US20100000725A1

US20100000725A1 - Heat exchanger and heating apparatus provided therewith

Info

Publication number: US20100000725A1
Application number: US12/303,393
Authority: US
Inventors: Karel Hubau; Hugo Lievens; Paul Thijssen; Jan van Peteghem
Original assignee: Bekaert NV SA; Bekaert Combustion Technology BV
Current assignee: Bekaert NV SA; Bekaert Combustion Technology BV
Priority date: 2006-06-08
Filing date: 2007-06-08
Publication date: 2010-01-07
Also published as: WO2007142527A2; WO2007142527A3; EP2035756A2

Abstract

A heat exchanger, provided with a body with at least one flue gas channel and at least one water carrying channel, at least one burner space and at least one flue gas discharge, wherein the at least one flue gas channel extends at least partly between at least a burner space and at least one flue gas discharge and at least a portion of the at least one flue gas channel comprises at least one porous or gas-transmissive heat exchange element.

Description

The invention relates to a heat exchanger.
It is known from practice to manufacture heat exchangers for, for instance, heating apparatus, hot water supplies and the like from, for instance, steel or iron or light metal such as aluminum. As a rule, a casting method is applied here. Casting techniques offer a relatively large design choice but complex casting moulds. As a rule, in existing heat exchangers, heat transfer increasing elements are provided in a flue gas channel, which elements are cast integrally in the casting moulds, at least when casting techniques are used. The heat transfer is then not always optimal.
The object of the invention is to provide a heat exchanger.
In a first aspect, a heat exchanger according to the invention is characterized in that a body is provided with at least one flue gas channel and at least one water carrying channel, at least one burner chamber and at least one flue gas discharge, wherein the at least one flue gas channel extends at least partly between the at least one burner space and at least one flue gas discharge, and at least one portion of the at least one flue gas channel comprises at least one porous or gas transmissive heat exchange element.
Herein, a porous or gas transmissive heat exchange element is understood to mean an element with a structure and/or manufactured from a material with continuous openings, such that gas can flow through the heat exchange element(s), from, in flow direction, a side proximal to the burner space to a side proximal to the flue gas discharge. The openings can comprise, for instance, pores and/or channels.
Preferably, in the flow direction of the flue gases, the porosity increases and/or the density decreases of the heat exchange element or, if several heat exchange elements or parts thereof are provided successively in the flow direction, of the successive heat exchange elements, or parts thereof, so that the flow resistance decreases and the heat transfer can be further optimized. For instance, a first part of the heat exchange element, or with several successive elements, a first heat exchange element, adjacent the burner space, can have a relatively low porosity and high density, for instance a density of more than 70%, while a second part of the heat exchange element or, in flow direction, a trailing second heat exchange element, can have a relatively low density and high porosity, for instance a porosity of more than 70%. Preferably, especially in this manner, at least two successive zones are formed in the flue gas channel, with different average porosity and/or density. These values mentioned should not be taken as being limitative in any manner and serve merely as an example. On the basis of the further design of a heat exchanger, a skilled person can chose and calculate suitable values.
Independently of the first aspect of the invention, and according to a second aspect, the invention provides a first part of a heat exchange element wherein the minimal thicknesses and/or cross-sections of the at least one heat exchange element of the first part are, in fact, greater than those of the at least one heat exchange element of the second part. This serves the purpose of providing a more massive first heat exchange element, which can resist the high temperatures of the combustion gases.
In a third aspect, a heat exchanger according to the invention is characterized in that the or at least one heat exchange element is manufactured at least partly utilizing metal foaming. Preferably, the entire, or all heat exchange elements that are placed in a flue gas channel are manufactured utilizing metal foaming.
Alternatively or additionally, the at least one heat exchange element can comprise fibers, in particular metal fibers.
Such fibers can be from, for instance, metal or ceramics and be processed into a porous mass, for instance a woven or non-woven element. The fibers ensure a relatively large contact surface in relation to the volume, in particular if the fibers are relatively thin, for instance an average thickness of less than 1 micrometer to a few tens or hundreds or micrometers. Preferably, the fibers have an average thickness of between 0.5 and 200 micrometer, more particularly between 0.5 and 50 micrometer.
In an advantageous manner, a heat exchange element can be utilized that is at least partly wintered.
In a fourth aspect, a heat exchanger according to the invention is characterized in that body parts are provided which are manufactured at least partly through extrusion or through casting techniques. Light metal, such as aluminum or an alloy thereof, can then be utilized.
In a fifth aspect, the invention is characterized in that at least one, and preferably each body part is provided with recesses, in particular on a side remote from the flue gas channel, in which parts of a second water carrying channel part are formed or included.
The aspects mentioned and other aspects of the invention can be utilized separately as well as in combination.
The invention further contemplates providing a body part for such a heat exchanger, and a heat exchange element therefore.
The invention furthermore contemplates providing a method for the manufacture of a heat exchanger.
In a first aspect, a method is characterized in that at least two body parts are formed, in particular through extrusion or casting techniques, which body parts each comprise at least a portion of a water carrying channel part, which body parts are mutually connected by end parts and/or at least one heat exchange element, such that the body parts are thus held at a mutual distance from each other while forming a flue gas channel in which said at least one heat exchange element extends, and preferably the water carrying channel parts in the two body parts are mutually connected.
Alternatively, one body part can be utilized in which the entire flue gas channel is formed, which is at least partly filled with at least one at least partly porous or otherwise gas transmissive heat exchange element.

The invention will be further elucidated on the basis of exemplary embodiments, with reference to the drawing. In the drawing:

FIGS. 1A and B show, in front and side view, a heat exchanger without side parts;

FIG. 2 shows, in perspective view, a heat exchanger according to FIG. 1;

FIG. 2A shows, in slight enlargement, a part of a heat exchanger according to FIG. 2;

FIG. 3 shows, in front view, a heat exchanger, in a second embodiment, without side parts;

FIG. 4 shows, in perspective side view, a heat exchanger according to FIG. 3;

FIG. 4A shows, in slight enlargement, a portion of a heat exchanger according to FIG. 4;

FIG. 5 shows, in perspective view, a body part for a heat exchanger according to FIGS. 1-2;

FIGS. 5A and 5B show embodiments of a heat transferring element according to the invention;

FIGS. 5C and 5D schematically show, in side view and front view, an alternative embodiment of a heat transferring surface increasing element;

FIG. 6 shows, in perspective view, a body part for a heat exchanger according to FIGS. 3-4;

FIG. 7 shows, in side view, an alternative embodiment of a heat exchanger according to FIG. 1; and

FIG. 8 schematically shows a heating apparatus with a heat exchanger, in particular according to FIG. 7.

