DE2250222B2 - Plate-shaped heat exchanger wall - Google Patents

Description

The invention relates to a plate-shaped heat exchanger wall, which at least in certain surface areas with essentially evenly distributed frustoconicals pointing in the same direction Stützyorsprüngen is provided in the form of wall bulges, which at their ends a load-bearing Have support surface which is designed so that they are against a corresponding support surface of a can support further heat exchanger wall.

Heat exchanger walls of the type indicated are preferred for the construction of coolers for water-cooled Internal combustion engines used in the automotive industry. Especially with this one Area of application, it is essential that the individual heat exchanger elements are light and cheap. Since motor vehicle engines work at elevated temperatures today and will continue to do so in the future it is to be expected that these temperatures will increase, it is already largely necessary that in Motor vehicle radiators are operated with a certain overpressure. Motor vehicle radiators are therefore for design a pressure of at least 1.02 bar.

With lamellar coolers and similar designs in which the components carrying the coolant do not themselves represent the heat-exchanging surfaces, but rather are designed as tubes, which in turn come with Secondary heat exchange surfaces such as fins or the like. Are occupied, offers the requirement for one A certain pressure increase is not a problem, since the pipes carrying the coolant are dimensioned accordingly can be.

The situation is different with heat exchangers of the so-called primary surface type, in which the components enclosing the media or media are at the same time the heat-exchanging surfaces. These primary surface heat exchangers are constructed, for example, from plate-shaped heat exchanger walls of the type mentioned at the beginning and generally have neither to increase the strength nor to improve -! The heat transfer is enhanced by any additional internal or external components, such as reinforcing ribs , fins or the like. Rather, the heat transfer takes place directly between the plates and the flowing media. Relatively high demands are placed on the plate-shaped heat exchanger walls used for this, ίο because on the one hand they are intended to ensure optimal heat exchange and on the other hand must absorb the entire hydraulic or pneumatic load.

When building heat exchangers, the plate-shaped heat exchanger walls used for this must do not necessarily remain flat throughout, they can also be curved or to form closed channels returned to themselves and to one another at their ends be connected. In the case of individual heat exchanger elements or channels manufactured in this way are, there is the possibility that the frustoconical support projections either all for Inside the channel element are directed, or protrude into the outer surrounding space. In the case of inwardly pointing support projections, the distance between the walls of the channel element is determined by the abutting support projections of the adjacent walls. This type

jo is preferred when the medium has higher pressure flows around the individual channel elements constructed in this way from the outside. The opposite walls of the duct element are under complete pressure equalization, as both walls

) 5 on the other hand, are equally burdened and by means of their Support projections in the interior of the channel element can support each other. The higher one rules Pressure inside the channel element, it is expedient in this design, the two heat exchanger walls to connect to each other at their mutually touching support projections. This can done for example by soft soldering, hard soldering or by gluing.

If the pressure inside the duct elements is higher, however, it is also possible to design them in such a way that that the support projections point outwards. With this type of construction, a heat exchanger can easily be Way can be put together in that several channel elements are joined together in a stack be, the distance between the individual channel elements by the abutting Support projections of adjacent channel elements is determined. With such a structure, however, there is no complete pressure equalization given, on the outside of the stack must be additional, load-bearing Components are provided.

Heat exchangers with plate-like heat exchanger walls of the type indicated at the outset are for example from DE-OS 1601154 and DE-OS

bo 1501537 known. While DE-OS 1601154 especially in the Fig. 3 shows a type in which the support projections of a channel element according to face outside and thereby determine the mutual distance between adjacent duct elements,

-b5 shows the DE-OS 1 501537 in its Fig. 3 an embodiment, in which the support projections are directed towards the interior of the channel element. As Walls of the heat exchanger surfaces used in these

Sen documents described above devices are indeed with frustoconical support projections provided in the form of one-sided wall bulges, which are used to provide a spacer and To achieve pressure support between the individual heat exchanger walls, in none of these However, there is a reference to how these frustoconical wall bulges can be found in publications are to be dimensioned favorably. Only the figures dgt DE-OS 1601154 one can see a cone angle of 45 ° for these bulges, see the perspective representations in the DE-OS 1501537, on the other hand, hardly allow any conclusion to be drawn selected cone angle. A hint for the choice of this construction parameter can possibly also be from GB-PS 820554, however, the heat exchanger walls with bulges on both sides shows. In the associated description, a cone angle of 60 ° is expressly stated for the bulges in the wall called. About other dimension-determining parameters of the support projections in the known The cited publications, however, do not reveal anything about heat exchangers.

