GB2048452A - Heat exchanger, eg for heating water - Google Patents

Abstract

A heat exchanger is formed of a once-flat wall (101) shaped in a spiral and having end caps (C1, C2) so as to form a spiral enclosure for the circulation (arrow A) of one of the fluids between the turns of the wall. The other fluid flows (arrow B) either in a network of tubes integral with the spiral wall (Figs. 1-7), or within the wall itself, this being hollow, and possibly having two internal paths for two different fluids. Welding points (102) cause turbulence in the path(s) in the hollow wall. Discontinuities, e.g. holes, can be formed in the spiral wall to break up the flow in the spiral enclosure. The central space (104) can form a combustion chamber for a burner (106). The path(s) in the hollow wall can be used for heating water while hot gases flow along the axial and spiral paths between the turns of the spiral. <IMAGE>

Description

SPECIFICATION Heat exchanger The present invention reiates to a heat exchanger of the type used for obtaining a heat transfer between at least two moving fluids without contact between these fluids.

Such heat exchangers are known and used in numerous applications and appear in various forms comprising generally at least two enclosures separated by a common wall. The fluids flow respectively in each of these enclosures at different temperatures, a heat exchange being obtained through the common wall. In their most usual form exchangers of this type are formed by a network of tubes forming a first enclosure and through which flows one of the fluids, said network being inserted in a second enclosure through which flows the other fluid. Thus is obtained a large exchange surface increased moreover, in numerous cases, by the addition of internal and/ or external wall elements, added afterwards or not. These wall elements are generally in the form of fins or ribs disposed perpendicularly to the axis of the above-mentioned tubes.

Heat exchangers are also known in which the networks of parallel tubes form bands which are spirally wound and are housed in an enclosure.

Heat exchangers are also known in which two fluids flow along two spiral paths parallel to each other, by means of a spiral conduit housed in one enclosure.

This invention provides a heat exchanger between at least two fluids characterized in that it comprises an originally flat wall formed into a spiral, with closure means mounted at both its ends perpendicular thereto, so as to form a spiral enclosure for the flow of one of the fluids between the turns of the wall, means being provided for circulating the other fluid.

The invention also provides such a heat exchanger in which the means for circulating the other fluid are formed by a network of tubes integral by their generatrices with the spiral wall and parallel to an axis about which said wall is wound.

Finally, the invention provides such a heat exchanger in which the means for circulating the other fluid are formed by the wall itself having at least two parallel faces connected together along two parallel edges, so as to form a hollow wall for circulating said fluid.

This latter exchanger may, furthermore, comprise one or more of the following features: (a) Obstacles are formed inside and/or outside the hollow wall so as to form one or more paths creating eddies.

(b) The faces of the hollow wall are connected together at a plurality of points so as to form an inner zigzag path between two adjacent faces and projections and hollows between the turns of the hollow wall.

(c) The connecting points of the faces are welding points.

(d) The spiral wall has three faces so as to form two internal spiral paths, the connecting points of one system with two faces being wider spaced than those of the other system with two faces, so that the flow speed in one path is different from that in the other path.

(e) The spiral path has n faces so as to form n-1 internal spiral paths, the connecting points of each system of faces having a different spacing than that of the other system, so as to obtain different flow speeds between all the systems.

(f) The spiral wall is disposed vertically and closed on itself and a suction device is mounted laterally at its lower end so as to carry the condensed fluid and/or the mist to the lower part of the apparatus.

(g) The spiral wall is disposed vertically and closed on itself and a suction device is mounted under the central region so as to carry the condensed fluid and/or the mist to the lower part of the apparatus.

(h) The spiral wall is disposed vertically and closed on itself and a discharge pipe with removable closure is mounted at its lower part so as to draw the condensed fluid to the lower part of the apparatus.

(i) The closure means at both ends of the wall are formed by the connection of lower and upper extensions of the opposite faces of the hollow wall.

(j) The connection of the extensions of the opposite faces of the hollow wall is a weld or stapling.

(k) The central space or the outer region of the exchanger placed vertically is formed into a combustion chamber where a burner is housed.

