US3820356A - Absorption refrigeration plant with auxiliary gas - Google Patents

Abstract

A refrigeration or cooling plant based on the absorption principle using auxiliary gas. The auxiliary gas circulating system in the vaporizer and heat exchanger sections of the plant, is subdivided into two or more circulating lines. An upward and downward directed channel is provided for each circulating line and serves as tbe driving means for moving flow through the lines. The driving means and inflow lines to the circulating lines provide for uniform distribution of the flow through the circulating lines. Hydrogen is used for the auxiliary gas in the cooling plant.

Description

United States Patent [191 Stierlin ABSORPTION-REFRIGERATION PLANT WITH AUXILIARY GAS Hans Stierlin, Rainweg 15,, 8952 Schlieren, Switzerland Filed: May 1, 1972 Appl. No.: 251,536

Inventor:

Foreign Application Priority Data May 7, 1971 Switzerland 6878/71 References Cited UNITED STATES PATENTS 11/1928 Munters 62/490 X 7/1936 Sa'rnmark 62/492 3/1939 Nelson 62/110 8/l942 Thomas 62/333 X Raw-was" [111 3,820,356 [451 June '28, 1974 FOREIGN PATENTS OR APPLICATIONS 520,953 5/1940 Great Britain. 62/492 752,285 7/1956 Great Britain..... 62/492 Primary Examiner-William F. ODea Assistant Examiner-Peter D. Ferguson 7 Attorney, Agent, or Firm-Michael S. Striker [5 7] ABSTRACT channel is provided for each circulating line and serves as the driving means for moving flow through the lines. The driving means and inflow lines to the circulating lines provide for uniform distribution of the flow through the circulating lines. Hydrogen is used for the auxiliary gas in the cooling plant.

9 Claims, 10 Drawing Figures PATENIEnJum IB 31820356 sum 20H -52 v v v m y zutvkwwkiwfi SUB. 0Q H om 7 v. .ow J 3. v om 5 M N .o o3 fifz o8 0% 4 Q2 PATENTEnJuazs 1m 3820 356 SHEET 5 UF- 7 PATENTEDJUH 28 m4 'SHEEI 7 or 7' Fig.10

ABSORPTION-REFRIGERATION PLANT WITH AUXILIARY GAS BACKGROUND OF THE INVENTION The present invention relates to an absorption refrigeration plant or apparatus using auxiliary gas, particularly, H

The absorption system with auxiliary gas is adapted well for two-temperature refrigerators, since the cooI- ing power is produced on the sliding temperature. With a relatively little amount of circulating auxiliary gas, the cooling requirements at low and intermediate temperatures can be met in'a simple manner. The problem becomes difficult, however, when the entire cooling power is used to produce solely a very low temperature, as is required, for example, in low temperature cooling units or plants. Such units may also be referred to as deep freeze units or plants. The required hydrogen circulation is then increased enormously, and the drive for the auxiliary gas that is available becomes, thereby, only a fraction of the previous values. As a result, substantially unsolvable problems arise in the conventional art, between the rising and downward moving auxiliary gas in the heat exchanger.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an arrangement which avoids the conventional problems in the heat exchange between rising and downward moving auxiliary gas in absorption refrigeration apparatus.

It is also an object of the present invention to provide an arrangement of the foregoing character which may be economically fabricated and readily maintained.

A further object of the present invention is to provide an arrangement asset forth whichmay be easily installed and simply operated.

