US20020179296A1

US20020179296A1 - Heat exchanger

Info

Publication number: US20020179296A1
Application number: US10/148,518
Authority: US
Inventors: Jean Jassens
Original assignee: Scambia Industrial Developments AG
Current assignee: Scambia Industrial Developments AG
Priority date: 1999-12-02
Filing date: 2000-12-01
Publication date: 2002-12-05

Abstract

The heat exchanger has an axis and at least one heat-exchange body (5) encompassing said axis, annular in cross-section and comprising sheet metal elements (23, 27) which are present in succession around the axis and are involute in cross-section and between which edge strips (24, 25, 28, 29) welded to said sheet metal elements alternately at their involute side edges (23 c, 23 d, 27 c, 27 d) and at their inner and outer edges (23 a, 23 b, 27 a, 27 b) are arranged and which alternately bound passages (33, 34) for a first and a second fluid (15, 16). Each passage (33, 34) contains an intermediate layer (31, 32) which consists of a knitted wire fabric. The edge strips (24, 25, 28, 29) and the knitted wire fabrics hold the successive sheet metal elements (23, 27) in a stable and durable manner a distance apart and result in only little thermal conduction in the direction of flow.

Description

FIELD OF THE INVENTION

The invention relates to a heat exchanger comprising at least one heat-exchange body having successive sheet metal elements which, together with gas-permeable intermediate layers arranged between them, alternately bound passages for a first fluid and a second fluid.

The heat exchanger is provided in particular for transferring heat between two gaseous fluids. The heat exchanger can be used, for example, for recovering heat from hot exhaust gas of a hot gas engine, such as a Stirling engine or a gas turbine, and transferring it to originally cold air which is heated by the heat transfer and is then fed to a burner.

PRIOR ART

A heat exchanger disclosed in GB 892 962 A has a heat-exchange body which is annular in cross-section and comprises sheet metal elements. These have a middle section with the shape of an Archimedean screw and with wavy ribs which run along said section and evidently rest against an adjacent sheet metal element and keep the ribless regions of the middle sections a distance apart so that they bound spiral passages. The inner and outer edge sections of the sheet metal elements are multiply angled or curved so that they rest against one another at the innermost or outermost part-sections and bound axial channels. The sheet metal elements are connected to one another by welding or soldering. Rings which alternately close the axial channels present in succession along the circumference or connect said channels to an adjacent space by means of a hole are fastened at the two ends of the heat-exchange body. During operation of the heat exchanger, hot exhaust gas is passed from the inside to the outside and cold air is passed from the outside to the inside through the heat-exchange body.

The exhaust gases flowing out of a Stirling engine or a gas turbine have, in the case of modern engines or gas turbines, high temperatures which are frequently 500° C. to about 1000° C. or even slightly higher. If such exhaust gas is fed to a heat-exchange body, its sheet metal elements are subjected to large temperature changes at the beginning and at the end of operation of the heat exchange. Furthermore, considerable temperature gradients occur along the flow paths of the fluids in a heat-exchange body with through-flow during operation. Such temperature changes cause changes in dimensions, which differ from place to place owing to the temperature gradients.

Sheet metal elements according to GB 892 962 A which are provided with ribs and are multiply angled or curved at the inner edges and outer edges can be highly and permanently deformed by the dimensional changes occurring at high exhaust gas temperatures and the stresses associated therewith. The deformations are further increased by the fact that the curved edge sections of the sheet metal elements, which sections are adjacent to one another, connect all sheet metal elements relatively rigidly and inflexibly to one another. The deformations produced in turn have the result that the passages are widened in parts and narrowed in parts or even more or less completely closed, with the result that the properties of the heat exchanger are very adversely affected. Moreover, GB 892 962 A does not reveal whether and how the spiral passages at the two ends of the heat-exchange body are closed and whether and how mixing of the hot exhaust gas with the air can be prevented there and at the axial channels of the heat-exchange body. Owing to the complicated shapes of the sheet metal elements, because the rings mentioned must have a hole flush with the channel for every second axial channel and because the inner ends of the spiral middle sections of the sheet metal elements make, in a section perpendicular to the axis, a fairly acute angle with the inner lateral surface of the heat-exchange body, the latter—in the case of a specific, given internal diameter, can moreover have only a relatively small number of passages distributed around its inner lateral surface. Furthermore, the production of the curved edge sections is complicated and expensive.

U.S. Pat. No. 4,506,502 A discloses a heat exchanger comprising an annular heat-exchange body having spiral passages. The heat-exchange body consists of ceramic or steel, but the internal structure and the production of the heat-exchange body are not disclosed in more detail. In addition, the hot exhaust gas is passed from the outside to the inside through the heat-exchange body during operation. The heat-exchange body therefore becomes very hot at its outer lateral surface, so that a great deal of heat is released to the environment and high heat losses occur.

The heat exchanger disclosed in U.S. Pat. No. 3,741,293 A has an annular heat-exchange body with flat, radial sheet metal elements and secondary surface elements which are arranged in rows in between and are formed by peeling. Since the passages are radial, they become broader toward the outside and have only a small length. In addition, the distance between the adjacent sheet metal elements is relatively large. This heat-exchange body therefore gives only a low heat-exchange performance based on a specific volume. Moreover, this heat exchanger also has some disadvantages similar to the heat exchanger according to the first-cited GB 892 962 A.

A heat exchanger disclosed in U.S. Pat. No. 5,060,721 A has an annular heat-exchange body with in general involute sheet metal elements. Each of these forms an irregular hexagon in the unwound, flat state and has a trapezoidal middle section and a wing on both sides of this. The middle section has waves running along the involutes. The wings have in part waves which form channels approximately parallel to the axis of the heat-exchange body. This heat exchanger has some disadvantages similar to the heat exchanger according to GB 892 962 A, in particular the production and the assembly of complicated sheet metal elements being time-consuming and expensive.

GB 1 172 247 A discloses heat exchangers comprising an approximately right parallelepiped heat-exchange body. This has a stack of rectangular plates with a flat main section and edge sections bent upward. An intermediate layer consisting of a wire lattice is arranged between the adjacent plates. In the case of the variants shown in the different figures of the drawings, the wire lattices consist of wires resting one on top of the other and intersecting one another at right angles. According to the figures, said wires make angles of about 45° with the rectangular sides of the plates. When the heat exchanger is used, the fluids flowing through it generally have directions of flow which are more or less parallel to the longer sides of the rectangle. The wire lattices therefore result in fairly good thermal conduction along the flow paths of the fluids. As a result of this, a large part of the heat supplied by the hotter fluid is transported away again from this out of the heat exchanger and is not transferred. Furthermore, the plates are provided at their edges with rubber seals which are not suitable for high temperatures. These known heat exchangers would therefore not be suitable for exhaust gases having temperatures up to about 1000° C. and emitted by internal combustion engines and gas turbines.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a heat exchanger which makes it possible to avoid disadvantages of known heat exchangers. In particular, the sheet metal elements should on the one hand be connected to one another in a manner which is sufficiently stable and durable so that the passages for the two fluids are and remain satisfactorily separated from one another. On the other hand, the sheet metal elements should retain their shapes as well as possible also when a fluid having a very high temperature is fed in and should ensure that all passages permit uniform fluid flow. Furthermore, the heat exchanger should be capable of being produced economically and should enable the heat losses to the environment to be kept low.

This object is achieved, according to the invention, by a heat exchanger having the features of claim 1, i.e. by a heat exchanger comprising at least one heat-exchange body which is annular in cross-section, encompasses an axis and has sheet metal elements which are present in succession around said axis and together alternately bound first passages for a first fluid and second passages for a second fluid, each sheet metal element having an inner edge, an outer edge and two side edges running from the inner edge to the outer edge, adjacent sheet metal elements having substantially constant distances from one another along their side edges and the heat exchanger being characterized in that each sheet metal element forms a quadrilateral, the [sic] metallic edge strips are arranged between the sheet metal elements together bounding a first passage and run along the side edges of said sheet metal elements and are firmly and tightly connected to the relevant sheet metal elements and that metallic edge strips are arranged between the sheet metal elements together bounding a second passage and run along the inner edges and the outer edges of said sheet metal elements and are firmly and tightly connected to the relevant sheet metal elements.

The invention furthermore relates to a heat exchanger comprising at least one heat-exchange body having successive sheet metal elements which alternately bound passages for a first fluid and a second fluid and between which gas-permeable intermediate layers are arranged, each sheet metal element [lacuna] two side edges facing away from one another and the heat exchanger being characterized in that the side edges of the sheet metal elements belonging to the same heat-exchange body and/or edge strips arranged at these side edges together define two end surfaces of the heat-exchange body, that, at each end surface, at least one metallic foil rests against the side edges of the sheet metal elements and that a heat insulation is arranged on that side of each foil which faces away from the sheet metal elements.

The invention furthermore relates to a heat exchanger comprising at least one heat-exchange body which is annular in cross-section, encompasses an axis and has sheet metal elements which are present in succession around said axis and together alternately bound first passages for a first fluid and second passages for a second fluid, each sheet metal member having an inner edge, an outer edge and two side edges running from the inner edge to the outer edge, adjacent sheet metal elements having substantially constant distances from one another along their side edges, the passages extending between orifices in the vicinity of the inner edges and orifices in the vicinity of the outer edges and the heat exchanger being characterized in that the sheet metal elements have a dimension, measured along their side edges, which is at least twice the dimension of the sheet metal elements which is measured along the axis.