(I) The surface of the wall of the combustion chamber according to k/ is treated so as to absorb the radiation from the flame of the burner so as to lower the temperature of the material of the burner.

(m) At least some welding points on the faces of the hollow wall are pierced at their centre so as to break up the limit layers of the fluid flowing between the turns of the hollow wall.

(n) Means are arranged between the spiral space and the suction device to bring to this latter a flow of heat for heating the saturating vapours penetrating into the suction device.

(o) The winding in a spiral of the hollow wall is variable in pitch so as to optimize the heat exchange by increase of the pressure drop inversely proportional to the temperature gradient of the fluid flowing between the turns of the hollow wall.

(p) The spacing of the welding points on the hollow wall is variable so as to increase the exchange by turbulence with the diminu tion of the temperature gradient of the fluid flowing between the turns of the hollow wall.

(q) The winding of the turns of the hollow wall presents a conical conformation with the apex upwards so that the spiral space and the hollow wall are inclined from the horizontal, this facilitating condensation of the fluid(s) and the flow of the condensates in the low part of the exchanger.

(r) The heat exchanger is manufactured by placing two or more metal sheets one on the other, by joining them with numerous welding points, by welding the edges, by applying a pressure between the metal sheets, by filling the space between the metal sheets with a product capable of being eliminated, by effecting the curving and by eliminating the above product.

(s) The heat exchanger is manufactured by placing two or more metal sheets one on the other, by joining them with numerous points of welding, by welding the edges, by exerting a pull on the metal sheets during formation into a spiral, and by applying a pressure between the metal sheets to obtain swelling.

The above and other features, objects and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred, but nonetheless illustrative, embodiments in accordance with the present invention and taken in conjunction with the accompanying drawings wherein:: Figure 1 shows an elevational view of one embodiment of the exchanger of the invention; Figure 2 shows a perspective view of the exchanger shown in Fig. 1; Figure 3 shows a developed view of the exchanger shown in Figs. 1 and 2; Figure 4 is a perspective view of a portion of the wall forming the exchanger before winding; Figure 5 is a perspective view with parts cut away of the above exchanger whose wall presents through apertures; Figure 6 is a similar view of a portion of the wall of the exchanger of Fig. 5 before winding; Figure 7 is a similar view showing very schematically a device for heating the burnt gases; Figure 8 shows a perspective view of another preferred embodiment of the invention; Figure 9 is a similar view of a portion of the hollow wall of the exchanger of Fig. 8 before winding;; Figure 10 is a partial section of the hollow wall in the case where there is exchange between three fluids; Figure 11 is a schematical perspective view of a heat exchanger embodying the invention, in the case of an exchange between three fluids, the exchanger being associated with a centrally mounted burner and with a draw fan; Figure 12 is a partial vertical section of the exchanger of Fig. 11 passing through the axis of the draw fan; Figure 13 is a partial horizontal section of the hollow wall of the exchanger of Fig. 11 showing the connection with the fluid output tubes; Figure 14 is a schematical perspective view of a heat exchanger embodying the invention in the case of an exchange between three fluids, the exchanger being associated with a burner placed outside the spiral wall and with a centrally mounted fan;; Figure 15 is a partial vertical section of the exchanger of Fig. 14 passing through the burner; and Figure 16 is a partial section of the hollow wall similar to that of Fig. 10 showing welding points pierced at certain places.

In all the figures the same references designate the same parts or elements.

There is shown in Figs. 1 and 2 a two-fluid heat exchanger the fluids being respectively shown by references A and B. The flow direction of each of the fluids is indicated by arrows. The exchanger comprises a network of tubes 1 for circulating fluid B, these tubes being integral with a wall 2 in contact with said tubes by their generatrices.

In the embodiment shown the network of tubes and the wall are formed by the wall known commercially under the name of "Roll- Bond" (Fig. 4). This wall is obtained by partially welding two metal sheets a and b made from an aluminium alloy or a stainless steel alloy, and by leaving non-welded strips.

