EP0190319A1

EP0190319A1 - Refrigerator or heat pump and jet pump therefor.

Info

Publication number: EP0190319A1
Application number: EP85904230A
Authority: EP
Inventors: Michael Laumen
Original assignee: Individual
Current assignee: M LAUMEN THERMOTECHNIK GmbH
Priority date: 1984-08-24
Filing date: 1985-08-23
Publication date: 1986-08-13
Also published as: DE3570915D1; WO1986001582A1; EP0190319B1; JPS62500045A; US4748826A; DE3431240A1

Abstract

Machine frigorifique ou pompe à chaleur avec pompe à jet (1) en tant que compresseur, où l'évaporateur du circuit de la machine frigorifique ou de la pompe à chaleur est incorporé dans la pompe à jet (1). Dans le cas le plus simple, ceci est obtenu en montant dans la conduite d'admission une paroi (18, 39, 40, 41) constituée en un matériau poreux, par exemple du métal fritté, et qui exerce une action de régulation entre la pression du condenseur et la pression d'évaporation et sur la grande surface interne de laquelle a lieu l'évaporation simultanée du milieu de travail. L'alimentation en chaleur d'évaporation résulte du fait que seule une partie du milieu de travail liquide arrivant du condenseur (3) est évaporée, et que d'autre part de la chaleur peut être alimentée de l'extérieur via des échangeurs de chaleur (21, 27). Des circuits de machine frigorifique ou de pompe à chaleur ayant une pompe à jet de ce type (1, 24, 30) peuvent également être conçus avec plusieurs étages de sorte qu'un échange de chaleur interne peut s'effectuer de plusieurs manières. Les compresseurs à jet (1) utilisés peuvent également inclure des pompes à jet avec une multitude de buses (31, 32, 33, 34) situées les unes derrière les autres et formant une multitude d'étages de pompes à jet connectées en série.Refrigerating machine or heat pump with jet pump (1) as compressor, where the evaporator of the refrigerating machine or heat pump circuit is incorporated in the jet pump (1). In the simplest case, this is obtained by mounting in the inlet pipe a wall (18, 39, 40, 41) made of a porous material, for example sintered metal, and which exerts a regulating action between the condenser pressure and evaporation pressure and on the large internal surface of which the simultaneous evaporation of the working environment takes place. The evaporative heat supply results from the fact that only a part of the liquid working medium arriving from the condenser (3) is evaporated, and on the other hand heat can be supplied from the outside via heat exchangers (21, 27). Refrigeration machine or heat pump circuits having such a jet pump (1, 24, 30) can also be designed with several stages so that internal heat exchange can take place in several ways. The jet compressors (1) used can also include jet pumps with a multitude of nozzles (31, 32, 33, 34) located one behind the other and forming a multitude of stages of jet pumps connected in series.

Description

Chiller or heat pump and jet pump therefor

The invention relates to a refrigerator or heat pump according to the preamble of claim 1, and to a jet pump which is particularly suitable for use here.

Chillers of this type, in which compression is carried out in a jet pump without a compressor, have been described many times in the literature. An example of this in connection with a cooling system in chemical process engineering is explained, for example, in the magazine "Wärmepumpen" 1978, 161, 168, from which the invention is based.

Low-pressure water vapor from an evaporation condenser is used as motive steam for a jet pump in the form of a steam jet compressor and sucks in water vapor as suction vapor from a trickle evaporator. The mixture of motive steam and suction steam is then condensed in a condenser and fed to a throttle device in the form of a standpipe. From there, on the one hand, the portion provided for the formation of the motive steam is pumped back into the evaporation condenser and, on the other hand, the portion intended for the formation of the suction vapor is returned via egg NEN heat exchanger, in which heat is supplied to the condensate, to the evaporator. In the evaporator, the condensate is only partially evaporated and the non-evaporated portion of the condensate is recirculated to the circuit. The evaporation energy is taken in the evaporator from the elevated temperature of the condensate supplied, so that the non-evaporated condensate leaves the evaporator at a low temperature.

In this known chiller, just like in other chillers working with jet pumps, it is disadvantageous that the evaporator, which is arranged as a separate component outside the jet pump, but directly adjacent to one another, is expensive in terms of equipment and in some cases requires very considerable installation space, so that it considerably complicates the chiller and more expensive. The generation of the steam outside the jet pump also requires the transport of the low-pressure steam of low density via correspondingly large-volume line elements, which also contribute to increasing the cost and increasing the space required.

In addition, in all known refrigeration machines or heat pumps with jet pumps as compressors, the ratio of suction steam quantity to motive steam quantity, i.e. the delivery number, relatively small, so that an economical use of such known refrigeration machines or heat pumps is only possible if propellant steam is cheaply available.

Another disadvantage is that the jet compressors of such refrigeration machines or heat pumps work optimally only closely around the design point of the jet pump, i.e. react to changes in pressure or temperature conditions with a drastic deterioration in the delivery number.

The object of the present invention is therefore to provide a refrigerator or heat pump of the type specified in the preamble of claims 1 and 15, in which the delivery number of the jet compressor is considerably improved.

This object is achieved by the characterizing features of claim 1.

It is thereby achieved that in the simplest case the evaporator is formed by a wall made of porous material such as sintered metal, over the thickness of which there is a pronounced pressure drop when the suction vapor is sucked in by the propellant. The porous wall acts as a throttle device. The suction power of the blowing agent results on the downstream side of the wall a pressure dependent on the throttling effect of the wall, which in any case falls below the evaporation pressure at the given temperature of the condensate. A further decrease in this pressure is counteracted by the evaporation of the condensate, so that there is a dynamic balance between the pressure which arises and the amount of condensate evaporated, since a further decrease in pressure would lead to increased steam generation. In this way it is ensured that due to the pressure drop in the interior of the porous material of the wall, which runs continuously over the thickness of the wall, condensate is evaporated, in which case the large inner surface of the porous material, preferably sintered metal, acts as the evaporation surface. The amount of heat required for evaporation is either taken from non-evaporating condensate, which is then discharged at a low temperature, or from a heat source that is thermally conductive to the wall and thus supplies energy for the evaporation, whereby the evaporation can then also take place completely . As a result of the removal of the heat of vaporization, the temperature of the porous material of the wall drops, so that for a heat source and for the inflowing condensate there is an increased, for a given chiller essentially the maximum possible corresponding temperature difference, which results in the heat transfer of the heat of vaporization from the heat source or Condensate favored on the porous material. With good thermal conductivity of the material of the wall, for example metal, this results in a largely uniform temperature over the thickness of the wall and therefore also in the case of evaporation which occurs only in the region of the downstream side, a sharp drop in temperature of the upstream side of the wall exposed to the condensate, and on any surface through which heat enters the wall.

