EP0062577A1 - Heat exchanger comprising a battery of tubes - Google Patents

Abstract

1. A heat exchanger for exchanging heat between a fluid and at least air of the atmosphere, of the type comprising : a) a battery of tubes (1) of great length disposed in accordance with an assembly of super-imposed layers of tubes, each layer being formed by an assembly of parallel tubes, said fluid circulating inside the tubes and the air of the atmosphere circulating outside the tubes in a direction perpendicular to said layers of tubes ; b) connecting boxes (18a, 18b) connected to the ends of some of these tubes and adapted to supply said fluid to these tubes or to discharge it, and c) means for interconnecting the other ends of the tubes so as to permit the passage of said fluid in succession inside at least two tubes, characterised in that it comprises a series of juxtaposed sub-batteries whose connecting boxes (18a, 18b) are connected solely to the ends of a row of tubes extending in the direction perpendicular to said layers or to the ends of a limited number of such successive rows of tubes and whose means for interconnecting the other ends of the tubes are formed by substantially horizontal connecting elements which interconnect two neighbouring tubes of the same layer.

Description

The present invention relates to heat exchangers comprising tube batteries.

In such exchangers, the heat exchange takes place between a first fluid circulating inside the tubes of the battery, called "internal fluid" and a second fluid licking the tubes externally, called "external fluid".

In atmospheric exchangers, that is to say those in which the external fluid is atmospheric air, there may also be an external supply of the tubes distributing a liquid called "spraying fluid", generally water, falling by gravity, dripping onto the outside surface of the tubes: these are so-called "dry sprinkled" refrigerants.

The internal fluid is either a liquid, a gas, a gas in the process of condensation, or a boiling liquid. The tubes are either plastic or metallic; they are smooth or provided with complementary exchange surfaces, such as fins.

The batteries consist of a set of .. superimposed tube beds, each bed being made up of an alignment of tubes in a plane substantially perpendicular to the flow of the external fluid. The length of the tubes defines the length of the bed and that of the battery. The width of the bed defines the width of the battery. The dimension of the battery parallel to the flow of the external fluid is its thickness.

In each bed, the tubes are generally equidistant from each other and, between them, the beds are equidistant from each other. On the other hand, from a bed to an adjoining bed, the tubes are generally offset so that the tubes of a bed lie between those of the adjoining bed, that is to say that, in any plane perpendicular to the length of the battery, the tubes have a staggered arrangement.

For economic reasons, it is sought during the dimensioning of the refrigerants to have as large battery dimensions as possible, which are generally limited by the conditions of handling and transport.

The lengths are generally 10 to 12 m and the widths generally 2 to 3 m. As for the thicknesses, they are much smaller, from 0.50 to 1 m.

In known heat exchangers, the ends of these tubes are connected to two connection boxes intended to bring the first fluid to these tubes and to evacuate it. However, to improve the heat exchange between the first and the second fluid, the connection boxes used to bring and evacuate the first fluid are only connected to certain ends of the tubes, the other ends being connected to each other by connection boxes so as to allow the passage of the first fluid successively inside at least two tubes, or better still several, before its evacuation. The first fluid is thus generally made to pass four times through the battery before discharging it. In practice, connection boxes are provided at each end of the battery and these boxes are divided into as many chambers as necessary to obtain the desired number of passes.

However, these connection boxes are expensive, difficult to install and do not easily allow leak detection and repair.

The object of the invention is to remedy the drawbacks presented by these connection boxes.

• a) une batterie de tubes de grande longueur disposés suivant un ensemble de lits de tubes superposés, chaque lit étant constitué d'un ensemble de tubes parallèles, ledit fluide circulant à l'intérieur des tubes et l'air atmosphérique circulant à l'extérieur des tubes perpendiculairement aux lits de tubes;
• b) des boîtes de connexion raccordées aux extrémités de certains de ces tubes et destinées à amener ledit fluide à ces tubes ou à l'évacuer; et
• c) des moyens pour raccorder entre elles les autres extrémités des tubes de façon à permettre le passage dudit fluide successivement à l'intérieur d'au moins deux tubes,

caractérisé en ce que les boîtes de connexion sont raccordées uniquement aux extrémités d'une rangée de tubes s'étendant dans le sens perpendiculaire aux lits ou aux extrémités d'un nombre limité de telles rangées de tubes successives et en ce que les moyens pour raccorder entre elles les autres extrémités des tubes sont constitués par par des éléments de liaison substantiellement horizontaux qui raccordent deux tubes successifs d'un même lit.To this end, the subject of the present invention is a heat exchanger between a fluid and at least atmospheric air, of the type comprising:

• a) a battery of very long tubes arranged in a set of superimposed tube beds, each bed consisting of a set of tubes parallel, said fluid circulating inside the tubes and atmospheric air circulating outside the tubes perpendicular to the tube beds;
• b) connection boxes connected to the ends of some of these tubes and intended to bring said fluid to these tubes or to evacuate it; and
• c) means for connecting the other ends of the tubes together so as to allow the passage of said fluid successively inside at least two tubes,

characterized in that the connection boxes are connected only to the ends of a row of tubes extending in the direction perpendicular to the beds or to the ends of a limited number of such successive rows of tubes and in that the means for connecting between them the other ends of the tubes are constituted by substantially horizontal connecting elements which connect two successive tubes of the same bed.

