EP1305561B1 - Heat transfer device - Google Patents

Description

The invention relates to a device for heat transfer from a first fluid to a second fluid separated from the first fluid with at least two layers, in particular plates, comprising a stack-shaped or shell-like structure according to the preamble of claim 1.

State of the art

So far, for example, heat exchangers are provided with a flowed through by a high-pressure side refrigerant first channel and a low-pressure-side refrigerant, separated from the first channel second channel in a CO ₂ vehicle air conditioning.

In order to increase the performance and efficiency of the CO ₂ process, a so-called internal or internal heat exchanger is provided. The internal heat exchanger is flowed through by the refrigerant (CO ₂ ) in a countercurrent or DC principle. The fluids flow through the heat exchanger once on the way from the gas cooler to the evaporator and the second time between evaporator and compressor. The main task of the internal heat exchanger is to additionally cool the refrigerant before expansion. The heat is from the high pressure side of the gas cooler to the Low pressure side after the evaporator (before entering the compressor) delivered. The partially still liquid refrigerant evaporates completely before it reaches the compressor.

Possible applications are for corresponding heat exchangers in vehicle air conditioners, heat pumps, portable air conditioners low power, dehumidifiers, dryers, fuel cell systems and similar applications.

There are already known heat exchangers, which are made comparatively compact for mass and volume reduction. In order to transmit large amounts of heat in a small construction, for example, so-called micro-heat exchangers are provided. These consist in particular of structured plates which are stacked one above the other and either soldered together, screwed or connected accordingly. In this case, correspondingly provided channels of the heat exchanger are also sealed at the same time. The fluids that make thermal contact with each other in the heat exchanger are passed through the channels between the plates.

In the micro-heat exchanger, the fluids are passed through inlet openings or outlet openings in the individual layers, so that in different layers alternately flows a heat-absorbing and a heat-emitting fluid. The distribution or merging of the fluids to or from the individual channels takes place here in the entry or exit area. In these areas, the respective fluid flow splits or collects.

In this case, the overlap of the inlet region with the outlet region results in a so-called free cross section.

Due to the large pressure difference between the two fluids, the individual layers in the region of the free cross section must withstand the widely differing pressure levels.

The large pressurized area in the region of the free cross-section causes large material stresses to occur, resulting in material deformations, eg. B. flow, or may come to failure of the component.

WO-A-88 09 473, DE-C-31 52 944, WO-A-96 41 995, the abstract of Japanese Patent Application JP-A-62 2001 91 and EP-A go from the state of the art -0,252,275. However, these all describe heat exchangers with comparatively large dimensions, which are constructed of sheets, and on which the necessary contours are formed by molding or deep drawing in a deforming manner. Although this also embodiments of heat exchangers are to be taken, which have support elements in the inlet and / or outlet, due to the relatively coarse structures, a use of such heat exchanger as a micro heat exchanger in the sense described in the introduction is not possible. In particular, since due to the high pressure differences between the heat-exchanging fluids in such large-area structures extremely high forces occur, which can not be coped with by the sheet metal layers and their compounds, as disclosed in these five publications.

Advantages of the invention

Accordingly, the invention has the object to provide a device for heat transfer, which realizes a comparatively large heat-transmitting surface with a small volume and thereby ensures trouble-free operation even at a large different pressure level of the two fluids.

This object is achieved on the basis of a prior art of the aforementioned type by the characterizing features of claim 1.

The measures mentioned in the dependent claims advantageous embodiments and developments of the invention are possible.

Accordingly, a device according to the invention is characterized in that the inlet and / or outlet region comprises at least one support element which, like the channels, is formed by means of an applied or abrasive manufacturing process on the relevant, preferably plate-shaped layers of the device. According to the invention, the resultant free cross-section and in particular the bending moment occurring in the entry or exit area is thereby substantially reduced, with particularly small geometric dimensions being able to be realized by the machining or removal manufacturing process. In this case, an etching method can preferably be used. This ensures that the pressurized surface, in particular on the side operated with a comparatively low pressure, is supported and thus an adverse deformation of the plate is prevented.

In addition, in an advantageous arrangement of the support elements provided on each plate inventive support element corresponding pressure forces from plate to plate forward to possibly a comparatively massive cover plate absorbs the compressive forces, so that deformation of the plates or a failure of the entire component is effectively prevented.

Preferably, numerous support elements are provided both in the entry and in the exit area, so that both the resulting free cross sections and the bending stresses occurring are further reduced.

According to the broadening of the inlet region, this advantageously has comparatively many support elements on the side facing the heat transfer region. However, comparatively few supporting elements are provided on the side of the entry region facing the inlet opening. The corresponding is advantageously transferred to the exit area.

