DE2058161A1 - Cooling unit, consisting of an absorption cooling device and a secondary system connected to it for heat transfer - Google Patents

Description

Dipl.-Ing. W. Beyer Dipl.-Wirtsch, -Ing. B. Jochem

6 Frankfurt am Main Freiherr-vom-Stein-Strasse

In matters:

Aktiebolaget Electrolux
Lux baking 1
Stockholm / Sweden

I Cooling unit, consisting of an absorption chiller and a secondary system connected to it in a thermally conductive manner.

The invention relates to a Γ cooling unit, consisting of a with a carrying auxiliary gas operated Absorbtionskälteapat and a closed one with evaporation and condensation Secondary refrigerant system. , its capacitor is thermally connected to the evaporator of the Absorbtionskälteapparats and its evaporator as a cooler of a cooling or The freezer compartment

With absorption refrigerators that use an inert auxiliary gas work, the arrangement of the individual parts of the vaporizer system depends on several conditions, which it to the designer make it difficult to design the evaporator in all respects and to arrange it in such a way as it is desirable in a particular case would be »For example, the evaporator must be so much below the Condenser lie that the refrigerant condensate occurring in the latter can flow freely into the evaporator, depending only on the hydrostatic difference. That’s why it has to be a sufficient height difference between these two parts be available because when the device is commissioned, the in Condensate formed, specifically light condensate capable must be the specifically heavier absorption solution that

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is still in the condensate line on this occasion, to displace. In addition, the evaporator must be designed in such a way that no liquid locks can form prevents the circulation of the auxiliary gas carried. Simultaneously the diameter of the evaporator tube must also be chosen to be relatively large, so that too great a pressure drop in the gas circuit is avoided. However, the diameter of the evaporator tube has an impact on the design options

of the pipes to be bent, because the smallest possible radius of the Pipe bends depends on the pipe diameter. Ultimately, the evaporator must therefore be as far above the absorber as possible be arranged so that there is a sufficiently strong flow in the gas circulation system.

Inxdem a closed secondary system with the absorption chiller is connected in a thermally conductive manner, it is possible to a certain extent to avoid the restrictions mentioned in the free choice of design and bypassing the arrangement of the evaporator. Such secondary systems have been known for a long time. You either work with a heat-transferring liquid which, as a result of convection, circulates within the various parts of the secondary system, or with a liquid refrigerant, which is used in the Part is evaporated and then condensed again by the evaporator of the absorption refrigeration apparatus.

In the evaporator of an absorption refrigeration device, refrigerant evaporates, and the refrigerant vapor mixes with a circulating auxiliary gas flow. As evaporation continues, the partial pressure of the refrigerant in the gas flow increases and thus also the evaporation temperature. As the temperature rises, so too does the amount to be evaporated per unit of time Refrigerant corresponding to the saturation curve for pressure and temperature of the refrigerant larger. The nature of that saturation curve is the same for all refrigerants.

For the reason mentioned, there is between the temperature characteristics of the evaporator of the absorption refrigeration apparatus and that of the condenser of the secondary system a Diskrepanä; j that not again

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Reversible heat transfers and losses result Has. If a non-evaporating liquid is circulating, which generally has a constant specific heat, these are

Losses a little less than in the case of a secondary system that involves evaporation and condensation of a refrigerant uniform temperature works. However, because the adaptability and heat transfer capacity in the latter Systems are considerably better and larger, this becomes the first mentioned circulating fluid system in general preferred.

The losses that occur in the previously known refrigeration units, which consist of an absorption chiller and a secondary system working with evaporation and condensation are, however

because
considerable, / the achieved uniform cooling temperature of the secondary system can only correspond to the highest ("warmest") temperature in the evaporator of the absorption chiller. So if it is desired to operate the secondary system at a very low temperature, the absorption chiller must be given a cooling effect which achieves even lower temperatures than the desired one. It is clear that such a mode of operation of the absorption refrigeration apparatus leads to a relatively high energy consumption and a comparatively low efficiency of the entire system. For this reason, the combined system described was only used when the operating temperature range of the Absqrbtionskälteapparates was only small under all circumstances, such as in freezers and freezers.