The steam generated on the downstream side of the wall arrangement is immediately in the suction chamber Jet pump, so that large-volume lines and flow losses are largely avoided and a compact design can be achieved.

The mass flow resulting from the given performance of the jet pump as well as the temperature of the generated steam can be adjusted by dimensioning the consistency and the thickness of the wall arrangement, that is to say by choosing its throttling effect. A certain throttling effect results in the minimum possible achievable suction pressure and thus minimum steam temperature. A further increase in the throttling effect from this optimal point would only lead to a reduction in the mass flow, which is generally not desirable. A decrease in

The throttling effect, on the other hand, leads to an increase in the mass flow when the temperature of the steam generated increases, which can be aimed for in some operating states.

In order to ensure evaporation inside the porous material of the wall arrangement with a large evaporation surface, at least the upstream surface layers of the porous material of the wall arrangement must be permeable to condensate. However, it is not necessary that condensate can completely penetrate the wall arrangement. If downstream surface layers of the wall arrangement have a consistency impermeable to condensate, this can ensure that only saturated steam, which has contributed to the cooling capacity, reaches the suction chamber. The wall arrangement can thus consist of a plurality of layers or layers of a porous material of different consistency and optionally also of a plurality of spaced-apart individual walls, which can have a different consistency over their thickness and in comparison with one another. The space between adjacent walls is particularly suitable, for example for the removal of non-evaporated condensate in case of circulation cooling.

It is already known from DE-AS 15 01 591 to let a liquid flow through porous material of a heat exchanger, which liquid is in heat exchange with another liquid which is guided in liquid-tight compartments in the porous material. In this case, however, there is no phase change of the liquid flowing through the porous material, and the throttling effect occurring when flowing through the porous material is intrinsically undesirable and must be minimized. Furthermore, there is no reference to a use in the power section of a refrigerator, for which such a known heat exchanger could not be used.

Furthermore, it is already known from US Pat. No. 4,352,392 to apply a liquid medium to porous material in the form of sintered metal which penetrates into the material and evaporates there. Here, however, the sintered metal is a surface-side coating of a surface to be cooled, which is effectively cooled by the generation of steam, the steam emerging again at the inlet side of the liquid into the sintered metal. Again, there is no reference to the power section of a refrigeration machine, for which the known cooling device could not be used.

The energy required for the evaporation can advantageously take place according to claim 2 via a thermally conductive connection between the wall arrangement and a heat source. If the heat source according to claim 3 is a medium surrounding the jet pump, such as air in a closed room, then heat can be removed directly from this closed room. Such a variant is therefore particularly suitable as an integrated power and evaporator part for cold rooms such as refrigerators or freezers, the wall arrangement being arranged very simply in the interior of the cold room. A Improvement of the heat transfer between the surrounding medium and the porous material results according to claim 4 by sheathing the wall arrangement with fins to enlarge the heat exchange surfaces, the sheathing according to claim 5 can be produced particularly advantageously as an extruded piece cut to length. Even when the wall arrangement is tightly encased, the condensate can be introduced without problems even when the steam generated is drawn off on the side of the porous material opposite the casing in that, according to claim 6, the condensate is formed by forming appropriate channels in the casing and / or in the porous material the area of the porous material covered by the jacket is supplied.

Instead of a heat-conducting connection with a heat source or in addition to this, the heat source can also be formed by a heat transfer medium which is guided in a metallic pipe coil and is in contact with the wall arrangement by means of surface-side installation or completely or partially embedded. Even in the case of a heat-conducting connection to a heat source via a closely fitting sheathing, such a coil could in principle be embedded in the porous material of the wall to use the heat of a heat transfer medium. However, such a coil is advantageous on the surface of the wall arrangement opposite the exit of the vapor from the porous material, possibly with a few pipe windings also at a distance from this surface - arranged in a prechamber which is sealed off from the environment and in which the condensate is also present, so that a Heat transfer from the coil to the condensate can take place before the condensate enters the upstream surface of the wall arrangement; In this way, pre-evaporation can already be achieved and condensate in the form of wet steam can be supplied to the wall arrangement. In a particularly preferred manner, the pipe coil can be arranged according to claim 8 when the wall arrangement is divided into a plurality of individual walls in a corresponding number of levels in the spaces between such walls and through which the heat transfer medium flows in such a way that there is a heat exchange between the liquid or in the evaporation condensate and the heat transfer medium in countercurrent. Such an arrangement of pipe coils in the gap between adjacent individual walls has the advantage of a more straightforward production compared to a basically conceivable embedding of the pipe coil in corresponding planes inside the porous material. In any case, the heat transfer medium, which can also be the medium to be cooled, for example, can be removed from the coil in the coil at low temperature differences and thus under the most favorable exergetic conditions with optimal heat transfer conditions. When dividing the wall arrangement into individual walls with a gap in between, it is irrelevant whether the gap receives a coil or not - fresh condensate can also be added between the walls further downstream in order to achieve a desired moisture content of the medium entering the individual walls, which is 70% should lie upright.

Through the process control explained, it can be achieved that the entire condensate is converted into saturated steam. Alternatively, however, evaporation can also be carried out using the circulation method, in particular if a heat source connected to the wall arrangement in a thermally conductive manner is not available or is not to be used, or if the amount of heat required for full evaporation is not introduced by means of an additional heat transfer medium.

The only source of heat that can be used is the condensate itself, the large surface area of the porous material acting like a trickle evaporator. In this case, the heat required for the evaporation of part of the condensate is extracted from the condensate itself, so that non-evaporated condensate remains with a correspondingly low temperature. This can be done according to claim 9 by means of a liquid drainage via an external

Heat exchangers, with which a medium is cooled, are returned to the circuit.

According to claim 10, in a particularly preferred embodiment of the invention, it is provided that the wall arrangement encloses the suction space of the jet pump on the circumference, in particular is arranged approximately concentrically to the central axis of the jet pump. With such a basically sleeve-shaped design of the wall arrangement, the flow through the wall arrangement is essentially radial from the outside inwards. The wall arrangement can enclose the suction chamber with a small diameter by means of a corresponding structural design and can thus be arranged as close as possible to the coldest point of the refrigerator, so that at the same time the so-called "dead space" is minimized.