Preferably can be acted upon by reducing the material stresses, for example, compared to a prior art construction and design of the heat exchanger according to the invention with larger pressure differences. Alternatively, the heat exchanger according to the invention compared to the prior art at the same pressure differences between the two fluids have much thinner plates, which can preferably lead to a given mass to be transferred heat and in particular to a significant mass and volume reduction of the entire heat exchanger.

Advantageously, the support elements increase the heat-transmitting surface, so that the heat transfer of the heat exchanger according to the invention is additionally improved. As a result, the volume of a heat exchanger according to the invention can be additionally reduced in an advantageous manner for a given heat output to be transferred.

In a particular embodiment of the invention, the length of the support element is designed as a multiple of its width. This ensures that the support element, for example, with a comparable flow resistance has a much greater support effect and heat-transferring surface. According to the invention, the heat exchanger can hereby advantageously be subjected to a greater pressure difference between the two fluid streams without any disadvantageous material deformation or failure of the heat exchanger.

Advantageously, the support element is designed as a fluid guide element. This makes it possible that an improved fluid flow can be generated by means of the support elements according to the invention. Preferably, by means of support elements according to the invention, the fluid is uniformly distributed to the channels of the heat transfer area or streamlined from the channels and forwarded to a corresponding collection channel. This can be implemented a more uniform distribution of the channel structure of the heat transfer area, which in turn leads to improved heat transfer of the heat exchanger.

In a particular embodiment of the invention, two adjacent support elements are arranged at an angle of less than 20 °, preferably between 10 ° and 15 ° to each other. The opening angle of the fluid flow, the so-called Diffuser angle, according to the prior art, in contrast, is often over 50 °. A comparatively small opening angle between two adjacent support elements according to the invention prevents, for example, a detachment of the fluid flow in the entry or exit area, so that disadvantageous energy losses can be minimized and at the same time uneven loading of the channel structure of the heat transfer area can be prevented. Of crucial importance here is also dependent on the prevailing flow conditions Reynolds number, which is dependent for example on the opening angle, the fluid pressure and the arrangement or design of the support elements or the channels of the heat transfer area.

In particular, for improving the flow conditions, the side wall of the support element is rectilinear and / or curved. Here, the configuration of a support element as a polygon is also conceivable. Preferably, the support elements are material technically and geometrically designed such that they achieve the greatest possible support effect and a very good flow distribution with a comparatively low flow pressure loss. Optionally, elongate support members may advantageously have widened portions for improving the support effect and the flow guidance.

In a particular embodiment of the invention, at least one support element is formed as an extension of a partition between two channels of the heat transfer area. As a result, for example, a much more uniform admission of the channels of the heat transfer area can be realized.

With a corresponding arrangement of the support elements, a further improvement of the flow guidance can be implemented. Is a Support member formed as an extension of the channel partition wall, it is preferably provided a curved transition from the support member to the channel partition. A curved transition can lead to an advantageous fluid flow, so that disadvantageous pressure losses can be minimized. Here, for example, not only the support element may have a curved side wall, but also the channel partition wall may have a curvilinear side wall having at least in the edge region, so that a more favorable fluid flow can be generated. Also, this is a transition with a slight fold, which has a relatively small kink, feasible.

Preferably, the various layers of the stack-shaped or cup-shaped device are formed as flat or curved plates or as cylindrical, stackable due to different diameter components, so that an advantageous production of the heat exchanger according to the invention can be realized. In the variant with flat plates preferably the heat exchanger final cover plates are provided.

In principle, the design and arrangement of the support elements is adapted to the channels of the heat transfer area. For example, the channels and the support elements are produced on or in the layers by means of a removing or applying manufacturing process, so that the support elements and the channels are relatively small to produce.

Preferably, corresponding recesses of the plates are produced by a photolithographic patterning process with a subsequent etching process, so that optionally all process steps both for the production of the channels of the heat transfer region as well as for the production of the support elements in the entry or exit area in each case a work step can be realized.

In a specific embodiment, the heat exchanger is formed by plates stacked on top of one another and soldered together, in which at least partially the corresponding recesses, for example for the formation of the channels or support elements, are provided. In this case, at least one soldering layer can be provided between the plates for a soldering process. The soldering process is advantageously carried out in a vacuum or in an inert gas atmosphere. Preferably, the plates are stacked with at least one intermediate solder layer in the later arrangement of the component on each other and in particular in the cold state, even before the soldering process, pressed. By pressing the plates before the actual soldering process is dispensed with a strong compression of the plates under relatively high temperatures. As a result, relatively expensive pressing tools are dispensed with, which would have to withstand the high soldering temperatures.

embodiment

An embodiment of the invention is illustrated in the drawing and will be explained in more detail with reference to FIGS.