When arranging the support projections, it is important that they are in a sufficient number and appropriate distribution are provided in order to act on the heat exchanger walls pressure loads as far as possible to be sufficiently absorbed in the entire surface area of the wall. But has one Increasing the number of support projections at the same time has the disadvantage that this results in the free flow cross section between two by means of these projections mutually supported walls is reduced. On the other hand, if you choose a larger wall thickness for the heat exchanger walls in question, the heat transfer through them deteriorates.

The invention is based on the object of providing heat exchanger walls of the type indicated at the outset to improve that they have an increased pressure resistance with improved flow conditions at the same time and have good heat transfer, with the aim of making the heat exchanger walls thinner and Easier to perform without the number of mutual formed by the bulges Support points of the walls increased or other additional support parts used in the finished heat exchanger would have to be. It is also thought of because of the improvements sought possibly cheaper construction materials with a possibly slightly poorer heat transfer value to be able to use without the heat exchange effect known designs to worsen significantly.

According to the invention, this object is achieved by the dimensions specified in the characterizing part of the patent claim solved.

The inventive design of the conical support projections with a small angle of inclination is beneficial in two ways. Once it has surprisingly been found that the cone angle below 35 ° in connection with the corresponding transition in the heat exchanger wall to a substantial lead to higher strength, on the other hand, projections formed in this way reduce dead flow corners within the channel element, so that this design also improves the heat transfer can be.

This means that the heat exchanger wall does not

necessarily made of a highly thermally conductive material needs to exist. Metals, metal alloys, clad metals, but also use plastics, plastic-coated metals and the like. Among the metals come in particular Copper, steel, magnesium and titanium in question.

In order to reduce the flow resistance due to the support projections and the degree of effectiveness the heat transfer for each specific flow area of a heat exchanger channel as possible To keep the wall large, the frustoconical projections supporting the wall should only be in such Size, number and distribution can be provided and arranged as required by need will be able to withstand the maximum differential pressure that occurs. If doing of more uniform Distribution of the support projections is in question, it does not need this over the entire heat exchanger wall to pass. The distribution pattern can, for example, also include progressive changes have in the spacings of the support projections at least along one axis of the heat exchanger wall. It is only essential that the support projections of adjacent heat exchanger walls on the same Places lie. As a stress concentration in the bending area of a heat exchanger wall in its Intended use can occur, additional, the wall-supporting frustoconical Projections can also be provided in the vicinity of the bending area to avoid the stresses occurring better to balance over the entire heat exchanger wall.

In the following the invention is described in more detail with reference to the drawings. It shows

Fig. 1 is a diagram showing the surface deflection of a heat exchanger wall made of aluminum shows as a function of the pressure applied, once for a heat exchanger wall with support projections in a stressed training with cone angles of 30 ° and to the other for a heat exchanger wall in conventional design with conical angles of the support projections from 45 °,

Fig. 2 is a perspective view of a row of adjacent, channel elements of a heat exchanger made of heat exchanger walls designed according to the invention, their supporting projections are directed outwards,

3 shows a schematic cross section through the channel elements along the line IU-III in FIG the characteristic dimensions of the conical support projections can be seen, and

F i g. 4 shows a section through part of a heat exchanger in which the conical support projections of the plate-shaped heat exchanger walls directed towards the interior of the channel elements formed from them are.

Reference is first made to FIG. 3, which is a schematic cross-section through three contiguous Channel elements of a heat exchanger shows that by bending a plate-like Wärmetauccherwand have arisen, the conical support projections with respect to the respective channel element are directed outwards. Is indicated in Fig. 3, the cone angle β of the support projections, the in the execution exampleDiel 32 ° concerned. Still anee-

give is the radius of curvature R in the transition area of the base of the conical jacket surface of a support projection into the flat base surface of the heat exchanger wall. Finally, D denotes the center-to-center distance of two conical support projections that are closest to one another. Further relevant parameters for the dimensioning of plate-like heat exchanger walls with one-sided convex, frustoconical support projections are the height H of these support projections and the diameter d of the support surface at the head of each support projection. If the support projections do not have a circular support surface, the equivalent diameter d of the support surface results as the quotient of four times the area dimension of the support surface and the circumference of the support surface.