In a particularly preferred embodiment of the invention, a plurality of jet pumps can be connected in series, the mixed steam of an upstream jet pump serving either as a propellant - series connection - or as suction steam - cascade connection - of the subsequent jet pump (claims 11 and 12). If more than two jet pumps are connected in series, the circuit can be implemented partly as a series connection and partly as a cascade connection.

The series circuit according to claim 11 enables optimal use of the impulse of the propellant, as is known per se from WO 80 02 863 for vacuum technology; the nozzles of the jet pumps connected in series are matched to one another in such a way that the greatest possible pulse utilization of the propellant is achieved. In this way, the pressure of the Mixed steam from a jet pump can be used in a subsequent jet pump without adverse effects on the function of the jet pump, although in the following jet pump the temperature and pressure reduction of the previous jet pump can no longer be fully achieved. By means of such a series connection, a plurality of jet pumps with an increasingly lower temperature drop can thus be operated with a single propellant flow, so that either individual cooling circuits with different cooling temperatures can be connected to the individual jet pumps, or a plurality of jet pumps connected in series can be detected by a single cooling circuit can, wherein the heat cooling medium is first fed to the last jet pump and finally leaves the first jet pump of the series with a correspondingly reduced temperature. Here, the countercurrent principle explained above in connection with claim 8 is applied to a plurality of jet pumps connected in series, and can of course also be used in addition in each individual jet pump, so that overall there is heat exchange in an approximately ideal counterflow.

In the cascade circuit according to claim 12, each jet pump switched in this way receives the full propellant pulse. As a result of the interconnection in cascade form, a jet pump arrangement can be achieved which, compared to the temperature difference achievable with one stage between the suction chamber and mixed steam outlet, can produce a significantly increased temperature difference, in that the mixed steam pressure increases within the jet pump arrangement, so that after a plurality of stages at the outlet the arrangement has a high mixed steam pressure which enables condensation at high temperature. In this way, cooling to low temperatures, for example -10 ° C., can also be achieved if necessary, even if condensation, for example in a hot environment, at egg ner high temperature of 40 ° C, for example.

Even with such a cascade connection, a flow of cooling medium through the individual jet pumps can take place in the manner already described above in countercurrent from jet pump to jet pump and, if appropriate, within each jet pump.

Due to the above-described mode of operation, such a cascade connection is very well suited for use as a heat pump.

A particularly advantageous further development of the cascade circuit described consists in assigning a separate coolant to each jet pump or each specific group of jet pumps, which can be connected in series or cascade connection, and the separate cooling circuits thus formed within the cascade arrangement of the jet pumps to a certain extent to be connected in series so that the evaporator of the downstream jet pump is in heat exchange with the condenser of the upstream jet pump. If the refrigerants are selected differently in such a way that the refrigerant of the upstream jet pump has a condensation temperature at its mixed steam pressure that is at least very slightly higher than the evaporation temperature of the refrigerant of the downstream jet pump at its suction pressure, then the downstream jet pump can be located in the area of the evaporator a heat exchange in a double phase change take place in such a way that the refrigerant to be evaporated extracts at least part of its heat of vaporization from the refrigerant to be condensed and this condenses in the process. The two different refrigerants in the separate cooling circuits can serve different cooling purposes at different temperature levels. In claim 15, a refrigeration machine or heat pump is defined which works with a jet pump as a compressor, which has a plurality N of nozzles arranged one behind the other, which are assigned to N-1 jet pump stages connected in series. The mixed steam of an upstream jet pump stage is used as motive steam for the subsequent jet pump stage. In contrast to the operating characteristics of single-stage jet pumps, in which the optimal ratio of suction gas quantity to propellant gas quantity is only met for the design point of the jet pump, the multi-stage jet pump has a delivery range due to the series-connected jet pump stages, in which the optimal ratio of suction gas quantity to propellant gas quantity can be found significantly improved with increasing suction pressure or decreasing condensation pressure. By adapting the nozzle configuration, ie by determining the nozzle spacing, nozzle lengths of the nozzle inlet and outlet cross sections, the ratio of suction gas quantity to propellant gas quantity can be optimized for a desired design area and not just for one design point. Due to the equivalence of the switching of the individual jet pump stages of such a multiple ejector with the switching of individual jet pumps explained in connection with claim 11, the ones explained here can be explained

Transfer circuit examples for chillers or heat pumps accordingly.

According to claim 16, the nozzles of the individual jet pump stages advantageously have a diverging flow channel in the outlet-side nozzle end, with which the impulse of the mixed steam is converted into a pressure increase.

It should be noted that the multiple ejector arrangement according to claims 15 and 16 also with the forms of the invention according to the other an Can combine sayings in an advantageous manner.

In claim 17, a jet pump is specified, which in. Preamble of the jet pump according to DE-OS 29 37 438 starts. In this known jet pump, liquid is filled into the suction chamber in such a way that the liquid level is exposed to the negative pressure generated. As a result, part of the liquid evaporates from the liquid surface and is supplied as steam to the liquid propellant jet, where the steam is re-condensed, after which the mixed liquid is drawn off. In order to support the evaporation of the liquid in the suction chamber, the suction chamber is surrounded by an essentially cylindrical peripheral wall made of porous material, which is permeable to gas, but impermeable to liquid. As a result of the negative pressure prevailing in the suction space, gas is drawn in through the gas-permeable porous wall, which foams up the liquid and thus increases the evaporation surface. Here, the porous wall does not serve as an evaporator, but rather deteriorates the efficiency of the jet pump due to the additional air intake through the porous wall.

The characterizing features of claim 17, however, ensure that such a jet pump can be used for use in a refrigeration machine or heat pump according to the invention, the porous wall acting as a throttle device and evaporator for the condensate. However, such a jet pump can also be advantageously used independently of a refrigeration machine according to the invention, for which it is particularly suitable, for example as a filter if particles, for example oil particles, are to be extracted from the suction flow through the porous wall. As a result of the manageable and predictable pressure and, in particular, temperature conditions that occur during operation of the jet pump, use as a fractional filter is also possible, with only those fluid fractions that are seen in the thermodynamic setting being eliminated State as a fluid or as a solid, while other substances, such as gaseous or as a fluid, are let through.

