EP1050721A1 - Heat exchanger for a water heater - Google Patents

Abstract

The water boiler heat exchanger has tubes (10) circulating coolant liquid near a burner. The tubes have circular cross-secti at ends, near tubular plates (not shown). In the center, each tube has a pentagonal cross-section. Transition zone (18) occurs betw pentagonal and circular cross-sections. Pentagonal section has large base (20), two lateral walls (22), and two top walls (24). is oriented towards burner.

Description

The present invention relates to a heat exchanger intended to equip a hot water boiler.

In a hot water boiler, there is usually a burner placed in the heart of the boiler and which allows the exothermic combustion of a fuel. The amount of heat as well released is partially recovered by a heat exchanger placed around of the burner. This heat exchanger has tubes in which circulates water. The tubes are heated and the heat is thus transferred to the water flowing inside them.

The simplest exchangers have a sheet of tubes arranged around the burner. However, the efficiency of such an exchanger Is not very good. It is then known to use two layers of tubes. This significantly improves the efficiency of the exchanger.

In such exchangers, the tubes used are tubes of circular section. They are mounted between two plates called plates tubular. On each tube plate is mounted a water box allowing irrigation and circulation of water in the tubes. The tubes are fixed to the tubular plates by welding. Circular section tubes are preferably used because it is the easiest form of tubes solder.

To be able to resist the mechanical stresses appearing at the level of the tube plate, stresses due in particular to differential expansion problems, the space between two neighboring tubes is relatively large. As a result, the speed of the gases flowing between the tubes is relatively small. Higher speed is favorable for increase the efficiency of the exchanger.

It is also known to use tubes of non-cross section circular. Thus, document FR 2 694 388 discloses a heat exchanger with water tubes having section water tubes substantially trapezoidal. This form increases the yield of the exchanger but the tubes are very close to each other what which poses problems of mechanical stress by expansion differential at the level of the tubular plates.

The object of the present invention is therefore to provide an exchanger heat intended to equip a hot water boiler allowing to have good energy efficiency without weakening mechanically the tubular plates.

To this end, it offers a heat exchanger of the type comprising at least one ply of tubes each intended for circulation of a heat transfer liquid and arranged near a burner.

According to the invention, at least one tube present near its ends a first cross section, preferably circular, while at a distance from its ends it has a cross section distinct, preferably substantially polygonal.

Thanks to the tubes having different sections at ends relative to the rest of their length it is possible to have on the one hand, a section at the ends to facilitate assembly tubes, by choosing for example a circular section which is easy to weld on a tubular plate and whose width is controlled and other share a section on the largest part of the tube which allows to favor good heat exchange between the hot gases and the tubes.

The tube at least one present at a distance from its ends for example an irregular pentagonal section, symmetrical by relative to a plane passing through the axis of the burner, the pentagon comprising a long side facing the burner and two short sides extending substantially at right angles to the long side, in a radial plane with respect to the burner. This fairly flat section shape allows a good exchange of heat.

We can imagine layers of flat tubes but the tubes are preferably arranged parallel to each other to form one or more circular cylindrical layers.

A heat exchanger according to the invention comprises advantageously near the burner, a first layer of tubes of circular section and a second ply of tubes having at their ends a cross section separate from their cross section at distance from these ends. The first layer of tubes is in contact with gases when these are still very hot. It is then not necessary try to optimize the heat exchange so as not to get overheating in the tubes. Once the first layer of tubes has passed, the gases are less hot and the shape of the tubes is optimized to try to recover maximum calories (1 calorie = 4.185 J) with gas.

For better performance, folded sheets forcing the hot gases along the wall of the tubes of the second layer of tubes are advantageously provided beyond the second ply of tubes. We force thus the gases to remain in contact as long as possible with the tubes of the second tablecloth.

In one embodiment, each folded sheet has stamped ribs, the top of which is intended to come into contact with tubes of the second layer, thus creating baffles in which the hot gases must pass. The ribs are then advantageously inclined with respect to the tubes so as to allow the evacuation of water of condensation.

When folded sheets are provided beyond the tubes of the second layer, it is better to also provide a piece of profile metallic with a slight play the contour of passage at each end of the folded sheets, at the tube ends and in the tube transition zones, in order to avoid creating a preferential passage for gases in which the gases give off fewer calories to the tubes than level of the folded sheets.

To further increase the efficiency of the exchanger, it is advantageously made of stainless steel. It is then possible to do so work in condensation.