The cone angle Θ should be less than 35 ° and the ratio RID greater than approximately 0.075. The distance D itself is expediently between approximately 0.5 and 6.4 cm. The ratio DId can be selected between 3 and 10 and the ratio HId approximately between 0.05 and 0.2. The preferred wall thickness t is between about 0.076 and 6.4 mm.

The limitation of the distance D arises because a distance of less than 0.5 cm would result in very narrow gaps as passage channels on the side of the heat exchanger wall provided with the projections, whereby there is the risk of clogging, for example due to impurities contained in the flowing medium . Furthermore, there would be a high external pressure drop per unit length of the flow path. If the distance D approaches 6.4 cm, this would lead to a small heat exchange area per unit space of the heat exchanger volume, so that the manufacturing costs would be high and the efficiency would be low. The ability of the material to withstand a differential pressure on both sides of the wall with the same wall thickness would also be reduced if the distance between the support projections is too great.

If the ratio DId is less than 3, the permissible differential pressure on both sides of the wall of a heat exchanger element consisting of a duct increases, but a large proportion of the area would be lost for heat exchange purposes. On the other hand, a ratio DId of more than 10 would require very close manufacturing tolerances in order to ensure the meeting of the load-bearing sections (bosses) of walls in contact with one another; in addition, this would localize and concentrate the load on the contact points of the load-bearing sections, so that such high stresses occur that lead to breakage or severe deformation of the walls.

A heat exchanger with channels with frustoconical projections, in which the ratio HID is less than 0.05, has the risk of clogging and has a high external pressure drop per unit length of the flow path. For an HID ratio of more than 0.02, a small heat exchange area per unit of space of the heat exchanger volume is obtained, as a result of which the manufacturing costs are high and the efficiency is lower. A RID ratio of less than 0.075 results in high stresses at the delimiting line of intersection of the conical protrusion with the undeformed wall surface near the protrusion. The delimiting cutting line becomes a line of high stress concentration.

A heat exchanger wall with frustoconical projections with a cone angle of more

"> than 35 ° would lead to high deflections if the wall is pressurized. If such deflections occur repeatedly during operation, the material can tire and break after a relatively short period of operation. In addition,

U) like deflections the available distance between the heat exchanger walls in the passage channels with lower pressure and lead either to a higher pressure drop or to a lower flow rate.

A material thickness of less than 0.076 mm would be unsuitable because of local errors in the metal like them during rolling, corrosion or erosion. Embodiments in which the compressive forces are not balanced within the channels,

2i) require strong external components to withstand the load take up, while embodiments with balance of forces, in which the wall supporting Projections are connected to each other and are under tensile load, a considerable tension con-

- ' ^r > have centering in these connected surface areas.

In order to meet the special requirements for heat exchangers used as coolers for internal combustion engines should serve the ranges given above

so narrowed in the following way: the recurring distance D should be approximately between 0.5 and 1.5 cm; the ratio DId should be approximately between 3 and 7; the HID ratio should be approximately between 0.05 and 0.12; the angle Θ should be less than about 35 °, preferably less than about 30 "; the ratio RID should be greater than about 0.075; the plate or wall thickness should be between about 0.076 mm and 0.5 mm. The preferred dimensions of a surface with frustoconical projections for use as a motor vehicle radiator are: a recurring distance D of about 1 cm, a height H of about 0.9 mm, a support surface diameter d of about 2.3 mm, a ratio DId of about 4.8, a ratio HID of about 0.08, an angle Θ of less than about 30 °, a ratio RID of greater than about 0.075, and a wall thickness of about 0.2 mm.

To explain the invention, the following

ίο described a motor vehicle radiator as an example, at which the above-described heat exchanger elements of the primary surface type are used.

The deflection of frustoconical projections walls necessary for the application in automotive radiators have been investigated and curves of the applied Pressure (bar) plotted against the surface deflection (mm) for aluminum sheets with a thickness of 0.2 mm, which have frustoconical projections with taper angles of 30 ° and 45 °.

The sheets were stamped with frustoconical projections supporting the wall arranged in a square pattern. The distance D between the projections was 1 cm and the height H of the supporting projections was 0.9 mm. Then pressure was applied to the surface of the aluminum sheet on the intended side in order to stress the material of the cone in pressure; the

Deflection in the center of the diagonal of the square pattern was measured. These values are in Fig. 1 plotted as curves for cone angles of 30 ° and 45 °.

