EP1305561A1

EP1305561A1 - Heat transfer device

Info

Publication number: EP1305561A1
Application number: EP01951364A
Authority: EP
Inventors: Stephan Leuthner; Petra Beil
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-07-21
Filing date: 2001-06-09
Publication date: 2003-05-02
Anticipated expiration: 2021-06-09
Also published as: ES2248358T3; JP2004504584A; KR20020032602A; BR0106982A; US7040387B2; US20030094271A1; WO2002008680A1; EP1305561B1; DE50107511D1; DE10035939A1

Abstract

The invention relates to a device for transferring heat from a first fluid to a second fluid that is separate from said first fluid. Said device comprises a stack or shell structure comprising at least two layers (1, 2, 3), especially boards (1, 2, 3). Every layer (1, 2, 3) comprises a heat transfer zone with a plurality of channels (11, 12, 13), an inlet zone disposed upstream, in the direction of flow, of the heat transfer zone and an outlet zone disposed downstream, in the direction of flow, of the heat transfer zone. The aim of the invention is to improve such a device in such a way that it provides a comparatively large heat-transferring surface while having a small volume and that it allows a troublefree operation even if there is a large pressure difference between the two fluids. To this end, the inlet and/or outlet zone comprises at least one support element (18).

Description

"Device for heat transfer"

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

State of the art

So far, for example, heat exchangers with a first channel through which a high-pressure refrigerant flows and a second channel through which low-pressure refrigerant flows and separated from the first channel are provided in a C0 ₂ vehicle air conditioning system.

To increase the performance and efficiency of the C0 ₂ process, a so-called internal or internal heat exchanger is provided. The internal heat exchanger is flowed through by the refrigerant (C0 ₂ ) in the counterflow principle or in the cocurrent principle. The fluids flow through the heat exchanger once on the way from the gas cooler to the evaporator and the second time between the evaporator and the compressor. The main task of the internal heat exchanger is to additionally cool the refrigerant before expansion. The heat is transferred from the high pressure side to the gas cooler Low pressure side delivered after the evaporator (before entering the compressor). The partially still liquid refrigerant evaporates completely before it reaches the compressor.

Possible areas of application are for corresponding heat exchangers in vehicle air conditioners, heat pumps, portable air conditioners of low output, dehumidifiers, dryers, fuel cell systems and similar possible applications.

Heat exchangers are already known which are manufactured in a comparatively compact manner in order to reduce mass and volume. To transfer large amounts of heat in a small design, so-called micro heat exchangers are provided, for example. These consist in particular of structured plates that are stacked on top of one another and either soldered, screwed or connected accordingly. Correspondingly provided channels of the heat exchanger are also sealed at the same time. The fluids, which come into thermal contact with one another in the heat exchanger, are conducted via the channels between the plates.

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

The overlap of the entry area with the exit area results in a so-called free cross-section. Due to the large pressure difference between the two fluids, the individual layers in the area of the free cross-section have to withstand the very different pressure levels.

The large pressurized area in the area of the free cross-section leads to large material stresses, which leads to material deformation, e.g. B. flow, or failure of the component.

Advantages of the invention

In contrast, the object of the invention is to propose a device for heat transfer which, with a small volume, realizes a comparatively large heat-transfer surface and thereby ensures trouble-free operation even at large different pressure levels of the two fluids.

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

Advantageous designs and developments of the invention are possible through the measures mentioned in the subclaims.

Accordingly, a device according to the invention is characterized in that the entry and / or exit area comprises at least one support element. According to the invention, the resulting free cross-section and in particular the bending moment that occurs in the entry or exit area are substantially reduced as a result. This ensures that the surface under pressure, in particular on the side operated with comparatively low pressure, is supported and is therefore disadvantageous Deformation of the plate is prevented.

In addition, in an advantageous arrangement of the support elements, a support element according to the invention provided on each plate can transmit corresponding pressure forces from plate to plate until a comparatively massive cover plate absorbs the pressure forces, so that deformation of the plates or 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 that occur are further reduced.

Corresponding to the widening of the inlet area, this advantageously has a comparatively large number of support elements on the side facing the heat transfer area. However, comparatively few support elements are provided on the side of the entry area facing the entry opening. The corresponding is advantageously transferred to the exit area.

Preferably, by reducing the

Material stresses, for example, compared to a design and construction of the heat exchanger according to the invention corresponding to the prior art, are subjected to greater pressure differences. As an alternative to this, the heat exchanger according to the invention can have much thinner-walled plates in comparison to the prior art with the same pressure differences between the two fluids, which can preferably lead to a significant reduction in mass and volume of the entire heat exchanger, given the heat output to be transferred. The support elements advantageously increase the heat-transferring surface, so that the heat transfer of the heat exchanger according to the invention is additionally improved. This means that, given the heat output to be transferred, the volume of a heat exchanger according to the invention can be additionally reduced.