By causing swelling with appropriate means at the non-welded places tubular regions c are obtained which form the tubes 1 described above. It will be readily understood that the product obtained is particularly appropriate for manufacturing the evaporators of refrigerators or domestic deep freezers. This product is also very appropriate for implementing the present invention but the tubular wall could of course be constructed in another way.

As can be seen more especially in Fig. 2, the wall is formed in a spiral so as to cause to appear between the successive turns a space 3 in which flows in the present case fluid A.

So as to confine liquid A in a specific circuit, the exchanger comprises closure means formed by lids 4, 5 made integral with the respectively upper and lower edges of wall 2 so as to provide for fluid A an inlet 6 and an outlet 7. Of course, the central turn 8 is not completely closed on itself so as to allow fluid A to flow.

There is shown in Fig. 3 a developed view of wall 2 and of tube network 1 for the flow of fluid B. This network is formed by an assembly of collectors 1 a, joined together by tubes 1 connected in parallel between collec tors 1 a. The flow direction of fluid B is indicated by the arrows and this sufficiently explicitly for it not to be necessary to describe the process.

The fluid is in fact forced to proceed from one collector to the next by the existence of obstacles such as the interruption 9 between two collectors. It will be noted that the net works of tubes 1 are disposed substantially perpendicularly to the direction of flow of fluid A.

The operation of the exchanger one embodi ment of which has just been described will now be explained with reference to a type of use in which fluid A is in the gaseous state, for example is formed by combustion gases, and fluid B in the liquid state, formed for example by the water of a heating circuit.

Considering the pressure losses opposing the flow of the fluids in the exchanger, it is evident that these latter are pulsed or drawn by a motor means, for fluid A as well as for fluid B. These means are well-known per se and have therefore not been shown. The gases penetrate axially at a high temperature through inlet 6 of space 3, undergo a sub stantially 90 change in flow direction then travel towards outlet 7. The return water of the heating circuit penetrates into the network of tubes 1 in a counter-current direction to the gases, i.e. on the side adjacent outlet 7 for the gases then flows towards the central spiral 8 and is evacuated towards the start of the heating circuit in the gas inlet zone 6.During their progress it will be readily understood that the gases are cooled in contact with the walls of the exchanger in which flows the colder water for heating. Conversely, the water gradually heats up as in any methodic exchange process.

The construction of the network of tubes 1 such as shown in Fig. 3 allows considerable dividing up of the flow of fluid B in tubes 1 to be obtained and consequently both a large exchange surface and a high flow speed to be obtained in the tubes, which improves the exchange coefficient. Thus is obtained an extremely high-performing exchanger. In the above application this allows the dew point of the smokes to be reached for condensation operations.

So as to improve the efficiency of the above-described exchanger, there may be formed on the surface of wall 2 which is not in contact with the outside discontinuities formed by through apertures 10a, 10b, 10c which are formed through the whole wall as can be seen in Figs. 5 and 6. These through apertures may be of small size such as apertures 1 0a, elongated and situated close to one end of the device such as apertures 1 orb, or of an even more elongated form such as apertures 10c.

These perforations may of course exist only on certain turns. The leading edges of these perforations operate to break up the limit layers which increases the efficiency of the apparatus. Furthermore, the perforations re duce considerably the pressure losses due to the flow of the fluid in the spiral space.

As explained above, the discontinuities may also be formed by hollows in one part of the thickness of the wall, or by projections or by a combination of these three discontinuities.

They may also exist only on one part of the surface of wall 2 which is not in contact with the outside.

To further increase the efficiency, the wall is wound in a spiral so that the spacing between the turns diminishes progressively towards the outlet of the burnt gases, so as to increase the heat exchange as the temperature of the gases drops.

Finally, a simple device for drying the burnt gases is shown very schematically in Fig. 7.

On the upper lid 4 has been mounted a Ushaped element 11. A flow derived from fluid A arrives at A1 at one end of the U-shaped element and leaves therefrom at A2 where it mixes with fluid A for drying it.

Another preferred embodiment will now be described, even more efficient, easy to construct and allowing heat exchanges between more than two fluids.