The objects of the present invention are achieved by providing that the auxiliary gas circulation within the vaporization and heat exchanging section is distributed among two or more circulatory systems. Preferably, there is provided a number of individual circulating systems, each having in particular a rising and downward directed channel, and an individual drive for moving the fluid medium. Means is, furthermore, provided for applying the distribution uniformly among the circulating systems.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic drawing of the circulating sys tem of a refrigeration unit for a two-temperature refrigerator;

FIG. 2 is a combined graphical representation of the vaporization temperature of NI-I or the NI-I concentration in deficient auxiliary gas H as a function of the vaporized NI-I quantity, or the required theoretical power;

FIG. 3 is a graphical representation of heat transfer as a function of the auxiliary gas quantity for different embodiments of heat exchangers, with respect to theory and actual practice;

FIG. 4 is a schematic drawing of the circulating system of a cooling plant with exclusive low temperature vaporization; 1

FIG. 5 is a partial sectional view taken along line 5-5 in FIG. 4;

FIG. 6 is a schematic diagram of a further embodiment of a heat exchanger in a circulating system which is analogous to that shown in FIG. 4, with a seriesfiowing NI-I from the liquefier;

FIG. 7 is a schematic diagram analogous to that shown in FIG. 6, in which parallel streams of distributed NH emerge from the liquefier;

FIG. 8 is a schematic diagram of the upper portion 0 a heat exchanger with individual NI-I connection from the liquefier;

FIG. 9 is a schematic diagram and shows in perspective a section of the upper portion of a heat exchanger without upper covering; and

FIG. 10 is a schematic diagram analogous to that of FIG. 4, and shows a partial section of a low temperature refrigerator, in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, FIG. 1 shows the circulation system or fiow system of a two temperatureabsorption refrigerator in schematic form. This flow system has a vaporizer or generator 1 connected to a liquefier tube or condenser 2, a low temperature vaporizer 3 within the so-called low temperature compartment or freezer compartment of a refrigerator, a vaporizer 4 which is followed by a gas heat exchanger 5, and NH absorber 6, and an accumulator or reservoir 7. As may be seen from the diagram of FIG. 1, the cooling liquid or refrigerant returns again to the vaporizer or generator 1. The heat exchanger 5 has a line or channel 8 through which cooling mans from the liquefier is passed to the vaporizer 4. The heat exchanger 5, furthermore, has channels 10 and 12. The channel or flow line 10 has a deficiency of cooling medium, whereas the channel or flow line 12 is enriched with cooling medium in the form of a gas. The fiow line with NH from the liquefier 2 is designated by the reference numeral 14. In this region 14, the NI-I is vaporized in the carrier gas which is normally hydrogen. FIG. 1 further shows that a temperature of minus 30 may be attained in the deep freezer compartment with the low temperature vaporizer 3, whereas the temperature within the refrigerator is maintainted at 5, as determined by the vaporizer 4. I

The circulation of the gas within the flow lines 10 and 12 is due to the difierence of the specific weights of the rising and falling gases, multiplied by the height H. Since only minimal temperature differences. prevail in the gas heat exchanger 5, these specific weight differences arise exclusively from the different ammonia content of the two gas columns in the flow lines 10 and 12. The vaporization of the NI-I from the liquefier commences, thereby, in the inflow region 14.

For purposes of simplification, it is possible to assume that the NH concentration, poor, within the rising or upward stream U within the flow line 10 is substantially constant for corresponding dimensions of the absorber 6 and the remaining parts of the cooling plant. Thus,

X poor "NH /Nl-l l "H e.g., 0.25 25 percent) (G weight) The larger quantity or content of NH;, from the flow line 8 to the downward directed column D in the flow line 12, depends upon the amount or quantity of ammonia which is evaporated in the Vaporizers 3, 4 from the gas volume or quantity which is circulated. This is called charging of the gas. The larger such charging, the larger is the specific weight difference within the flow lines or channels 10 and 12, and as a result, the driving characteristics of the system are larger for a given H.