The invention is described on the basis of a number of embodiments thereof. These are not to be construed to be limitative in any manner. In particular, also, combinations or parts of the embodiments shown and loose parts thereof are understood to fall within the invention. Furthermore, variations thereon are understood to be also represented herein.
In FIG. 1A, in front view, and in FIG. 1B in side view, as well as in FIG. 2, a body 1 of a heat exchanger 1 is shown, assembled from two body parts 3, 4 and a burner hood 5 with burner deck 6. The body parts 3, 4 and preferably also the burner hood 5 are preferably manufactured from aluminum or an alloy thereof, although they can also be manufactured from other material, such as iron or steel. In an advantageous embodiment, the body parts 3, 4 are manufactured substantially through extrusion. This is a simple and relatively inexpensive manufacturing method. However, casting is an option too. Especially in the extruded embodiment, the body parts 3, 4 have a substantially constant cross-section in one direction, in FIGS. 1A and 3 at right angles to the plane of the drawing.
In FIG. 1, adjacent a first end 7 of the body 2, the burner hood 5 is secured, for instance by screws 8, while the burner deck 6 is confined between the burner hood 5 and two flanges 9 extending in two directions at the end 7. Optionally, a suitable gasket (not shown) may have been inserted for a flue gas-tight sealing. In the burner hood 5, a central opening 10 is provided, through which, during use, gas or a gas/air mixture can be introduced to be burned, so that heated flue gases are obtained, formed in a flue gas channel 11 between the two body parts 3, 4 as will be described hereinafter.
In this embodiment, the body 2, in particular the body parts 3, 4 each comprise a first part 12 and a second part 13, which here, link up with each other. The first part 12, viewed in front view as in FIG. 1A, has a meandering configuration. To that end, each of the body parts 3, 4 comprises a series of bends 14, in the embodiment shown four bends 14A-D, 15 A-D, respectively. In this embodiment, the meandering configuration is designed so as to be somewhat sinusoidal. Each body part has an outside 16 and an opposite side 17 proximal to the flue gas channel 11. The meandering first part can therefore have elevations 18 and lows 19. Here, as elevations 18 are seen the parts located furthest from a central plane V, and, as lows, the parts located therebetween. As central plane V, a plane V can be seen, extending approximately midway between two imaginary planes V1 and V2, with the planes V1 and V2 extending parallel to each other over the elevations 18 located furthest from the plane V of the respective body parts 3, 4. In this first part, the configuration of the body parts 3, 4 and the channels 11 is, in fact, a zigzag configuration so that a large heat transferring surface can be obtained in a compact space. It is noted that the first part 12 can also have a different, for instance straight configuration, in the sense that no bends or meanderings are included, while the first part 12 and the second part 13 have a parallel flow direction, or can mutually include an angle. Then, with the construction height remaining the same, in principle, the length of the flue gas channel 11 in the flow direction from the burner space B to the flue gas discharge R will be smaller than in an embodiment where indeed a meandering part 12 is included, but a reduced flow resistance can be formed.
In this embodiment, the second part 13 of the each body part 3, 4 has a substantially straight form, with an outside 16 and an opposite side 17 proximal to the flue gas channel 11. In this embodiment, the plane V extends midway between these two body parts 3, 4. However, this may also be offset over a distance relative therefrom, to the left or the right, in side view. On the side 17 proximal to the flue gas channel part 11, in the second part 13, on each body part 3, 4, one or a plurality of heat transferring surface increasing element(s) 20 is/are present or provided thereon, fastened thereon by, for instance, gluing, welding, forcing, clamping, sintering, soldering or fastened in a different manner, which element(s) form heat exchange elements. Also the or each heat exchange element can be clamped between the two parts 3, 4. The heat exchange element(s) extend(s) in the flue gas channel 11 and/or partly define this, and are porous or gas transmissive such that, during use, flue gases can flow through the or each heat exchange element while exchanging heat. As a result of the porosity or the gas transmissivity of the elements 20, a greater contact surface is obtained between heated flue gases in the flue gas channel 11 and the surface 17 and/or heat transfer increasing elements provided thereon. If several heat exchange elements are utilized, they can be placed both one behind the other and side by side in flow direction.
In the first part 12 of the flue gas channel 11 too, one or more heat exchange elements 20 can be provided, preferably with a porosity that is higher than that of the or a heat exchange element 20 in the second part 13.
Herein, porous is at least understood to include manufactured from a material and/or with a method such that open pores are provided that are in communication with each other and are, for instance, continuous. Herein, gas transmissive is at least understood to include an element provided with channels or such continuous openings through which flue gases can flow, while exchanging heat to the environment, in particular to the respective element, such as for instance foams, fins, fiber mat. The porosity and density can be expressed in a percentage, while with porosity, the percentage represents the part of the volume not filled by the solid material such as metal and, hence, suitable for through-flow by flue gases. For the density, the percentage signifies the part formed by the solid material.
In an advantageous embodiment, the or each heat exchange element 20 is at least partly formed through metal foaming, as schematically shown in FIG. 5B, so that a porous mass is obtained that can be manufactured or brought into a desired form, for instance by mechanical and/or removing operations. With it, an optimal shape for the heat exchange elements can be obtained, with optimal abutment against the inside 17 of the second part 13. Metal foam can offer a relatively robust element that may be constructively advantageous and can ensure a good heat exchange between the flue gases and the metal, and a good transfer to the elements 3, 4. As a technique, metal foaming is sufficiently known from practice, as are the means to then create and influence, for instance, porosity, so that in each part of an element obtained through metal foaming, a desired predetermined porosity can be achieved, in any case on average.
In an alternative embodiment, fibers are used for the heat exchange element, as schematically shown in FIG. 5A, for instance metal fibers or ceramic fibers. A woven or non-woven element can, for instance, be formed therefrom. In an alternative embodiment, the elements 20 can be at least partly formed by removing or non-removing operations of the body parts or, when for instance a casting process is utilized for forming the body parts, through integral forming, in particular casting, during manufacture, while for forming the elements, gas can for instance be blown through the liquid material. Also, ribs can be extruded. Alternatively or additionally, porous and/or gas transmissive materials can be used, such as metals or ceramic filling materials. In the drawing, the heat transferring surface increasing elements are represented in a simplified manner as rectangles. The design of such elements can simply be selected by skilled person.
Fibers for an element 20 according to the invention can be at least partly manufactured through drawing or extrusion, in particular through bundle drawing or multi fiber extrusion, through hot drawing from a weld pool, through cold or through hot rolling, a removing and/or pressing techniques and/or through foaming or blowing. The or a heat exchange element can at least partly be manufactured from a woven or a non-woven material, for instance from fibers, in particular metals and/or ceramic fibers. It is preferred that a heat exchange element 20 according to the invention is at least partly sintered, so that an element is obtained which is heat and moisture resistant and can be placed as a unit.
