WO1990005887A1

WO1990005887A1 - Heat exchanger

Info

Publication number: WO1990005887A1
Application number: PCT/DK1989/000277
Authority: WO
Inventors: Uffe Dan Nielsen
Original assignee: Uffe Dan Nielsen
Priority date: 1988-11-22
Filing date: 1989-11-21
Publication date: 1990-05-31
Also published as: EP0458786A1; DK649988D0; AU4645489A; EP0458786B1; DE68908720D1

Abstract

A heat exchanger has walls of plastic foil for demarcation between two groups of slot-formed channels for a first and a second fluid respectively. In order to hold the walls (10, 14, 15) of the channels at a mutual distance, in each channel there is disposed a continuous distance-holding layer (7, 9) of metal or plastic material which is configured as projections, ribs or another surface structure, so that a fluid can flow through the channel (6, 8) while the channel's walls (10, 14, 15) lie up against the distance-holding layer (7, 9). The structure formed by the walls (10, 14, 15) and the distance-holding layers (7, 9) is built into a compression casing (11, 12, 13, 16, 17), so that an over-pressure in the channels (6, 8) is transferred to the compression casing (11, 12, 13, 16, 17). The walls (10, 14, 15) can be wound in spiral form. The heat exchanger can be built up of a foil tube, in which is placed an inner distance-holding layer (7), and which is wound together with an outer distance-holding layer (9) placed on the outside of the foil tube. By melting down, plane end plates (18, 19) can be formed in the ends of the heat exchanger. The distance-holding layers are of metal and/or plastic wave.

Description

HEAT EXCHANGER

The invention relates to a heat exchanger, where the fluids which are required to exchange heat are separated from each other by walls of plastic.

Compared to metals, plastic materials have a number of advantageous characteristics which can prompt the use of plastic materials instead of metals in heat exchangers. Of such characteristics can be mentioned better resistance against corrosion, lower specific weight, easier and less energy-demanding moulding and lower price than metals. The poor heat conduct¬ ing abilities of the plastic materials, which typ- ically comprise a hundredth or less of the heat con¬ ducting abilities of metals, are however an argument against a production of heat exchangers of plastic. The same applies for the relatively poor heat-resis¬ tance of the plastic materials, in that many plastic materials lose a considerable part of their strength as soon as they are heated to the boiling point of water or less.

In spite of these drawbacks, heat exchangers of plastic have gained a footing in a number of areas of application. The most important of these areas is probably that of heat pumps, where heat exchangers of plastic are today finding widespread use as earth heating pipes, heat absorbers in stables and cow- sheds, energy-recovery devices and similar applica¬ tions. Common to all these areas of application is that a relatively large volume stands at disposal for the heat exchanger, so that in the light of the plastic materials' good characteristics, one can compensate for the poor heat conductivity by in¬ creasing the heat exchange area.

It has proved that with gas/gas and gas/fluid heat exchanging, only a modest increase in the area is required in order to compensate for the lower heat conducting abilities of the plastic materials, in that it is the transitional resistance from the gas to the heat exchanger wall rather than the heat conducting ability which is the limiting factor.

Theoretical calculations show that the increase in area required lies typically between 10% arid 50%. The conditions with fluid/fluid heat exchanging are otherwise, in that here the heat conducting ability is the decisive factor, and theoretical calculations show that the area must be multiplied by a factor of between 5 and 25 in order to achieve the same capa¬ city in a heat exchanger of plastic as that in a corresponding heat exchanger of metal.

Attempts have been made to compensate for the poor heat conductivity by reducing the thickness of the material. This has led to the development of heat exchangers on the basis of thin-walled foil tubes as described, for example, in DE document no. 24 06 974.

The heat exchanger according to this document is equipped with a number of foil tubes with a wall thickness of between 10 and 50 micrometers. The tubes are surrounded by a reinforced grid or net for the purpose of absorbing the pressure load from the fluid carried in the tubes. From DE publication no. 26 45 072 is known a heat exchanger which has a number of walls built up of extruded channel profiles of plastic with rectang¬ ular or round channels for the demarcation of a first group of slot-formed channels, which are in¬ tended for the through-flow of a first fluid, from a second group of slot-formed channels which are intended for the through-flow of a second fluid, and where the second group's channels lie between the first group's channels, and where elements are provided in each channel for holding the channel' s walls at a distance from each other.

