EP0581663A1 - Heat exchanger with annularly mounted water-tubes, in particular for a condensing boiler - Google Patents

Abstract

A large number of separators (12) each covering a sector of a number of water pipes (1) are regularly distributed on the inside and on the entire circumference of an upper distributing ring (2) and of a lower distributing ring, between which the water rises and falls in the adjacent pipe bundles. Each separator isolates its sector from the neighbouring sector which is not provided with a separator. The water admission pipe (10) and the water discharge pipe (11) are mounted in a diametrically opposite manner on this upper distributing ring (2). Application to condensing-boiler heat exchangers. <IMAGE>

Description

The invention which relates to a heat exchanger, in particular for a condensing boiler, relates more precisely to the distribution of the flow rates inside the sheet of water tubes which constitute the cylindrical exchanger.

The cylindrical exchangers of condensing type boilers are usually produced in the form of a sheet of water tubes which are distributed vertically - evenly - around a central burner and which define a combustion chamber.

The cylindrical sheet is wrapped in a sealed shell intended to collect the combustion products which are evacuated through a chimney. This arrangement allows partial or total recovery of the latent heat of condensation of the water vapor contained in the combustion gases, thanks to the large exchange surfaces provided between the water tubes and these gases. These exchange surfaces result from a particular profile of each water tube, advantageously of oblong section and fairly flattened. In this known type of exchanger, the heating water circulates in the tubes of the sheet, going up by a few neighboring tubes forming a bundle, then going down by a neighboring bundle, and so on.

This upward and downward circulation takes place between a lower distributing ring and an upper distributing ring, one of the two receiving a supply duct and a water outlet duct. In each distributing ring are provided baffles which insulate the different sectors that they delimit. A bundle of rising tubes and a bundle of descending tubes thus opens into each sector. In this way the water performs several "round trips" from one ring to another, between the supply pipe and the outlet pipe.

The baffles in question constitute partitions between the sectors and they must be sufficiently tight so that said sectors are perfectly isolated from each other. This is even more important for the baffle which is located in a distributor ring, between the supply pipe and the water outlet pipe. Otherwise, at least part of the water flow is bypassed towards the outlet or the neighboring sector, to the detriment of the proper functioning of the exchanger. To avoid this, you must therefore ensure the quality of the baffle seals. If soldering is carried out for this, this imposes costly machining operations, and this does not exclude having to carry out subsequent rework in the workshop if leaks are still found during use. Admittedly, thought has been given to using removable baffles of particular shape which fit directly into the water tubes without the need for welding and which are capped with a seal, as described in FR-A 2 508 157 au name of the Applicant, but the sealing of the seals is sometimes also questionable after a long period of use.

This flow distribution system, apart from the aforementioned difficulties linked to the existence of these baffles, has other drawbacks.

In fact, we have noticed that in each sector of the distributing rings where, as we know, the water undergoes a sudden change of direction between the upward and downward bundle of tubes, there is not a homogeneous distribution of the flow in each tube of the same beam.

The heterogeneities of water velocities in each of them and of the swirling effects in the sectors result in irregularities in the temperatures of the tubes and internal blockages of some of them, resulting from the irregular precipitation of the particles in suspension in the water.

The invention therefore proposes a heat exchanger with a layer of water tubes which overcomes the aforementioned drawbacks, by not using the usual baffles, said exchanger allowing a better distribution of the flows, with a low pressure drop.

A main object of the invention therefore consists of a heat exchanger with a cylindrical layer of water tubes arranged around a central burner and which open into lower and upper distributor rings between which the water performs several reversals of direction. circulation up and down successively in the bundles of adjacent tubes, exchanger according to which a plurality of separators each covering a sector of several water tubes are regularly distributed inside and around the entire periphery of each distributor ring and isolate their sector of the neighboring sector not provided with a separator, the separators of the upper distributor ring and those of the lower distributor ring being offset from each other and the water inlet pipe and the water outlet pipe being mounted diametrically opposite on the same distributor ring.

According to a particular characteristic of the invention, the separators of the upper distributor ring cover an odd number of water tubes and the water inlet and outlet pipes take on the upper distributor ring each in a sector comprising an even number of water tubes, without a separator.

In the upper distributor ring, the number of water tubes in the water inlet sector is different from that of the water outlet.

Finally all the sectors of the lower distributor ring, those capped with a separator and those which are not have an odd and identical number of tubes, and plumb with the water inlet and outlet pipes two separators are placed at the limit of the diameter of the ring, in line with said conduits.