For the latter use, too, an embodiment of the porous material as a metallic material with good heat conduction and in particular as a sintered metal is advantageous.

Further details, features and advantages of the invention result from the following description of embodiments with reference to the drawing.

It shows

1 is a circuit diagram of a refrigerator or heat pump according to the invention,

2 according to line II-II in FIG. 3 shows a longitudinal section through a jet pump in a first embodiment, as can be used in a refrigerator according to FIG. 1,

3 is a cross section through the jet pump of FIG. 2 along line III-III in FIG. 2,

4 shows a longitudinal section corresponding to FIG. 2 through another embodiment of a jet pump according to the invention,

Fig. 5 shows the detail according to circle V in Fig. 4 in an enlarged view, but in a modified embodiment. 6 shows a longitudinal section corresponding to FIG. 2 or FIG. 4 through a further embodiment of a jet pump according to the invention,

7 according to line I-I in FIG. 6 shows a cross section through the jet pump according to FIG. 6,

8 is a circuit diagram of another embodiment of the refrigerator according to the invention with internal heat exchange,

9 is a circuit diagram of a further embodiment of the refrigeration machine according to the invention, in which the medium to be cooled is in direct thermal contact with the porous material,

10 is a circuit diagram of yet another embodiment of the refrigeration machine according to the invention in a recirculating cooling process,

11 is a circuit diagram of another

Embodiment of the refrigeration machine according to the invention with two jet pumps in series connection,

12 is a circuit diagram of yet another embodiment of the refrigeration machine according to the invention with two jet pumps in cascade connection, and

13 is a circuit diagram of yet another embodiment of the refrigeration machine according to the invention with two jet pumps in cascade connection and two cooling circuits in series connection.

Fig. 1 shows the basic scheme of a refrigeration cycle according to the present invention. A jet pump 1 with the integrated evaporator 2 made of porous material is driven by motive steam from the steam generator 4. The mixed steam generated in the jet pump is condensed in the condenser 3 and part of this condensate is fed back to the evaporator 2. The other part of this condensate is conveyed back into the propellant generator 4 via the liquid pump 5. The drive energy Q _ex is supplied to the steam generator 4, the heat of condensation Q _c is withdrawn from the condenser 3 and the heat Q _o necessary for the evaporation of the refrigerant is supplied to the evaporator 2. The liquid refrigerant penetrates into the evaporator 2 made of porous material and changes to the gaseous state on the large inner surface of the porous material. At the same time, the liquid refrigerant is throttled by the condenser pressure P _c to the pressure P _o prevailing in the suction chamber of the jet pump. The heat Q _o necessary for the evaporation of the refrigerant can be introduced into the porous material by heat conduction _or , in a special embodiment, can be removed directly from the liquid refrigerant.

It should be noted here that the temperature which can be achieved in the capillary evaporator can be considerably lower than the temperature which results from the pressure P _o prevailing in the suction frame of the jet pump. This effect of

Lowering of pressure in capillary systems has already been found in connection with absorption processes. See also the Refrigeration Technology Manual by Rudolf Planck, Volume 7, Absorption Chillers by Dr. Ing. Wilhelm Niebergall, page 246, Springer-Verlag 1959. Therefore, if the heat exchange on the cold side of the refrigerator is carried out via the sintered metal, these low temperatures can be used technically. The refrigerant used is thus cooled significantly below the temperature that would result from the pressure conditions in the suction chamber.

Another effect that shifts the temperature in the capillary system down is probably a Joule / Thomson effect when the vaporized gas emerges from the capillary system and probably also a venturi effect in the capillaries due to the suction gas flowing quickly at a 90 ° angle to the capillary outlet.

In experiments with the refrigerant R113 at a pressure of 0.462 bar in the suction chamber, the surface temperature of the sintered metal evaporator was 12.5 ° C measured. This temperature is about 10 K below the evaporation temperature associated with the above pressure in the free environment. In other words, a conventional jet pump would have to achieve a suction pressure that is 0.17 bar lower.

FIG. 2 shows a longitudinal section of an embodiment of the jet pump 1. A blowing agent, for example steam, is introduced via a blowing agent nozzle 11 and collected in a mixing nozzle 12. A suction chamber i3 is arranged between the driving nozzle 11 and the mixing nozzle 12. A vacuum P _{o is} generated in the suction chamber 13 in the known manner by the propellant jet.

Condensate is fed via lines 14 and 15 to a storage space 16 and 17, respectively, and from there to a wall arrangement 18 in the radially outer region.

As can also be seen in particular from FIG. 3, the wall arrangement 18 is closely surrounded on its outside by a metallic sheathing 19 which projects into the wall arrangement 18 with lamellae 20 and projects into the surrounding atmosphere with lamellae 21. The fins 20 and 21 serve as heat exchange surfaces.

To supply the condensate to the wall arrangement 18 in its radially outer region, channels 22 are provided between the casing 19 and the outer region of the wall arrangement 18, which are formed by a corresponding shape or recess both on the inside of the casing 19 and on the outer circumference of the wall arrangement 18. Instead, of course, the channels 22 can be formed solely in the area of the casing 19 or Wall arrangement 18 take place, openings being possible in the area of wall arrangement 18 in its surface area.

The wall arrangement 18 consists of porous material, sintered metal in the example, and is permeable to the liquid condensate at least in its surface layers. When condensate is supplied through the lines 14 and 15 via the supply spaces 16 and 17, it thus reaches the channels 22, which are distributed in a plurality over the circumference of the wall arrangement 18, and from there penetrates into the sintered metal of the wall arrangement essentially uniformly 18 a. The wall arrangement 18 serves as a throttle for the flow of the condensate, so that in the region of the thickness of the wall arrangement

18 a pressure drop occurs, the pressure in the region of the downstream surface 23 of the wall arrangement 18 reaching the suction pressure P _o . In the manner explained in detail in the introduction, evaporation of the condensate inevitably occurs, which leaves the surface 23 as steam and is supplied to the propellant jet.

The thermal energy required for the evaporation is achieved by heat conduction via the fins 21, the casing

19 and the fins 20 introduced into the porous material. In this case, heat is extracted from the surroundings of the fins 21. This heat extraction results in the desired cooling capacity.

As can be seen in particular from FIG. 3, the wall arrangement is designed as an elongated part with the same cross section, namely outer slats 21 and inner slats 20. Therefore, the casing can be expediently made available as an extruded piece cut to length.