Figure 1 est une vue schématique en coupe longitudinale d'un échangeur de chaleur selon l'invention,

Figure 2 est une vue en coupe selon la ligne de coupe ll-ll de la figure 1 à échelle très agrandie,

Figure 3 est une vue en coupe longitudinale à échelle agrandie d'un tube utilisé dans l'échangeur de la figure 1,

Figure 4 est une vue en coupe à échelle agrandie de deux tubes voisins selon la ligne de coupe IV-IV de la figure 3, et

Figure 5 est une vue de face d'une chicane utilisée dans l'échangeur de la figure 1.

In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended diagrammatic drawing, representing by way of nonlimiting example a preferred embodiment of a heat exchanger according to the invention .

FIG. 1 is a schematic view in longitudinal section of a heat exchanger according to the invention,

FIG. 2 is a sectional view along the section line II-II of FIG. 1 on a very enlarged scale,

FIG. 3 is a view in longitudinal section on an enlarged scale of a tube used in the exchanger of FIG. 1,

FIG. 4 is a sectional view on an enlarged scale of two neighboring tubes along the section line IV-IV of FIG. 3, and

Figure 5 is a front view of a baffle used in the exchanger of Figure 1.

Figure 1 shows a general view of a heat exchanger heat for a hot water boiler. At the heart of this exchanger, a space 2 is left free to allow the placement of a non-burner represented. The exchanger comprises an upper water box 4, a box lower water 6, a first layer of tubes 8 and a second layer of tubes 10. The upper water box is connected to a hot water network by via two water taps 12. The tubes 8 of the first ply and the tubes 10 of the second ply are welded to each of their end on a tube plate 14 and water circulates inside these.

The tubes of the first layer, that is to say the tubes placed at the closer to the burner are cylindrical tubes of circular section. We see these tubes in section in Figure 2. Over their entire length, between the two tubular plates 14, these tubes 8 have a constant section. All the tubes 8 are placed on a cylinder of circular section and having an axis 16. The boiler burner is centered on this axis 16.

The tubes 10 of the second heat exchanger ply are also arranged on a cylinder of circular section and axis 16. This second cylinder is larger in diameter than the cylinder corresponding to the first ply of tubes 8. The tubes 10 are at each times placed angularly between two neighboring tubes 8. So the hot gases of the burner are forced to zigzag between the tubes 8 and 10 which favors better heat exchange.

The tubes 10 have at their ends close to the plates tubular 14 a circular section. At their center, they present a pentagonal section. This polygonal section is constant over almost the entire length of the tubes 10, except in the end zones. A zone transition 18 exists between the parts of circular section and the center of pentagonal section. Such a tube 10 is for example obtained by stamping. Only the central part of the tube is stamped, the ends of the tube retaining the original shape of the deformed tube.

The pentagonal section of the tubes 10 is flattened in the direction radial of the cylinder formed by the ply of tubes 10 and is widened in the direction circumferential of this cylinder. Therefore, the space left free between two neighboring tubes 10 is much weaker in the center of tubes 10 than at their end. The pentagonal section of the tubes 10 has a large base 20, two side walls 22 and two top walls 24.

The base 20 of the pentagonal section is oriented towards the burner. This base is substantially tangential to the second layer of tubes 10. The side walls 22 extend substantially radially by relative to the axis 16. They form an angle with the base 20 which is slightly greater than 90 ° The length of these side walls is substantially less than the length of the base 20. The two walls of vertex 24 close the pentagonal section and have a shape reminiscent of a roof.

On the outer face of the second ply of tubes 10, are arranged bands of stamped and folded metallic material. These strips are called corrugated baffles 26. These folded strips are at each placed on horseback on two tubes 10. The baffles 26 extend over the entire length of the pentagonal section of the tube 10. They have a V section. The point of the V is placed between two tubes 10 while the angle formed by the V is such that the branches of the V are at each time parallel to a top wall 24 of a tube 10. The baffles 26 have ribs 28 projecting from the side of the tube 10. The top of these ribs 28 rests on the top wall 24 corresponding. Thus are created passage channels for the gases of the burner. The ribs 28 are inclined relative to the axes of the tubes 10 to allow the water which condenses on the baffle 26 to be brought to the low.

To force the hot gases from the burner to pass through the baffles corrugated 26 it is planned to have at each end of the tube 10, in the transition zone 18 as well as in the end zone of circular section an end profile which fits with a slight play the passage outline.