According to another particular characteristic of the invention, each separator consists of a folded sheet forming a bridge over several neighboring tubes, the two vertical sides of the separator which converge towards the center of the ring coming to bear against the base of the distributor ring , between two neighboring tubes.

• figure 1 une vue générale en perspective de l'échangeur de chaleur ;
• figure 2 une vue en coupe verticale diamétrale dudit échangeur ;
• figure 3 une vue en perspective du séparateur et figure 4 ledit séparateur monté au-dessus de plusieurs tubes d'eau ;
• figures 5 et 6 des vues en plan respectivement de l'anneau répartiteur supérieur et de l'anneau répartiteur inférieur dont les couvercles ont été ôtés ;
• figure 7 une vue déroulée schématique en élévation d'une moitié de l'échangeur.

Other particular characteristics and advantages of the invention will emerge from the description which follows of an embodiment, taken by way of example, in which reference will be made to the appended drawings which represent:

• Figure 1 a general perspective view of the heat exchanger;
• Figure 2 a diametral vertical sectional view of said exchanger;
• Figure 3 a perspective view of the separator and Figure 4 said separator mounted above several water tubes;
• Figures 5 and 6 plan views respectively of the upper distributor ring and the lower distributor ring whose covers have been removed;
• Figure 7 a schematic view in elevation of a half of the exchanger.

Referring to Figures 1 and 2, we see that the exchanger consists of a cylindrical layer of water tubes 1 which connect an upper distributor ring 2 and a lower distributor ring 3. The tubes 1 define a combustion chamber 4 inside which is arranged a radial burner not shown. The upper distributor ring 2 is closed by an annular cover 5 and the lower ring 3 also by another cover 6. The combustion chamber 4 is closed, at the lower distributor ring by a bottom 7. The ring upper distributor 2 is secured to a support plate 8 by which the exchanger is held in place in the device. On this plate are provided hooking lugs 9 for the burner. The upper distributor ring 2 communicates with the water inlet and outlet pipes respectively by a supply connection 10 and by an outlet connection 11, the two connections being diametrically opposite on the ring.

A plurality of separators 12, the profile and the arrangement of which can be seen better in FIGS. 3 and 4 are placed inside each distributor ring. Each separator 12 consists of a folded sheet, forming a bridge 15 above several neighboring tubes 1 and the two vertical sides 13 of the separator which converge towards the center of the ring come to bear against the base of the ring distributor, between two neighboring tubes. The central part of the separator 12 forms a slight elevation 14 relative to the bridge 15 and bears against the annular cover 5 or 6 of the distributor ring considered, to which it is brazed. The separator is thus perfectly held in place. It will be noted that the vertical sides of each separator are spaced apart by a distance corresponding to nine tubes 1.

FIG. 5 illustrates the space occupied by the separators 12 inside the upper distributing ring 2. This figure shows the regular distribution of the seventy-two tubes 1 which constitute the exchanger. The water inlet 10 and the water outlet 11 which are on the same diameter AA ′ are shown on the dotted lines on each side of the distributor ring.

On the side of the water inlet 10, eight tubes, that is to say four on each side of the diameter AA ′ are supplied with water and are not capped by a separator. On either side, on the other hand, nine neighboring tubes are capped by a separator 12; the tubes then appear in dotted lines in the figure. Then the nine neighboring tubes are opened and the following tubes capped with a separator and so on. It will be noted that the sector of the water outlet tube 11 is - like the sector of the water inlet tube 10 - devoid of a separator. Each separator therefore covers a sector of nine water tubes, ie an odd number of tubes, and isolates it from the neighboring sector not provided with a separator.

Figure 5 shows that there are four sectors with a separator, covering 36 tubes. Between each sector equipped with a separator, there is a sector that is not. We have seen that the entrance sector occupied eight tubes. The intermediate sectors have nine tubes. On the other hand, the outlet sector on the side of the conduit 11, on the diameter AA 'concerns 10 tubes. There is therefore between the inlet area and the outlet area of water a difference in the number of tubes whose interest will appear later. Thus the inlet 10 and outlet 11 conduits take on the upper distributor ring in a sector comprising an even number of water tubes, devoid of separator.

FIG. 6 shows that the space occupied by the separators 12 inside the lower distributor ring 3 - With respect to the same diameter AA ′ of the exchanger, it can be seen that the separators are offset with respect to the separators in FIG. 5 and are at the limit of said diameter. Thus on the side of the water inlet 10 a vertical flank 13 of the separator 12 is on the diameter AA ′, that is to say that the separator is offset by four tubes relative to that of the distributor ring superior. This offset is found on the side of the water outlet 11. A vertical flank of the separator is also located on the diameter AA ′, but this time it is offset by five tubes relative to that of the upper distributing ring. It will thus be noted that the eight sectors of the lower distributing ring, that is to say the four which are capped with a separator and the four which are not, each cover 9 tubes.