In a heat exchanger according to the invention, use is preferably made of zones that succeed each other in flow direction s, in which zones the heat exchange can be different. To that end, the porosity or density of the respective heat exchange element 20 or part thereof extending in a respective zone I, II, can deviate from that in a different zone. In FIG. 1, two zones I, II are shown. However, several zones can be provided too and the first zone can for instance extend in the first part 12 and the second zone in the second part 13, as shown in FIG. 1, or both zones I, II can extend in the second zone 13 as shown in FIG. 3, with the first part 12 not comprising a porous heat exchange element. By way of illustration, the first zone I can for instance have a porosity of less than 70%, and a relatively high density of, for instance, more than 70%, for instance 95%, while then, the second zone II has, for instance, a relatively low density, for instance less than 70%, and a relative high porosity, such as over 70%, more particularly for instance 95%. As a result, the flow resistance will decrease in flow direction. In the first zone, during use, heated flue cases will give off the greatest part of the heat, be cooled from, for instance, well over above 1000° C., for instance approximately 1600° C., to well over 1000° C., for instance to approximately 450° C. In the second zone, the heat exchange will be continued so that the flue gases can be cooled down further, for instance to a condensing temperature.
The use of metal foaming offers the advantage that a heat exchange element clamped only against the parts 3, 4 ensures a particularly good heat transfer when compared to, for instance, fins or plate parts. For obtaining a changing porosity and/or density, different heat exchange elements with different porosities and/or densities can be placed side by side and/or one behind the other, or the porosity and/or density in a heat exchange element can be varied.
In the first part 12 and the second part 13, parts 21 of a water carrying channel 22 are provided. In the exemplary embodiment shown, these parts 21 are all tubular with a constant cross-section, which have a longitudinal direction L, approximately at right angles to the plane of the drawing in FIGS. 1A and 3, which longitudinal direction L is parallel to an extrusion direction for the body parts, if these are extruded. Adjacent the first end 7, in each body part 3, 4, a first part 21A is provided as the beginning of the meandering first part 12, directly below the burner deck 6. Then, two parts 21B are provided in the second part 13. Preferably, the channel parts 21 on both sides of the flue gas carrying channel 11 are mutually connected for forming a channel 22 circumventing the heat exchanger, but, optionally, the channel parts on both sides of the flue gas carrying channel 11 can also, each, form a channel part 22 that can be used for, for instance, different heat exchange circuits, or be mutually connected outside the heat exchanger 1.
In the channel parts 22, also, heat transferring surface increasing elements can be utilized which can be integrally formed especially through extrusion, while the channel parts themselves need not be divisible, while to that end, also, porous materials and/or elements can be used as described hereinabove.
It is preferred that the channel parts 21 are mutually connected through end hoods 24 and connecting channel parts extending therein (FIG. 8). These end hoods 24 may further comprise the connections for the heating circuits, gas and air supply pipes and the like. The end hoods can simply be fastened, with interposition of suitable gaskets, against the sides of the parts 3, 4 arranged side by side, so that a flue gas channel 11 closed towards the sides and a continuous water channel 22 or water channels 22 are obtained, while furthermore, the parts 3, 4 are held in a suitable position and at a suitable distance.
With the embodiment shown, the channel parts 21 are provided on the outside of the parts 3, 4, so that the sides thereof facing inwards, i.e. towards the flue gas channel 11, can be designed to be relatively flat, at least without protrusions formed by the channel parts. They can, however, also be positioned differently, for instance partly outside and partly inside the flue gas channel 11 or entirely inside the flue gas channel 11. This holds both for the individual channel parts and for the assembly thereof. Preferably, the or each channel 22 is laid out such that it can function in counterflow to the flow direction of the flue gases through the flue gas channel 11, so that an improved efficiency can be obtained. To that end, for instance, the through-flow opening in the different channel parts can be adjusted in order to generate a flow speed change in the channel, for a further optimisation of the heat exchange.
At the underside of the heat exchanger 1, a foot 23 is provided on which the heat exchanger can be mounted.
In FIGS. 3 and 4, an alternative embodiment is given of a heat exchanger according to the invention, wherein, substantially, only those parts are described that deviate from the other embodiments. Further, reference is made to the further description, in particular of FIGS. 1, 2 and 8. In this embodiment, each of the parts 3, 4 in the first part 12 has a meandering flow gas channel part 11A formed between bends 14A-D, 15A-D respectively, formed such that five flue gas sub channel parts 11A¹-11A⁵are obtained, which are mutually connected by bend parts 11B and extend approximately parallel to each other. In the first part 3, in the first bend 14A, two water channel parts 21 are included, parallel to each other, located at a distance D from each other, between a relatively wide first flue gas sub channel part 11A¹linking up with the burner deck 6 of the burner 5 and a second flue gas sub channel part 11A²located therebeneath, respectively, and between a third flue gas sub channel part 11A³and a fourth flue gas sub channel part 11A⁴located therebeneath, respectively. These water channel parts 21 are located, for instance, adjacent the bends 11B. In a comparable manner, in the second and fourth bend 15B, 15D of the second part 4, channel parts 21 are provided at a distance D from each other, between the second flue gas sub channel part 11A²and a third flue gas sub channel part 11A³located therebeneath and between, at least under, the fourth flue gas sub channel part 11A⁴and a fifth flue gas sub channel part 11A⁵located therebeneath, respectively. The channel parts are therefore always in communication by at least one, and in most cases, two flue gas sub channel parts 11A¹-11A⁵, for optimal heat exchange.
With this heat exchanger, the burner deck is at an angle α relative to the plane V, for instance between 20 and 85°. In the exemplary embodiment shown, this angle is approximately 30°.
As clearly appears from the Figures, in the bends 11B, further heat transfer increasing elements 20A can be provided, in the form of, for instance, ridges, projections or fins, whose intermediate passages are for instance disposed in the flow direction of the flue gases, or at an angle thereto. These heat transfer increasing elements 20A which can also be utilized in the other or alternative embodiments, form, in principle, a porous surface, viewed in flow direction of the flue gases. In a frontal surface, at right angles to the flow direction, the elements 20A preferably form at least approximately 70% of this surface so that the passages therebetween form less than 30%. More particularly, preferably 70% of the volume of the volume described by the elements 20A is filled by the material of the elements 20A. The minimal measured thicknesses/cross-sections of the portion of the surface that is not porous, is greater than 3 mm, preferably greater than 5 mm or 1 cm, respectively.
In FIGS. 5 and 6, schematically and in perspective view, a part 3 of a heat exchanger according to FIGS. 1 and 2 and FIGS. 3 and 4, respectively, are represented, viewed from the flue gas side 17. In FIG. 5A, schematically, a side view of a portion of an element 20 is shown, in which fibers 40 are clearly recognizable, which can form a regular or, as shown, an irregular pattern and define continuous pores 41. FIG. 5B schematically shows, in side view, a portion of an element 20, in particular manufactured through metal foaming, wherein material 42 is clearly recognizable, in which continuous pores 41 are recognizable. Preferably, the metal foams are made of aluminum of an aluminum alloy.
FIGS. 5C and D schematically show alternative embodiments of a heat transferring element 20 in two views at right angles to each other, which element 20 comprises a series of profile parts 45 which form at least an undulating and/or ribbed part 43. This part 43 or at least the profile parts are preferably formed with ribs and/or undulations from folded and/or bent plate material, for instance steel or aluminum or a porous material, for instance a woven or non-woven fiber-based material as described hereinabove. This undulating and/or ribbed part may have been formed from at least one plate or a series of plates which is or are folded such that always a channel 44 is confined by a plate part 45 and a part, for instance wall 17, of the heat exchanger against which the part 43 is provided, which channel 44, in cross-section, preferably has a substantially triangular or trapezoid-shaped section and, in a longitudinal direction at right angles to said cross-section, has a somewhat meandering configuration, as is clearly visible in FIG. 5C, so that each time, the flow direction of flue gases is changed and a good heat exchange can take place.