The invention also relates to a heat exchanger comprising at least one heat-exchange body having successive sheet metal elements which alternately bound passages for a first fluid and a second fluid and between which gas-permeable intermediate layers are arranged, each sheet metal element having two side edges which face away from one another and are parallel to one another and at least substantial parts of the passages running along the side edges and the heat exchanger being characterized in that each intermediate layer consists of a knitted wire fabric which has rows of stitches comprising stitches adjacent to one another and formed from cohesive wire sections and that these rows of stitches are generally approximately at right angles to the side edges of the sheet metal elements.

Advantageous embodiments of the heat exchanger are evident from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject of the invention is explained in more detail below with reference to embodiments shown in the drawings. In the drawings, [0016]
FIG. 1 shows simplified, schematic oblique view of a heat exchanger, [0017]
FIG. 2 shows a simplified, schematic axial section through the heat exchanger and its heat-exchange body, [0018]
FIG. 3 shows a schematic cross-section through the annular heat-exchange body of the heat exchanger, [0019]
FIG. 4 shows a schematic section along the line IV-IV of FIG. 3 through a first involute fluid passage of the heat-exchange body, [0020]
FIG. 5 shows a section along the line V-V of FIG. 3 through a second fluid passage of the heat-exchange body, [0021]
FIGS. 6 and 7 show views of edge sections of the unwound, second sheet metal element shown in FIG. 5, in the directions of view indicated in FIG. 5 by the arrows V and VI, respectively, on a larger scale, [0022]
FIG. 8 shows a view of the unwound, first sheet metal element shown in FIG. 4, on a larger scale, [0023]
FIG. 9 shows a cut-out from FIG. 8 on an even larger scale, [0024]
FIG. 10 shows a view of the first sheet metal element shown in FIGS. 4, 8 and [0025] 9, in the direction of view indicated by X in these figures, on the same scale as FIG. 9,
FIG. 11 shows a simplified cross-section through a region of that end section of the heat-exchange body which is present at the top in FIG. 2, on a larger scale than FIG. 2, [0026]
FIG. 12 shows a schematic, simplified oblique view of a region of the heat-exchange body with a direction of view onto the inner edge of the end surface present at the top in FIG. 2, [0027]
FIG. 13 shows a simplified oblique view of another, cut-away heat exchanger having only one heat-exchange body, [0028]
FIG. 14 shows a simplified plan view of the upper end of the heat-exchange body shown in FIGS. 12 and 13 and foil resting on it, [0029]
FIG. 15 shows a section along the arc XV-XV of FIG. 14 through the heat-exchange body and the foils resting on it, [0030]
FIG. 16 shows an axial section through a region of the heat exchanger according to FIG. 13 on a larger scale, [0031]
FIG. 17 shows a simplified, schematic axial section through a heat exchanger having two heat-exchange bodies, [0032]
FIGS. 18 and 19 show sections, analogous to FIGS. 4 and 5, through the heat-exchange body according to FIG. 17, along first and second, involute passages, [0033]
FIG. 20 shows a schematic axial section through a heat exchanger having six heat-exchange bodies and [0034]
FIG. 21 shows a schematic axial section through a heat exchanger having four heat-exchange bodies.[0035]
Regarding FIGS. 4, 5, [0036] 12 and 13, it may also be noted that the sections shown in them run along an involute passage so that the sheet metal elements appear to be in the unwound, flat state. However, those parts of the housing and of the fluid conducting means which are adjacent to the heat-exchange bodies are shown in a section radial with respect to the axis, for simplification. Moreover, it may also be noted with regard to FIG. 12 that, for simplification, no knitted wire fabrics are shown therein. Furthermore, the sheet metal elements essentially distributed around an arc-shaped section of the cylindrical, inner lateral surface of the heat-exchange body are shown as if their inner edges are lying in a plane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The [0037] heat exchanger 1 shown in FIGS. 1 and 2 has an axis 2. The heat exchanger 1 has only one housing 3 shown partly and schematically. Said housing contains a heat-exchange body 5 which is described in more detail. The heat exchanger 1 and in particular its heat-exchange body 5 are substantially rotationally symmetrical with respect to the axis 2. The heat exchanger 1 has fluid conducting means 7 which are formed partly by housing parts and, like the housing, are shown only partly and schematically. The housing 3 and/or the fluid conducting means 7 have a first fluid entrance 8, a first fluid exit 9, a second fluid entrance 10 and a second fluid exit 11.
Furthermore, two gaseous, flowing fluids, namely a [0038] first fluid 15 and a second fluid 16, are indicated by arrows in FIGS. 1 and 2. The arrows representing the first fluid 15 are shown with solid lines and the arrows representing the second fluid 16 are shown with dashed lines. The heat exchanger 1 may belong, for example, to an apparatus which also has a hot gas engine or Stirling engine which is not shown or possibly a gas turbine. The engine or the turbine can then feed to the first fluid entrance 8 hot exhaust gas which forms the first fluid 15 and, after passing through the heat-exchange body 5, is then passed from the first fluid exit 9, for example by an additional heat exchanger serving for the production of hot water and/or via a filter and/or any other apparatus, into the environment. The second fluid 16 consists, for example, of air, which is sucked in by a suction apparatus from the environment and possibly compressed and fed to the second fluid entrance 10. After passing through the heat-exchange body, the air is fed from the second fluid exit 11, for example, to a burner for operating the hot gas engine or the gas turbine.
The heat-[0039] exchange body 5 and parts thereof are shown particularly clearly in FIGS. 3 to 12. The heat-exchange body 5 is annular in cross-section and forms a ring and/or a sleeve. The heat-exchange body 5 has an inner lateral surface 5 a, an outer lateral surface 5 b and two end surfaces 5 c and 5 d facing away from one another. The two lateral surfaces 5 a, 5 b are parallel to the axis 2 and substantially cylindrical and are circular in cross-section. The two end surfaces 5 c, 5 d make an angle with the axis 2, namely a right angle, and are flat and parallel to one another. The heat-exchange body 5 has first fluid conducting elements 21 and second fluid conducting elements 22 alternately in succession around the axis 2. One of the first fluid conducting elements 21 is shown in part separately in FIGS. 8, 9 and 10. Each first fluid conducting element 21 has a first sheet metal element 23 and two first edge strips 24 and 25. Sections of a second fluid conducting element 22 are also shown in FIGS. 6 and 7. Each second fluid conducting element 22 has a second sheet metal element 27 and two second edge strips 28, 29. Gas-permeable, first and second intermediate layers 31 and 32 are arranged between the successive sheet metal elements 23, 27. The successive sheet metal elements, together with the gas-permeable intermediate layers 31, 32 arranged between them, bound first and second fluid passages 33, 34 for the first fluid 15 and second fluid 16, respectively.
The first and second [0040] sheet metal elements 23, 27 are identically formed and have both identical shapes and identical dimensions. The sheet metal elements 23, 27 have four edges opposite one another in pairs, are tetragonal in the flat, unbound state and form a right-angle parallelogram, namely a rectangle. The sheet metal elements 23, 27 are parallel to the axis 2 and, in a cross-section perpendicular to said axis, extend outward in an involute manner away from the axis 2. The two shorter edges of each sheet metal element 23, 27 are straight, parallel to one another and to the axis and designated below as inner edge 23 a, 27 a and outer edge 23 b, 27 b, respectively, the inner edges 23 a, 27 a being present at the ends close to the axis and the outer edges 23 b, 27 b being present at those ends of the sheet metal elements which are further away from the axis. The two longer edges of each sheet metal element 23, 27 are curved and parallel to one another and are designated below as side edges 23 c, 23 d and 27 c, 27 d, respectively. The sheet metal elements 23, 27 have a dimension measured along the curved side edges 23 c, 23 d, 27 c, 27 d, i.e. length, which is at least 2 times, preferably at least 2.5 times and, for example, at least or about 3 times that dimension, i.e. width, of the sheet metal element which is parallel to the axis 2. The edge strips 24, 25, 28, 29 consist of a metallic material, namely of metal strips. The first edge strips 24, 25 belonging to one of the first fluid conducting elements 21 are arranged at the two side edges 23 c, 23 d of the first sheet metal element 23 of the relevant fluid conducting element and run along these curved side edges. The second edge strips 28, 29 belonging to the second fluid conducting elements 22 are arranged at the inner edge 27 a and outer edge 27 b, respectively, of the second sheet metal element 27 of the relevant fluid conducting element and extend along these straight edges 27 a, 27 b parallel to the axis 2. The various edge strips 24, 25, 28, 29 are rectangular in cross-section and rest with their broader longitudinal surfaces on the sheet metal elements. The a [sic] narrower longitudinal surfaces of the edge strips are at least approximately flush with the sheet metal element edges along which they run. The various edge strips 24, 25, 28, 29 extend at least approximately along the whole sheet metal element edges at which they are arranged. The edge strips 24, 25 running along the curved side edges extend, for example, along the whole length of the side edges from the inner edge to the outer edge of the sheet metal elements. On the other hand, the edge strips 28, 29 running along the straight edges 23 a, 23 b, 27 a, 27 b may be, for example, slightly shorter than these edges. The ends of the edge strips 28, 29 are then slightly offset, for example about 2 to 4 mm, away from the side edges of the sheet metal elements 23 and 27—as shown for the upper end of inner edge strips 28 in FIG. 12. The ends of the first and second edge strips should, however, preferably partly overlap at the corners of the sheet metal elements in a projection parallel to the axis 2 and to the lateral surfaces 5 a, 5 b.