In a special development 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 substantially 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 disadvantageous material deformation or failure of the heat exchanger.

The support element is advantageously designed as a fluid guide element. This enables an improved fluid flow to be generated by means of the support elements according to the invention. Preferably, the fluid is distributed uniformly over the channels of the heat transfer region by means of support elements according to the invention or is merged from the channels in a flow-favorable manner and passed on to a corresponding collecting channel. With this, a more evenly distributed loading of the channel structure of the heat transfer area can be implemented, which in turn leads to an improved heat transfer of the heat exchanger.

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

In particular in order to improve the flow conditions, the side wall of the support element is straight and / or curved. The design of a support element as a polygon is also conceivable. The support elements are preferably constructed in terms of materials and geometry in such a way that they achieve the greatest possible support effect and a very good flow distribution with a comparatively low loss of flow pressure. If appropriate, elongated support elements can advantageously have widened sections to improve the support effect and the flow guidance.

In a special development of the invention, at least one support element is designed as an extension of a partition between two channels of the heat transfer area. This makes it possible, for example, to implement the channels of the heat transfer region in a much more uniform manner.

With a corresponding arrangement of the support elements, a further improvement of the flow control can be implemented. Is a Support element formed as an extension of the channel partition, a curved transition from the support element to the channel partition is preferably provided. A curved transition can lead to an advantageous fluid flow, so that disadvantageous pressure losses can be minimized. In this case, for example, not only can the support element have a curved side wall, but the channel partition wall can also have a curved side wall, at least in the edge region, so that a more favorable fluid flow can be generated. A transition with a slight bend, which has a comparatively small kink, can also be realized here.

The various layers of the stack-like or shell-shaped device are preferably designed as flat or curved plates or as cylindrical components which can be stacked one inside the other due to different diameters, so that advantageous production of the heat exchanger according to the invention can be realized. In the variant with flat plates, cover plates closing the heat exchanger are preferably provided.

Basically, the design and arrangement of the support elements are 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 removal or coating manufacturing process, so that the support elements and the channels can be produced comparatively small.

Corresponding recesses in the plates are preferably produced by means of a photolithographic structuring process with a subsequent etching process, so that, if appropriate, all process steps both for producing the channels of the heat transfer region and for producing the support elements in the entry and exit regions in each case one step can be implemented.

In a specific embodiment, the heat exchanger is formed by plates stacked one on top of the other and soldered to one another, in which at least some of the corresponding recesses are provided, for example for forming the channels or support elements. At least one solder 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. The plates are preferably stacked one above the other with at least one intermediate solder layer in the later arrangement of the component and pressed in particular in the cold state, even before the soldering process. By pressing the plates before the actual soldering process, the plates are not pressed firmly at comparatively high temperatures. This eliminates the need for comparatively complex pressing tools that would have to withstand the high soldering temperatures.

embodiment

An embodiment of the invention is shown in the drawing and is explained in more detail below with reference to the figures.

Show in detail

FIG. 1 shows a schematic representation of the structural and flow conditions of a heat exchanger according to the prior art, FIG. 2 shows a schematically illustrated free cross section by overlapping two layers according to the prior art,

FIG. 3 shows a schematically illustrated, reduced free cross section according to the invention with straight support elements,

Figure 4 is a schematically illustrated entry or exit area according to the invention with reinforced support elements and

FIG. 5 shows a schematically illustrated further entry or exit area with curved support elements.

A heat exchanger according to the prior art is shown in FIG. The heat exchanger comprises individual plates 1, 2, 3 for heat transmission, which are soldered or welded together, packed between two cover plates 8, 9 and provided with small channels 11, 12, 13 and flow openings 4, 5, 6, 7. At an inlet opening 14 of the cover plate 8 flowing C0 ₂ high pressure (arrow FE2) flows through the flow opening 4 of the heat transfer plate 1 to the middle heat transfer plate 2, through its channels 12 down in the direction of the arrow and from there continues to flow through the flow opening 6 of the heat transfer plate 1 and through the outlet opening 16 of the cover plate 8 (arrow FA2). Furthermore, as the hatched arrows indicate, C0 ₂ low pressure (arrow FEI) 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 through to the heat transfer plate 3 and there also through its 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 Cover plate 8 off (arrow FA1).

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

The heat exchanger shown in Figure 1 has only three heat transfer plates 1, 2, 3, due to a more advantageous representation. This consists of individual layers defined by the heat transfer plates 1, 2, 3, which are in counterflow from the C0 ₂ , which is on one side at high pressure (up to approximately 150 bar) at high temperature and on the other side at low pressure ( up to approximately 60 bar) and at a low temperature.