Referring also to FIG. 7, we now describe how the water circulates in the exchanger between inlet 10 and outlet 11.

The water admitted by the inlet 10 into the upper distributor ring 2 will descend into the eight tubes of the sector considered. A deflector not shown is advantageously placed in the supply connection 10 so that the water is distributed in the eight starting tubes. The vertical parts 13 of the two separators (Figure 5) isolate the eight tubes from their neighbors. The water descending in these eight tubes reaches the lower distributor ring 3. Due to the partition that constitutes the vertical flank 13 of the separator located as we have seen, on the diameter AA ', that is to say in the middle of the sector of the eight tubes, the descending water will be distributed on both sides of this partition and go back up in the neighboring tubes. We see that this first downward flow will be split on either side of the diameter AA '. This means that the water circulation will be from the inlet 10 to the outlet 11, by the two sides of the exchanger which considerably reduces the pressure losses compared to a single circulation. FIG. 7 schematically shows one half of the exchanger in an unrolled view between the water inlet 10 and the outlet 11. The water admitted at 10 therefore descends through the eight starting tubes then separates to go up through five neighboring tubes before going down by four and so on until exit 11. This alternation of five and four tubes is explained as follows. The water descending in the first four tubes has the five neighboring tubes capped by the same separator to go up towards the upper distributor ring.

This rising water then has four neighboring tubes capped by the same separator of the upper distributor ring to descend to the lower distributor ring and so on. The indication in Figure 7 of the four down pipes and five up pipes as well as the arrows marking of the water circulation, illustrates this process well.

Due to this particular arrangement according to which the number of rising water tubes differs from the number of descending tubes, at the change of direction of the water under the separator, a certain turbulence is created which prevents the formation of continuous water between a rising tube and a falling tube. Therefore all the tubes are supplied with water with substantially equivalent flow rates. The absence of heterogeneities in the flow velocities eliminates the risks of localized overheating and internal blockage of the tubes. Therefore, it is no longer necessary to use bridges to promote the distribution of fluids in the distributor rings.

We have seen that the fact of moving the water supply tube from the outlet tube, and of distributing the flow of water in circulation on the two sides of the exchanger reduced the pressure drops. This arrangement also has the advantage that in the event of a leak in the level of the separators and more precisely of their partitions, the small water leakage which results therefrom has no effect on the operation of the exchanger, and in all case there is no longer a direct bypass between the input and the output since the two corresponding conduits are distant from each other.

Claims (7)

1. Heat exchanger with a cylindrical layer of water tubes arranged around a central burner and which open into lower and upper distributor rings between which the water performs several reversals in the direction of circulation, going up and down successively in bundles of adjacent tubes characterized in that a plurality of separators (12) each covering a sector of several water tubes (1) are regularly distributed inside and around the entire periphery of each distributor ring and isolate their sector from the sector neighbor not provided with a separator, in that the separators of the upper distributing ring (2) and those of the lower distributing ring (3) are offset from one another and in that the inlet duct of water (10) and the water outlet pipe (11) are mounted diametrically opposite on the same distributor ring. 2. Heat exchanger according to claim 1 characterized in that the separators (12) of the upper distributor ring (2) cover an odd number of water tubes (1) and in that the inlet conduits (10 ) and water outlet (11) take on the upper distributor ring each in a sector comprising an even number of water tubes, devoid of separator. 3. Heat exchanger according to claim 2 characterized in that, in the upper distributor ring (2), the number of water tubes (1) of the water inlet sector (10) is different from that of water outlet (11). 4. Heat exchanger according to claim 1 characterized in that all the sectors of the lower distributor ring (3), those capped with a separator (3) and those which are not, have an odd and identical number of tubes 1. 5. Heat exchanger according to claims 1 and 4 characterized in that in the lower distributor ring (3), directly above the inlet pipes (10) and water outlet (11), two separators ( 12) are placed at the limit of the diameter AA ′ of the ring at the right of said conduits. 6. Heat exchanger according to claim 1 characterized in that each separator (12) consists of a folded sheet forming a bridge (15) over several neighboring tubes (1) and in that the two vertical sides (13) of the separator which converge towards the center of the ring bear against the base of the distributor ring, between two neighboring tubes. 7. Heat exchanger according to claim 6 characterized in that the central part of the separator (12) forms an elevation (14) relative to the bridge (15) and bears against the cover (5, 6) of the ring dispatcher considered.

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