As will be explained in more detail, the [0041] passages 33, 34 and the fluid flows therein are at least in general in the longitudinal directions of the sheet metal elements 23, 27 and thus parallel to their side edges 23 c, 23 d, 27 c, 27 d. The side edges of the sheet metal elements and/or the edge strips 24, 25 running along the side edges therefore also form the side edges of the passages 33, 34. The sheet metal elements 23, 27, the edge strips 24, 25 running along their side edges and the passages 33, 34 are substantially and at least approximately involute in a section perpendicular to the axis 2. However, their shapes may be flattened in the inner and/or outer edge regions in which the edge strips 28, 29 are arranged and may deviate a [sic] slightly from the ideal involute shape. Apart from this, each sheet metal element is free of angled and/or curved edge sections and also free of protuberances and/or indentations, such as waves and/or ribs and the like. Each sheet metal element is thus completely straight and smooth everywhere in the axial direction and substantially—i.e. apart from any stated small deviations at the inner edge and outer edge—at least approximately involute and smooth in cross-sections at right angles to the axis 2. Each sheet metal element is accordingly continuously and smoothly curved substantially everywhere [lacuna] a section at right angles to the axis 2 and in particular everywhere on the same side so that the curvature has the same sign at all points of the sheet metal element.
In a section perpendicular to the [0042] axis 2, those edge sections of the sheet metal elements 23, 27 which form the inner edges 23 a, 27 a of the sheet metal elements are preferably more or less perpendicular to that cylindrical, inner lateral surface 5 a of the heat-exchange body 5 which is circular in cross-section. The sheet metal elements or the tangents to them can then make with the inner lateral surface 5 a an angle which is 65° to 115°, preferably 80° to 100° and, for example, about 85° to 95°. Accordingly, said tangents are also at least approximately radial to the axis 2. This ensures that the first fluid can readily flow into the first passages during operation and that the number of sheet metal elements and passages distributed around the inner lateral surface 5 a has at least approximately the largest possible value at a certain, predetermined diameter of the inner lateral surface 5 a and when the adjacent sheet metal elements are certain distances apart and at certain thicknesses of the sheet metal elements. Since the sheet metal elements are involute, the adjacent sheet metal elements are the same distance apart everywhere from the inside to the outside. In addition, the dimension or length of a sheet metal element, measured along an involute, is of course greater than the difference between the radii of the two lateral surfaces 5 b and 5 a.
Each [0043] intermediate layer 31, 32 consists of a wire lattice which, for example, is approximately quadrilateral, namely a knitted wire fabric, which is shown particularly clearly in FIG. 9 and is denoted there by 27. The knitted wire fabric 37 has a number of rows 37 a of stitches comprising stitches 37 b. The adjacent stitches 37 b belonging to the same row 37 a of stitches are formed by cohesive wire sections. The wire sections belonging to successive rows 29 a of stitches intersect one another at intersection points 37 c and form a sort of node there. Each row 37 a of stitches is in general transverse and at right angles to the side edges 23 c, 23 d, 27 c, 27 d of the sheet metal elements 23, 27 and hence also in general transverse and at right angles to the longitudinal directions and side edges of the passages 33, 34. Each row of stitches, i.e. the straight line defined by those positions of the stitches of this row of stitches which correspond to one another—for example of the summits of the stitches—can make, with the side edges 23 c, 23 d, 27 c, 27 d of the sheet metal elements 23, 27, an angle which is preferably 70° to 90° and better 80° to 100° or even 85° to 95° and as far as possible exactly 90°. The rows 37 a of stitches which are adjacent to one another are intertwined.
The wire lattice or knitted [0044] wire fabric 37 is produced, during its production, by knitting from a single continuous wire. During the knitting, for example, a loop is first formed. This is then cut open in its longitudinal direction and cut into approximately even pieces of the desired sizes. Originally, all rows 37 a of stitches thus also consist of a continuous wire. If a knitted wire fabric is arranged between two sheet metal elements, each pair of successive rows 37 a of stitches is associated at most at one end or even nowhere over a continuous wire section.
The width of each first [0045] intermediate layer 31 is approximately equal to the width of the first passage 33 present between the edge strips 24, 25. Each first intermediate layer furthermore extends at least approximately from the inner edge 23 a to the outer edge 23 b of the coordinated first sheet metal element 23 and hence substantially over the whole length of the first passage 33. The width of each second intermediate layer 32 is approximately equal to the whole width of the sheet metal elements 23, 27. Each second intermediate layer 32 furthermore connects approximately to the edge strips 28 arranged at the inner edge 27 a of the coordinated sheet metal element 27 and extends in the longitudinal direction of the sheet metal element 27 and of the second fluid passage 34 over the major part of the length of the fluid passage 34 but not completely to the edge strip 29, so that a strip-like region of the second passage 34 remains free there, said strip-like region being parallel to the axis and to the outer edge 27 c.
The [0046] sheet metal elements 23, 27, the edge strips 24, 25, 28, 29 and the knitted wire fabrics 37 consist, for example, of stainless, chromium-containing steel. The sheet metal elements have a thickness which—depending on the other dimensions of the sheet metal elements—is at most 5 mm, expediently at most 1 mm, preferably at most 0.5 mm, usually even better at most 0.3 mm and, for example, about 0.2 mm. The thickness of the wires forming the knitted wire fabrics is, for example, the same for all intermediate layers but could possibly be different for the first and second intermediate layers and, likewise depending on the size of the sheet metal elements, is at most 5 mm, expediently at most 1 mm, preferably at most 0.8 mm and, for example, about 0.3 mm to about 0.7 mm. The open area of the knitted wire fabrics 37 is preferably at least 50% and, for example, about 60% to 90% of the total area occupied by the knitted wire fabric.
The wires of the knitted [0047] wire fabrics 37 are preferably circular in cross-section. Each edge strip 24, 25, 28, 29 has a thickness which is approximately equal to two times the diameter of the wires and/or possibly a little larger than this diameter. Two sheet metal elements 23, 27 adjacent to one another are adjacent to those two surfaces of the edge strips 24, 25 or 28, 29 present between them which face away from one another. Furthermore, the two sheet metal elements are in each case adjacent to one of the intersecting wire sections at the intersection points 37 c of the wire lattice 37 present between said sheet metal elements. The edge strips 24, 25, 28, 29 and the intermediate layers 31, 32 each consisting of a knitted wire fabric thus serve as spacer means and keep the adjacent sheet metal elements the desired distance apart. In those regions of an intermediate space between two adjacent sheet metal elements which are not occupied by intersection points 37 c, this intermediate space is free. The intermediate layers 31, 32 arranged in the intermediate spaces between the sheet metal elements are thus—as stated above—gas-permeable, so that the intermediate spaces form the fluid passages 33, 34.
The [0048] sheet metal elements 23, 27 adjacent to one another are firmly connected to the edge strips 24, 25 or 28, 29 arranged between them and thus also in pairs to one another. In the production of the heat-exchange body 5, for example, the first edge strips 24, 25 are fixed by a few spot weld joints denoted by 35 in FIGS. 8, 9 to the coordinated, first sheet metal element 23 and the second edge strips 28, 29 are fixed by a few spot weld joints to the coordinated, second sheet metal element. The first and second fluid conducting elements 21 and 22 are formed thereby. Furthermore, each of the intermediate layers 31, 32 consisting of a knitted wire fabric is fastened at some points by spot weld joints to the coordinated sheet metal element 23 or 27, respectively. Each knitted wire fabric is thus fastened at most to a single sheet metal element, so that the knitted wire fabrics support the sheet metal elements between which they are arranged but are not rigidly connected to one another. If the edge strips and knitted wire fabrics were fixed in the manner described to the coordinated sheet metal element, the fluid conducting elements 21, 22 and intermediate layers 31, 32 or knitted wire fabric can be assembled to give the heat-exchange body and can be welded, for example, along the whole length of the edge strips arranged between them to said edge strips and at these possibly also directly to one another. The sheet metal elements are then also connected in pairs almost nondetachably and tightly to one another along the edge strips.
During welding of the sheet metal elements and edge strips, for example, a pair of [0049] sheet metal elements 23, 27 can first be arranged one on top of the other in a manner such that the inner edges 23 a, 27 a and the outer edges 23 b, 27 b and the edge strips 28, 29 running along these edges are flush. The sheet metal elements and edge strips adjacent to one another can first be connected to the straight edge strips 28, 29 and to one another along their inner edges 23 a, 27 a and outer edges 23 b, 27 b by weld joints 38 or weld seams shown in FIGS. 11 and 12 and 33 [sic]. If a plurality of, or all, sheet metal elements serving for the formation of the heat-exchange body are welded in pairs in this manner, these subunits each formed from a pair of sheet metal elements can be assembled to give a heat-exchange body and welded successively along the involute side edges 23 c, 23 d, 27 c, 27 d to the edge strips 24 and 25 running along said side edges and via said edge strips to one another. Weld joints or weld seams are formed, one of which is shown in FIG. 12 and denoted by 39. The sheet metal elements can then also possibly be connected, at the ends or end surfaces of the curved edge strips 24, 25, to these edges strips and to one another by weld joints 39 a. The sheet metal elements present in succession along the periphery of the heat-exchange body are then connected to one another alternately at their inner and outer edges or at their side edges along the latter via the edge strips arranged between the relevant edges. Weld joints which run continuously along the periphery of the inner edges and outer edges of the end surfaces 5 c, 5 d around the axis 2 can be formed at the four corners of the sheet metal elements. On the other hand, the sheet metal elements 23, 27 together in pairs bounding a first passage 33 are free of rigid connections at their inner edges 23 a, 27 a and at their outer edges 23 b, 27 b between the edge strips 24, 25 running along their side edges. In an analogous manner, the sheet metal elements 23, 27 together in pairs bounding a second passage 34 are free of rigid connections between the sheet metal elements at their side edges 23 c, 23 d, 27 c, 27 d between the edge strips 28, 29 arranged at their inner edges 23 a, 27 a and outer edges 23 b, 27 b and running along said edges.