With such charging of the gas stream with NH the partial pressure of the ammonia rises, and this also increases correspondingly the vaporization temperature at which the cooling medium is evaporated. This vaporization temperature in the system plays animportant part for the NFL, charging and the resulting system drive. Corresponding to the vaporization temperature, there is also for a predetermined total pressure, a predetermined concentration, x rich, of the enriched gases, i.e., the NI-I quantity within H or The drive or circulation obtained through the difference in specific weights and height H (the height differ ence between absorption and evaporation points), op-

poses the pressure loss Ap of the fluid flow through the piping system. From these two parameters is obtained the quantity of gas circulated per unit of time. The actual pressure loss Ap must, thereby, taken into account for the prevailing substance characteristics and circulating velocities. For practical usage, it is advantageous to replace this effective pressure loss through a normalized pressure loss, Ap Norm, which may be readily measured. Thus, such a normallized pressure drop may be obtained, for example, through the pressure drop which prevails upon moving or blowing 100 liters of air per hour under normal pressure and temperature. Consequently,

m. Ap/ /100 1m, air

If two geometrically different plants (having no losses) are to be maintained thermally equal, then the same amount of gas is to be circulated, whereby only H and Ap come into consideration. An important parameter may be derived from this in the form of (I-I/Ap) driving height (m)/Norm-pressure loss With the aid of further computations, it is possible to obtain from these considerations, a set of curves shown in FIG. 2. These curves show the ideal vaporization-end temperature attainable as a function of the amount of ammonia vaporized per hour for different I-I/Ap. Aside from this, the specific volume of gas circulated is also to be noted, since this is important for further consideration. Finally, the the heat transfer KF for the heat exchanger 3, 4, are also indicated. These give a loss of approximately percent of the cooling power through the heat exchanger, and therefore the heat transfer curves will coincide with the curves indicating the ratio H/AP.

FIG. 2 illustrates the following example through broken lines: Let 250 grams NH, become vaporized between the theoretical temperatures of 37 and 9. The end vaporization temperature is, for example, 9 in the refrigerator vaporizer 4. It is desired to find the relationship for the driving height. The pressure loss is I-I/Al p, the eridconcentration'of the enrichdgases is k rich, and the circulating quantity of auxiliary gas H per unit of weight of NH and the heat exchange quantity for the heat exchanger is kF E. The solution to the problem is given by the two lines a and b. The intersection of these two lines lies on the curve H/Ap= 0.5. The desired apparatus can. for example, be 1 meter in height, and can have a total pressure loss Ap of 2mm water column in the hydrogen flow line. The apparatus can also be only 0.2 meter in height, whereby the pressure loss is then reduced to 0.4 mm. x rich becomes thereby 58 percent. 0.7 X 250 ltr H /h flow thereby, and the gas heat exchanger has a kF of 8 Kcal/m /h/ C.

From the curves of FIG. 2,, it is possible to see the difficulties of the problem For each 45 watts of cooling power and for each 5 At from the theoretical end vaporization temperature to the effective average refrigerator temperature at a height of H 0.4m, and neglecting the Ap of the vaporizer and absorber which can be maintained small if necessary, the following applies:

2 Temp. Refrigerator Deep Freezer Reference point R "NH kg/h 0.l5 0.l5 H/Ap 0.125 2.0 kF kcal/L/m /C 2 32 ApNorm 3.2 0.2

Thus, for a deep freezer the problem is to develop a heat transfer is 16 times greater with a pressure loss 16 times smaller.

It is possible to see from the foregoing, the enormous difficulties. In practice, however, the difficulties are even larger than expected. This may be seen from FIG. 3. A larger number of measurements were taken on dif ferent gas streams in the heat exchanger. In particular, this was applied to hydrogen under 20 atmospheres of pressure and variable quantity. It was pointed out, thereby, that the pressure loss is variable for similar variations in dimensions. As a result,

where d is channel diameter.

The heat transfer kF is substantially independent of the diameter d of the pipe line or channel. Results obtained from computational methods known in the art differ from results obtained experimentally in practice, the more complex, the construction of the heat exchanger. This is applicable for highly laminar streams. In particular, for small volume rates, the measured results are only fractions of what one would expect from computation. The basis for this appears to be from the condition that so-called dead-water zones prevail which do not take part any longer in the heat exchange. Furthermore, non-uniform mass distribution prevails in parallel streams, which are very disadvantageous from the view point of heat balancing.