In Fig. 8 can be seen a two-fluid exchanger, each of the fluids being respectively designated by the letters A and B, and the flow direction of the fluids indicated by arrows.

Fluid A is for example hot air and fluid B water.

The exchanger is essentially formed by a vertically disposed spiral hollow wall 101 having here two faces 101 a and 101 b (Figs. 8 and 9). This wall is obtained by placing two stainless steel metal sheets one on the other, for example 101 a, 101 b and welding them to one another by numerous welding points 102. The metal sheets are flat or previously embossed. The welding points are obtained preferably by means of programmed resistance welding wheels. All the edges are then welded, while leaving beyond the welding non-welded strips which will be subsequently brought together after formation for providing the space between the external faces of the hollow walls, as will be seen further on.

With a high pressure applied between the two metal sheets, for example hydraulically, swelling is obtained at the non-welded places as can be seen in Fig. 9. This results in a hollow wall with two faces having numerous connection points between the two faces. To then obtain the spiral form, the space between the metal sheets is first of all filled with a product capable of being eliminated, for example a soluble or sublimable salt. In fact, if this precaution is not taken, the metal sheets will be flattened out during bending.

Then the bending is carried out after which the salt is eliminated by dissolving or by sublimation.

The hollow spiral wall thus obtained forms a zigzag path 103 for one of the fluids, for example fluid B.

Another method for obtaining the hollow spiral wall, without using salt, consists in shaping the metal sheets after welding by exerting a pull thereon during winding. This pull prevents the metal sheet which has the smallest radius from being compressed. Swelling is then effected after formation, possibly after annealing.

The wall has been given a spiral shape so that the turns are brought close together while leaving at the centre a central hollow 104, the purpose of which will be seen further on.

There is then between the turns a space 105 in which flows the other fluid for example fluid A. A lid C1 closes the upper end of the apparatus whereas the lower end is closed by a wall C2.

In the example of Fig. 8 there is shown very schematically a centrally placed burner 106 for causing hot air to pass between the turns, whereas fluid B, for example water, is introduced into the path 103 of the hollow wall by a tube 107, and leaves therefrom by a tube 1 08. Naturally, conventional or not suction or delivery devices are required for causing the fluids to flow but they have not been shown for the sake of simplicity.

It will be readily understood that the path of the two fluids is neither completely rectilinear nor completely helical. Moreover, the numerous welding points form for the inner path 103 a zigzag path. These welding points form furthermore on the external faces of the hollow wall projections and hollows so that space 105 also causes eddies in the flow of fluid A.

This similar action on each fluid is eminently favourable to the exchange of heat.

The constructional principle of the hollow wall allows several paths to be formed inside the wall. Fig. 10 shows a wall with two paths, a second path 109 being formed by means of a third substantially metal sheet 101 cwhose points of welding with metal sheet 101 a are, for example, twice as close as the welding points for path 103. Thus is obtained, if fluid B is water, both water for heating and water at a lower temperature for domestic uses.

Fig. 11 shows a heat exchanger embodying the invention in which the hollow wall has two paths. To the two tubes 107, 108 of the preceding example there have been added two tubes 11 0, 111 corresponding to path 109 of Fig. 10. Fig. 1 3 shows how the tubes 108, 111 are connected respectively to the paths 103 and 109. Here the exchanger is associated with a centrally placed burner 106, which has been shown very schematically, and with a fan 112 driven by a motor 113, mounted at the lower part of a metal sheet wall 114, which closes laterally the spiral space and forms a free space outside the spiral. The fan acts through its orifice 11 5.

Naturally, the fluids in paths 103 and 109 are caused to move by circulation pumps mounted in the tubes connected to tubes 107, 110 or 108, 111. These pumps have not been shown so as to simplify the drawing.

Fan 11 2 drives not only the gaseous fluid but also the condensed fluid and/or the mist to the lower part of the apparatus. This condensed fluid may also be discharged through a discharge tube 116, with removable closure means, not shown.