The heat-[0050] exchange body 5 can also be provided with at least one retaining ring 40 encompassing its outer lateral surface and preferably with two or more such rings, two retaining rings 40 a distance apart in the axial direction being shown in FIG. 2 by way of example. Each retaining ring has, for example, a metallic band consisting of stainless steel and possibly a clamping device for clamping the band so that, in the assembled state, said band rests firmly against those outer edges of the sheet metal elements and/or edge strips which define the outer lateral surface 5 b of the heat-exchange body. The retaining rings can furthermore be secured by additional retaining means to prevent axial displacements but should not be welded or otherwise rigidly connected to the sheet metal elements or at any rate not to successive sheet metal elements.
The [0051] housing 3 has two annular retaining members 41 and 42 for holding the heat-exchange body 5 at its end surfaces 5 c, 5 d. Each retaining member 41, 42 has an annular, metallic wall 43 or 44, respectively, which is angular in axial section and has two conical parts or limbs inclined inward or outward away from its peak. A metallic foil 45 or 46 which rests against the end surface 5 c or 5 d, respectively, of the body 5 is held on those edges of said wall which face away from the peak. At least some of said edges of the walls 43, 44 can furthermore be tightly welded to those points of the sheet metal element edges and edge strips present next to them. For example, the inner edge of the lower wall 43 and the outer edge of the upper wall 44 can be welded at the inner edge of the lower end surface 5 c and at the outer edge of the upper end surface 5 d of the heat-exchange body to the latter. On the other hand, the outer edge of the lower wall 43 and the inner edge of the outer wall 44 are, for example, not welded to the heat-exchange body. The cavity bounded by the angular wall 43, 44 and the foil 45 or 46 contains a heat-insulating, elastically deformable insulation 47 or 48. This is heat-resistant up to very high temperatures of, for example, at least about 1000° C. Each insulation 48 may consist, for example, of a preshaped, deformable body and contain, for example, a fibre material and a binder. However, the insulation can also consist of a filler material only loosely aggregated and capable of being introduced into the cavities of the walls. Each insulation 47, 48 rests against that side of the foil 45 or 46 which faces away from the heat-exchange body, and presses said foil against the end surface 5 c or 5 d of the heat-exchange body. The walls 43, 44 and foils 45, 46 consist, for example of stainless, chromium-containing steel. While the walls 43, 44 are, for example, about 1 mm to 2 mm thick, the thickness of the foils 45, 46 is at most 0.1 mm and, for example, 0.03 mm to 0.07 mm. The foils are therefore fairly readily deformable and can fit snugly against one another and against the end surfaces 5 c, 5 d. The foils 45, 46 cover the major parts of the side edges of the sheet metal elements 23, 27 and fluid passages 33, 34 and at least approximately tightly seal the major parts of the second fluid passages 34 which are open at to [sic] the end surfaces 5 c, 5 d, at the side edges of said passages.
Each [0052] first fluid passage 33 has a first fluid inlet orifice 33 a and a first fluid outlet orifice 33 b for the first fluid 15. Each second fluid passage 34 has a second fluid inlet orifice 34 a and a second fluid outlet orifice 34 b for the second fluid. These orifices 33 a, 33 b, 34 a, 34 b are all formed by slots between edge sections of adjacent sheet metal elements 23, 27 bounding the relevant passage. Each first inlet orifice 33 a is present between the inner edges 23 a, 27 a of two sheet metal element [sic] 23, 27. Each first outlet orifice 33 b is present between the outer edges 23 b, 27 b of two sheet metal elements 23, 27. The orifices 33 a, 33 b extend in the axial direction from an edge strip 24 to an edge strip 25. Each second inlet orifice 34 a is present between sections of the side edges 23 c, 27 c of two sheet metal elements 23, 27 in the proximity of the outer edges 23 b, 27 b of these sheet metal elements. Each second inlet orifice is approximately adjacent to the outer lateral surface 5 b and in fact runs away from an edge strip 29 inward to retaining member 41 and extends only over a section of the side edges 23 c, 27 c which is very much shorter than the total side edges. Each second outlet orifice 34 b is present between sections of the side edges 23 d, 27 d of two sheet metal elements 23, 27 in the proximity of the inner edges of the sheet metal elements. Each second outlet orifice 34 b is approximately adjacent to the inner lateral surface 5 a and in fact runs away from an edge strip 28 outward to the retaining member 42 and extends only along side edge sections which are very much shorter than the total side edges 23 d, 27 d.
The [0053] first inlet orifices 33 a of the various first passages together define a first inlet region 5 e of the heat-exchange body 5. The first outlet orifices 33 b analogously define a first outlet region 5 f. Furthermore, the second inlet orifices together and the second outlet orifices together define a second inlet region 5 g and a second outlet region 5 h, respectively. Each of these regions is annular and is in an area encompassing the axis 2. The first inlet region and the first outlet region are present at the inner lateral surface 5 a and at the outer lateral surface 5 b, respectively, and extend in the axial direction over the major part of the lateral surfaces. The second inlet region 5 g and the second outlet region 5 h are present at and/or in one of the two end surfaces 5 c or 5 d facing away from one another, but extend only over a small part thereof in the radial direction. The first inlet region and the second outlet region are present at the inner edges or in the proximity thereof, but these two regions are spatially separated from one another. Similarly, the first outlet region and the second inlet region are also spatially separated from one another. The inlet and outlet regions adjacent to one another in pairs are a distance apart in the axial direction by an amount equal to the width of a first edge strip 25 or 24 and along the involute side edges of the sheet metal elements by an amount equal to the width of a second edge strip 28 or 29.
The inner [0054] lateral surface 5 a of the heat-exchange body 5 encompasses a first, substantially cylindrical inlet chamber 51 which is adjacent to the first inlet region 5 e of the heat-exchange body. The housing 3 and/or the fluid conducting means 7 furthermore bound a first outlet chamber 52, a second inlet chamber 53 and a second outlet chamber 54. The first inlet chamber 51 is closed, for example, at its end at the bottom in FIG. 2 by a hollow closure member 57 which has metallic walls 58 and contains a heat insulation 59. The three chambers 52, 53, 54 are annular and, for example, bounded by metallic walls and are adjacent to the first outlet region 5 f or the second inlet region 5 g or the second outlet region 5 h of the heat-exchange body 5. The fluid conducting means 7 have a conical inlet part 61 which connects the first fluid entrance 8 to the first inlet chamber 51, widens toward the first inlet chamber 61 and is connected, namely welded, tightly to the heat-exchange body approximately at the annular edge between the surfaces 5 a, 5 d of said heat-exchange body. The fluid conducting means furthermore connect the first outlet chamber 52 to the first fluid exit 9, the second fluid entrance 10 to the second inlet chamber 53 and the second outlet chamber 54 to the second fluid exit 11, all these connections being tight.
The first and second sheet metal elements are completely identical apart from the edge strips fastened to them. As stated above, the sheet metal elements are completely straight everywhere in axial sections from one side edge to the other side edge and are substantially completely involute everywhere from the inner edge to the outer edge in sections transverse to the [0055] axis 2. They thus have no curved or angled edge sections. This contributes toward economical production of the heat exchanger.
The [0056] orifices 33 a, 33 b, 34 a, 34 b of the passages 33, 34 connect the relevant passage between said edges of the sheet metal elements through to a space adjacent to these edges, in the vicinity of the heat-exchange body, namely to one of the chambers 51, 52, 53, 54. Those orifices of the heat-exchange body which serve for passing the fluids into the heat-exchange body and for discharging the fluids from the heat-exchange body are thus formed by constructionally simple means. The inlet and outlet orifices can be formed in particular without the heat-exchange body having to be provided with additional channels for this purpose as is the case for various known heat exchangers. This also contributes toward economical producibility of the heat exchanger.
During the use of the [0057] heat exchanger 1, the first fluid 15 consisting of exhaust gas has, in the first inlet chamber 51, an inlet temperature which is very much higher than the inlet temperature of the second fluid 16 consisting of air in the second inlet chamber 53. The first fluid 15 is distributed in the inlet chamber 51 over the first fluid inlet orifices 33 a and flows in these into the first fluid passages 33, through these outward away from the axis 2 and then through the first fluid outlet orifices 33 b into the first outlet chamber 52. The first fluid flows in the heat-exchange body 5 in general approximately transversely to the axis 2 along the involute, first passages. The second fluid 16 flows from the second inlet chamber 53 initially approximately parallel to the axis 2 through the second fluid inlet orifices 34 a into the second fluid passages 34, is distributed in those initial sections of said passages which are free of knitted wire fabric over the axial dimension of the second passages, then flows approximately transversely to the axis 2 along the involute passages from outside to inside toward the axis 2, is deflected again in the proximity of the inner ends of the passages into an approximately axial direction and then flows through the second fluid outlet orifices 34 b into the second outlet chamber 54. Since the second inlet orifices 34 a and the second outlet orifices 34 b are located at the end surfaces 5 c, 5 d which face away from one another, the second fluid 16 follows approximately Z-shaped flow paths in the axial section shown in FIG. 5, but the major part of these flow paths are approximately transverse to the axis 2 along involutes.