In FIG. 3 the measured values of kF per 1 m of heat exchanger length areindicated, and these are representative for different constructions. In the heat exchanger construction of embodiment I there are two parallel running pipelines which are lengthwise connected through welded seams. These pipelines are denoted by A,, A In the embodiment or construction II, one pipeline lies concentrically within the other. In the construction III additional heat exchanging surfaces and the formation of channels to further subdividing, are provided. For the construction IV, there is a heat exchanger in which 52 parallel pipes are bundled within an exterior or covering pipe. When V 60 ltr./h flow rate, the values for the construction I to IV are very similar, even though the theoretical values in IV are, for example, at least times higher. With increasing flow rate, the measured parameters approach theoretical results. However, the deviations of III and IV are considerably large in the practically used regions (V ltr/h). Only the clear simple flow in accordance with the embodiment or construction I, is applicable over the entire region. In embodiment II at least the upper portion of the expected results are applicable. Further, studies are required to establish the phenomena for these results.

FIG. 4 shows schematically a plant or apparatus which differs from that of FIG. 1, in that parallel flow streams 22 prevail in the evaporation and heat exchanger 18 and vaporizer 20. As a result, the pressure loss Ap of these component parts are substantially very small, and a larger volume of circulated fluid results. One should, therefore, also be able to expect a corresponding larger refrigeration power or cooling power at lower temperatures. (I-l/Ap large, kF large for FIG. 2).

In conventional constructions of heat exchangers (not shown), practical measurements provide poor results where the rising flow streams are directed upward to a common space from which downward directed streams initiate.

The vaporizing power as well as the heat transfer are disapointing. The latter attains only somewhat thevalue of the embodiment of IV in FIG. 3. The reason for this is that the non-uniformities in construction and in the passages lead to non-uniform mass or flow distribution over the cross section. The non-uniform vaporization at the capillary layer causes a non-uniform charging of the individual streams within the channels, so that driving differences follow the paths of least resistance. These driving differences result again in velocity and mass differences in the cross section.

The preceding conditions may be improved when the construction in accordance with FIG. 4 is carried out with the channel construction as shown. This is because the vaporizer is led upward through individual channels 22, and through the adjacently line pairs of channels or flowlines A, A B, B C, C which are each connected through an opening 23, or through radial steps 28 which connects them in groups and through tangential separating webs or elements 30. Cross communication of, for example, the channel A, with channel B, or of channel A with channel B are practically no longer possible for H, or H NI-I even though the entire interior surface of the outer wall 26 is uniformly covered with the NH,, film.

For each pair of channels, thereby, there is a mass balance since channel A can receive flow only from that which has risen in channel A, (increased by the amount of vaporized Nl-I Each channel 22 is, moreover, associated with its own charging apparatus or drive. This charging drive is substantially constant in each channel in view of the horizontal temperature compensation within the entire heat exchanger for each channel. Through a large number of parallel channels 22, a quantity of gas may be transported under uniform conditions. In this arrangement, all of the parallel channel 22 transports flow equally.

It is not simple to measure the kF values of such a system. Measurements resulting from the passage of H,, as previously carried out, provide unsatisfactory results. Although the mass balance per pair of channels prevails, there is no uniform distribution of flow through the individual pairs of channels. Only through the construction of complete plants or apparatus, and through temperature measurements in conjunction with that, the sought after kF values may be obtained.

Also this is not very simple, since in accordance with ammonia cooling the entire heat balance of the gas heat exchanger is positive, negative or correct. Furthermore, post vaporization can occur and the flow lengths under high temperature differences can be considerably disadvantageous from the view point of weight. All of this must be taken into account.

In FIG. 4 a secondary system is shown which has a covering 24 in which a secondary cooling medium is inserted from below and removed in the cold state from above. This covering permits application of a cooling effect at any location independent of the location of the primary refrigeration.