This heat exchanger, which is shown in fig. 2 of the publication, is built up of four spirally-wound channel profiles, between which are placed corrugated bands of metal or hard plastic. The channel profiles are relatively flat, extruded bands with two plane walls, between which connection ribs are extended at regular intervals. The ribs hold the walls of the tubes at a distance from each other, while at the same time they hold these band-formed tubes in shape. The heat exchanger is intended for air/water heat exchanging of the cross-flow type, in that water flows through the spirally-wound tubes while the air flows through the spaces between the tube windings transversely to the water's direction of flow.

According to the information in the DE publication no. 26 45 072 referred to, the flattened, relatively thin-walled bands with slot-formed channels des¬ cribed, which are seen in fig. 1B of the publica¬ tion, can only be used at low pressure and low tern- peratures, whereas a use with higher pressures and higher temperatures requires a more thick-walled configuration of the plastic tube band with round channels as shown in the publication's fig. 1A.

Seen in relation to the technique known from this DE publication no. 26 45 072, the technical object of the invention is to provide a heat exchanger which can be used at higher pressures than the hith- erto known constructions, said heat exchanger being also capable of being used with relatively large differential pressure between the channels, and for the function of which it is of no significance which of the two media which shall exchange heat has the greater pressure. Furhermore, the heat exchanger shall also be capable of being used both as a cross -flow and as a counter-flow heat exchanger.

This object is achieved with a heat exchanger of the above-mentioned type, said heat exchanger according to the invention being characteristic in that the mentioned elements for holding the walls of the channel at a distance from each other comprise a continuous distance-holding layer of metal and/or plastic material disposed in the channel and con¬ figured with projections, ribs or other surface structure in such a manner that a fluid can flow through the channel while the channel's walls lie up against the distance-holding layer, and that the structure formed by the walls and the distance -holding layers is built into a pressure-absorbing casing in such a manner that each wall either lies between and up against two distance-holding layers or between and up against a distance-holding layer and the casing, whereby an over-pressure in the channels is transferred to the pressure-absorbing casing.

In the heat exchanger according to the invention, there is thus disposed a continuous distance-hold¬ ing layer of metal and/or plastic material in all channels. The heat exchanger hereby distinguishes itself from the heat exchanger described in the publications referred to, in which according to the first-mentioned publication there are no means whatsoever for holding the walls of the channels away from each other, and wherein according to the second publication there is relatively large dis- tance between the separated ribs which hold the walls of the channels at a distance from each other.

With the special configuration of the surface of the distance-holding layer according to the invention, it is effectively prevented that a channel is closed for through-flow by a possible external over-pres¬ sure. The heat exchanger according to the invention hereby distinguishes itself from the heat exchangers described earlier, in that the plastic tubes in these constructions will be pinched together if the outer pressure lies above the pressure inside the plastic tubes . The separate ribs in the flat tube bands described in the last-mentioned publication do not effectively safeguard against such a pinch- ing flat of the tube bands, the reason being that the connecting ribs between the walls do not form a continuous layer in the plastic tube.

The applicability of the heat exchanger according to the invention at greater values of pressure is ensured by the building-in of a pressure-absorbing casing in the manner disclosed in claim 1 , in that this construction has the effect that the load from an inner over-pressure is transferred to and ab¬ sorbed by the compression casing. By disposing all of the plastic walls in contact with the distance -holding layers, it is also ensured that the plastic walls do not move to any substantial degree with changes in the pressure conditions in the heat ex¬ changer, and that it is without significance for the operation of the heat exchanger which fluid exercises the greater pressure.

Compared to the known heat exchangers of plastic, the heat exchanger according to the invention can be characterized as a minimum construction. In ef¬ ficient plastic heat exchangers, for reasons of the poor heat conducting abilities of the plastic, the transition of heat is almost proportional to the material thickness of the heat exchanger surfaces. From this it follows that the performance of a heat exchanger of plastic is approximately proportional to said material thickness.

Therefore, for an increase in performance, it is of vital significance to minimize this thickness, which is directly dependent on the power effects which have to be absorbed by the heat exchanger surfaces.