If the two [0058] fluids 15, 16 flow through the heat-exchange body in directions of flow which are for the most part opposite to one another, the originally much hotter, first fluid 15 consisting of exhaust gas releases heat to the initially cold, second fluid 16 consisting of air. The first fluid is thus cooled along its flow paths from inside to outside, while the second fluid is heated from outside to inside. The temperature of the heat-exchange body 5 thus decreases in an outward direction away from the axis so that the heat-exchange body has only a low temperature deviating at most slightly from ambient temperature at its relatively large, outer lateral surface 5 b. Since the sheet metal elements 23, 24 are very thin, they conduct only little heat to the outside. The intermediate layers 31, 32 consisting of knitted wire fabrics 37 have only small material cross-sectional surfaces in comparison with the cross-sectional dimensions of the fluid passages 33, 34 and accordingly result in only little heat conduction. Since the rows 37 a of stitches of the wire lattices 37 are transverse to the longitudinal direction of the passages, to the main directions of flow of fluids and to the temperature gradients in the heat-exchange body, the heat conducted by the wire lattices must moreover pass contact points of wire sections in order to pass from one row 37 a of stitches to the next. In particular, the wire lattices therefore conduct only very little heat away from the inside along the passages to the outside. The metallic foils 45, 46 present at the end surfaces 5 c, 5 d of the heat-exchange body are very thin and accordingly also result in only little heat conduction. Furthermore, the foils in the axial direction are insulated by the insulations 47 and 48. For all these reasons, the heat exchanger releases only little heat to the environment so that a very large part of the heat of the hot exhaust gas or first fluid 15 can be recovered.
The temperature of the [0059] first fluid 15 consisting of exhaust gas may be, for example, 500° C. or about 1000° C. or possibly even more when passed into the heat exchanger. The various parts of the heat-exchange body 5 are therefore greatly expanded during operation in the inner region of the heat-exchange body by the increase in temperature. The sheet metal elements 23, 27 adjacent to one another are supported in a stable manner against one another by the edge strips 24, 25, 28, 29 by those wire sections of the knitted wire fabrics 37 which rest against one another at the intersection points 37 c and against the sheet metal elements, so that the diameters of the passages can be changed approximately by the same amount for all passages even with large temperature changes. The wires of the knitted wire fabrics are capable of relatively free deformation between the intersection points 37 c, so that the temperature changes and temperature gradients do not cause any excessive stresses and any damage to the knitted wire fabrics and the sheet metal elements supported by them. The sheet metal elements present in succession around the axis 2 are—as described above—connected to one another in each case at two edge strips 24, 25 or 28, 29 and are at least substantially unconnected at the other edges. Furthermore, the sheet metal elements are free of rigid connections in their main regions present between the edge strips. The described manner for connecting the sheet metal elements to give a heat-exchange body helps to ensure that the sheet metal elements are not damaged even by large temperature changes and temperature gradients. Furthermore, the formation of the two retaining members 41, 42 engaging the end surfaces of the heat-exchange body ensures that the sheet metal elements can also move slightly perpendicularly to the axis 2 relative to the retaining members and that the latter can adapt to axial dimensional changes of the heat-exchange body. As described, the length of the sheet metal elements and passages measured along the curved side edges is at least 2 times and, for example, at least or about 3 times the width, parallel to the axis, of the sheet metal elements and passages. This large ratio of length to width makes the heat-exchange body readily deformable. For all these reasons, the heat exchanger 1 is very solid and durable.
During tests, in particular numerous cold starts were also carried out, in which hot exhaust gas having temperatures of the order of about 700° C. was abruptly fed to a cold heat exchanger. Although the heat exchanger is subjected to very high stresses during such cold starts, no damage at all was found even after a large number of such cold starts. [0060]
The internal diameter of a heat-exchange body may be, for example, 250 mm to 1 m or more. Sheet metal elements adjacent to one another may then have, for example, spacings of about 1 mm, the thickness of the sheet metal elements being, for example, about 0.2 mm. The heat-exchange body can then have at least 500 or even at least 1000 sheet metal elements and passages distributed around its axis. The large number of passages results in intensive heat exchange. The knitted wire fabrics moreover produce microturbulence in the fluids flowing through the passages. Consequently, the heat exchange between the two fluids is further improved. [0061]
The heat exchanger shown in parts in FIGS. [0062] 13 to 16 has one, and only one, annular heat-exchange body 5, like the heat exchanger described above. Said heat-exchange body is formed substantially identically or similarly to the heat-exchange body described above and has in particular an inner lateral surface 5 a, an outer lateral surface 5 b and two end surfaces 5 c, 5 d facing away from one another. Once again, retaining members 41, 42 with walls 43, 44 for holding the heat-exchange body 5 are furthermore present. The lower retaining member 41 is, however, formed in such a way that it completely covers the lower end surface 5 c from the inner lateral surface 5 a to the outer lateral surface 5 b and seals the second passages more or less air-tight everywhere. In contrast, the upper retaining member 42 leaves both an annular region adjacent to the inner edge and an annular region adjacent to the outer edge free at the upper end surface 5 d. The second fluid 16 consisting of cold air can flow into the heat-exchange body at the outer, uncovered annular region of the upper end surface 5 d and can flow out of the heat-exchange body again at the inner, uncovered annular region of the same end surface 5 d. The second fluid 16 is thus passed along an approximately U-shaped flow path into the heat-exchange body, through the latter and out of it again. Under certain circumstances, this may be advantageous for reasons relating to space. The first fluid 15, on the other hand, is passed through the heat-exchange body analogously to the heat exchanger described with reference to FIGS. 1 to 12.
The heat exchanger according to FIGS. [0063] 13 to 16 furthermore differs from the heat exchanger described above in that, instead of a single foil 45 or 46, a plurality of metallic foils 75 or 76 distributed along the periphery of the heat-exchange body and shown particularly clearly in FIGS. 14 and 15 are present at each end surface 5 c, 5 d. Each involute sheet metal element and each fluid passage has, at each end surface 5 c, 5 d, parts which are covered by at least two different foils 75 and 76. The two fluid passages 34 are once again open at the end surfaces 5 c, 5 d. The foils 75, 76 resting against the end surfaces 5 c, 5 d overlap one another in such a way that the second fluid 16 emerges at the overlaps of the foils, in each case in an outlet section of a foil, from the region which is covered by said foil and in which this foil is already covered by the foil in succession in the direction of flow of the second fluid.
In addition to a main section resting against the heat-[0064] exchange body 5, each foil 75, 76 also has edge sections 75 a and 76 a, respectively. In the heat exchanger according to FIGS. 13 to 16, each cavity bounded by one of the walls 43, 44 furthermore contains an insulation 88 which is composed of two originally separated insulation parts 88 a and 88 b. The insulation part 88 a consists of a flat layer which rests against the main sections of the foils 75 and 76. The edge sections 75 a, 76 a of the foils are placed around the edges of the insulation parts 88 a. The insulation parts 88 b rest against the insulation parts 88 a and the surrounding edge sections 75 a, 76 a of the foils, thus clamp the surrounding edge sections and also serve for holding the foils firmly.
FIG. 16 also shows some weld joints, of which all those which connect the heat-[0065] exchange body 5 to parts of the housing and/or of the retaining members and/or fluid conducting means are denoted by 91.
Unless stated otherwise above, the heat exchanger according to FIGS. [0066] 13 to 16 may be formed identically or similarly to the heat exchanger according to FIGS. 1 to 12.
The [0067] heat exchanger 101 shown in FIGS. 17, 18 and 19 has an axis 2 and a housing 103. The housing contains a first heat-exchange body 105.1 and a second heat-exchange body 105.2. Furthermore, once again only schematically shown fluid conducting means 107 are present. FIG. 17 also shows parts of a gas turbine 112 whose housing is connected to the housing 103 and the fluid conducting means 107 of the heat exchanger 101. Furthermore, a first fluid 15 consisting of exhaust gas and a second fluid 16 consisting of air are represented by arrows.
Each heat-exchange body [0068] 105.1, 105.2 has first and second fluid conducting elements alternately in succession around the axis 2. The first fluid conducting elements are shown in FIG. 18 and are identically formed in the case of both heat-exchange bodies 105.1, 105.2 and also formed identically or similarly to the first fluid conducting elements of the heat-exchange body 5 and, like these, are denoted by 21. On the other hand, the second fluid conducting elements of the two heat-exchange bodies 105.1, 105.2 which elements are shown in FIG. 19, differ slightly from one another and are denoted by 122.1 and 122.2, respectively. Each first and second fluid conducting element has, as main component, a first sheet metal element or second sheet metal element, respectively. The sheet metal elements are all identically formed and dimensioned, also formed identically or similarly to sheet metal elements 23, 27 of the heat-exchange body 5 and, like these, denoted by 23 and 27, respectively. The sheet metal elements of the heat-exchange body 105.1, 105.2 are provided, identically or similarly to those of the heat-exchange body 5, with first edge strips 24, 25 and second edge strips 28, 29 and are connected to one another in pairs at these.
First and second intermediate layers are arranged alternately between those sheet metal elements of the heat-exchange bodies [0069] 105.1, 105.2 which are present in succession around the axis. The first intermediate layers of the two heat-exchange bodies, which layers are shown in FIG. 18, are all identically formed and arranged, furthermore formed identically or similarly to those of the heat-exchange body 5 and, like these, denoted by 31. Of the second intermediate layers shown in FIG. 19, those belonging to the first heat-exchange body 105.1 are formed and arranged identically or similarly to those of the heat-exchange body 5 and are denoted by 32. The second intermediate layers of the second heat-exchange body 105.2 are denoted by 132.2 and are arranged slightly differently to the second intermediate layers 32 of the first heat-exchange body 105. While each intermediate layer 32 is at least approximately adjacent to an edge strip 28 and is separated from the edge strip 29 by an axial, strip-like, free intermediate space, each second intermediate layer 132 is at least approximately adjacent to the edge strip 29 and is separated from the edge strip 28 by a strip-like, free intermediate space.