The measured results applicable to construction V for 22 parallel pipes and VI for 52 parallel pipes, are indicated in FIG. 3. With this graphical representation, the embodiments VI and IV can be compared, since each has 52 parallel channels. The embodiment VI has 50 times the value of embodiment I, for the entire region which may be expected theoretically. The construction IV has 4 V 60 ltr./h only about 3 percent, and 4 V 250 ltr./h only about 25 percent of the expected theoretical value.

Such a heat exchanger is self regulating:

If the gas deficiency in the rising channel is small, relatively more NH is vaporized.

The density difierence between enriched gas and deficient gas, and thereby between the drive and the driven sucked deficient gas, rises. If this quantity is too large in onechannel, then the pair of channels regulate themselves to smaller channel flow.

From the values of FIG. 3 and the flow volumes of FIG. '3, the following data is obtained:

I TABLn i it Two-temp. refrigerator: Refrigerating power=45 watt=0.15 kg.NH;/h,

H/Ap=0.125;Ap=3.2ZV=60;kF'=2 Construction I II III IV V VI kF./m 1.6 5. 0 12 20 as 83 Required measurement, m 20 6. 4 2. 7 1. 6 0.9 0. 4 7 Approx. diam. for Ap=0.2, mm 45 47 66 82 82 Approx. net volume, liter 32 11 9 8. 5 4. 8 3.2

1 GHE =gas heat; exchanger.

From the preceeding representation, it may be seen that the foregoing construction of gas heat exchangers for a two-temperature refrigerator presents few difficulties. Depending upon the requirement, one can select one of the constructions (I), (II) or (III).

It is entirely different when dealing with low temperature plants. The constructions I-IV cannot be considered in view of the required lengths and diameters, regardless of price. This is the reason that no genuine absorption deep freezer or low temperature units were built in the past. A new way must obviously be found.

In FIG. 2, let 150 gr NH be vaporized at 23. This also permits, for example, a multiplicity of individual apparatus or plants of other H/Ap, as for example through 2 X 75 gr with H/Ap l and kF 16 4 X 37.5 gr with H/Ap 0.5 and kF 8 16 X 9.4 gr with H/Ap= 0.125 and kF 2 This last case is indicated through point F of the diagrams of FIGS. 2 and 3. The individual plant corresponds now to the refrigerating plant and is easily constructed. The price of such apparatus consisting of sixteen individual refrigerating plants or apparatus, becomes prohibitively high. This path can hardly be taken. I 1

It is, however, not necessary to duplicate'all parts of the plant or apparatus. What is necessary, however, is that order must be created within the gas heat exchanger. This is made possible through a construction as shown in the embodiment of FIG. 4, for example.

A further embodiment for a heat exchanger is possible through the construction of FIG. 6. This heat exchanger 35 has three double pipes 37, 38 and 39. These double pipes are connected to an accumulating pipe 41, into which gas deficient in NH, flows from the absorber. From this accumulating pipe 41, the three inner pipes of the double pipes 37, 38 and 39 have flow applied to them as shown in FIG. 6. The ends of these inner pipes communicate or terminate in the outer pipes closed at the top. In this manner, the rising cooling medium in the form of deficient gascoming from the absorber, is deflected in the direction of the arrow, and is directed into the accumulating pipe 43. In the first double pipe 37, communicates or connects a line 45 for the inflow of NH from the liquefier' (not shown) in the upper reversing chamber of a double pipe. As a' result, the deficient gas rising through the center pipe vaporizes a portion of the on coming cooling medium. The deficient gas becomes thereby cooled and is directed downward in the direction of the arrow as a result of its greater attained specific weight. The NH;, not vaporized in the first double pipe or line 37, reaches the next double pipe 38 through. a connecting line 47, where the entire process is repeated. A further NH connecting line 48 leads from the upper part of the double pipe 38, to the third double pipe 39, in which the outer part of the remainder of the NIL, fluid is vaporized. Thus, the entire system is arranged so that the process can be carried out in this manner.