Naturally, channels 44 in a part 43 according to FIGS. 5C and 5D can have a different configuration, for instance less angularly undulating, or having acuter angles, of, for instance, 30, 45, 60 or 90 degrees or therebetween. The channels 44 can have a main direction G1 which is approximately parallel to the flow direction of flue gases HG1 from the burner chamber to the flue gas discharge, but can also include an angle thereto of, for instance, 30, 60 or 90 degrees, or therebetween. Several parts 43 can be stacked on top of each other, for obtaining a larger element 20, while the main direction of the channels of a underlying plate can, each time, be turned relative to the main direction S of an overlying plate, so that the through-flow of flue gases is hardly adversely affected, if at all. The angle of torsion can, for instance, be some degrees to some tens of degrees, or more. The parts 43 can have the plate parts 45 facing each other or even abutting each other, but can also, each time be, separated by, for instance, a plate 46, preferably a porous plate.
In FIG. 7, a heat exchanger according to FIGS. 1 and 2 is shown as an example while, however, a second water carrying channel 26 is provided. Thereto, grooves 27 and/or ribs 28 are provided on the parts 3, 4, between the first water carrying channel parts 21, for forming recesses in which a pipe 29 such as a metal or plastic pipe is secured, for instance through clamping, form-closing, gluing, welding or in another manner. The second water carrying channel 26 can be used for, for instance, tap water. The second (or, optionally, further) water carrying channel 26 can, for that matter, also be integrally formed into the parts 3, 4 comparable to, for instance, the first channel 22, if the used material allows this or, for instance, when the water or other medium to be heated therein is not used for consumption but for an indirectly heated boiler, floor or wall heating or the like. Preferably, the grooves and/or ribs extend parallel to the water carrying channel parts 21, so that extrusion is possible in simple manner.
As indicated, parts 3, 4 can be advantageously formed through extrusion, separately or jointly. With it, a relatively simple and economically advantageous production of such heat exchangers is possible. However, naturally, also other production manners can be utilized, such as casting, injection moulding and/or removing, so that somewhat more complex shapes become possible.
Preferably, the parts 3, 4 can be separated relatively easily, so that cleaning is simplified. To that end, the parts 3, 4 can be mutually screwed or clamped. This holds in particular also for the lowest, condensing part.
In FIG. 8, in top plan view, schematically, a portion of a heating apparatus 25 with a heat exchanger according to the invention is shown, in a highly simplified manner, connected to two heating circuits. A first heating circuit 30 is, for instance, a space heating circuit with radiator 36, connected to the water carrying channel 22, in which a first pump 31 is provided. A second heating circuit 32 is, for instance, a tap water heating circuit with tap 37 and, optionally, a second pump 33. A supply device for, for instance, gas and air is connected to the burner chamber 5, for forming a premix burner. Naturally, only gas or another fuel can also be supplied. Adjacent the underside of the heating apparatus 25, to the flue gas passage 11, a condensation discharge 34 as well as a flue gas discharge 35 may be connected.
It will be clear that also in other types of heat exchangers than in the exemplary embodiments shown, in one or more flue gas channels, a porous material or element can be included for increasing the heat transferring surface. The porosity can also, for instance, decrease in the flow direction of the flue gases, i.e. in the direction of the flue gas discharge, so that, at the beginning of the flue gas channel, hotter gases will flow through faster and, according as they cool down, the through-flow will be somewhat delayed. Many variations thereon are possible through variation of, for instance, the porosity, the through-flow surface, the extent to which the flue gas channel is filled with porous material and/or the porous elements and the like.
It will be clear that combinations of parts of the embodiments represented are also understood to be represented here.
The invention is not limited in any manner to the embodiments represented in the description and the drawings. Many variations thereon are possible within the framework of the invention as outlined by the claims. For instance, the meandering parts of the heat exchanger can have a different design and materials other than aluminum or an aluminum alloy can be utilized, for instance other (lighter) metals or ceramic materials. More or fewer water carrying channel parts may be provided, while the number of bends and the shape thereof can be adjusted to, for instance, the desired capacity. Instead of the burner with burner deck shown, a different burner can be utilized, for instance a known premix burner, which can be directly connected to the flue gas channel, in particular within the embodiment of the first flue gas sub channel part as shown in FIGS. 3 and 4, which part can then, optionally, function as a part of the burner chamber. The flue gas channel can have a decreasing or, conversely, increasing passage in the direction of the flue gas discharge, in order to influence the speed of the flue gases and, hence, the heat exchange.
The invention relates to a heat exchanger.
It is known from practice to manufacture heat exchangers for, for instance, heating apparatus, hot water supplies and the like from, for instance, steel or iron or light metal such as aluminum. As a rule, a casting method is applied here. Casting techniques offer a relatively large design choice but complex casting moulds. As a rule, in existing heat exchangers, heat transfer increasing elements are provided in a flue gas channel, which elements are cast integrally in the casting moulds, at least when casting techniques are used. The heat transfer is then not always optimal.
The object of the invention is to provide a heat exchanger.
In a first aspect, a heat exchanger according to the invention is characterized in that a body is provided with at least one flue gas channel and at least one water carrying channel, at least one burner chamber and at least one flue gas discharge, wherein the at least one flue gas channel extends at least partly between the at least one burner space and at least one flue gas discharge, and at least one portion of the at least one flue gas channel comprises at least one porous or gas transmissive heat exchange element.
Herein, a porous or gas transmissive heat exchange element is understood to mean an element with a structure and/or manufactured from a material with continuous openings, such that gas can flow through the heat exchange element(s), from, in flow direction, a side proximal to the burner space to a side proximal to the flue gas discharge. The openings can comprise, for instance, pores and/or channels.
Preferably, in the flow direction of the flue gases, the porosity increases and/or the density decreases of the heat exchange element or, if several heat exchange elements or parts thereof are provided successively in the flow direction, of the successive heat exchange elements, or parts thereof, so that the flow resistance decreases and the heat transfer can be further optimized. For instance, a first part of the heat exchange element, or with several successive elements, a first heat exchange element, adjacent the burner space, can have a relatively low porosity and high density, for instance a density of more than 70%, while a second part of the heat exchange element or, in flow direction, a trailing second heat exchange element, can have a relatively low density and high porosity, for instance a porosity of more than 70%. Preferably, especially in this manner, at least two successive zones are formed in the flue gas channel, with different average porosity and/or density. These values mentioned should not be taken as being limitative in any manner and serve merely as an example. On the basis of the further design of a heat exchanger, a skilled person can chose and calculate suitable values.
Independently of the first aspect of the invention, and according to a second aspect, the invention provides a first part of a heat exchange element wherein the minimal thicknesses and/or cross-sections of the at least one heat exchange element of the first part are, in fact, greater than those of the at least one heat exchange element of the second part. This serves the purpose of providing a more massive first heat exchange element, which can resist the high temperatures of the combustion gases.
In a third aspect, a heat exchanger according to the invention is characterized in that the or at least one heat exchange element is manufactured at least partly utilizing metal foaming. Preferably, the entire, or all heat exchange elements that are placed in a flue gas channel are manufactured utilizing metal foaming.