The [0070] housing 103 has retaining members 41 and 42 which are formed similarly to those of the housing 3 and, like these, are denoted by 41 and 42, respectively. Each of these retaining members engages one of the two flat end surfaces 105.1 c and 105.2 d of the two heat-exchange bodies 105.1, 105.2, which end surfaces are furthest away from one another. An annular retaining member 143 is arranged between the two heat-exchange bodies. Said retaining member has two short, cylindrical, metallic walls, namely an inner wall 144 and an outer wall 145, and two metallic foils 146, each of which rests against one of those end surfaces 105.1 d and 105.2 c of the two heat-exchange bodies 105.1, 105.2 which face one another. The interior encompassed by the walls 144, 145 and the foils 146 contains a heat-insulating, elastically deformable insulation 147. The retaining member 143 covers the major part of the end surfaces 105.1 d, 105.2 c of the two heat-exchange bodies but leaves one annular region each free on the inside and outside.
First and second fluid passages are present alternately between the sheet metal elements present in succession around the axis. The first fluid passages of the two heat-exchange bodies [0071] 105.1, 105.2, which passages are shown in FIG. 18, are all identically formed and identically or similarly formed to those of the heat-exchange body 5 and, like these, are denoted by 33.
The second fluid passages of the two heat-exchange bodies [0072] 105.1, 105.2 are denoted by 134.1 and 134.2. respectively. The second passages 134.1 of the first heat-exchange body 105 have a second fluid inlet orifice 134.1 a and a second fluid outlet orifice 134.1 b, analogously to the second fluid passages 34 of the heat-exchange body 34, and additionally have a fluid secondary outlet orifice 134.1 c. This is present at the end surface 105.1 d of the body 105 and is arranged in the axial direction relative to the second inlet orifice 134.1 a.
Each second fluid passage [0073] 134.2 of the second heat-exchange body 105.2 has a second fluid inlet orifice 134.2 a and a second fluid outlet orifice 134.2 b. These two orifices are arranged similarly to the corresponding orifices of the second passages of the heat-exchange body 5. However, that section of the passage 134.2 which is flush with the inlet orifice 134.2 a in the axial direction also contains a section of a second intermediate layer 132.2. Each second passage 134.2 of the second heat-exchange body 105.2 furthermore has a fluid secondary inlet orifice 134.2 c. This is present in the proximity of the inner edges of the second sheet metal elements of the second heat-exchange body 105.2 and lies in the end surface 105.2 c. Each secondary inlet orifice 134.2 c is arranged opposite the second outlet orifice 134.2 b in the axial direction and is connected to said outlet orifice by an axial strip-like region of the second passage 134.2 which is at least partly free, i.e. contains no section of the second intermediate layer 132.2.
The [0074] housing 103 and the fluid conducting means 107 are in part formed similarly to the housing 3 and the fluid conducting means 7 but also bound an inner and an outer connecting passage 155 or 156. The inner connecting passage 155 connects that annular, second outlet region of the first heat-exchange body 105.1 which is defined by the second outlet orifices 134.1 b to that annular secondary inlet region of the second heat-exchange body 105.2 which is defined by the secondary inlet orifices 134.2 c. The outer connecting passage 156 connects that annular secondary outlet region of the first heat-exchange body 105.1 which is defined by the secondary outlet orifices 134.1 c to that annular second inlet region of the second heat-exchange body 105.2 which is defined by the second inlet orifices 134.2 a.
When the [0075] heat exchanger 101 is used, originally hot exhaust gas flows as first fluid 15 from the inside to the outside through the first passages 33 of the two heat-exchange bodies 105.2 [sic] and 105.2. The second fluid 16 consisting of originally colder air is passed through the second inlet orifices 134.1 a of the first heat-exchange body 105.1 into its second passages 134.1 and then partly flows inward through these passages to the second outlet orifices 134.1 b and partly through the secondary outlet orifices 134.1 c and the outer connecting passage 156 to the second inlet orifices 134.2 a of the second heat-exchange body 105.2 and inward through its second passages 134.2 to its second outlet orifices 134.2 b. That part of the second fluid 16 which reaches the second outlet orifices 134.1 b of the first heat-exchange body 105.1 then flows through the inner connecting passage 155 to the secondary inlet orifices 134.2 c of the second heat-exchange body 105.2 into the exit end region of the second passages 134.2 of the second heat-exchange body 105.2. There, that part of the second fluid 16 which arrives from the first heat-exchange body 105.1 combines with that part of the second fluid which has previously flowed from the outside to the inside through the whole second heat-exchange body. Those parts of the second fluid 16 which have been combined with one another then flow through the second outlet orifices 134.2 b of the second heat-exchange body 105.2 and out of the latter.
Unless stated otherwise above, the [0076] heat exchanger 101 is similarly formed and is used and operated similarly to the heat exchanger 1 and has similar properties to it.
The [0077] heat exchanger 201 shown in FIG. 20 has a housing 203. This contains a plurality of, namely three, pairs of heat-exchange bodies. Each pair has a first heat-exchange body 205.1 and a second heat-exchange body 205.2. The heat-exchange bodies 205.1 and 205.2 are formed similarly to the heat-exchange bodies 105.1 and 105.2 of the heat exchanger 101. The three pairs of heat-exchange bodies are offset axially relative to one another and are held a distance apart by retaining members 206 arranged between them. These retaining members 206 are, for example, formed similarly to the retaining members 143 of the heat exchanger 101 but have larger axial dimensions. The fluid conducting means 207 of the heat exchanger 201 are formed for passing a first fluid 15 and a second fluid 16 through the heat-exchange bodies 205.1 and 205.2 belonging to the same pair, in a manner analogous to that described for the heat exchanger 101 having only a single pair of heat-exchange bodies.
The [0078] heat exchanger 301 shown in FIG. 21 has a plurality of, namely, for example, four annular heat-exchange bodies which are formed identically or similarly to those of the heat exchanger described first and are likewise denoted by 5. The annular heat-exchange bodies are a distance apart along the axis of the heat-exchanger and encompass a cavity with an axial pipe 303. The cavity region present between the inner lateral surfaces of the heat-exchange bodies 5 and the pipe 303 serves as a first inlet chamber 351 for the first fluid 15 and contains some conical baffle plates 305 which have an orifice in the central region and serve for distributing the first fluid over the various heat-exchange bodies 5. The heat-exchange bodies 5 have, at each of their two end surfaces inlet orifices for the second fluid 16 in the proximity of the outer lateral surface and outlet orifices for the second fluid 16 in the proximity of the inner lateral surface. The second fluid 16 flowing out of the uppermost heat-exchange body 5 at the upper end surface of said heat-exchange body passes into an annular, second outlet chamber 354. The remaining second fluid 16 flowing out of the heat-exchange bodies passes into annular, second outlet chambers 355 which are connected to the pipe 303 by radial connecting channels 356 arranged in a spoke-like manner. Said pipe is connected in the proximity of its upper end by a few connecting channels 357, for example inclined relative to the axis 2, to the second outlet chamber 354, from which the second fluid 16 can flow through an orifice of the housing of the heat exchanger and out of the latter. The connecting channels 356 are composed of half-shells. Furthermore, the other means for holding the heat-exchange bodies and for feeding the fluids to the heat-exchange bodies and for removing the fluids from the heat-exchange bodies are also formed in a substantially modular manner so that the number of identically formed heat-exchange bodies can be changed in a simple manner and adapted to intended fluid flow rates.
The heat exchangers can also be modified in other ways. Thus, in particular features of the various heat exchangers described can be combined with one another. For example, in the case of all embodiments, the foils can be formed and held in a manner similar to that described for the heat exchanger according to FIGS. [0079] 13 to 16. In addition, the knitted wire fabric shown in FIGS. 5 and 19 and serving as second intermediate layers 32 could extend over the whole lengths of the second fluid passages 34, 134.1, 134.2—i.e. from the inner to the outer edge strips. Furthermore, the wall 43 of the heat exchanger shown in FIGS. 1 to 12 could possibly also be welded at its outer edge facing the lower end surface 5 c—i.e. at the inner boundary of the second inlet region 5 g—to the heat-exchange body 5 and/or the wall 44 could possibly also be welded to the heat-exchange body 5 at its inner edge facing the upper end surface 5 d—i.e. at the outer boundary of the second outlet region 5 h. In the case of the heat exchanger shown in FIGS. 13 to 16, the wall 44 could possibly be welded in an analogous manner at its outer and/or its inner, the end surface 5 d [sic] of the heat exchanger 5 to the latter. The weld joints between the sheet metal elements and edge strips and between the heat-exchange bodies and those parts of the housing and/or fluid conducting means which are connected to said heat-exchange bodies can be replaced at least partly or completely with hard solder joints and/or adhesive bonds. The first inlet orifices and the second outlet orifices of a heat-exchange body could, for example, be axially offset relative to one another in the inner lateral surface of the heat-exchange body. The first outlet orifices and the second inlet orifices of a heat-exchange body could analogously be axially offset relative to one another in the outer lateral surface of the heat-exchange body.
Furthermore, the sheet metal elements in the unwound, flat state could form an oblique-angled parallelogram or have at least two nonparallel edges opposite one another. In these cases, at least one of the lateral surfaces and/or end surfaces of the heat-exchange body would then be conical. The sheet metal elements could possibly have even at least one edge curved in the unwound, flat state of the sheet metal elements. [0080]