In order to adapt the heat exchanger ideally to the heat transfer conditions that occur, it must be taken into account 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, the basic aim should therefore be that the product of the heat transfer coefficient and the heat transfer surface on the high pressure side be the product

Heat transfer coefficient and heat transfer area on the low pressure side is adjusted. For example in the compact heat exchanger shown, which consists of individual profiles, ie the heat transfer plates 1, 2, 3, into which the small channels 11, 12, 13 are incorporated, by appropriate adjustment of the hydraulic diameter of the small channels 11, 12, 13.

Furthermore, there is the possibility of increasing the heat transfer surface or the heat transfer coefficient of the heat transfer region by appropriate flow guidance of the small channels 11, 12, 13, for example in a zigzag shape.

A heat exchanger according to the invention can advantageously be produced from copper and copper alloy, stainless steel, aluminum and other materials.

A heat exchanger according to the invention can advantageously be used as the inner heat exchanger of a C0 ₂ -lima system in vehicles, in particular motor vehicles.

For example, the first (high pressure) flow channel marked by black arrows in FIG. 1 lies 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 lies in a second flow path from the evaporator to one Vehicle air conditioning compressor.

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

FIG. 2 schematically shows a free cross section 24, which arises, for example, by overlapping the inlet area E1 of the fluid I with the outlet area A2 of the fluid II according to the prior art. in this connection it becomes clear that the free cross section 24 has a comparatively large area under pressure and therefore has to absorb comparatively large material stresses, which can lead to deformations, in particular of the plates 2, 3, and to failure of the heat exchanger.

FIG. 3 shows a section of the two plates 2, 3 corresponding to the section of FIG. 2. Here, however, the entry or exit area 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, some support elements 18 'are formed as an extension of a duct partition 19.

It is also 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. The structuring by means of the support elements 18 thus distributes the flow of the fluids more evenly over the channels of the heat transfer area and the opening angle is reduced, for example, from approximately 50 ° to approximately 10 ° to 15 °. In particular, this has the result that a detachment 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 essentially depends on the 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 significantly reduces the pressurized pressure Represents area and thus significantly reduces the bending stresses that occur. This largely prevents deformation of the plates 1, 2, 3 or failure of the heat exchanger.

FIG. 4 shows, in particular, support elements 18 which have local reinforcements 20 to reinforce the support effect according to the invention.

5 shows support elements 18 which have 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 FIG. 5 have an angular transition 21. A curved transition 21, not shown in more detail, can lead to a further improvement in the flow guidance. In the case of a curved transition 21, a curved end region of the channel partition walls 19 can also be advantageous.

The support elements 18 according to the invention distributed the occurring load much better, so that they have an additional load-bearing function. According to the prior art, inter alia, the occurring load had to be taken over predominantly from the edge regions of the plates 1, 2, 3, so that material can be advantageously saved in the edge regions, for example, with the aid of the support elements 18 according to the invention.

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

Reference symbol list:

1 plate

2 plate

3 plate

4 opening

5 opening

6 opening

7 opening

8 cover plate

9 cover plate

11 channels

12 channels

13 channels

14 opening

15 opening

16 opening

17 opening

18 support element

19 partition

20 reinforcement

21 transition

23 cross section

24 cross section

FEI fluid I entry

FE2 fluid II entry

FA1 Fluid I outlet

FA2 outlet fluid II α angle ß angle

Claims

Expectations;

1. Device for heat transfer from a first fluid to a second fluid separated from the first fluid with * a stack-like or shell-shaped structure comprising at least two layers (1, 2, 3), in particular plates (1, 2, 3), each layer (1, 2, 3) comprises a heat transfer area which has numerous channels (11, 12, 13), an inlet area arranged upstream of the heat transfer area and an outlet area arranged downstream of the heat transfer area, characterized in that the inlet and / or exit area comprises at least one support element (18).

2. Device according to claim 1, characterized in that the length of the support element is designed as a multiple of its width.

3. Device according to one of the preceding claims, characterized in that the support element (18) is designed as a fluid guide element (18).

4. Device according to one of the preceding claims, characterized in that two adjacent support elements

(18) are arranged at an angle (α) of less than 20 ° to one another.

5. Device according to one of the preceding claims, characterized in that the side wall of the support element is rectilinear and / or curved.

6. Device according to one of the preceding claims, characterized in that at least one support element (18) is designed as an extension of a partition (19) between two channels.

7. Device according to one of the preceding claims, characterized in that a curved transition (21) from the support element (18) to the partition (19) is provided.

8. Device according to one of the preceding claims, characterized in that the layers (1, 2, 3) as flat or curved plates (1, 2, 3) or cylindrical, due to different diameters stackable components (1, 2, 3rd ) are trained.