Alternatively or additionally, the at least one heat exchange element can comprise fibers, in particular metal fibers.
Such fibers can be from, for instance, metal or ceramics and be processed into a porous mass, for instance a woven or non-woven element. The fibers ensure a relatively large contact surface in relation to the volume, in particular if the fibers are relatively thin, for instance an average thickness of less than 1 micrometer to a few tens or hundreds or micrometers. Preferably, the fibers have an average thickness of between 0.5 and 200 micrometer, more particularly between 0.5 and 50 micrometer.
In an advantageous manner, a heat exchange element can be utilized that is at least partly wintered.
In a fourth aspect, a heat exchanger according to the invention is characterized in that body parts are provided which are manufactured at least partly through extrusion or through casting techniques. Light metal, such as aluminum or an alloy thereof, can then be utilized.
In a fifth aspect, the invention is characterized in that at least one, and preferably each body part is provided with recesses, in particular on a side remote from the flue gas channel, in which parts of a second water carrying channel part are formed or included.
The aspects mentioned and other aspects of the invention can be utilized separately as well as in combination.
The invention further contemplates providing a body part for such a heat exchanger, and a heat exchange element therefore.
The invention furthermore contemplates providing a method for the manufacture of a heat exchanger.
In a first aspect, a method is characterized in that at least two body parts are formed, in particular through extrusion or casting techniques, which body parts each comprise at least a portion of a water carrying channel part, which body parts are mutually connected by end parts and/or at least one heat exchange element, such that the body parts are thus held at a mutual distance from each other while forming a flue gas channel in which said at least one heat exchange element extends, and preferably the water carrying channel parts in the two body parts are mutually connected.
Alternatively, one body part can be utilized in which the entire flue gas channel is formed, which is at least partly filled with at least one at least partly porous or otherwise gas transmissive heat exchange element.
The invention will be further elucidated on the basis of exemplary embodiments, with reference to the drawing. In the drawing:
FIGS. 1A and B show, in front and side view, a heat exchanger without side parts;
FIG. 2 shows, in perspective view, a heat exchanger according to FIG. 1;
FIG. 2A shows, in slight enlargement, a part of a heat exchanger according to FIG. 2;
FIG. 3 shows, in front view, a heat exchanger, in a second embodiment, without side parts;
FIG. 4 shows, in perspective side view, a heat exchanger according to FIG. 3;
FIG. 4A shows, in slight enlargement, a portion of a heat exchanger according to FIG. 4;
FIG. 5 shows, in perspective view, a body part for a heat exchanger according to FIGS. 1-2;
FIGS. 5A and 5B show embodiments of a heat transferring element according to the invention;
FIGS. 5C and 5D schematically show, in side view and front view, an alternative embodiment of a heat transferring surface increasing element;
FIG. 6 shows, in perspective view, a body part for a heat exchanger according to FIGS. 3-4;
FIG. 7 shows, in side view, an alternative embodiment of a heat exchanger according to FIG. 1; and
FIG. 8 schematically shows a heating apparatus with a heat exchanger, in particular according to FIG. 7.
The invention is described on the basis of a number of embodiments thereof. These are not to be construed to be limitative in any manner. In particular, also, combinations or parts of the embodiments shown and loose parts thereof are understood to fall within the invention. Furthermore, variations thereon are understood to be also represented herein.
In FIG. 1A, in front view, and in FIG. 1B in side view, as well as in FIG. 2, a body 1 of a heat exchanger 1 is shown, assembled from two body parts 3, 4 and a burner hood 5 with burner deck 6. The body parts 3, 4 and preferably also the burner hood 5 are preferably manufactured from aluminum or an alloy thereof, although they can also be manufactured from other material, such as iron or steel. In an advantageous embodiment, the body parts 3, 4 are manufactured substantially through extrusion. This is a simple and relatively inexpensive manufacturing method. However, casting is an option too. Especially in the extruded embodiment, the body parts 3, 4 have a substantially constant cross-section in one direction, in FIGS. 1A and 3 at right angles to the plane of the drawing.
In FIG. 1, adjacent a first end 7 of the body 2, the burner hood 5 is secured, for instance by screws 8, while the burner deck 6 is confined between the burner hood 5 and two flanges 9 extending in two directions at the end 7. Optionally, a suitable gasket (not shown) may have been inserted for a flue gas-tight sealing. In the burner hood 5, a central opening 10 is provided, through which, during use, gas or a gas/air mixture can be introduced to be burned, so that heated flue gases are obtained, formed in a flue gas channel 11 between the two body parts 3, 4 as will be described hereinafter.
In this embodiment, the body 2, in particular the body parts 3, 4 each comprise a first part 12 and a second part 13, which here, link up with each other. The first part 12, viewed in front view as in FIG. 1A, has a meandering configuration. To that end, each of the body parts 3, 4 comprises a series of bends 14, in the embodiment shown four bends 14A-D, 15 A-D, respectively. In this embodiment, the meandering configuration is designed so as to be somewhat sinusoidal. Each body part has an outside 16 and an opposite side 17 proximal to the flue gas channel 11. The meandering first part can therefore have elevations 18 and lows 19. Here, as elevations 18 are seen the parts located furthest from a central plane V, and, as lows, the parts located therebetween. As central plane V, a plane V can be seen, extending approximately midway between two imaginary planes V1 and V2, with the planes V1 and V2 extending parallel to each other over the elevations 18 located furthest from the plane V of the respective body parts 3, 4. In this first part, the configuration of the body parts 3, 4 and the channels 11 is, in fact, a zigzag configuration so that a large heat transferring surface can be obtained in a compact space. It is noted that the first part 12 can also have a different, for instance straight configuration, in the sense that no bends or meanderings are included, while the first part 12 and the second part 13 have a parallel flow direction, or can mutually include an angle. Then, with the construction height remaining the same, in principle, the length of the flue gas channel 11 in the flow direction from the burner space B to the flue gas discharge R will be smaller than in an embodiment where indeed a meandering part 12 is included, but a reduced flow resistance can be formed.
In this embodiment, the second part 13 of the each body part 3, 4 has a substantially straight form, with an outside 16 and an opposite side 17 proximal to the flue gas channel 11. In this embodiment, the plane V extends midway between these two body parts 3, 4. However, this may also be offset over a distance relative therefrom, to the left or the right, in side view. On the side 17 proximal to the flue gas channel part 11, in the second part 13, on each body part 3, 4, one or a plurality of heat transferring surface increasing element(s) 20 is/are present or provided thereon, fastened thereon by, for instance, gluing, welding, forcing, clamping, sintering, soldering or fastened in a different manner, which element(s) form heat exchange elements. Also the or each heat exchange element can be clamped between the two parts 3, 4. The heat exchange element(s) extend(s) in the flue gas channel 11 and/or partly define this, and are porous or gas transmissive such that, during use, flue gases can flow through the or each heat exchange element while exchanging heat. As a result of the porosity or the gas transmissivity of the elements 20, a greater contact surface is obtained between heated flue gases in the flue gas channel 11 and the surface 17 and/or heat transfer increasing elements provided thereon. If several heat exchange elements are utilized, they can be placed both one behind the other and side by side in flow direction.
In the first part 12 of the flue gas channel 11 too, one or more heat exchange elements 20 can be provided, preferably with a porosity that is higher than that of the or a heat exchange element 20 in the second part 13.