Claims

1. Heat exchanger comprising at least one heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) which is annular in cross-section, encompasses an axis (2) and has sheet metal elements (23, 27, 127) which are present in succession around said axis and together alternately bound first passages (33) for a first fluid (15) and second passages (34, 134.1, 134.2) for a second fluid (16), each sheet metal element (23, 27, 127) having an inner edge (23 a, 27 a), an outer edge (23 b, 27 b) and two side edges (23 c, 23 d, 27 c, 27 d) running from the inner edge (23 a, 27 a) to the outer edge (23 b, 27 b), adjacent sheet metal elements (23, 27, 127) having substantially constant distances from one another along their side edges (23 c, 23 d, 27 c, 27 d), characterized in that each sheet metal element (23, 27, 127) forms a quadrilateral, that metallic edge strips (24, 25) are arranged between the sheet metal elements (23, 27, 127) together bounding a first passage (33) and run along the side edges (23 c, 23 d, 27 c, 27 d) of said sheet metal elements and are firmly and tightly connected to the relevant sheet metal elements (23, 27, 127) and that metallic edge strips (28, 29) are arranged between the sheet metal elements (23, 27, 127) together bounding a second passage (34, 134.1, 134.2) and run along the inner edges (23 a, 27 a) and the outer edges (23 b, 27 b) of said sheet metal elements and are firmly and tightly connected to the relevant sheet metal elements (23, 27, 127).

2. Heat exchanger according to claim 1, characterized in that the inner edge (23 a, 27 a) and the outer edge (23 b, 27 b) of each sheet metal element (23 a, 27 a) [sic] are straight and parallel to one another and that the two side edges (23 c, 23 d, 27 c, 27 d) of each sheet metal element (23, 27, 127) are parallel to one another and at right angles to the inner edge (23 a, 27 a) and outer edge (23 b, 27 b).

3. Heat exchanger according to claim 1 or 2, characterized in that the sheet metal elements (23, 27, 127) are connected by welding or hard soldering or adhesive bonding to the edge strips (24, 25, 28, 29) and thus to one another.

4. Heat exchanger according to any of claims 1 to 3, characterized in that the sheet metal elements (23, 27, 127) together bounding a first passage (33) are free, at their inner edges (23 a, 27 a) and outer edges (23 b, 27 b), between the edge strips (24, 25) arranged at their side edges (23 c, 23 d, 27 c, 27 d), from rigid connections between said edge strips.

5. Heat exchanger according to any of claims 1 to 4, characterized in that the two side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127) and the edge strips (24, 25) running along them form end surfaces (5 c, 5 d) facing away from one another, that the two passages (34, 134.1, 34.2) [sic] have inlet orifices (34 a, 134.1 a, 134.2 a) lying in one of the end surfaces (5 c, 5 d) and outlet orifices (34 b, 134.1 b, 134.2 b) lying in one of the end surfaces (5 c, 5 d), that the sheet metal elements (23, 27, 127) together bounding a second passage (34, 134.1, 134.2) are free, at the side edges (23 c, 23 d, 27 c, 27 d) of these sheet metal elements (23, 27, 127), in at least one of the following regions, or rigid connections between them;

a) between the edge strips (28, 29) arranged at their inner edges (23 a, 27 a) and outer edges (23 b, 27 b),

b) between the inlet orifices (34 a, 134.1 a, 134.2 a) and the edge strips (28) arranged at the inner edges (23 a, 27 a) and between the outlet orifices (34 b, 134.1.b, 134.2 b) [sic] and the edge strips (29) arranged at the outer edges (23 b, 27 b),

c) between the inlet orifices (34 a) and the outlet orifices (34 b).

6. Heat exchanger according to any of claims 1 to 5, characterized in that each first passage (33) has, at the inner edges (23 a, 27 a) of the two sheet metal elements (23, 27, 127) bounding it, at least one orifice (33 a) which connects the first passage (33) between these inner edges (23 a, 27 a) through to a space adjacent to said edges and that each first passage (33) has, at the outer edges (23 b, 27 b) of the two sheet metal elements (23, 27, 127) bounding it, at least one orifice (33 b) which connects the first passage (33) between these outer edges (23 b, 27 b) through to a space adjacent to said edges.

7. Heat exchanger according to any of claims 1 to 6, characterized in that each second passage (34, 134.1, 134.2) has, in the proximity of the outer edges (23 b, 27 b) and in the proximity of the inner edges (23 a, 27 a) of the two sheet metal elements (23, 27, 127) bounding it, in each case at least one orifice (34 a, 34 b, 134.1 a, 134.1 b) which connects the second passage (34, 134.1, 134.2) between two opposite side edges (23 c, 23 d, 27 c, 27 d) of these sheet metal elements (23, 27, 127) through to a space adjacent to said edges.

8. Heat exchanger according to claim 7, characterized in that those orifices of the passages (33, 34, 134.1, 134.2) which are present at or near the inner edges (23 a, 27 d) of the sheet metal elements (23, 27, 127) serve as inlet orifices (33 a) of the first passages (3) or as outlet orifices (34 b, 134.1 b, 134.2 b) of the second passages (34, 134.1, 134.2), that those orifices of the passages (33, 34, 134.1, 134.2) which are present at or near the outer edges (23 b, 27 b) serve as outlet orifices (33 b) of the first passages (33 a) or as inlet surfaces (34 a, 134.1 a, 134.1 b) of the second passages (34, 134.1, 134.2), that fluid conducting means (7, 107, 207) are present in order to convey the first fluid (15) to the inlet orifices (33 a) of the first passages (33) and away from the outlet orifices (33 b) of the first passages (33) and in order to convey the second fluid (16) to the inlet orifices (34 a, 134.1 a, 134.1 b) of the second passages (34, 134.1, 134.2) and away from the outlet orifices (34 b, 134.1 b, 134.2 b) of the second passages (34, 134.1, 134.2), and that the fluid conducting means (7, 107, 207) are formed in order to feed the first fluid to the inlet orifices (33 a) of the first passages (33) at a temperature which is higher than the temperature at which the second fluid (16) is fed to the inlet orifices (34 a, 134.1, 134.2) of the second passages (34, 134.1, 134.2) so that the first fluid 825) [sic] releases heat to the second fluid (16) and the or each heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) has a temperature generally decreasing outward away from the axis (2).

9. Heat exchanger according to claim 8, characterized in that the inlet orifices (33 a) of the first passages (33) are arranged in a first inlet region (5 e), the outlet orifices (33 b) of the first passages (33) are arranged in a first outlet region (5 f), the inlet orifices (34 a, 134.1 a, 134.2 a) of the second passages (34, 134.1, 134.2) are arranged in a second inlet region (5 g) and the outlet orifices (34 b, 134.1 b, 134.2 b) of the second passages (34, 134.1, 134.2) are arranged in a second outlet region (5 h) of the or a heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) and that each inlet region (5 e, 5 g) and outlet region (5 f, 5 h) runs in an annular manner around the axis (2).

10. Heat exchanger according to any of claims 1 to 9, characterized in that the inner edges (23 a, 27 a) of the sheet metal elements (23, 27, 127) and the edge strips (28) arranged at the inner edges (23 a, 27 a) define an inner lateral surface (5 a), that the sheet metal elements (23, 27, 127) adjacent to one another are at least approximately a constant distance apart from their inner edges (23 a, 27 a) to their outer edges (23 b, 27 b) and that those sections of the sheet metal elements (23, 27, 127) which are adjacent to the inner edges (23 a, 27 a) have, in a cross-section at right angles to the axis (2), a tangent which makes with the inner lateral surface (5 a) an angle which is 65° to 115° and, for example, 80° to 100°, the sheet metal elements (23, 27, 127) being preferably substantially involute in a section at right angles to the axis (2).

11. Heat exchanger according to any of claims 1 to 10, characterized in that the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127) and the edge strips (24, 25) arranged at the side edges (23 c, 23 d, 27 c, 27 d) define two end surfaces (5 c, 5 d) of the or each heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) and that the inlet orifices (34 a, 134.1 a, 134.2 a) and the outlet orifices (34 b, 134.1 b, 134.2 b) of the second passages (34, 134.1, 134.2) are arranged at end surfaces (5 c, 5 d) facing away from one another.

