liquid-vapor separation device 15, 15A of known type. A heat 
exchanger 19 is included in the line 14A to further reduce the liquid 
temperature. 
It should be noted that reference numeral 11 indicates a component acting 
as a heating member for the absorbent liquid present in the generator 3 
while simultaneously acting as a cooling and condensing member for the 
superheated steam from the generator 3A. 
Whereas the absorbent liquid present in the generator 3 of the first device 
is heated and boiled by the member 11 forming part of the cooling and 
condensation circuit of the second device, the liquid present in the 
generator 3A is heated and boiled by the flame of a fuel burner 11A, 
generally using a gaseous fuel. 
The concentrated absorbent liquid obtained in each generator 3, 3A is 
returned to the respective absorber 2, 2A after passing through said heat 
exchanger 10, 10A (in which it transfers heat to the dilute absorbent 
liquid from the absorber) and through a return line 16, 16A which opens 
upstream of the pump P connected into the line 8, 8A. As can be seen from 
the drawing, a liquid-vapor separation device 17, 17A of known type is 
also included in the line 16, 16A. 
The liquid present in each absorber 2, 2A is cooled by a cooling heat 
exchanger. In the case of the absorber 2, the cooling heat exchanger is 
the actually already mentioned heat exchanger 5A forming part of the 
second absorption cooling device and also acting as a heat exchanger in 
which the water of the second device absorbs heat. In the case of the 
absorber 2A the heat exchanger for cooling the dilute absorbent liquid 
present in the absorber is indicated by the reference numeral 20 and forms 
part of a cooling circuit comprising a radiator or heat exchanger 21, 
which is independent of the two absorption cooling devices and transfers 
heat to the external environment. 
It can therefore be seen that the heat exchanger 5 of the first device in 
which the very cold water from the evaporator 1 absorbs heat is in 
practice the heat exchanger through which the air used for cooling the 
interior of a vehicle or a building passes, whereas the heat exchanger 5A 
of the second device in which the very cold water from the evaporator 1A 
absorbs heat operates as a heat exchanger for cooling the dilute absorbent 
liquid present in the absorber 2 of the first device (the heat exchanger 
for cooling the dilute absorbent liquid of the second device being the 
heat exchanger 21 which transfers heat to a fluid, generally air, external 
to the two devices). 
It can also be seen that the heating member 11 for the absorbent liquid in 
the generator 3 of the first device is in practice the heat exchanger for 
cooling and condensing the steam from the generator 3A of the second 
device, whereas in the generator 3A the heating member is a burner, in 
particular a gas burner. The superheated steam from the generator 3 is 
condensed by passing it through the heat exchanger 13 positioned upstream 
of the separation device 15. 
In all cases the pressure and consequently the temperature in each 
constituent component of the first device are always less than the 
pressure and temperature in the corresponding component of the second 
device. 
Preferably the hot water originating from the generator 3A via the line 14A 
is cooled in a cooling heat exchanger 19 connected to the line 6A. 
It will be assumed for example that very cold water at an inlet temperature 
of 4.degree. C. is required at the heat exchanger 5 for cooling the air. 
In this case the pressure in the evaporator 1 and in the absorber 2 must 
be the saturation pressure of water at this temperature. Any liquid able 
to absorb steam can be used as the absorbent liquid, for example an 
aqueous solution of lithium bromide with a concentration variable between 
about 65% by weight and 62% by weight. 
The heat water which is returned to the evaporator 1 partly evaporates on 
absorbing heat. The absorbent liquid which is returned to the absorber 2 
at a temperature of about 50.degree. C. absorbs heat in absorbing the 
steam, with the result that the dilute absorbent liquid present in the 
bottom of the evaporator must be cooled to a temperature of about 
42.degree. C. by the heat exchanger 5A. The liquid taken from the bottom 
of the absorber 2 is fed into the generator 3, which is at a pressure of 
about 1 ata and a temperature of about 160.degree. C., the steam present 
in it having a saturation temperature of 100.degree. C. (and hence easily 
coolable with air at ambient temperature, even in equatorial regions). 
The liquid from the generator 3 is cooled in the heat exchanger 10 to be 
fed to the line 7 at a temperature of about 60.degree. C. 
The superheated steam from the generator 3 is condensed and cooled in the 
heat exchanger 13 to be fed to the line 6 at a temperature of about 
45.degree. C. 
The heat exchanger 5A, through which water circulates at a temperature of 
about 35.degree. C., is used to cool the dilute absorbent liquid present 
in the absorber 2. The pressure in the evaporator 1A and absorber 2A is 
that corresponding to the water saturation pressure at the stated 
temperature. 
The absorbent liquid in the second device can have the same concentration 
as in the first device, the temperature of the liquid in the absorber 2A 
being about 80.degree. C. entering and 72.degree. C. leaving. This liquid 
is easily cooled with atmospheric air by means of the radiator 21, even in 
equatorial regions. 
In the generator 3A the temperature is about 230.degree. C. and the 
pressure about 7.5 ata, the saturation temperature of the steam present 
being 168.degree. C. and hence being able to heat the generator 3. If the 
saturation temperature of the steam produced in the generator 3A is not 
sufficiently high (in relation to the heat transfer area of the heating 
member 11) to concentrate the liquid in the generator 3, the burner 11A 
automatically raises this temperature to the optimum value. Consequently, 
temperature and pressure control in the two generators 3, 3A is automatic, 
depending on the cooling conditions in the condensing heat exchanger 13. 
This latter can be controlled to maintain constant pressure in the 
generator 3 to avoid the risk of the absorbent liquid crystallizing in the 
cooler parts of the apparatus. 
The heat exchanger 19 further cools the return liquid from the member 11 to 
about 45.degree. C., to further improve the system efficiency. 
The absorber of the first device shown schematically on the accompanying 
drawing is cooled by the heat exchanger 5A. This presupposes a transfer of 
sensible heat and hence a temperature difference between the cooling fluid 
entering and leaving said heat exchanger. In the apparatus according to 
the present invention, the cooling fluid is under saturation conditions 
and therefore absorbs heat by evaporation, the steam produced being 
absorbed directly by the absorber 2A of the second device. 
It should be noted that in the described apparatus, the heat exchanger 13 
is in series with the heat exchanger 21. Steam with a condensation 
temperature of 100.degree. C. is condensed in the heat exchanger 13, 
whereas in the heat exchanger 21 a liquid is cooled from an inlet 
temperature of 80.degree. C. to an outlet temperature of 72.degree. C. 
This enables a reduced quantity of cooling fluid to be used, and if air is 
used as the cooling fluid its throughput will be only about 50% of that 
required for a conventional compressor refrigeration unit. 
It is important to note that the apparatus of the present invention can 
function as a heat pump. In this respect, heat is developed in the 
absorber 2A, in the condensing heat exchanger 13 and in the heat exchanger 
19 at a minimum temperature of 72.degree. C. The total heat produced 
(which can be dispersed with water by suitably arranging the apparatus) is 
represented by the sum of two sources of heat, the first being the burner 
11A and the second being the heat transferred from a fluid external to the 
two devices by the heat exchanger 5. 
Consequently for a heat quantity X provided by the burner 11A, the 
apparatus is able to provide a heat quantity of X multiplied by the 
overall efficiency of the apparatus, which is variable depending on the 
operating conditions but is generally not less than 60%.