FIG. 4 illustrates another embodiment of a jet pump, designated 24, for a refrigeration machine according to the invention. The jet pump 24 has how around a driving nozzle 11a, a suction chamber 13a with the pressure P _o and a mixing nozzle 12a. A wall arrangement 18a made of porous material is also provided. In contrast to the embodiment according to FIGS. 2 and 3, however, a jacket for heat conduction is not provided close to the outer circumference of the wall arrangement 18a, but rather the wall arrangement 18a is surrounded by an annular prechamber 25 and is liquid-tight to the environment. Condensate is introduced into the prechamber 25 via a line 14a and from there is applied to the outer circumference of the wall arrangement 18a. In this embodiment, too, the condensate enters the surface area of the wall arrangement 18a which is permeable to condensate, evaporates there, exits as steam at the downstream surface 23a and is fed to the propellant jet.

However, while in the embodiment according to FIGS. 2 and 3 the heat required for evaporation is removed from the environment by heat conduction and supplied to the wall arrangement 18, in the case of the embodiment according to FIG. 4 the heat is supplied via a heat transfer medium in a line 26 which in the Area of the wall arrangement 18a is present as a highly conductive, that is metallic pipe coil 27 and closely surrounds the outer circumference of the wall arrangement 18a. In particular, if metal is used for the wall arrangement 18a, a rapid temperature compensation takes place in the area of the wall arrangement 18a, so that the heat removed for evaporation inside the wall arrangement 18a leads to a strong cooling of the outer circumference of the wall arrangement 18a as well. As a result, heat is removed from the heat transfer medium in the coil 27 by heat conduction, so that the heat transfer medium 7 is cooled accordingly, and this can absorb heat elsewhere for cooling purposes. The heat source for the evaporation thus represents the heat transfer medium flowing in the line 26, which is the cooling medium. As can be seen from Fig. 5, the detail

Circle V in FIG. 4 in an enlarged representation, but illustrated in a modified embodiment, a wall arrangement 18b can also consist of a plurality of individual walls, in the example case two walls 28 and 28a. Between the two walls 28 and 28a and on their outer sides, heat can be transferred to a coil 29 which is arranged in several layers or levels 29a, 29b and 29c. The direction of flow through the condensate or the evaporating condensate, illustrated by arrows in FIG. 5, illustrates that firstly the foremost plane 29a of the pipe coil comes into contact with the condensate, and this can already pre-evaporate to a certain extent. To achieve such a pipe evaporation, a further plane 29d of the pipe coil can also be arranged at a distance in front of the wall arrangement 18b, which only serves to preheat or pre-evaporate the condensate. The actual evaporation then takes place in the first wall 28 of the wall arrangement 18b in the manner already explained, wherein a large part of the condensate may pass into vapor form. There is then a further heat exchange also between the evaporating condensate and the second layer or level 29b of the pipe coil 29 and then the entry into the second wall 28a, in which, in the example case, the complete evaporation should take place. Insofar as the evaporation in the area of the wall 28 has already progressed so far that the condensate or the condensate vapor has a very low moisture content, for example below 70%, when it enters the second wall 28a, additional condensate can be supplied in the area of the plane 29b for rewetting will. In the case of complete evaporation, saturated steam is then present on the downstream surface 23b, which, like the adjacent surface of the wall 28a, comes into heat exchange with the last level 29c of the coil 29, so that the heat transfer medium flowing therein again receives heat, this time at the lowest occurring temperatures, is withdrawn. To achieve an exergetically favorable countercurrent heat exchange, the heat transfer medium first flows through the plane 29d, which is in the area with the highest temperature, and exits in the area of plane 29c, which is in the area with the lowest temperature, so that there are always minimal temperature differences. 6 to 11 show different circuits for a refrigeration machine according to the invention in a circuit diagram, whereby jet pumps of the basic design according to FIG. 4 (with prechamber 25 and heat exchange) are always used via a heat transfer medium, unless expressly stated otherwise. In order to improve the clarity, the diagrams also indicate the phase in which the medium is present, (1) denoting the liquid phase and (v) the gaseous phase. Furthermore, the pressures p and heat flows Q or energy are entered in the diagrams in the usual manner with the usual indices, so that the circuit diagrams are largely self-explanatory and are therefore only dealt with in the following on aspects to be explained in particular.

6 and 7 show a further embodiment of a jet pump, designated 30, for a refrigeration machine or heat pump according to the invention. FIG. 6 shows a longitudinal section of this embodiment of the jet pump 30 and FIG. 7 shows a section perpendicular to the plane designated by I-I in FIG. 6. In contrast to the embodiments of the jet pump according to FIGS. 2 and 4, the jet pump 30 consists of a plurality of jet pump stages connected in series. Four nozzles 31, 32, 33, 34 arranged one behind the other form pairs of jet pump stages I, II and III. The individual jet pump stages are separated from one another in a gas-tight manner by two boundary walls 35. Suction spaces 36, 37 and 38 of the respective jet pump stages are arranged between two nozzles. The suction spaces 36, 37 and 38 are each surrounded by wall arrangements 39, 40 and 41 made of porous material, which are enclosed by a good heat-conducting jacket 42 enveloping the entire jet pump. For example, four condensate feeds 43, 44, 45 and 46, which are in recesses of the

Wall arrangements 39, 40, 41 and / or the casing 42 are arranged, liquid refrigerant is supplied and passes through openings 47 in the condensate feeds into the wall arrangements 39, 40 and 41 of the respective jet pump stages.

In order to distribute the condensate evenly, the condensate feed could also be designed, for example, in such a way that in the individual jet pump stages the respective wall arrangement 39, 40, 41, annularly surrounding lines, are connected to the condensate feeds 43, 44, 45 and 46. Another option would be to guide the condensate feed in a spiral around the wall arrangements of the individual jet pump stages.

At the points at which the condensate feeds 43, 44, 45 and 46 penetrate the boundary walls 35, in A non-return valve 48 is arranged in each case in the direction of flow of the condensate. The heat necessary for the evaporation of the condensate is supplied directly from the environment via the heat-conducting jacket 42. Advantageously, the casing 42, as in the embodiment according to FIGS. 2 and 3, could also be provided with lamellae.

In a manner not shown, however, the jacket 42 could also be designed as a double jacket through which a heat transfer medium is passed, by means of which the heat necessary for the evaporation of the condensate is supplied or the cooling capacity is removed. It would also be possible to wrap around the casing 42 with a pipe coil in which a heat transfer medium circulates.