Figur 1

in schematischer Darstellung die Struktur- und Strömungsbedingungen eines Wärmetauschers gemäß dem Stand der Technik,

Figur 2

ein schematisch dargestellter freier Querschnitt durch Überlappung zweier Lagen gemäß dem Stand der Technik,

Figur 3

ein schematisch dargestellter erfindungsgemäßer, reduzierter freier Querschnitt mit geradlinigen Stützelementen,

Figur 4

ein schematische dargestellter erfindungsgemäßer Eintritts- bzw. Austrittsbereich mit verstärkten Stützelementen und

Figur 5

ein schematische dargestellter weiterer Eintritts- bzw. Austrittsbereich mit kurvenförmigen Stützelementen.

Show in detail

FIG. 1

schematically the structural and flow conditions of a heat exchanger according to the prior art,

FIG. 2

a schematically represented free cross section by overlapping two layers according to the prior art,

FIG. 3

a schematically illustrated invention, reduced free cross-section with rectilinear support elements,

FIG. 4

a schematic illustrated inventive entry or exit area with reinforced support elements and

FIG. 5

a schematic illustrated further entrance or exit area with curved support elements.

FIG. 1 shows a heat exchanger according to the prior art. The heat exchanger comprises individual plates 1, 2, 3 for heat transfer, which are soldered or welded together, between two cover plates 8, 9 are packed and with small channels 11, 12, 13 and flow openings 4, 5, 6, 7 are provided. At a inlet opening 14 of the cover plate 8 incoming CO ₂ high pressure (arrow FE2) flows through the flow opening 4 of the heat transfer plate 1 through the middle heat transfer plate 2, through the channels 12 in the direction of arrow down and flows from there through the flow opening 6 of the heat transfer plate first and through the outlet opening 16 of the cover plate 8 (arrow FA2). Furthermore, as indicated by the hatched arrows, CO _{2 of} low pressure (arrow FE 1) flows into an inlet opening 15 of the cover plate 8, through the channels 11 of the Heat transfer plate 1 from bottom to top, further through the flow opening 5 of the heat transfer plate 2 to the heat transfer plate 3 and there also through the small channels from bottom to top and through the corresponding flow openings 7 of the heat transfer plates 3, 2, 1 and then through the outlet opening 17 of the Cover plate 8 off (arrow FA1).

In this way, the illustrated heat exchanger is flowed through by the high-pressure side refrigerant (black arrows) in a first direction and in countercurrent to the low-pressure side refrigerant (hatched arrows).

The heat exchanger shown in Figure 1, due to a more advantageous representation, only three heat transfer plates 1, 2, 3, on. This consists of individual, defined by the heat transfer plates 1, 2, 3 layers in countercurrent to the CO ₂ , which is on one side at high pressure (up to approximately 150 bar) at high temperature and on the other hand at low pressure ( flows up to approximately 60 bar) and low temperature.

In order to adapt the heat exchanger ideally to the occurring heat transfer conditions, it must be considered that the heat transfer is determined by the material properties of the fluid and the flow state. However, the heat transfer coefficient on the low pressure side is generally much smaller than that on the high pressure side. In order to make the most efficient use of the volume of the heat exchanger, it is therefore desirable to match the product of heat transfer coefficient and heat transfer area on the high pressure side to the product of heat transfer coefficient and heat transfer area on the low pressure side. This can be, for example in the illustrated compact heat exchanger, which consists of individual profiles, ie the heat transfer plates 1, 2, 3, in which the small channels 11, 12, 13 are incorporated, carried out by appropriate adjustment of the hydraulic diameter of the small channels 11, 12, 13.

Furthermore, it is possible to increase the heat-transferring surface or the heat transfer coefficient of the heat transfer region by a corresponding flow guidance of the small channels 11, 12, 13, for example in zigzag form.

An inventive heat exchanger can be advantageously made of copper and copper alloy, stainless steel, aluminum and other materials.

An inventive heat exchanger can be used advantageously as an inner heat exchanger of a CO ₂ air conditioning system in vehicles, in particular motor vehicles.

For example, the first (high pressure) flow channel marked by black arrows in a first flow path from a gas cooler to an evaporator and the second (low pressure) flow channel marked by hatched arrows in the figure lie in a second flow path from the evaporator to one Compressor of the vehicle air conditioner.

In the first flow path, a high pressure up to approximately 150 bar and high temperature and in the second flow path, a low pressure to approximately 60 bar and relatively low temperature prevail.

FIG. 2 schematically shows a free cross-section 24 which arises, for example, as a result of overlapping the inlet region E1 of the fluid I with the outlet region A2 of the fluid II according to the prior art. in this connection It is clear that the free cross-section 24 has a comparatively large pressure-loaded surface and thus has to absorb comparatively large material stresses, which can lead to deformations, in particular of the plates 2, 3 and to the failure of the heat exchanger.