In order to achieve an optimum construction, it is expedient to allow the heat exchanger surfaces to participate as little as possible in the supporting construction. It is also expedient, in achieving an optimum construction in plastic, to allow the con¬ struction to absorb and transfer thrust forces and possibly purely tractive forces, but as few bending stresses as possible.

A small thickness of the exchanger surfaces is achieved by reducing the spans in a slack foil wall to a minimum, at the same time that the heat ex¬ changer wall does not participate in the supporting construction.

The pressure is absorbed by counter-pressure via the distance grid, and is transferred to a cylin¬ drical container wall where the forces are absorbed as traditional annular stresses in a pipe.

Plastic foils are at present characterized by being

2 highly technological products at extremely low m prices which can be produced with very small thick- nesses and extremely small tolerances.

2 The small amount of raw materials per m of the exchanger surface makes it economically realistic to use expensive heat-resistant and chemical-res- istant types of plastic.

With the heat exchanger according to the invention, there is thus achieved a construction which is both compact and robust with minimal material consump- tion and minimal production costs. Consequently, the price/performance ratio will be many times better than for existing solutions, particularly in the case of fluid/fluid and condensing solutions, where the solutions will be competitive with the most optimal metal solutions. For reasons of the drop-condensation and the extremely low material thickness, performances can be achieved which per

2 m of the exchanger surface are greater than with the best of the metal exchangers.

With the heat exchanger according to the invention, where the heat exchanger surfaces are of flexible plastic foils, in addition to the advantages al- ready described, there is also achieved the consid¬ erable advantage that the heat exchanger can be made at least partly self-cleaning, in that by changing the difference in pressure between the two exchanger circuits from plus to minus or vice versa, a deformation of the heat exchanger surfaces can be achieved which will result in possible deposits on these being loosened, so that these deposits can be carried away by the relevant fluid and rinsed out of the heat exchanger.

This will also apply if the relevant deposits con¬ sist of ice frozen to the surfaces or other frozen materials in a freezing or solidification process.

The heat exchanger according to the invention will be advantageous for use in the transfusion of blood etc. , where it is of importance that the material in the channels can be made sterile by simple means.

For the embodiments of the invention disclosed in the dependent claims, the following is to be noted:

With the spirally- ound embodiment disclosed in claim 2 , the inner thrust forces are absorbed as annular stresses in the surrounding tubular ele¬ ment, whereby the use of the bracing arrangements necessary in the plane constructions is avoided.

The special structure disclosed in claim 3 is par¬ ticularly simple to produce.

With the configuration of the heat exchanger as disclosed in claim 4, the end plates are formed as an integral part of the structure of the exchanger. Each plastic wall and each distance-holding layer serves as a staybolt extending between the end plates, which contributes towards making the heat exchanger usable with relatively high inner over -pressure. The construction requires a minimum of material consumption and is well-suited for an industrial production.

As an alternative to the configuration disclosed in claim 4, the heat exchanger can be produced, as dis¬ closed in claim 5, by the winding of the foil tube together with an outer distance-holding layer which is broader than the tube. The end plates are thus formed by mutual connection with each other of the broad distance-holding layer's windings, for example as disclosed in claim 6, by means of the plastic zippers well-known from plastic bags, where a rib on a band engages in a c-shaped slot in another band or, as disclosed in claim 7, by means of distance bands which, for example, can be welded in between the broad distance-holding layer's windings. In this embodiment of the heat exchanger according to the invention, the one fluid flows through the plastic tube which is enclosed between the broad distance -holding layer's windings, while the other fluid can flow through the broad distance-holding layer transversely to the first fluid.

As disclosed in claim 8, by using plastic netting consisting of two welded-together plastic strands as distance-holding layer, and which do not change between layers, a desirably high turbulence is ach- ieved in the flow of the fluids through the heat exchanger.

However, as disclosed in claim 9, in a number of cases it can be advantageous to use lengthwise bands for the inner distance-holding layer, so that the resistance to flow is reduced as much as possible.

As disclosed in claim 1-0 , it can be advantageous to use different distance-holding materials in the two sets of channels in the heat exchanger. For example, the one set of channels can be made more temperature -resistant than the other, or in other ways be ad¬ apted for a special application.