It is the object of the present invention in a refrigeration unit of the type mentioned to train the secondary system so that the mentioned losses can be avoided.

The above object is achieved according to the invention in that the The refrigerant of the secondary system is a mixture of liquids, which is within the temperature limits of the evaporator of the absorption chiller evaporated and / or condensed at different temperatures.

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The invention also extends the area of application of the refrigerator chambers or others to be cooled by means of a secondary system Cooling devices or systems expanded, indqm for example refrigerators with thermally insulated chambers of different temperatures can be operated. It is also possible to have several separate, preferably small, refrigerators to cool a single absorption chiller and one or more secondary systems. The success achieved is based on the fact that Using a mixture of two refrigerants results in a satisfactory match between the temperature characteristics of the evaporator of the absorption cold apparatus and that of the condenser of the secondary system can be achieved. The evaporation characteristics of the refrigerant mixture in the secondary system, consisting for example from two different refrigerants, initially depends on the components of the mixture itself, then the mixture proportions, thirdly from the operating pressure and fourthly from the ratio the amount of liquid circulating in the secondary system the amount of refrigerant vapor formed therein. This ratio in turn depends on the load on the secondary system as well as its flow resistance, which is essentially a function of the cross section. The circulation of the liquid in the secondary system comes about due to the steam formed in it. As the number of possible combinations of different refrigerants practically unlimited int, the invention is not limited on any special components. The possible mixes can initially be selected approximately theoretically if the thermodynamic properties of the components under consideration are known well enough, for example in the form of enthalpy-mixture diagrams are present. In such a case, a certain composition of the mixture will be the first approximation and the operating temperature. The evaporation characteristics thus obtained are then, preferably graphically, with the corresponding Characteristics of the evaporator of the absorption cold apparatus compared. Then the values initially assumed adjusted until a satisfactory match is obtained. As an example of one that may be eligible Mixture of "Freon 12" and "Freon 13" with un-

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J) O weight percent of the latter component mentioned.

The invention is described below with reference to exemplary embodiments shown in the drawing of the proposed here The principle of working cooling units is described. Show it:

Pig. 1 a refrigerator with a secondary system that works with is connected to the evaporator of an absorption chiller in a thermally conductive manner,

Pig. 2 another refrigerator, the same: kind of parts like Pig's. 1, but has a different structure,

Pig. 3 the temperature curve of an evaporator of an absorption refrigeration apparatus in comparison with the temperature curve of the condenser of a secondary system operated according to the invention.

In Fig. 1, a refrigerator is indicated with dash-dotted lines, the two chambers 1o and 11, which are thermally insulated from one another. The upper chamber 1o is a freezer while the lower chamber 11 forms a cooling compartment. Thermal energy is generated from these two chambers via a secondary system described below withdrawn and transported to an evaporator 12 of an absorption refrigeration apparatus, which can be designed in a conventional manner can, so that the representation of its other components has been omitted.

The upper end of the evaporator 12 of the absorption refrigeration apparatus is supplied via a line 13 with liquid refrigerant, and this condensate flows in countercurrent to an auxiliary gas flow, which is introduced at the lower end 14, through the evaporator 12. No heat supply through the secondary system evaporates refrigerant during such a whole flow through the evaporator 12, whereby the inert auxiliary gas is saturated with refrigerant vapor, which gas mixture then the evaporator 12 at its upper end

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15. Leaves via a connection line. The lowest temperature there is at the lower end 14 of the evaporator 12. Towards the upper endo 15, where the highest temperature prevails, is a continuous one - Determine temperature rise. The temperature of the The evaporator tube is therefore stable from the lower to the upper end greater.