Herein, porous is at least understood to include manufactured from a material and/or with a method such that open pores are provided that are in communication with each other and are, for instance, continuous. Herein, gas transmissive is at least understood to include an element provided with channels or such continuous openings through which flue gases can flow, while exchanging heat to the environment, in particular to the respective element, such as for instance foams, fins, fiber mat. The porosity and density can be expressed in a percentage, while with porosity, the percentage represents the part of the volume not filled by the solid material such as metal and, hence, suitable for through-flow by flue gases. For the density, the percentage signifies the part formed by the solid material.
In an advantageous embodiment, the or each heat exchange element 20 is at least partly formed through metal foaming, as schematically shown in FIG. 5B, so that a porous mass is obtained that can be manufactured or brought into a desired form, for instance by mechanical and/or removing operations. With it, an optimal shape for the heat exchange elements can be obtained, with optimal abutment against the inside 17 of the second part 13. Metal foam can offer a relatively robust element that may be constructively advantageous and can ensure a good heat exchange between the flue gases and the metal, and a good transfer to the elements 3, 4. As a technique, metal foaming is sufficiently known from practice, as are the means to then create and influence, for instance, porosity, so that in each part of an element obtained through metal foaming, a desired predetermined porosity can be achieved, in any case on average.
In an alternative embodiment, fibers are used for the heat exchange element, as schematically shown in FIG. 5A, for instance metal fibers or ceramic fibers. A woven or non-woven element can, for instance, be formed therefrom. In an alternative embodiment, the elements 20 can be at least partly formed by removing or non-removing operations of the body parts or, when for instance a casting process is utilized for forming the body parts, through integral forming, in particular casting, during manufacture, while for forming the elements, gas can for instance be blown through the liquid material. Also, ribs can be extruded. Alternatively or additionally, porous and/or gas transmissive materials can be used, such as metals or ceramic filling materials. In the drawing, the heat transferring surface increasing elements are represented in a simplified manner as rectangles. The design of such elements can simply be selected by skilled person.
Fibers for an element 20 according to the invention can be at least partly manufactured through drawing or extrusion, in particular through bundle drawing or multi fiber extrusion, through hot drawing from a weld pool, through cold or through hot rolling, a removing and/or pressing techniques and/or through foaming or blowing. The or a heat exchange element can at least partly be manufactured from a woven or a non-woven material, for instance from fibers, in particular metals and/or ceramic fibers. It is preferred that a heat exchange element 20 according to the invention is at least partly sintered, so that an element is obtained which is heat and moisture resistant and can be placed as a unit.
In a heat exchanger according to the invention, use is preferably made of zones that succeed each other in flow direction s, in which zones the heat exchange can be different. To that end, the porosity or density of the respective heat exchange element 20 or part thereof extending in a respective zone I, II, can deviate from that in a different zone. In FIG. 1, two zones I, II are shown. However, several zones can be provided too and the first zone can for instance extend in the first part 12 and the second zone in the second part 13, as shown in FIG. 1, or both zones I, II can extend in the second zone 13 as shown in FIG. 3, with the first part 12 not comprising a porous heat exchange element. By way of illustration, the first zone I can for instance have a porosity of less than 70%, and a relatively high density of, for instance, more than 70%, for instance 95%, while then, the second zone II has, for instance, a relatively low density, for instance less than 70%, and a relative high porosity, such as over 70%, more particularly for instance 95%. As a result, the flow resistance will decrease in flow direction. In the first zone, during use, heated flue cases will give off the greatest part of the heat, be cooled from, for instance, well over above 1000° C., for instance approximately 1600° C., to well over 1000° C., for instance to approximately 450° C. In the second zone, the heat exchange will be continued so that the flue gases can be cooled down further, for instance to a condensing temperature.
The use of metal foaming offers the advantage that a heat exchange element clamped only against the parts 3, 4 ensures a particularly good heat transfer when compared to, for instance, fins or plate parts. For obtaining a changing porosity and/or density, different heat exchange elements with different porosities and/or densities can be placed side by side and/or one behind the other, or the porosity and/or density in a heat exchange element can be varied.
In the first part 12 and the second part 13, parts 21 of a water carrying channel 22 are provided. In the exemplary embodiment shown, these parts 21 are all tubular with a constant cross-section, which have a longitudinal direction L, approximately at right angles to the plane of the drawing in FIGS. 1A and 3, which longitudinal direction L is parallel to an extrusion direction for the body parts, if these are extruded. Adjacent the first end 7, in each body part 3, 4, a first part 21A is provided as the beginning of the meandering first part 12, directly below the burner deck 6. Then, two parts 21B are provided in the second part 13. Preferably, the channel parts 21 on both sides of the flue gas carrying channel 11 are mutually connected for forming a channel 22 circumventing the heat exchanger, but, optionally, the channel parts on both sides of the flue gas carrying channel 11 can also, each, form a channel part 22 that can be used for, for instance, different heat exchange circuits, or be mutually connected outside the heat exchanger 1.
In the channel parts 22, also, heat transferring surface increasing elements can be utilized which can be integrally formed especially through extrusion, while the channel parts themselves need not be divisible, while to that end, also, porous materials and/or elements can be used as described hereinabove.
It is preferred that the channel parts 21 are mutually connected through end hoods 24 and connecting channel parts extending therein (FIG. 8). These end hoods 24 may further comprise the connections for the heating circuits, gas and air supply pipes and the like. The end hoods can simply be fastened, with interposition of suitable gaskets, against the sides of the parts 3, 4 arranged side by side, so that a flue gas channel 11 closed towards the sides and a continuous water channel 22 or water channels 22 are obtained, while furthermore, the parts 3, 4 are held in a suitable position and at a suitable distance.
With the embodiment shown, the channel parts 21 are provided on the outside of the parts 3, 4, so that the sides thereof facing inwards, i.e. towards the flue gas channel 11, can be designed to be relatively flat, at least without protrusions formed by the channel parts. They can, however, also be positioned differently, for instance partly outside and partly inside the flue gas channel 11 or entirely inside the flue gas channel 11. This holds both for the individual channel parts and for the assembly thereof. Preferably, the or each channel 22 is laid out such that it can function in counterflow to the flow direction of the flue gases through the flue gas channel 11, so that an improved efficiency can be obtained. To that end, for instance, the through-flow opening in the different channel parts can be adjusted in order to generate a flow speed change in the channel, for a further optimisation of the heat exchange.
At the underside of the heat exchanger 1, a foot 23 is provided on which the heat exchanger can be mounted.
In FIGS. 3 and 4, an alternative embodiment is given of a heat exchanger according to the invention, wherein, substantially, only those parts are described that deviate from the other embodiments. Further, reference is made to the further description, in particular of FIGS. 1, 2 and 8. In this embodiment, each of the parts 3, 4 in the first part 12 has a meandering flow gas channel part 11A formed between bends 14A-D, 15A-D respectively, formed such that five flue gas sub channel parts 11A¹-11A⁵are obtained, which are mutually connected by bend parts 11B and extend approximately parallel to each other. In the first part 3, in the first bend 14A, two water channel parts 21 are included, parallel to each other, located at a distance D from each other, between a relatively wide first flue gas sub channel part 11A¹linking up with the burner deck 6 of the burner 5 and a second flue gas sub channel part 11A²located therebeneath, respectively, and between a third flue gas sub channel part 11A³and a fourth flue gas sub channel part 11A⁴located therebeneath, respectively. These water channel parts 21 are located, for instance, adjacent the bends 11B. In a comparable manner, in the second and fourth bend 15B, 15D of the second part 4, channel parts 21 are provided at a distance D from each other, between the second flue gas sub channel part 11A²and a third flue gas sub channel part 11A3 located therebeneath and between, at least under, the fourth flue gas sub channel part 11A⁴and a fifth flue gas sub channel part 11A⁵located therebeneath, respectively. The channel parts are therefore always in communication by at least one, and in most cases, two flue gas sub channel parts 11A¹-11A⁵, for optimal heat exchange.