In a heat exchanger where the one fluid is gaseous while the other fluid is liquid, it is advantageous for the heat exchanger to be configured as disclosed in claim 11.

The performance of the heat exchanger can hereby be improved to a considerable degree.

In the following, the different preferred embodi¬ ments of heat exchangers according to the invention will be described with reference to the accompany¬ ing drawings.

Fig. 1 shows schematically a longitudinal sec¬ tion through a heat exchanger, where connection details have been omitted,

fig. 2 shows a cross-section through the heat exchanger,

fig. 3 shows a net for use as distance-holding layer in the heat exchanger,

fig. 4 shows the manufacture of a heat exchanger by the winding together of a foil tube and two distance-holding layers,

fig. 5 shows the forming of the end plates by melting down,

fig. 6 shows the heat exchanger structure formed by melting down,

fig. 7 shows details of the connections on a heat exchanger according to the inven¬ tion, and

fig. 8 shows a part of a longitudinal section through a cross-flow exchanger according to the invention, in which the windings of the one distance-holding layer are joined together with zipper bands.

The heat exchanger 1 shown schematically in longi- tudinal section and schematically in cross-section in figs. 1 and 2 respectively has at least one inlet 2 and an outlet 3 for a first fluid, and at least one inlet 4 and an outlet 5 for a second fluid. Be¬ tween the inlet 2 and the outlet 3 there extends a spirally-wound channel 6 through which flows the first fluid, and in which there is disposed a layer of distance-holding material 7 of metal or plastic, which is shown schematically with a zig-zag line.

Between the inlet 4 and the outlet 5 there extends a second spirally-wound channel 8 through which flows the second fluid, and in which there is dis¬ posed a second layer of distance-holding material 9 of metal or plastic, which is shown schematically with a wavy line. The windings of the one channel lie between the windings of the other channel, as will appear from figs. 1 and 2. The fluids flow through the channels 6, 8 in opposite directions.

The two channels 6, 8 are separated from each other by walls 10 which consist of thin plastic foil. Depending on the pressure conditions expected in the heat exchanger, the thickness of the plastic foil can lie between a few micrometers and a few hundred micrometers; the plastic foil used should preferably lie between 20 and 150 micrometers in thickness. A suitable foil material is polyethylene of low density, in trade circles known under the designation PEH. However, the use of other plastic materials which are available as thin foils is not excluded, for example other polyfines (PVDF) , and multi-layer foils of different materials will also be able to be used depending on requirements, pro- viding that special demands are made regarding dif¬ fusion density etc.

The distance-holding layers 7 , 9 consist of metal or plastic materials and have such a surface struc¬ ture that the fluids can flow through their respec¬ tive channels 6, 8 while the walls 10 lie up against the distance-holding layers 7, 9. The distance-hold¬ ing layers can, for example, be extruded or injec- tion moulded plastic layers with differently formed ribs or grooves, possibly with sporadic holes, pro¬ jections or perforations; they can be grids which can be formed in the manner of a expanded metal, they can be in the form of plastic weave, i.e. nets of plastic strands, or in any other suitable form such as lengthwise bands.

The surface structure of the distance-holding layers 7 , 9 is selected so that the distance-holding layers present a pattern of closely-lying support points or lines for the plastic walls 10. The distance between the support points is adapted to suit the thickness of the plastic walls 10, in that it is so small that the plastic walls 10 do not suffer any overload at the maximum operational differential pressure be¬ tween the two fluids prescribed for the heat exchan¬ ger, i.e. neither deformed so much that they are perforated, nor so much that they creep in between the supporting points and lie up against the dis- tance-holding layer in the channel with the lower pressure in such a manner that the through-flow is blocked in this channel.

The distance-holding layers 7, 9 and the plastic walls 10 are wound tightly in spiral form so that all of the walls 10 lie up against the most closely -lying distance-holding layer 7, 9. In the centre of the spiral-shaped structure formed hereby, there are injection-moulded connection pipes 11, 12 for the fluids, and the structure is surrounded by a cylindrical, tubular element 13 of a suitable mat¬ erial, such as metal or plastic, which forms an outer casing. The plastic walls 10 are formed by two foils 14, 15 which are welded firmly to the con¬ nection pipe 11 on each their sides of an outlet slot for the one fluid. The distance-holding layer 7 is led into the connection pipe 11 through this slot, and the other distance-holding layer 8 is led into the other connection pipe 12 through a corres¬ ponding slot.