If motive steam with the pressure P € X is now supplied to the first nozzle 31, a negative pressure P _{o1 is} generated in the jet pump stage I, so that the condensate supplied to the wall arrangement 39 evaporates and mixes with the motive steam from the nozzle 31 in the second nozzle 32 . The resulting mixed steam in nozzle 32 serves as motive steam for the second jet pump stage II, in the suction chamber 37 of which condensate in turn evaporates from the wall arrangement 40 at a somewhat higher pressure P _o2 . The mixed steam forming in the third nozzle 33 in turn serves as motive steam for the third jet pump stage III, in which condensate is _evaporated from the wall arrangement 41 at a pressure P _o3 which is higher than the pressure P _o2 , so that finally the fourth emerges at the outlet Nozzle 34 mixed steam with the condenser pressure P _c is present. The arrangement of four nozzles is of course only an example.

Corresponding to the increasing suction pressures P _o1 , P _o2 and P _o3 , the evaporation temperature of the condensate also increases in the respective jet pump stages. Will the Cooling power dissipated by a heat transfer medium, this is advantageously conducted in countercurrent from the third to the first jet pump stage. If the supplied heat transfer medium has a temperature which is below the evaporation temperatures in the jet pump stages II and III or if the temperature of the heat-conducting jacket 42 drops below these temperatures, then the non-return flaps 48 close due to the pressure conditions which can be achieved in the jet pump, so that the jet pump stages II and III are no longer supplied with condensate. In this way, a refrigeration machine or heat pump according to the invention equipped with such a jet pump regulates itself automatically according to the circumstances on the evaporator side. In the first jet pump stage, the lowest suction vapor pressure, but also the lowest heat flow, is reached, with increasing number of nozzles or from jet pump stage to jet pump stage, evaporation pressure and thus the evaporation temperature in the porous wall arrangements 39, 40, 41 as well as mass and heat flow in the respective one. Jet pump stage.

By calculating the nozzle inlet diameter d _e, the nozzle exit diameter d _a, the nozzle lengths 1 and the nozzle distances a from the thermodynamic characteristics of the desired Auslegebereiches and the refrigerant used can be optimized to blowing amount of steam, the ratio of Saugdampf-. The nozzle geometry can also be advantageously adapted to the throttling action of the wall arrangements 39, 40 and 41. This results in a significant improvement in the part-load behavior of the refrigeration machine or heat pump according to the invention.

If the temperature or pressure gain due to the reduction in evaporation temperature in the capillaries of the sintered metal evaporator is related to an optimization of the Ver ratio of suction gas to propellant gas, there is an approximately 25% lower propellant gas requirement due to the improved efficiency of multi-ejectors. The combination of the integrated sintered metal evaporator and the multi-ejector thus enables a steam jet pump which, based on the end operating point, saves around 25% in operating costs and has automatic control over a wide temperature range with a constantly improving ratio of suction gas to propellant gas towards the upper end of the design range. As a result, the economy of a refrigeration machine or heat pump equipped with such a multijector increases considerably.

Of course, the wall arrangements 39 to 41 can also be designed in accordance with the embodiment shown in FIG. 5. All of the options for guiding the heat transfer medium further mentioned in the explanation of the embodiments according to FIG. 4 are also possible in the embodiment according to FIG. 6.

All of the embodiments of the jet pump explained with reference to FIGS. 2 to 6 could advantageously also be modified in such a way that the driving nozzle and the catching nozzle or the majority of the ones arranged one behind the other

Nozzles are arranged in the area of the prechamber or casing and the condensate is fed centrally in the area of the suction chamber, so that prechamber and suction chamber would be interchanged. In this way, the steam expansion of the resulting suction steam could be taken into account and the counterflow principle realized. The embodiment according to FIG. 8 differs from that according to FIG. 1 essentially in that the condensate line 6 does not release the condensate in the prechamber 25 like the condensate line 14a, but rather the condensate initially in the sense of the heat transfer medium in line 26 in contact-free heat exchange is guided with the evaporator and thereby undergoes pre-cooling. Via a line 6a, the so pre-cooled, still liquid condensate one working in direct evaporation external evaporator 30 is supplied, is supplied in the heat and the condensate is evaporated, the heat required amount Q _o corresponding to the power output of the refrigerator. The vaporous refrigerant is then fed to the pre-chamber 25 via a line 6b and released in the pre-chamber 25 in a manner similar to that in the case of the condensate line 14a in FIG. 4. For the radio

tion of the jet pump 24, it is irrelevant whether the condensate line 14a in the prechamber 25 releases liquid condensate or already vaporous refrigerant.

In the embodiment according to FIG. 9, there is no internal heat exchange, as illustrated and explained in connection with FIG. 8, rather the liquid condensate branched off behind the condenser 3 is fed via the condensate line 14a, as explained in connection with FIG. 4, released in the pre-chamber 25 and evaporated in the evaporator 2. The heat of vaporization is withdrawn from the coil 27 or the liquid heat transfer medium flowing therein, which absorbs this heat in an external heat exchanger 31, on which the useful power of the refrigerator is available.

In the embodiment according to FIG. 10, as explained in connection with FIG. 4, liquid condensate is introduced into the pre-chamber 25 via the condensate line 14a and fed to the evaporator 2. In the example, the evaporator 2 or the wall arrangement 18a may not be able to absorb any significant amounts of heat through heat conduction or in any other way. In this case, the thermal energy required for evaporation is only available in the form of the energy content of the condensate. This removes heat from the condensate as evaporation begins, with the inner surface of the porous material acting like a trickle evaporator. The condensate which has passed into the vapor phase arrives in the propellant stream in the manner explained, while unevaporated, cooled condensate remains. This is drawn off from the area of the pre-chamber 25 or the evaporator 2 via a liquid discharge line 32 and returned to the circuit via a heat exchanger 33, as can be seen from FIG. 10. The useful output of the refrigerator is available at the heat exchanger 33. The condensate heated in the heat exchanger 33 is returned to the pre-chamber 25. So it happens circulation cooling.

In the circuit diagrams according to FIGS. 11 to 13, refrigeration machines are implemented in which a plurality of, in the example case, two jet pumps are connected in series. In all evaporators of the jet pumps, a cold-side circuit with internal heat exchange is shown. Instead, of course, any other variant of the heat exchange can be realized accordingly, as shown in FIGS. 9 or 10.