FIG. 7 shows a construction similar to that of FIG. 6, in which however the distribution of the Nl-I liquid from the liquefier 2, is made substantially uniform among the three double pipes 37, 38 and 39 with the aid of the inflow pipelines 45, 51 and 52. It is then possible to omit the connecting lines 47 and 48, and the cooling line is always regularly distributed among the three double pipes.

AEfibh 6? a further embodiment of a heat exchanger, is shown in FIGS. 8 and 9.-In this embodiment, an exterior wall 54 with an inflow line 55 for NH from the liquefier 2 is provided. An inner wall 56 as well as a separating wall 57 are also provided. In the separating wall 57 at the upper end, is an inner channel 60 and an outer channel 62, each of which is provided with an opening 59.

As may be seen from FIG. 9, the outer wall 54 is in the form of a planar wall upon which is welded a sepa rating wall 65, as well as an outer wall 66. The arrangement is such that the inner channel 60 and the outer channel 62 are formed thereby. The opening 59 is also visible in this Figure.

FIG. 10 shows schematically the circulating system of a refrigerating plant with exclusive low temperature vaporization, with a partial section for a low temperature refrigerator. The cooling plant is equipped with a heat exchanger which corresponds basically to the construction of FIGS. 9 and 8. It follows therefrom that the heat exchanger construction does not only meet the prevailing requirements, but also allows for an economical fabrication. The heat'exchanger, furthermore, has its front side adapted for a low temperature refrigerator 63. In FIG. 10, the rear wall 64 and the upper portion as well as the door 65 are shown in section, of this low temperature refrigerator 63. The heat exchanger forms a part of the rear wall-and the upper portion.

The advance in the state of the art resulting from the heat exchanger in accordance with the present invention, is very considerable and opens the construction to a genuine mechanical absorption low temperature unit without movable parts.

Such vaporizer-gas heat exchanger systems can, as may be seen, constructed in the form of four different embodiments. The basic guide line, thereby, however is that the parallel pairs of channels are well separated from each other from the view points of vaporization and heat exchange. Furthermore, each channel is provided with its own drive.

Genuine household low temperature units constructed in accordance with the absorption principle using auxiliary gas,- could not be constructed until now. This is due to the condition that the required gas heat exchangers with corresponding power capacity has not been available. Through extensive investigation and the application of new principles, in accordance with the present invention, this problem has been solved, and the present invention makes it possible to construct units of such type.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of refrigeration apparatus differing from the types described above.

While the invention has been illustrated and described as embodied in a refrigeration apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from of said generator; a vapor conduit connecting said generator to said condenser for feeding refrigerant vapor produced in said generator into said condenser; an evaporator and heat exchanger connected to said condenser for evaporating the condensate received from said condenser; a reservoir adapted to be filled up to a predetermined level with a rich solution; an absorber communicating at one end with said reservoir above the level of liquid therein and at the other end with said evaporator; and two conduits, one extending between said absorber and said generator and the other between pairs of closely adjacent passages are formed by three upright concentric cylindrical walls spaced in radial direction from each other and a plurality of radially extending webs separating adjacent pairs of passages from each other.

4. A combination as defined in claim 1, wherein each pair of passages comprises an outer tube and an inner said reservoir and said generator, said evaporator and heat exchanger comprising aplurality of pairs of separate and distinct passages extending inclined to the horizontal, each pair of passages communicatingonly at the upper end with each other and having at least one common wall one of the passages of each pair communicating at the lower end with said reservoir and the other with said absorber, each of said pair of passages receiving at the upper end condensate from said condenser which evaporates in said evaporator so that fluid medium rises through said other passage and flows downwardly in said one passage of each 'pair of passages.

2. A combination as defined in claim 1, wherein said pairs of passages are arranged closely adjacent to each other in circumferential direction.

3. A combination as defined in claim 2, wherein said tube communicating at its upper end with saidouter tube, said inner tube being connected at its lower end to said absorber and said outer tube being connected at its lower end to said reservoir.