There can be seen shown very schematically at 11 7 a pipe bringing to the orifice 11 5 of the fan a flow of heat from the spiral space so as to heat the saturating vapours penetrating into the fan.

As in the example shown in Fig. 8, a lid C, can be seen at the upper part of the apparatus, but in fact the closure at the top and at the bottom is obtained in another way shown in Fig. 1 2. It can be seen that the opposite faces 101 b, 101 C, for example, of the hollow wall have been extended, bent and brought together, then welded or stapled (riveted) at their upper and lower ends.

In the embodiment shown in Figs. 14 and 15, the spiral wall has been bent at its outlet end so as to form a swelling 11 8, forming a combustion chamber for a burner 106 shown very schematically. Furthermore, fan 11 2 with its motor 11 3 has been shown under the central region 104 of the apparatus.

The surface of the combustion chamber, in this embodiment, as in the embodiment of Fig. 11 is advantageously treated so as to be preferably blackened. In fact, this surface thus treated partially absorbs the intense radiation from the flame of the burner, which lowers to a great extent the temperature of the material of the burner and increases the life thereof.

Finally Fig. 1 6 shows a portion of the spiral wall in which the facing welding points have been pierced at their centre at 119. This arrangement breaks up the limit layers of the fluid flowing between the turns of the hollow wall.

By way of a purely illustrative example and of course non-limiting of the invention, the stainless steel metal sheets 101 a, 101 b and 1 01 c mutually welded together at points 102 may have a thickness between 0.3 and 0.8 mm, preferably of the order of 0.4 mm, the spacing of points 102 may be between 1 5 and 50 mm, being preferably of the order of 35 mm for the path of the heating water, the number of turns of the exchanger may be between 2 and 10, being preferably of the order of 4 or 5, the mutual spacing between turns may be between 10 and 30 mm and the hydraulic pressure used for "opening" the paths reserved in the hollow wall for fluid B after effecting the welding points may be between 20 and 40 bars on the assumption that none of the mutually welded metal sheets has been previously embossed, ie deformed so as to provide depressions at the welding points to be formed.

The overall space taken up by the exchanger obtained is much less than that of known exchangers of a comparable heat-exchange power, its overall volume being several times less than that of these known exchangers.

The heat exchangers illustrated with a spiral wall forming an enclosure allow high performance to be achieved but can still be manufactured at low cost. As is seen it is possible to associate the enclosure formed by the spiral wall with a burner.

It is evident that the embodiments described above and shown in the drawings have been given only by way of non-limiting examples. Thus, instead of suction devices, delivery devices could be used. Similarly, the spiral winding could be variable in pitch so as to optimize the heat exchange by increasing the pressure drop in a way inversely proportional to the temperature gradient of the heatcarrying fluid. Finally the spacing between the welding points may be variable so as to increase the exchange by turbulence as the temperature gradient of the fluid flowing between the turns of the hollow wall decreases.

All these variations which can be understood without drawings have not been shown in the drawings. Similarly, the winding of the turns of the hollow wall could have conical shape with upward-turned apex so that the spiral space and the hollow wall are inclined with respect to the horizontal, so as to facilitate condensation of the fluids and the flow of the condensates. It has been thought pointless to show this variation which is immediately understood.

Claims (21)

1. A heat exchanger between at least two fluids characterized in that it comprises an originally flat wall shaped in a spiral, with closure means mounted at both its ends perpendicularly thereto, so as to form a spiral enclosure for the circulation of one of the fluids between the turns of the wall, means being provided for circulating the other fluid.

2. The heat exchanger as claimed in claim 1, characterized in that the means for circulating the other fluid are formed by a network of tubes integral by their generatrices with the spiral wall and parallel to an axis about which said wall is wound.

3. The heat exchanger as claimed in one or other of claims 1 and 2, characterized in that the spiral-shaped wall has on its surface which is not in contact with the outside hollow or projecting discontinuities of any shape so as to form leading edges for the circulation of the fluid in the continuous spiral enclosure.