FIG. 3 shows a section of the two plates 2, 3 corresponding to the section of FIG. 2. In this case, however, the entry or exit region of the plates 2, 3 according to the invention has support elements 18 according to the invention. The support elements 18 according to FIG. 3 are designed as rectilinear support elements 18. Here are some support elements 18 'formed as an extension of a channel partition 19.

Furthermore, it becomes clear from FIG. 3 that an opening angle α, which is formed from two adjacent support elements 18, is substantially smaller than an opening angle β without support elements 18 according to the prior art according to the invention. Thus, by the structuring by means of the support elements 18, the flow of the fluids distributed more evenly on the channels of the heat transfer area and the opening angle is reduced, for example, from about 50 ° to about 10 ° to 15 °. This leads in particular to the fact that a replacement of the fluid flow, which entails energy losses and an uneven loading of the channel structure 11, 12, 13, is largely prevented. The prevention of detachment and thus the reduction of energy losses depends essentially on the prevailing Reynolds number. This in turn depends, among other things, on the opening angle and also on the set pressures of the fluids.

In addition, FIG. 3 illustrates that the reduced free cross-section 23, compared to the free cross-section 24 of FIG. 2, represents a substantial reduction in the pressure-applied Represent surface and thus significantly reduces the bending stresses occurring. As a result, deformation of the plates 1, 2, 3 or a failure of the heat exchanger is largely prevented.

In particular, supporting elements 18 are shown in FIG. 4, which have local reinforcements 20 for reinforcing the supporting effect according to the invention.

In Figure 5 support elements 18 are shown having a curved side wall. This inventive design of the support elements 18 leads in particular to an advantageous flow guidance and distribution of the fluids to the channels 11, 12, 13. The curved support elements 18 shown in Figure 5 have a polygonal transition 21. A not-shown curved transition 21 can lead to a further improvement of the flow guidance in this case. In the case of a curved transition 21, a curved end region of the channel partition walls 19 may also be advantageous.

The support elements 18 according to the invention distributed the load occurring much better, so that they have an additional supporting function. According to the state of the art, among other things, the occurring load had to be taken over predominantly by the edge regions of the plates 1, 2, 3, so that material can advantageously be saved with the aid of the support elements 18 according to the invention, for example in the edge regions.

Basically, the plates 1, 2, 3 are alternately flowed through by a heat-absorbing and a heat-emitting fluid in a countercurrent or co-current principle. Here, for example, to increase the heat-absorbing or heat-emitting surface more, z. B. two adjacent plates 1, 2 are flowed through by the same fluid and only the subsequent plate 3 and also several adjacent plates are flowed through by the other fluid.

LIST OF REFERENCE NUMBERS

1

plate

2

plate

3

plate

4

opening

5

opening

6

opening

7

opening

8th

cover plate

9

cover plate

11

channels

12

channels

13

channels

14

opening

15

opening

16

opening

17

opening

18

support element

19

partition wall

20

reinforcement

21

crossing

23

cross-section

24

cross-section

FE1

Admission fluid I

FE2

Admission fluid II

FA1

Outlet fluid I

FA2

Outlet fluid II

α

angle

β

angle

Claims (9)

1. Device for heat transmission from a first fluid to a second fluid separated from the first fluid, with a stack-like or tray-like construction comprising at least two layers (1, 2, 3), in particular plates (1, 2, 3), each layer (1, 2, 3) comprising a heat transmission region which has numerous ducts (11, 12, 13), an inlet region arranged upstream of the heat transmission region in the direction of flow, and an outlet region arranged downstream of the heat transmission region in the direction of flow, the inlet region and/or outlet region comprising at least one supporting element (18), characterized in that the ducts (11, 12, 13) and/or the supporting element (18) are produced by means of a material-building and/or material-removing manufacturing method.
2. Device according to Claim 1, characterized in that the removing method is an etching method.
3. Device according to Claim 1 or 2, characterized in that the length of the supporting element is designed as a multiple of its width.
4. Device according to one of the abovementioned claims, characterized in that the supporting element (18) is designed as a fluid guide element (18).
5. Device according to one of the abovementioned claims, characterized in that two adjacent supporting elements (18) are arranged at an angle (α) of less than 20° to one another.
6. Device according to one of the abovementioned claims, characterized in that the side wall of the supporting element is of rectilinear and/or curved design.
7. Device according to one of the abovementioned claims, characterized in that at least one supporting element (18) is designed as a prolongation of a partition (19) between two ducts.
8. Device according to one of the abovementioned claims, characterized in that a curved transition (21) from the supporting element (18) to the partition (19) is provided.
9. Device according to one of the abovementioned claims, characterized in that the layers (1, 2, 3) are designed as plane or curved plates (1, 2, 3) or are cylindrical structural elements (1, 2, 3) stackable one in the other on account of different diameters.

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