The secondary system, which works with evaporation and condensation, is closed after it has been evacuated and then a suitable mixture of liquid refrigerants has been filled. The liquid level in a vertical pipe 1? outside of the chambers 1o and 11 of the refrigerator is then at a level 16. A condenser 18 of the secondary system is connected to the evaporator 12 of the absorption refrigeration apparatus in a thermally conductive manner, by, for example, as in l ^? ig. 1 and 2, these two parts consist of parallel tubes that are thermally connected by welding. On the secondary system side, refrigerant vapor is supplied to the upper end of the condenser 18. The condensation is set so that the refrigerant mixture is then liquefied at the lower end of the condenser 18. In the condenser, those constituents of the refrigerant vapor which have a high boiling temperature, or at least mainly such constituents, are first condensed, and the condensation of the constituents of the vapor mixture with low boiling temperature then progresses in increasing amounts to the lower end of the evaporator. The liquid refrigerant flows from the condenser 18 into the lower toilet of the low-temperature pre-evaporator 19. The heat contained in oi ngolog lon üogennlitimlon precedes actual evaporation in the evaporator part 19. Vapor bubbles arise which rise in the evaporator and convey condensate through the evaporator into the standpipe 17. For this purpose, the evaporator tube 19 has only a relatively small inner diameter. The refrigerant vapor separates from the refrigerant liquid in the standpipe 17. The steam flows through a steam line 2o to the condenser 18, while

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the liquid through the standpipe 1? into an evaporator 21 of the secondary system for a higher operating temperature. This evaporator 21 is installed in the cooling chamber 11, and

it also finds a flow in it as a result of the formation of gas bubbles of the liquid-vapor mixture in the upward direction. The evaporator 21 opens into the standpipe 17 at the upper end above the level of the liquid 16. As above. The description makes it clear, is divided into this .Execution example the secondary system in two flow circuits, which have part of the system in common.

Because the pressure in the entire secondary system is the same and the the liquid Kälteiitbännsiiurig supplied to the evaporator 19 operating at a lower temperature ■ more constituents with lower Contains boiling temperature than the liquid Kaitmittelmischurig fed to the evaporator 21, turns itself into completely automatically the higher located evaporator 19 a lower temperature than in'dem lower located evaporator 21. On both evaporators 19 and 21 are each the lowest at the bottom Recorded evaporation temperature. It rises over the length the vaporizer increases continuously upwards. This is not a disadvantage, but one of the reasons that the System as a whole can work with a very high degree of efficiency.

It goes without saying that FIG. 1 is only a very schematic representation, which is only intended to show very generally how the newly proposed cooling unit can be constructed. Each of the two evaporators present in this case protrudes into a thermally insulated space of the refrigerator. If desired, means for increasing the surface area can additionally be attached to the evaporators. However, it is also possible to connect either both or only one evaporator in a thermally conductive manner to an inner wall made of a suitable metal of the respective refrigerator compartment. The evaporators can also be arranged on the outside of the inner wall of the refrigerator rooms within the thermal insulation surrounding them, whereby they are connected to the inner walls in a thermally conductive manner. Although in the drawings P 1.87 / ^ 111970 ¹⁰⁹⁸² * ^{/ 1183}

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Figures is not shown that outer parts of the system are provided with thermal insulation, so this goes without saying in the present case by itself, both the standpipe sf ^ be-k as well as the line 2o and the "through the evaporator of the Abrorbtionskälteapparates and the condenser, the secondary systems formed heat exchangers are with a thermal insulation to include. It is clear, however, that a designer has great freedom in the design and arrangement of the exterior Has parts of the secondary system.