12. Heat exchanger according to claim 1, characterized in that it has at least one pair of heat-exchange bodies, comprising a first heat-exchange body (105.1, 205.1) and a second heat-exchange body (105.2, 205.2), that each heat-exchange body (105.1, 105.2, 205.1, 205.2) has an inner and an outer lateral surface, that the second passages (134.1) having the inlet orifices (134.1 a) arranged in an end surface (105.1 c) of the first heat-exchange body (105.1, 205.1) have secondary outlet orifices (134.1 a) arranged in the other end surface (105.1 d) in the proximity of the outer lateral surfaces of the first heat-exchange body (105.1, 205.1), that the second passages (134.2) having the outlet orifices (134.2 b) of the second heat-exchange body (105.2, 205.2) which are arranged in an end surface (105.2 c) have secondary inlet orifices (134.2 c) arranged in the other end surface (105.2 c) in the proximity of the inner lateral surface of the second heat-exchange body (105.2, 205.2) and that the fluid conducting means (107, 207) are formed in order to convey the second fluid (16) into the first heat-exchange body (105.1) at those inlet orifices (134.1 a) of the second passages (134.1) which are arranged in an end surface (105.1 c) and then to convey part of this fluid (16) from the secondary outlet orifices (134.1 c) of the first heat-exchange body (105.1) to those second inlet orifices (134.2 a) of the second heat-exchange body (105.2, 205.1) which are arranged in an end surface (105.2 c) and in order to convey second fluid (16) which flows out of the second outlet orifices (134.1 b) arranged in an end surface (105.1 b) of the first heat-exchange body (105.1, 205.1) to the secondary inlet orifices (134.2 c) of the second heat-exchange body (105.2, 205.2).

13. Heat exchanger, in particular according to any of claims 1 to 12, comprising at least one heat-exchange body (5, 105, 105.2, 205.1, 205.2) having successive sheet metal elements (23, 27, 127) which alternately bound passages (33, 34, 134.1, 134.2) for a first fluid (15) and a second fluid (16) and between which gas-permeable intermediate layers (31, 32, 132.2) are arranged, each sheet metal element (23, 27, 127) having two side edges (23 c, 23 d, 27 c, 27 d) facing away from one another, characterized in that the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127) belonging to the same heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) and/or edge strips (24, 25) arranged at these side edges (23 c, 23 d, 27 c, 27 d) together define two end surfaces (5 c, 5 d, 105.1 c, 105.1 d, 105.2 c, 105.2 d) of the heat-exchange body (5, 105.1, 105.2, 205.1, 205.2), that at least one metallic foil (45, 46, 75, 76, 146) rests against the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127) at each end surface (5 c, 5 d, 105.1 c, 105.1 d, 105.2 c, 105.2 d) and that a heat insulation (47, 48, 88, 157) is arranged on that side of each foil (45, 46, 75, 76, 146) which faces away from the sheet metal elements (23, 27, 127).

14. Heat exchanger according to claim 13, characterized in that each foil (45, 46, 75, 76, 146) is at most 0.1 mm and, for example, 0.03 mm to 0.07 mm thick.

15. Heat exchanger according to claim 12 or 13, characterized in that the insulation (47, 48, 88, 147) presses the foil (45, 46, 75, 76, 146) against the sheet metal elements (23, 27, 127), the insulation (47, 48, 88, 147) being, for example, elastically deformable.

16. Heat exchanger according to any of claims 13 to 15, characterized in that at least two foils (75, 76) which have sections which are adjacent to the end surfaces (5 c, 5 d, 105.1 c, 105.1 d, 105.2 c, 105.2 d) and overlap one another are present at each end surface (5 c, 5 d, 105.1 c, 105.1 d, 105.2 c, 105.2 d) of the or each heat-exchange body (5, 105.1, 105.2, 205.1, 205.2).

17. Heat exchanger, in particular according to any of claims 1 to 16, comprising at least one heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) which is annular in cross-section, encompasses an axis (2) and has sheet metal elements (23, 27, 127) which are present in succession around said axis and together alternately bound first passages (33) for a first fluid (15) and second passages (34, 134.1, 134.2) for a second fluid (16), each sheet metal element (23, 27, 127) having an inner edge (23 a, 27 a), an outer edge (23 b, 27 b) and two side edges (23 c, 23 d, 27 c, 27 d) running from the inner edge (23 a, 27 a) to the outer edge (23 b, 27 b), adjacent sheet metal elements (23, 27, 127) having substantially constant distances from one another along their side edges (23 c, 23 d, 27 c, 27 d), the passages (33, 34, 134.1, 134.2) extending between orifices (33 a, 134.1 b, 134.2 b, 134.2 c) in the proximity of the inner edges (23 a, 27 a) and orifices (33 b, 34 a, 134.1 a, 134.1 c, 134.2 a) in the proximity of the outer edges (23 b, 27 b), characterized in that the sheet metal elements (23, 27, 127) have a dimension, measured along their side edges (23 c, 23 d, 27 c, 27 d), which is at least two times a dimension of the sheet metal elements (23, 27, 127) which is measured along the axis (2).

18. Heat exchanger according to claim 17, characterized in that it has at least two heat-exchange bodies (105.1, 105.2, 205.1, 205.2) a distance apart along the axis (2).

19. Heat exchanger according to claim 17 or 18, characterized in that the distance between adjacent sheet metal elements (23, 27, 127) is at most 10 mm and preferably at most 2 mm.

20. Heat exchanger according to any of claims 17 to 19, characterized in that the or each heat-exchange body (5, 105, 105.2, 205.1, 205.2) has at least 500 passages (33, 34, 134.1, 134.2) distributed around the axis (2).

21. Heat exchanger, in particular according to any of claims 1 to 20, comprising at least one heat-exchange body (5, 105, 105.2, 205.1, 205.2) having successive sheet metal elements (23, 27, 127) which alternately bound passages (33, 34, 134.1, 134.2) for a first fluid (15) and a second fluid (16) and between which gas-permeable intermediate layers (31, 32, 132.2) are arranged, each sheet metal element (23, 27, 127) having two side edges (23 c, 23 d, 27 c, 27 d) facing away from one another and parallel to one another, and at least substantial parts of the passages (33, 34, 134.1, 134.2) running along the side edges (23 c, 23 d, 27 c, 27 d) characterized in that each intermediate layer (31, 32, 132.2) consists of a knitted wire fabric (37) which has rows (37 a) of stitches comprising stitches (37 b) which are adjacent to one another and are formed from cohesive wire sections, and that these rows (37 a) of stitches are generally approximately at right angles to the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127).

22. Heat exchanger according to claim 21, characterized in that each knitted wire fabric (37) is fastened at points to one, and only one, sheet metal element (23, 27) adjacent to it, for example each knitted wire fabric (37) being fastened by a few spot welds to said sheet metal element (23, 27) adjacent to it.

23. Heat exchanger according to claim 21 or 22, characterized in that two rows (37 a) of stitches present in succession along the side edges (23 c, 23 d, 27 c, 27 d) have at most a single cohesive wire section, apart from the interlinked stitches (37 b).

24. Heat exchanger according to any of claims 21 to 23, characterized in that the or each heat-exchange body (5, 105.1, 105.2, 205.1, 205.2) encompasses an axis (2) and is annular in a cross-section at right angles to said axis, that each sheet metal element (23, 27, 127) has an inner edge (23 a, 27 a) and an outer edge (23 b, 27 b), that the side edges (23 c, 23 d, 27 c, 27 d) run from the inner edge (23 a, 27 a) to the outer edge (23 b, 27 b) and make an angle with the axis (2), that sheet metal elements (23, 27, 127) adjacent to one another have substantially constant distances from one another along the whole lengths of their side edges (23 c, 23 d, 27 c, 27 d) and that the passages (33, 34, 134.1, 134.2) are closed along at least the largest parts of the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127).

25. Heat exchanger according to claim 24, characterized in that a first passage (33) for the first fluid (15) and a second passage (34, 134.1, 134.2) for the second fluid (16) are present alternately in succession around the axis (2), that edge strips (24, 25) running at each first passage (33) along the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127) bounding this first passage (33) are arranged between the two sheet metal elements (23, 27, 127) and are connected firmly and tightly to the latter and that edge strips (28, 29) running at each second passage (34, 134.1, 134.2) along the inner edges (23 a, 27 a) and along the outer edges (23 b, 27 b) of the sheet metal elements (23, 27, 127) bounding this second passage (34, 134.1, 134.2) are arranged between the sheet metal elements (23, 27, 127) and are firmly and tightly connected to the latter.

26. Heat exchanger according to claim 24 or 25, characterized in that the sheet metal elements (23, 27, 127) adjacent to one another are everywhere at least approximately a constant distance apart, apart from any edge strips (24, 25, 28, 29) connected at edges (23 a, 23 b, 23 c, 23 d, 27 a, 27 b, 27 c, 27 d) of said sheet metal elements to said sheet metal elements and arranged between adjacent sheet metal elements (23, 27, 127), are completely smooth, straight and parallel to one another in the axial direction and are curved completely parallel to one another and smooth and, for example, substantially involute in sections perpendicular to the axis (2), so that the sheet metal elements (23, 27, 127) are free of protuberances and indentations, such as, for example, waves and/or ribs and the like, and of angled and/or curved edge sections.

27. Heat exchanger according to any of claims 21 to 26, characterized in that each sheet metal element (23, 27, 127) has a thickness which is at most 5 mm, expediently at most 1 mm, preferably at most 0.5 mm and, for example, at most 0.3 mm, and that the knitted wire fabrics (37) consist of wires whose thickness is at most 5 mm, expediently at most 1 mm, preferably at most 0.8 mm and, for example, 0.3 mm to 0.7 mm, the sheet metal elements (23, 27, 127) and knitted wire fabrics (37) preferably consisting of stainless steel.