With this heat exchanger, the burner deck is at an angle α relative to the plane V, for instance between 20 and 85°. In the exemplary embodiment shown, this angle is approximately 30°.
As clearly appears from the Figures, in the bends 11B, further heat transfer increasing elements 20A can be provided, in the form of, for instance, ridges, projections or fins, whose intermediate passages are for instance disposed in the flow direction of the flue gases, or at an angle thereto. These heat transfer increasing elements 20A which can also be utilized in the other or alternative embodiments, form, in principle, a porous surface, viewed in flow direction of the flue gases. In a frontal surface, at right angles to the flow direction, the elements 20A preferably form at least approximately 70% of this surface so that the passages therebetween form less than 30%. More particularly, preferably 70% of the volume of the volume described by the elements 20A is filled by the material of the elements 20A. The minimal measured thicknesses/cross-sections of the portion of the surface that is not porous, is greater than 3 mm, preferably greater than 5 mm or 1 cm, respectively.
In FIGS. 5 and 6, schematically and in perspective view, a part 3 of a heat exchanger according to FIGS. 1 and 2 and FIGS. 3 and 4, respectively, are represented, viewed from the flue gas side 17. In FIG. 5A, schematically, a side view of a portion of an element 20 is shown, in which fibers 40 are clearly recognizable, which can form a regular or, as shown, an irregular pattern and define continuous pores 41. FIG. 5B schematically shows, in side view, a portion of an element 20, in particular manufactured through metal foaming, wherein material 42 is clearly recognizable, in which continuous pores 41 are recognizable. Preferably, the metal foams are made of aluminum of an aluminum alloy.
FIGS. 5C and D schematically show alternative embodiments of a heat transferring element 20 in two views at right angles to each other, which element 20 comprises a series of profile parts 45 which form at least an undulating and/or ribbed part 43. This part 43 or at least the profile parts are preferably formed with ribs and/or undulations from folded and/or bent plate material, for instance steel or aluminum or a porous material, for instance a woven or non-woven fiber-based material as described hereinabove. This undulating and/or ribbed part may have been formed from at least one plate or a series of plates which is or are folded such that always a channel 44 is confined by a plate part 45 and a part, for instance wall 17, of the heat exchanger against which the part 43 is provided, which channel 44, in cross-section, preferably has a substantially triangular or trapezoid-shaped section and, in a longitudinal direction at right angles to said cross-section, has a somewhat meandering configuration, as is clearly visible in FIG. 5C, so that each time, the flow direction of flue gases is changed and a good heat exchange can take place.
Naturally, channels 44 in a part 43 according to FIGS. 5C and 5D can have a different configuration, for instance less angularly undulating, or having acuter angles, of, for instance, 30, 45, 60 or 90 degrees or therebetween. The channels 44 can have a main direction G1 which is approximately parallel to the flow direction of flue gases HG1 from the burner chamber to the flue gas discharge, but can also include an angle thereto of, for instance, 30, 60 or 90 degrees, or therebetween. Several parts 43 can be stacked on top of each other, for obtaining a larger element 20, while the main direction of the channels of a underlying plate can, each time, be turned relative to the main direction S of an overlying plate, so that the through-flow of flue gases is hardly adversely affected, if at all. The angle of torsion can, for instance, be some degrees to some tens of degrees, or more. The parts 43 can have the plate parts 45 facing each other or even abutting each other, but can also, each time be, separated by, for instance, a plate 46, preferably a porous plate.
In FIG. 7, a heat exchanger according to FIGS. 1 and 2 is shown as an example while, however, a second water carrying channel 26 is provided. Thereto, grooves 27 and/or ribs 28 are provided on the parts 3, 4, between the first water carrying channel parts 21, for forming recesses in which a pipe 29 such as a metal or plastic pipe is secured, for instance through clamping, form-closing, gluing, welding or in another manner. The second water carrying channel 26 can be used for, for instance, tap water. The second (or, optionally, further) water carrying channel 26 can, for that matter, also be integrally formed into the parts 3, 4 comparable to, for instance, the first channel 22, if the used material allows this or, for instance, when the water or other medium to be heated therein is not used for consumption but for an indirectly heated boiler, floor or wall heating or the like. Preferably, the grooves and/or ribs extend parallel to the water carrying channel parts 21, so that extrusion is possible in simple manner.
As indicated, parts 3, 4 can be advantageously formed through extrusion, separately or jointly. With it, a relatively simple and economically advantageous production of such heat exchangers is possible. However, naturally, also other production manners can be utilized, such as casting, injection moulding and/or removing, so that somewhat more complex shapes become possible.
Preferably, the parts 3, 4 can be separated relatively easily, so that cleaning is simplified. To that end, the parts 3, 4 can be mutually screwed or clamped. This holds in particular also for the lowest, condensing part.
In FIG. 8, in top plan view, schematically, a portion of a heating apparatus 25 with a heat exchanger according to the invention is shown, in a highly simplified manner, connected to two heating circuits. A first heating circuit 30 is, for instance, a space heating circuit with radiator 36, connected to the water carrying channel 22, in which a first pump 31 is provided. A second heating circuit 32 is, for instance, a tap water heating circuit with tap 37 and, optionally, a second pump 33. A supply device for, for instance, gas and air is connected to the burner chamber 5, for forming a premix burner. Naturally, only gas or another fuel can also be supplied. Adjacent the underside of the heating apparatus 25, to the flue gas passage 11, a condensation discharge 34 as well as a flue gas discharge 35 may be connected.
It will be clear that also in other types of heat exchangers than in the exemplary embodiments shown, in one or more flue gas channels, a porous material or element can be included for increasing the heat transferring surface. The porosity can also, for instance, decrease in the flow direction of the flue gases, i.e. in the direction of the flue gas discharge, so that, at the beginning of the flue gas channel, hotter gases will flow through faster and, according as they cool down, the through-flow will be somewhat delayed. Many variations thereon are possible through variation of, for instance, the porosity, the through-flow surface, the extent to which the flue gas channel is filled with porous material and/or the porous elements and the like.
It will be clear that combinations of parts of the embodiments represented are also understood to be represented here.
The invention is not limited in any manner to the embodiments represented in the description and the drawings. Many variations thereon are possible within the framework of the invention as outlined by the claims. For instance, the meandering parts of the heat exchanger can have a different design and materials other than aluminum or an aluminum alloy can be utilized, for instance other (lighter) metals or ceramic materials. More or fewer water carrying channel parts may be provided, while the number of bends and the shape thereof can be adjusted to, for instance, the desired capacity. Instead of the burner with burner deck shown, a different burner can be utilized, for instance a known premix burner, which can be directly connected to the flue gas channel, in particular within the embodiment of the first flue gas sub channel part as shown in FIGS. 3 and 4, which part can then, optionally, function as a part of the burner chamber. The flue gas channel can have a decreasing or, conversely, increasing passage in the direction of the flue gas discharge, in order to influence the speed of the flue gases and, hence, the heat exchange.