5. A combination as defined in claim 4, wherein each pair of passages is directly connected at its upper end with said condenser so that said pairs of passages are connected in parallel.

6. A combination as defined in claim 4, wherein only one of said plurality of pairs of passages is directly connected at the upper end thereof with said condenser and including additional passages leading from a portion of said outer tube of said one pair of passages downstream of the upper end thereof to the upper end of the adjacent pair of passages, and from a portion of said outer tube of said adjacent pair of passages downstream of the upper end thereof to theupper end of the next adjacent pair of passages to thus connect said pairs of passages in series with each other.

7. Acombination as defined in claim 1,-wherein said pairs of passages are arranged closely adjacent each other and are formed by a pair of corrugated metal sheetshaving corrugations of different height extend-. 'ing in the direction of said passages, with the corrugations of smaller height projecting into the corrugations of larger height, and a third-planar sheet metal closing the open side of the corrugations of smaller height. I

8. A combination as defined in claim 1, and including a secondary system surrounding the upper part of said pairsof passages of said evaporator.

9. A combination as defined in claim 1, wherein said auxiliaryygas is hydrogen.

Claims (9)

1. In an absorption refrigeration system with auxiliary gas, a combination comprising a generator producing from a rich solution fed into said generator a refrigerant vapor and a poor solution; a condenser downstream of said generator; a vapor conduit connecting said generator to said condenser for feeding refrigerant vapor produced in said generator into said condenser; an evaporator and heat exchanger connected to said condenser for evaporating the condensate received from said condenser; a reservoir adapted to be filled up to a predetermined level with a rich solution; an absorber communicating at one end with said reservoir above the level of liquid therein and at the other end with said evaporator; and two conduits, one extending between said absorber and said generator and the other between said reservoir and said generator, said evaporator and heat exchanger comprising a plurality of pairs of separate and distinct passages extending inclined to the horizontal, each pair of passages communicating only at the upper end with each other and having at least one common wall one of the passages of each pair communicating at the lower end with said reservoir and the other with said absorber, each of said pair of passages receiving at the upper end condensate from said condenser which evaporates in said evaporator so that fluid medium rises through said other passage and flows downwardly in said one passage of each pair of passages.

2. A combination as defined in claim 1, wherein said pairs of passages are arranged closely adjacent to each other in circumferential direction.

3. A combination as defined in claim 2, wherein said pairs of closely adjacent passages are formed by three upright concentric cylindrical walls spaced in radial direction from each other and a plurality of radially extending webs separating adjacent pairs of passages from each other.

4. A combination as defined in claim 1, wherein each pair of passages comprises an outer tube and an inner tube communicating at its upper end with said outer tube, said inner tube being connected at its lower end to said absorber and said outer tube being connected at its lower end to said reservoir.

5. A combination as defined in claim 4, wherein each pair of passages is directly connected at its upper end with said condenser so that said pairs of passages are connected in parallel.

6. A combination as defined in claim 4, wherein only one of said plurality of pairs of passages is directly connected at the upper end thereof with said condenser and including additional passages leading from a portion of said outer tube of said one pair of passages downstream of the upper end thereof to the upper end of the adjacent pair of passages, and from a portion of said outer tube of said adjacent pair of passages downstream of the upper end thereof to the upper end of the next adjacent pair of passages to thus connect said pairs of passages in series with each other.

7. A combination as defined in claim 1, wherein said pairs of passages are arranged closely adjacent each other and are formed by a pair of corrugated metal sheets having corrugations of different height extending in the direction of said passages, with the corrugations of smaller height projecting into the corrugations of larger height, and a third planar sheet metal closing the open side of the corrugations of smaller height.

8. A combination as defined in claim 1, and including a secondary system surrounding the upper part of said pairs of passages of said evaporator.

9. A combination as defined in claim 1, wherein said auxiliary gas is hydrogen.

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