In the embodiment according to FIG. 11, a first jet pump 24 with a driving nozzle 11a, suction chamber 13a and mixing nozzle 12a is provided, the outlet of the mixing nozzle 12a being connected to the driving nozzle 11a of the downstream jet pump 24. The mixed steam of the upstream jet pump thus serves as a propellant for the downstream jet pump 24. As a result, the pressure at the outlet of the mixing nozzle of the first jet pump 24 can be used again in the downstream jet pump 24, albeit using a lower pulse, so that the _Suction pressure P _{o1 of} the upstream jet pump 24 is lower than the suction pressure P _{o2 of} the downstream jet pump 24.

In both cases, the cooling of a heat transfer medium takes place in accordance with the circuit according to FIG. 8. The heat transfer medium flows in a line 6c corresponding to the line 6 according to FIG. 8 in the area of the evaporator 2 of the downstream jet pump 24, flows through a pipe coil 27, but at the outlet thereof does not become the heat exchanger 30 but continues to a corresponding pipe coil 27 of the Evaporator 2 of the upstream jet pump 24 guided and there again at a lower temperature than in the area of the downstream jet pump 24, so that heat is removed. In this way, heat exchange in countercurrent is realized. Of course, in the area of both ver Steamer 2 of the two jet pumps 24 each again - a heat exchange in countercurrent, as is explained in connection with FIG. 5.

From the evaporator 2 of the upstream jet pump 24, the liquid heat transfer medium in line 6c finally reaches the heat exchanger 30, where direct evaporation takes place. The vaporous heat transfer medium is fed via a line 6d, which is branched, to the prechambers 25 of the two jet pumps 24 via a check valve 34. Complete evaporation takes place to form saturated steam from the wet steam introduced in line 6a (or in FIG. 8 and further 6b) or generated at least in the region of tube coil 27. If necessary, the condensate can be moistened further, thus increasing the energy extracted by evaporation, as is explained in more detail in connection with FIG. 5.

If required, a second external evaporator 30 can be connected in the manner shown in dashed lines in FIG. 11, the arrangement being such that each evaporator 30 is assigned to one of the jet pumps 24, so that there is normally no flow in the region of the non-return valve 34 is present.

In the case of two evaporators 30, which each work with a jet pump 24, each of the evaporators operates in the power range of the associated jet pump 24. If only one evaporator 30 is connected to both jet pumps 24 in the manner explained above, this can be used in the entire area P _o1 and P _{o2 can be} regulated while maintaining the optimum efficiency of the propulsion jet pulse.

While in the embodiment according to FIG. 11 the jet pump 24 was connected in the manner of a series connection, in the embodiments according to FIGS. 12 and 13 there is one Circuit provided in the manner of a cascade connection; in which the mixed steam from the mixing nozzle 12a of the upstream jet pump 24 is fed to the suction side of the downstream jet pump 24, that is to say its prechamber 25. In principle, this ensures that the mixed steam pressure present at the outlet of the mixing nozzle 12a in the cascade connection increases from the upstream jet pump 24 to the downstream jet pump 24, so that the last mixing nozzle 12a has a much higher pressure than with only one jet pump 24 would be achievable for a given suction pressure P _o and driving pressure P _ex .

11, since in each case propellant has to be introduced into the system at each jet pump 24, in contrast to the series circuit according to FIG. 11, the live steam propellant generator 4 serving as the propellant can be taken from different pressure levels, as is additionally illustrated in dashed lines in FIG. 12. A connection between the first propellant generator 4 and the propellant nozzle of the first jet pump 24 is closed by a schematically illustrated shut-off device 35, this line, which is only required when both jet pumps 24 are operated by a single propellant generator 4, of course also in the case of two propellant generators 4 can be completely eliminated. The jet pump 24 forming the last stage is connected to the propellant generator 4 which generates the highest propellant pressure in order to achieve the highest possible back pressure at the associated mixing nozzle 12a. in the

For example, this may be the blowing agent generator 4 shown with solid lines. The heating medium output of the propellant generator 4 illustrated with solid lines can in turn be connected to the heating medium input of the propellant generator 4 shown in dashed lines, so that it works at a lower pressure and is connected to the upstream jet pump 24. With regard to the further training on the cold side, there are no differences from the embodiment according to FIG. 9, so that reference can be made to this for further details.

In the embodiment according to FIG. 13, the cascade circuit according to FIG. 12 is also used in principle, but both jet pumps work with different refrigerants. The first jet pump 24 is assigned a cooling circuit, designated overall by 36, which instead of the usual condenser 3 has a condenser 37 which is explained in more detail below, but otherwise works according to the embodiment according to FIG. The downstream jet pump 24 is assigned a cooling circuit 38 which, in principle, corresponds to the embodiment

FIG. 9 corresponds, wherein a circulation method according to FIG. 10 can also be used instead of the embodiment according to FIGS. 8 and 9.

The peculiarity of this embodiment is that the condenser 37 is in heat exchange with the evaporator 2 of the downstream jet pump 24, that is to say releases the heat of condensation to the downstream evaporator 2. For this purpose, the refrigerants in the cooling circuits 36 and 38 must be selected differently, in such a way that the refrigerant of the cooling circuit 36 assigned to the upstream jet pump 24 has a condensation temperature which is approximately the same or higher at the pressure prevailing at the outlet of the upstream jet pump 24 than the evaporation temperature of the refrigerant in the cooling circuit 38 of the downstream jet pump 24 at its suction pressure P _o , so that the heat required for evaporation of the refrigerant in the circuit 38 can be obtained from the condensation of the refrigerant from the circuit 36 in the region of the condenser 37.

The jet pump 24 according to FIG. 4 with a wall arrangement 18a concentrically surrounding the central axis in the manner of a sleeve made of sintered metal is not only ideally suited for use in all of the circuits shown for refrigeration machines or heat pumps, but also has its own meaning; For example, another medium can be sucked in through the sintered metal instead of a refrigerant and the filtering effect of the sintered metal or another porous wall can be used to filter out substances from this medium, as explained in more detail in the introduction.

A particular advantage of the refrigeration machine or heat pump according to the invention is that the integration of the evaporator or the integration of several jet pump stages in a jet pump results in a very compact design. Maintenance is also simplified since no moving parts are required apart from a liquid pump and check valves.