Deflections of the material, which lead to a deformation of the wall, are undesirable and should be kept as low as possible, even if such deflections are still undoubtedly below of the bulging point of the material. In addition, the material will usually flex when it deflects subjected to bending and shearing; if the deflections are very high, the material can Experience tensions that go to the yield point in limited areas. When this deflection occur repeatedly during operation, the material can become fatigued and after a relatively short period of operation break. In addition, the deflections reduce the available space between the heat exchanger walls in the passage channels with lower pressure, resulting in either a higher pressure drop or a reduced flow rate leads. From Fig. 1 it can be seen that the area used in the experiment with 30 "cones is a relatively small deflection in the middle of the diagonal of the square pattern of the frustoconical Shows protrusions at differential pressures of 2.5 bar. In contrast, the deflection was the The area with the 45 "cones is about twice as large as the curvature of the area with the 30 ° - Cones for differential pressures up to this limit of 2.5 bar.

In the tests described with surfaces with a 30 ° and 45 ° cone angle, the material tension was also measured directly by means of strain gauges at 2.1 bar differential pressure. The stress was measured on the diagonal at the point where the inclined surface of the conical protrusions meets the flat undeformed surface section of the material, ie in the arc with the radius R. The following values were obtained:

area

tension

30 "cone 127 kPa

45 "cone 289 kPa

The values show the higher tension when using the surface with 45 "cones instead of 30 ° cones; one recognizes the high tension in the arc with the radius R in the surface with the 45" cones.

It is essential that the entire surface area, except for the area supporting the wall, is unhindered so that it can bend freely and therefore remains free from local mechanical stress. As can best be seen from FIGS. 2 and 3, the undeformed ones disappear when they are glued together Areas the passage channels between the

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sen surfaces glued together; if bars or supports are used, a suitable distance apart to create in between, a major advantage of this design is lost.

When the dimensions of the desired frustoconical projections supporting the wall of a heat exchanger element and the dimensional relationships between them are determined, a Die od. The like. Be prepared in the usual way. The die can be made in conventional devices used to form the desired frustoconical projections by pressing, stamping or rolling in a thin-walled, thermally conductive sheet or sheet, for example made of aluminum. For use as a cooler or radiator, a rectangular aluminum sheet with the frustoconical Projections by punching or the like. Are provided. When the sheet metal will be folded should, then the middle fold area remains free of jumps. The sheet metal can be of any desired thickness, with a thickness of about 0.2 mm being preferred will.

2 and 3 show as an example some channel-like heat exchanger elements 21, which are made of plate-shaped Heat exchanger walls exist or are made and outwardly pointing support projections 22 have. The passage channels 23 in the elements 21 form a group of closed Passage channels independently and separately from a second group of passage channels 24, the are formed between adjacent elements 21. A fluid that can flow, shown with the lines drawn out Arrows, can be passed through the passage channels 23 in the elements 21 while at the same time a second cooler medium, shown with broken arrows, through the passage channels 24 can be conducted to ensure effective heat transfer from the hotter medium to the cooler Medium without these being mixed. Fig. 4 shows a similar stack of Elements 30, but with the projections 31 supporting the wall facing inward. Passage channels 32 within the elements 31 are independent and separate from the passage channels 33 between them adjacent elements 30 are formed. A fluid medium, represented by solid lines Arrows, can be passed through the passage channels 32, while at the same time a second cooler Flowable medium can be passed through the passage channels 33 to an effective To achieve heat transfer from the hotter medium to the cooler medium without these being mixed will. For this type of element arrangement, spacers 34 are required to the To keep elements 30 at a sufficient distance to form the passage channels 33.

In addition 3-sheet drawings

Claims (1)

Claim: Plate-shaped heat exchanger wall, which is provided at least in certain surface areas with essentially evenly distributed, pointing in the same direction, frustoconical support projections in the form of wall bulges, which have a load-bearing support surface at their ends, which is designed so that they are against a corresponding support surface of a can support further heat exchanger wall, characterized in that the ratio R / D is greater than approximately 0.075 and the cone angle θ less than 35 °, where R is the radius of curvature of the surface pieces on both sides of the delimiting line of intersection through the support projection and the undeformed surface of the Wall is formed near the projection, D is the distance between the centers of the closest adjacent support projections of the wall, and Θ the acute angle between the horizontal, undeformed surface of the wall near the support projection and the substantially straight line along the sloping jacket surface surface of the support projection is.