In Figure 2, arrows 30 symbolize the passage of gases hot from the burner. These gases pass on either side of the tubes 8 of the first layer then pass between the tubes 10 of the second layer. The passage between the tubes 10 is substantially narrower than the passage between the tubes 8. The channel thus obtained extends radially and has a substantially constant width over the entire length of the side walls 22 corresponding tubes 10. Therefore, there is between the tubes 10 a relatively high gas speed which promotes good heat exchange between these gases and the tubes 10. The hot gases then pass into the corrugated baffles 26 to optimize the heating of the water circulating in the tubes 10.

The gases then again supply the top walls 24 with 10 calories tubes. The cooling of the corrugated baffles 26 is as for it ensured by the multiple contacts existing between these baffles 26 and the corresponding tubes.

As we have just seen, the shape of the tubes 10 allows to have a good heat exchange. This good energy efficiency does not imply an increase in mechanical stresses in the exchanger. At the attachment of the tubes 10 to the plates tubular 14, as can be seen in Figure 4, we see that the space between two adjacent welds is much greater than the space left between the tubes 10 in the center of these. So we find mechanical stresses by differential expansion similar to constraints that would be encountered if the tubes 10 had over their entire length a circular cross section.

The exchanger according to the invention therefore makes it possible to have a good energy efficiency, to have tubes easy to assemble since round tubes are easy to weld while keeping a ligament (space between two neighboring tubes at the level of the tube plate) sufficient for a mounting with seals and without creating mechanical stress by high differential expansion.

The pentagonal shape of the tubes of the second layer of tubes optimizes the heat exchange between hot gases and water (or other liquid) circulating in the tubes. The base of the pentagon, arranged tangentially between two tubes of the first layer forms a barrier that the gases are forced to go along. The side walls allow define a radially extending channel in which the gases flow at high speed thus promoting heat exchange. Finally, the walls of top allow centering of the baffles.

This exchanger described above can be made of steel, stainless steel, copper or any other metallic material. However, to further increase the performance of this exchanger, by terms of heat transfer, we can, by an all-steel design stainless steel, allow this exchanger to work in condensation.

It goes without saying that the invention is not limited to the form of preferential embodiment described above by way of nonlimiting example; on the contrary, it embraces all the variant embodiments in the The scope of the claims below.

So for example the section of the tubes of the second layer might be different. We could have a section at the ends not circular. The section in the center is not necessarily pentagonal. We could find other sections of tubes that allow to have at the level of the tubular plates a sufficient ligament while having in the center of the tube sections allowing a passage between tubes narrow. So for example we could have a square section at ends and a flattened rectangular section in the center of the tube.

The first layer of tubes is shown here with tubes of constant circular section over the entire length of the tube. We could of course also have tubes at the level of the first ply whose end section is different from the center section.

The presence of wavy baffles is optional. These baffles increase the efficiency of the exchanger but do not not part of the invention.

Claims (9)

Heat exchanger comprising at least one layer of tubes (8, 10) each intended for the circulation of a heat-transfer liquid arranged near a burner,
characterized in that at least one tube (10) has near its ends a first cross section, preferably circular, while at a distance from its ends it has a separate cross section, preferably substantially polygonal. Heat exchanger according to claim 1, characterized in what the tube (10) at least one of them presents at a distance from its ends an irregular pentagonal section, symmetrical with respect to a plane passing through the axis of the burner, the pentagon having a large side (20) facing the burner and two short sides (22) extending substantially at right angles to the long side (20), in a radial plane by report to the burner. Heat exchanger according to one of claims 1 or 2, characterized in that the tubes (8, 10) of each layer of tubes are arranged parallel to each other on a section cylinder circular. Heat exchanger according to one of claims 1 to 3, characterized in that it comprises near the burner a first layer of tubes (8) of circular section and a second ply of tubes (10) having at their ends a cross section distinct from their cross section away from these ends. Heat exchanger according to one of claims 1 to 4, characterized in that beyond the second ply of tubes (10) are provided with folded sheets (26) forcing the hot gases to run along the wall (24) tubes (10) of the second ply of tubes. Heat exchanger according to claim 5, characterized in that each folded sheet (26) has stamped ribs (28), the top is intended to come into contact with the tubes (10) of the second ply, thus creating baffles through which the hot gases must pass. Heat exchanger according to claim 6, characterized in that the ribs (28) are inclined relative to the tubes (10) of so as to allow the evacuation of condensation water. Heat exchanger according to one of claims 5 to 7, characterized in that a piece of metal profile conforming to a slight clearance the passage outline is provided at each end of the folded sheets (26), at the tube ends (10) and in the transition zones (18) tubes. Heat exchanger according to one of claims 1 to 8, characterized in that it is made of stainless steel.

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