Claims

1. Chiller, or heat pump, with a compressor in the form of a jet pump (1; 24; 30), a downstream of the jet pump condenser (3; 37) and an evaporator (2) connected to the jet pump, in the low-tension suction steam Suction can be generated by the propellant in the suction chamber (13; 13a; 36, 37, 38) of the jet pump (1; 24; 30), with a throttle device for in front of the suction chamber (13; 13a; 36, 37, 38) of the jet pump the condensate is arranged, characterized in

that the evaporator (2) is at least formed as part of the throttle device and has the shape of a wall arrangement (18; 18a; 39, 40, 41) made of porous material, preferably metallic material such as sintered metal, whose downstream surface (23; 23a ) forms at least part of the boundary of the suction chamber (13; 13a, 36, 31, 38) of the jet pump (1; 24; 30) and the lateral edges of which are sealed liquid-tight, with at least the upstream surface layers of the first (28 ) or single wall of the wall arrangement (18; 18a; 18b; 39, 40, 41) are designed to be permeable to condensate.

2. Chiller according to claim 1, characterized net that the wall arrangement (18; 18a; 18b; 39, 40, 41) made of porous material is thermally conductively connected to a heat source that delivers thermal energy at a temperature level that is above the evaporation temperature of the condensate at the surface lying downstream (23 ; 23a; 23b) of the wall arrangement (18; 18b; 39, 40, 41) prevailing pressure.

3. Chiller according to claim 2, characterized in that the heat source by a jet pump

(1; 30) surrounding medium such as air or water is formed, and that a tight-fitting metallic sheath (19; 42) of the wall arrangement (18; 39, 40, 41) is provided as the heat-conducting connection.

4. Refrigerating machine according to claim 3, characterized in that the casing (19; 42) with outer, projecting into the medium and / or inner, in the wall arrangement (18; 39, 40, 41) projecting fins (21 or 20) is provided.

5. Chiller according to claim 4, characterized in that the fins (20, 21) of the casing (19; 42) extend in the longitudinal direction thereof, and the casing (19; 42) is formed as an extruded piece with the same cross-section at each point.

6. Chiller according to one of claims 3 to 5, characterized in that the condensate in channels (22; 43, 44, 45, 46) in the material of the casing (19; 42) and / or in the material of the wall arrangement (18; 39 , 40, 41) within which condensate-permeable surface layers are guided.

7. Chiller according to one of claims 1 to 6, characterized in that the heat source is formed by a heat transfer medium which is in a line (6; 6c; 26) that the wall of the line formed as a metallic pipe coil (27; 27a) is in contact with the wall arrangement (18a; 18b), and that the pipe coil (27; 27a) is arranged in a prechamber (25) which is sealed off from the surroundings.

8. Chiller according to claim 7, characterized in that the coil (27a) in a plurality of

Layers (29a, 29b, 29c) are arranged on individual walls (28, 28a) of the wall arrangement (18b) and through which the upstream layers (29a, 29b) flow in the direction of the downstream layers (29b, 29c) of heat transfer medium.

9. Refrigerating machine according to one of claims 1 to 8, characterized in that in the region of the wall arrangement (18a; 18b) a liquid discharge (32) opens out by means of the non-evaporated condensate. an external heat exchanger (33) can be returned to the circuit (FIG. 10).

10. Chiller according to one of claims 1 to 9, characterized in that the wall arrangement (18; 18a;

18b; 39, 40, 41) encloses the suction space (13; 13a; 36, 37, 38) of the jet pump (1; 24; 30) on the circumference, in particular is arranged concentrically to the central axis of the jet pump (1; 24; 30).

11. Chiller according to one of claims 1 to 10, characterized in that a plurality of jet pumps (1; 24; 30) is connected in series in such a way that the mixed steam of an upstream jet pump serves as a propellant of the downstream jet pump (Fig. 11).

12. Chiller according to one of claims 1 to 10, characterized in that a plurality of jet pumps (1; 24; 30) is connected in series in such a way that the mixed steam of an upstream jet pump serves as suction steam of the downstream jet pump (Fig. 12, 13 ).

13. Refrigerating machine according to claim 11 or 12, characterized in that the medium to be cooled is passed in countercurrent through a group of series-connected jet pumps (1; 24; 30) that it first with the condensate or evaporating condensate of the downstream jet pump ( 1; 24; 30) of the group and finally brought into heat exchange with the condensate or evaporating condensate of the upstream first jet pump (1; 24; 30) of the group.

14. Chiller according to claim 12, characterized in that each jet pump (1; 24; 30) has its own

Has cooling circuit (36; 38) with an associated refrigerant, the refrigerants being different in such a way that the refrigerant of the upstream jet pump (1; 24; 30) condenses at its mixed steam pressure at a temperature which is at least slightly higher than that Evaporation temperature of the refrigerant of the downstream jet pump (1; 24; 30) at its suction pressure, and that the condenser (37) for the refrigerant of the upstream jet pump with the wall arrangement (18a;

18b) the downstream jet pump (1; 24; 30) is in heat exchange.

15. Chiller or heat pump, with a compressor in the form of a jet pump (1; 24; 30), one of the

Jet pump downstream condenser (3; 37) and an evaporator (2) connected to the jet pump, in the low-tension suction steam for suction by the propellant into the suction chamber (13; 13a; 36, 37, 38) of the jet pump (1; 24; 30) can be generated, in front of the suction chamber (13; 13a; 36, 37, 38 ) a throttle device for the condensate is arranged in the jet pump, characterized in that

that the jet pump (1; 24; 30) has a plurality N of nozzles (31, 32, 33, 34) arranged one behind the other, which form N-1 jet pump stages (I, II, III) connected in series, the mixed steam consisting of one upstream jet pump stage serves as motive steam for a downstream stage.

16. Refrigerating machine according to claim 15, characterized in that the outlet-side nozzle ends of the plurality of nozzles (31, 32, 33, 34) have a diverging flow channel.

17. Jet pump, in particular for a refrigerator or heat pump according to at least one of claims 1 to 14, with an at least part of the circumferential boundary of the suction space (13a) forming, in particular concentric to the central axis of the jet pump (24) arranged wall arrangement (18a; 18b) porous

Material, characterized in that the outer periphery of the wall arrangement (18a; 18b) is liquid-tight to the environment, and that at least the radially outer surface layers of the wall arrangement (18a; 18b) are designed to be permeable to liquid.

18. Jet pump according to claim 17, characterized in that the porous material is a metallic material, in particular sintered metal.