In Fig. 2 is another embodiment of the invention shown in which the secondary system consists of a single self-contained circuit. In contrast to FIG. 1, where the freezer compartment 1o is arranged above the refrigerator compartment 11 in the embodiment according to FIG. 2, a freezer compartment 22 below a cooling compartment 23. The evaporator 12 of the absorption refrigeration apparatus can be designed in the same way as in FIG. 1 and also has the same function. In the condenser 18 of the secondary system condensed refrigerant mixture flows down into a standpipe 24, where the liquid level is at level 25. from there is condensate in the lower part of a low temperature evaporator 26, where the components of the refrigerant geminches, which have a low boiling point evaporate. The gas bubbles formed in the process carry condensate with them upwards into an evaporator part 271 which is operated at a higher temperature and which is installed in the cooling compartment 23. There he sits down Evaporation process continues, for the most part the mixture components evaporate at a higher boiling temperature. The vapor mixture is passed through line 28 to the top of the condenser 18 returned. The secondary system can also be simpler Way are designed so that the refrigerant vapor exerts a pumping effect on the liquid, which this at least partially drives into the capacitor 18.

In Fig. 3 temperature curves are shown with which indicated should be, which the ideal conditions for the dom evaporator 12 and the condenser 18 existing heat exchanger are. The solid curve illustrates

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that over the length L of the pre-steamer 12 from its lower end 14- evaporation temperature applied up to its upper end 15. The upper, dashed curve shows the condensation temperature in the capacitor 18, also plotted over the length L, for expression. To achieve a good level of efficiency To obtain, it is necessary that at each point of the heat exchanger a certain C temperature difference between the evaporator 12 and capacitor 18 are, as shown by, a spacing of the two curves in FIG. 3 is shown. Certain smaller or larger deviations in parallelism of the two curves that affect the choice of the components of the refrigerant mixture and the pressure conditions in the absorption refrigeration unit and the secondary system can be accepted in practice. Even if not the one drawn The ideal state is achieved, are cooling units, their secondary system with a refrigerant mixture selected as suitable are operated, clearly superior to previously known designs.

Expectations

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Claims (7)

Expectations Cooling unit consisting of a carrying auxiliary gas operated absorption chiller and a closed one with evaporation and condensation of a refrigerant working secondary system, its capacitor is thermally connected to the evaporator of the absorption chiller and its evaporator as a cooler of a cooling or Used freezer compartment, characterized in that the refrigerant of the secondary system (17 to 21 or 18, 24 to 28) is a mixture of liquids which is within the temperature limits of the Evaporator (12) of the absorption refrigerator evaporates and / or condenses at different temperatures. 2. Cooling unit according to claim 1, characterized in that that the condenser (18) of the secondary system with respect to the flow path of the refrigerant has a temperature characteristic which is approximately equal to that of the evaporator (12) of the absorption cold apparatus is. 3. Cooling unit according to claim 1 or 2, characterized in that that the evaporator (19> 21) or (26, 27) of the secondary system with parts of different Temperature in mutually thermally insulated refrigerator or freezer rooms (1o, 11) or (22, 23) is installed. 4. Cooling unit according to claim 3> characterized in that the secondary system (18, 24 to 28) consists of a single flow circuit, the evaporator (26, 27) both in a lower freezer compartment (22) and in an upper cooling compartment (23) installed. El P 1487 / 11/24/197g 9824/1183 BATH ₀ R, G, NAt 5. Cooling unit according to claim 3, characterized ο i c h η et that the secondary system (17 "to 21) is made there are two interconnected circuits, one of which leads to a freezer compartment (1o) and dor other is led to a cooling room (11). 6. Cooling unit according to one or more of the preceding claims, characterized in that that the evaporator (19, 21, 26, 27) of the secondary system at least partially thermally conductive connected to an inner wall of a refrigerator or freezer room (1o, 11, 22, 23) is. 7. Cooling unit according to one or more of the preceding claims, characterized in that that the heat-conducting connection between the evaporator (12) of the absorption chiller and the condenser (18) of the secondary system along a two-channel pipe one channel to the circuit of the absorption chiller and its other channel to the circuit of the secondary system heard. El P 1487 / 11/24/1970 109824/1183