Injection-r-moulded connection pipes 16, 17 can also be provided in the periphery of the spiral-shaped structure, these being disposed diametrically in the casing 13. The connection pipes 16, 17 are formed in one with special wedge-shaped equalizing elements which serve to fill out the space between the spirally-wound plastic walls 10, 14, 15 and distance-holding layers 7, 9.

The object of these equalizing elements and the tight winding of the spiral-shaped structure is to hold the structure slightly under pressure within the outer casing 13, and to ensure that the foil walls 10, 14, 15 throughout the structure either lie between and up against two distance-holding layers or between and up against one distance-hold¬ ing layer and the casing 13, or respectively the inner and the outer connection pipes, which to all intents and purposes can be considered as being a part of the casing. The result of this is that a rising pressure in one of the heat exchanger's channels will always be absorbed by the distance

-holding layers which surround the plastic walls of this channel, and via the structure's remaining parts will be transferred until it is absorbed as annular stress in the casing 13. This makes it pos- sible to use the heat exchanger at greater values of pressure and with relatively large differences in pressure between the two fluids.

The end plates 18, 19 of the heat exchanger are formed by the melting down of the foil walls 10, 14, 15, the distance-holding layers 7, 9 and the pipe section 13, which will be described in more detail in the following. All of the mentioned struc¬ tural elements 7, 9, 10, 13, 14, 15 in the heat ex- changer thus serve as staybolts for the end plates 18, 19, which makes the heat exchanger resistant to a high internal over-pressure.

The upper sketch in fig. 3 shows a plan view of a weave 21 of metal or plastic strands which can serve as distance-holding layer 7, 9. The weave is made up of two layers 22, 23 of strands, one on top of the other, and are welded together in the crossing points between the two layers. This is best seen in the direction parallel with the strands 22 in one of the layers (as indicated by the arrow 20 and shown from the side in the lower sketch in fig. 3) . The net 21 can be placed in the channels for the two fluids in such a manner that the flow of the fluids is not parallel, neither with the one nor the other layer of strands, for example in the direction of the arrow 24. This has the advantage_¬ ous effect that the fluid must constantly flow from the one surface of the net to the other in the slot- formed channels which are formed between the strands of the net and the plastic walls of the heat exchan_¬ ger. This increases the fluid's turbulence and here_¬ with the efficiency of the heat exchange. If, how_¬ ever, this proves to be undesirable, the net 21 can naturally be placed so that the fluid flows parallel with the strands in the one direction.

Figs. 4, 5 and 6 serve to illustrate the manufac_¬ ture of a heat exchanger according to the invention. Inthese figures, all details of connections have been omitted.

One places a layer of distance-holding material 7 in a foil tube 25. A layer of distance-holding mat_¬ erial 9 is then placed on top of the foil tube, and these three parts are rolled up in spiral form as shown in fig. 4. The space in the foil tube will thus come to serve as the one channel of the heat exchanger, while the space between the windings of the foil tube will come to serve as the second channel of the heat exchanger.

The spirally-wound structure is then placed between two heating elements 26, which in the plastics trade are also known as heat reflectors, which are moved towards each other. It is presupposed that the component parts of the structure, i.e. the foil tube 25 and the distance-holding layers 7, 9, are thermoplastic, weldable materials. Under the effect of the heat reflectors, these structure parts 7, 9 and 25 melt together with one another at the ends of the heat exchanger structure, whereby the earl_¬ ier-described elted-down end plates 18, 19 are formed. The heat reflectors are then removed again.

In the described melting-down of the end plates 18, 19, the foil tube 25 loses its tobular character, in that its walls become an integral part of the fin_¬ ished heat exchanger structure. Providing that the foil tube 25 and the distance-holding layers 7, 9 consist of identical material, after the melting ^down of the end plates it will require a very close investigation of the conduction path in the heat exchanger to determine which of the two distance -holding layers 7, 9 it was that was place_d inside the foil tube 25.