Claims

1. A heat exchanger, provided with a body with at least one flue gas channel and at least one water carrying channel, at least one burner space and at least one flue gas discharge, wherein the at least one flue gas channel extends at least partly between at least a burner space and at least one flue gas discharge, and at least a portion of the at least one flue gas channel comprises at least one porous or gas-transmissive heat exchange element.

2. A heat exchanger according to claim 1, wherein the gas transmissivity of the or each heat exchange element in the direction away from the at least one burner space varies.

3. A heat exchanger according to claim 2, wherein a first heat exchange element or first part of a heat exchange element is provided, adjacent a burner space, with a relatively low porosity and relatively high density, and a second heat exchange element or second part of a heat exchange element is provided, on a side of the respective burner space remote from said first heat exchange element or first part thereof, with a relatively high porosity and relatively low density.

4. A heat exchanger according to claim 1, wherein at least a part of the or a heat exchange element is at least partly manufactured through metal foaming, in particular metal foam from aluminum or an aluminum alloy.

5. A heat exchanger according to claim 1, wherein the at least one heat exchange element is included between at least a first and a second body part of the body.

6. A heat exchanger according to claim 1, wherein the body parts each comprise at least a first part with a meandering configuration, which body parts are positioned relative to each other such that the meandering parts engage each other at least partly and therebetween a first part of the flue gas channel is formed, wherein each body part comprises at least a portion of the at least one water carrying channel, wherein said first part of each body part comprises at least a first and a second bend, wherein the first bend of a first body part reaches into the first bend of the second body part and the second bend of the second body part reaches into the second bend of the first body part and/or in each first part of a body part and preferably, in each bend therein, at least a part of said at least one water carrying channel is provided.

7. A heat exchanger according to claim 1, wherein the heat exchange element comprises fibers, in particular metal fibers.

8. A heat exchanger according to claim 1, wherein the or a heat exchange element is at least partly manufactured from a woven or a non-woven material.

9. A heat exchanger according to claim 1, wherein fibers are used in the or a heat exchange element with an average diameter between 0.5 and 200 micrometers, more particularly between 0.5 and 50 micrometers.

10. A heat exchanger according to claim 1, wherein the or a heat exchange element has a porosity of between 75 and 97%.

11. A heat exchanger according to claim 1 wherein the or a heat exchange element comprises at least an undulating and/or ribbed part, in particular ribbed and/or undulating formed from folded and/or bent plate material or fiber plate material.

12. A heat exchanger according to claim 11, wherein said undulating and/or ribbed part is formed from at least one plate or a series of plates which is or are folded such that, each time, a channel is confined by a plate part and a part of the heat exchanger against which the part is provided, which channel, in a cross section, preferably has a substantially triangular or trapezoidal section and, in a longitudinal direction at right angles to said cross-section, has a somewhat meandering configuration.

13. A heat exchanger according to claim 1, wherein in a first part of each body part at least two bends are provided which engage in or engage around a bend in an adjoining first part of the other body part, wherein the bends are formed such that they each cut a plane located midway between two parallel planes defined by the outsides of the bends which are located furthest apart in the respective first parts, measured in a direction at right angles to said parallel planes, while, during use, flue gases flow between said engaging bends of the body parts.

14. A heat exchanger according to claim 1, wherein at least one, and preferably each body part is provided with recesses, in particular on a side remote from the flue gas channel, in which parts of a second water carrying channel are formed or included.

15. A heat exchanger according to claim 14, wherein said parts of the second water carrying channel are provided, in particular clamped, in said recesses.

16. A heat exchanger according to claim 1, wherein body parts are manufactured substantially through extrusion.

17. A heat exchanger according to claim 16, wherein as heat transferring surface increasing elements heat exchange elements are provided on at least a part of at least one of the body parts, which elements are formed as separately provided elements and/or through removing operations of the extruded body parts.

18. A heat exchanger according to claim 1, wherein the body parts and the heat exchange elements are at least partly manufactured from aluminum or an aluminum alloy.

19. A heat exchanger according to claim 1, wherein in a first part of the flue gas channel heat transferring surface increasing elements are provided, in particular fins, projections and/or ridges, and, in a second part, at least one porous or gas transmissive heat exchange element.

20. A body part for a heat exchanger according to claim 1.

21. A body part according to claim 20, wherein the body part comprises at least a first part with a meandering configuration, wherein each body part comprises at least a portion of the at least one water carrying channel and, in addition to at least a part of said portion of the water carrying channel, is provided on a part forming the flue gas channel wall with heat transferring surface increasing elements.

22. A body part according to claim 20, substantially formed through extrusion.

23. A heat exchange element for use in a heat exchanger according to claim 1, preferably at least partly manufactured through metal foaming.

24. A method for forming a heat exchanger, wherein at least two body parts are formed, in particular through extrusion or casting techniques, which body parts each comprise at least a portion of a water carrying channel part, which body parts are mutually connected by end parts and/or at least one heat exchange element in a manner such that the body parts are thus held at a mutual distance from each other while forming a flue gas channel in which said at least one heat exchange element extends and preferably the water carrying channel parts in the two body parts are mutually connected.

25. A method according to claim 24, wherein the at least one heat exchange element is at least partly manufactured through metal foaming or from fibers.

26. A heating apparatus, provided with a heat exchanger according to claim 1.