4. The heat exchanger as claimed in claim 1, characterized in that the means for circulating the other fluid are formed by the wall itself, having at least two parallel faces connected together at two parallel edges so as to form a hollow wall allowing circulation of said fluid.

5. The heat exchanger as claimed in claim 4, characterized in that obstacles are formed inside and/or outside the hollow wall so as to form one or more paths creating eddies.

6. The heat exchanger as claimed in claim 5, characterized in that the faces of the hollow wall are joined together at a plurality of points for example by welding so as to form an inner zigzag path between two neighbouring faces and projections and hollows between the turns of the hollow wall.

7. The heat exchanger as claimed in any one of claims 4 to 6, characterized in that the spiral wall has three faces so as to form two internal spiral paths, the joining points of one system of two faces being spaced further apart than those of the other system of two faces, so that the flow speed in one path is different from that existing in the other path.

8. The heat exchanger as claimed in any one of claims 4 to 6, characterized in that the spiral wall has n faces so as to form n - 1 internal spiral paths, the joining points of each system of faces having a spacing different from that of the other systems, so as to obtain different flow speeds between all the systems.

9. The heat exchanger as claimed in any one of claims 4 to 8, characterized in that the spiral wall is disposed vertically and closed on itself and a suction device is mounted laterally at its lower end so as to drive the condensed fluid and/or the mist to the lower part of the apparatus.

1 0. The heat exchanger as claimed in any one of claims 4 to 8, characterized in that the spiral wall is disposed vertically and closed on itself and a suction device is mounted under its central region so as to drive the condensed fluid and/or the mist to the lower part of the apparatus.

11. The heat exchanger as claimed in any one of claims 4 to 10, characterized in that the spiral wall is disposed vertically and closed on itself and a discharge pipe with removable closure is mounted at its lower end so as to draw the condensed fluid to the lower part of the apparatus.

1 2. The heat exchanger as claimed in any one of claims 4 to 11, characterized in that the closure means at both ends of the wall are formed by the joining of the lower and upper extensions of the opposite faces of the hollow wall.

1 3. The heat exchanger as claimed in any one of claims 4 to 12, characterized in that the central space or the outer region of the vertically placed exchanger is shaped as a combustion chamber where a burner is housed.

1 4. The heat exchanger as claimed in claim 13, characterized in that the surface of the wall of the combustion chamber is treated so as to absorb the radiation from the flame of the burner, in order to lower the temperature of the material of the burner.

1 5. The heat exchanger as claimed in any one of claims 6 to 14, characterized in that at least some joining points of the faces of the hollow wall are pierced at their centre so as to break up the limit layers of the fluid flowing between the turns of the hollow wall.

1 6. The heat exchanger as claimed in any one of claims 9 to 15, characterized in that means are arranged between the spiral space and the suction device to bring to this latter a flow of heat so as to heat the saturating vapours penetrating into the suction device.

1 7. The heat exchanger as claimed in any one of claims 4 to 16, characterized in that the winding inner spiral of the hollow wall is variable in pitch so as to optimize the heat exchange by increasing the pressure drop inversely proportional to the temperature gradient of the fluid flowing between the turns of the hollow wall.

1 8. The heat exchanger as claimed in any one of claims 6 to 17, characterized in that the space between the joining points of the hollow wall is variable so as to increase the exchange by turbulence as the temperature gradient of the fluid flowing between the turns of the hollow wall decreases.

1 9. The heat exchanger as claimed in any one of claims 4 to 18, characterized in that it is obtained by the following steps: two or more metal sheets are placed one on the other, they are connected by numerous welding points, their edges are welded, a pressure is applied between the metal sheets, the space between the metal sheets is filled with a product capable of being eliminated, the filled sheets are bent in a spiral and the above product is eliminated.

20. The heat exchanger as claimed in any one of claims 4 to 18, characterized in that it is obtained by the following steps: two or more metal sheets are placed one on other, they are joined together by numerous welding points, their edges are welded, a pull is exerted on the metal sheets during spiral formation, and a pressure is applied between the metal sheets to obtain swelling.

21. A heat exchanger substantially as herein described with reference to the drawings.