It will, however, also be possible to produce a corresponding heat exchanger by the winding up of a sandwich structure which consists first of a _dis_¬ tance-holding layer, then a foil layer followed by a distance-holding layer, and finally yet another foil layer, after which a corresponding melting-down of the end plates is carried out. Before the wind_¬ ing up, the two layers of foil can be welded to_¬ gether with one or more suitably designed pipe el_¬ ements for the supply of fluids. The details of these more production-technical aspects will not be discussed here, in that many alternative possi_¬ bilities of preliminary work will present them_¬ selves to those familiar with the art. In fig. 7 is seen a segment of a simplified longi¬ tudinal cross-section through a completely assembled heat exchanger according to the invention, where the inner structure is shown only schematically.

After the formation of the melted-down end plates 18, 19, of which only one 18 is shown, clearance for the connection pipes is provided. The end casing 30 with threaded stuhε 31 for the fluids shown in fig. 7 is welded on. The end casing can be provided with the heat exchanger's type designation, technical data etc.

Spirally- ound heat exchangers according to the in- vention can also, be realized as cross-flow heat ex¬ changers, providing that the spiral structure's end plates are configured in such a manner that they are permeable for one of the two fluids which are required to exchange heat. How this can be effected is shown in fig. 8, which schematically shows a segment of a longitudinal cross-section through a spirally-wound cross-flow heat exchanger according to the invention.

One of the fluids, for example water, flows through a spirally-wound foil tube 40 of plastic in which there is placed a layer of distance-holding plastic material 41. A second layer of distance-holding plastic material 42 is wound together with the foil tube 40. This second distance-holding layer 42 carries the second fluid, for example exhaust gas, which flows transversely to the direction of flow of the first fluid, as shown by the arrows 50. The one fluid thus flows tangentially in the struc- ture, while the other fluid flows axially.

The second layer of distance-holding material 42 is broader than the foil tube 40, so that its wind- ings project from the windings of the foil tube at both ends of the spiral structure formed by the winding up. These projecting ends of the windings of the distance-holding layer 42 are mutually con¬ nected with each other by means of the zipper bands of plastic 43 shown in fig. 8. The zipper band. 43 consists of a first part 44 with two projecting ribs which run lengthwise along the band, and a second part 45 with two corresponding c-shaped slots. The parts 44, 45 are welded to each their sides of the distance-holding layer 42, so that the ribs can be pressed into the slots as shown with the winding of the spiral-shaped structure.

The foil tube 40 is thus enclosed within the struc- ture formed by the distance-holding layer 42 and the zipper bands, where the zipper band 43 serves as the end plate for each individual winding of the foil tube 40. The parts 44 and 45 of the zipper are welded firmly to the distance-holding layer 42 in such a manner that the welding does not hinder the through-flow 50 of the second fluid. An ordi¬ nary plastic band, which is welded in between the windings of the distance-holding layer 42, is also able to be used.

The shown construction of a cross-flow heat exchan¬ ger is intended namely for use as a gas/fluid heat exchanger, where the gas flows axially, for example for the recovery of heat from waste gas. In this case, the distance-holding layer 42 could be of polybutene in order to achieve a greater degree of thermostability, while the foil tube 40 and the distance-holding layer 41 , for reasons of their effective cooling, could still be of polyethylene. Such a waste-gas heat exchanger produced of plastic materials offers obvious advantages with regard to corrosion resistance in the normally very corrosive waste-gas environment. With this application, it is advantageous for the distance-holding layer 41 to be formed of longitudinal bands, which present the least possible resistance to the flow.

With a gas/fluid heat exchanger, it is of advantage for the distance-holding layer ori the gas side to be of metal which is easily moistened.

The reason for this is that in the condensation of steam on a metal surface, there is normally formed a film of liquid which prevents a good transfer of heat, whereas with plastic surfaces of, for example, PE, PVDF and PTFE, the condensation takes place as drop condensation. This means that exchangers of plastic foil can achieve considerably better per-

2 formance per m of exchanger surface - up to 2 times higher.

If the exchanger surfaces are of plastic and the distance-holding net on the gas side is of metal, the drops will be caught by and will run down the metal net. It is hereby avoided that the condensate forms an insulating film or a drop layer further down on the surfaces. On the basis of the described construction prin¬ ciple, with the characteristic features disclosed in claim 1 , it is not only possible to produce spiral-shaped heat exchanger structures as described above, but also heat exchangers in block form, where the individual walls of plastic foil and the dis¬ tance-holding layers are plane, and where any con¬ ceivable combination of inlet and outlet connection or connections and positioning is feasible.

Claims

C L A I M S

1. Heat exchanger with a number of walls of plastic foil for the demarcation of a first group of slot -formed channels which are intended for the through -flow of a first fluid, from a second group of slot -formed channels which are intended for the through -flow of a second fluid, where the channels of the second group lie between the channels of the first group, and where elements are provided in each chan¬ nel for holding the walls of the channels at a dis¬ tance from each other, c h a r a c t e r i z e d in that said elements for holding the walls (10, 14, 15) at a distance from each other in all channels 6, 8) consist of a continuous distance-holding layer (1 , 9) of metal and/or plastic material which is configured with projections, ribs or another sur¬ face structure (22, 23) , disposed in the channel (6, 8) in such a manner that a fluid can flow through the channel (6,8) while the channel's walls (10, 14, 15) lie up against the distance-holding layer (7, 9) , and in that the structure formed by the walls (10, 14, 15) and the distance-holding layers (7, 9) is built into a compression casing (11, 12, 13, 16, 17) in such a manner that each wall (10, 14, 15) either lies between and up against two distance -holding layers (7, 9) or between and up against a distance-holding layer (7, 9) and the casing (11, 12, 13, 16, 17), whereby an over-pressure in the channels (6, 8) is transferred to the compression casing (11, 12, 13, 16, 17).

2. Heat exchanger according to claim 1 , c h a r ¬ a c t e r i z e d in that the walls (10, 14, 15) and the distance-holding layers (7, 9) are wound in spiral form around a common axis for the formation of a substantially cylindrical, spiral-formed struc¬ ture, and that this structure is surrounded by a tubular element (13) of metal or plastic which serves as a compression casing for radially-direc¬ ted thrust forces in the structure.

3. Heat exchanger according to claim 2, c h a r - a c t e r i z e d in that the spiral-formed struc¬ ture is formed by spirally-winding a foil tube (25) , in which there is placed an inner distance-holding layer (7) , together with an outer distance-holding layer (9) disposed on the outside of said foil tube.

4. Heat exchanger according to claim 2 or 3, c h a r a c t e r i z e d in that substantially plane end plates (18, 19) are formed in the ends of the heat exchanger by the melting-down of the walls (10, 14, 15), the distance-holding layers (7, 9) and the tubular element (13).

5. Heat exchanger according to claim 3, c h a r ¬ a c t e r i z e d in that the outer distance-hold- ing layer (42) is broader than the foil tube (40) , and in that the windings (42) of the outer distance -holding layer are mutually connected with each other at the ends of the heat exchanger for the formation of pressure-absorbing end plates, between which the windings (40) of the foil tube are en¬ closed.

6. Heat exchanger according to claim 5, c h a r ¬ a c t e r i z e d in that the windings (42) of the outer distance-holding layer are mutually connected by means of zipper bands (43 - 45) which are dis¬ posed in between and fastened to these windings (42) in the ends of the heat exchanger.

7. Heat exchanger according to claim 5, c h a r ¬ a c t e r i z e d in that the windings (42) of the outer distance-holding layer are mutually connected by means of distance bands which are disposed in be- tween and fastened to these windings (42) in the ends of the heat exchanger.

8. Heat exchanger according to one of the claims 1 - 6, c h a r a c t e r i z e d in that plastic weave (fig. 3) is used as distance-holding layer

(7, 9, 42), said weave having at least two crossing layers of plastic strands (22, 23), where the strands are welded together at the crossing points, and where the strands (22, 23) do not change layers.

9. Heat exchanger according to one of the claims 1-6, c h a r a c t e r i z e d in that longitudi¬ nal bands are used as inner distance-holding layer (41).

10. Heat exchanger according to claim 8, c h a r - a c t e r i z e d in that the distance-holdincf lay-₇ er (41) in the channels (40) for the one fluid is of another material than the distance-holding layer (42) in the channels for the other fluid (50) .

11. Heat exchanger according to any of the claims 1-9, where the one fluid is gaseous while the other is liquid, c h a r a c t e r i z e d in that the distance-holding layer on the gas side is of an easily moistened material, for example metal.