The prior art and the invention will be described below with the aid of the accompanying drawings in their application to sprayed dry atmospheric refrigerants, consisting of horizontal batteries of tubes cooled by atmospheric air circulating vertically against the current of a flow of water falling in free fall through the battery by trickling on the tubes.

• les Fig. la, 1b, lc, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b et 4 représentent des échangeurs de chaleur en dehors de l'invention;
• les Fig. 5a, 5b, 5c, 6a, 6b, 6c représentent des échangeurs de chaleur selon la présente invention; les indices a, b et c désignant respectivement les vues en élévation , les vues en plan et les vues de côté.
• La Fig. l représente un échangeur de chaleur de l'art antérieur.
• La vue en élévation le représente dans son épaisseur, et celle en plan, dans sa largeur.

In these drawings:

• Figs. 1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b and 4 represent heat exchangers outside the invention;
• Figs. 5a, 5b, 5c, 6a, 6b, 6c represent heat exchangers according to the present invention; the indices a, b and c respectively designating the elevation views, the plan views and the side views.
• Fig. l shows a heat exchanger of the prior art.
• The elevation view represents it in its thickness, and that in plan, in its width.

This exchanger comprises a battery of straight tubes 1 arranged in superimposed horizontal beds, each bed being made up of a set of parallel tubes.

These tubes are joined together from distance to distance by bracing devices 2 and are connected in leaktight manner at their two ends to a first connection box 3 and to a second connection box 4. The connection box 3 is divided into three compartments 3a, 3b, 3c by horizontal partitions 5 and 6. The compartment 3a comprises a member 7 for connection to an inlet pipe for the internal fluid to be cooled and the compartment 3c comprises a member 8 for connection to a discharge pipe cooled internal fluid. The connection box 4 is divided by a horizontal partition 9 into two compartments 4a and 4b.

Atmospheric refrigeration air is introduced under the battery and is sucked in or discharged upwards according to arrow A. Water is sprayed above the battery and trickles down the tubes according to arrow E. The fluid to be cooled which enters compartment 3a according to arrow I successively carries out four passes, namely between compartments 3a and 4a, 4a and 3b, 3b and 4b and 4b and 3c and leaves compartment 3c according to arrow J.

où Q est le débit d'eau du réfrigérant

• Np est le nombre de passes
• Nb est le nombre de batteries
• Nl est le nombre de lits de tubes par batterie
• Nt est le nombre de tubes par lit
• S est la surface de la lumière d'un tube

In the frequent case where the internal fluid is liquid water, the speed of the water in a tube is:

where Q is the refrigerant water flow

• Np is the number of passes
• Nb is the number of batteries
• Nl is the number of tube beds per battery
• Nt is the number of tubes per bed
• S is the surface of the light of a tube

Acceptable values for v are within narrow limits, the maximum being determined by hydraulic pressure losses and erosion and the minimum by the quality of the heat exchange and the cost (depending on the total quantity of tubes = Nb.Nl.Nt and their dimension S), v must, for example , be between 0.5 and 2.0 m / s.

Nl is determined by the requirements of the heat exchange, as well as by the proportional air pressure losses.

When the battery consists of plastic tubes, these are of small section (diameter of the order of magnitude of 10 to 20 mm) and the number of beds is relatively high (16 to 50 for example).

There is shown in FIG. 2 a heat exchanger in which the connection boxes of the exchanger shown in FIG. l which cover the complete section (width x thickness) of the battery, by two connection boxes, one 10 for supplying the internal fluid into the upper tubes 1 corresponding to the first pass and the other 11 for discharging the internal fluid of the last pass, with elbows 12 ensuring the connection of the tubes between the different passes, from the first to the last.

This arrangement is also not satisfactory because the connection boxes are still relatively large, supplying several beds, and therefore expensive, that the elbows have very varied dimensions and are therefore expensive to manufacture and to assemble, that the The dimensions of the hydraulic connections are large and the elbows overlap, making access to the interior elbows practically impossible.

To overcome these drawbacks, a heat exchanger could be designed, as shown in FIG. 3, in which the connection boxes 13 and 14 respectively for supplying the internal fluid and discharging the internal fluid are connected only to two beds of tubes 1 and in which the connections between the various passes are made by identical bends 15. With this configuration, the thickness of the connection boxes is reduced, but the number of passes is increased.

• Δ h_h proportionnel à
  

As the hydraulic pressure drop in the tubes A h _h is proportional to the length of tubes traversed by the water, i.e. to the product L (length of the battery) x Np (number of passes) and approximately squared the speed v, we have:

• Δ h _h proportional to
  

The term squared is more or less fixed by the internal fluid flow and by the thermal load and is independent of the hydraulic arrangement of the batteries. The hydraulic pressure drop is therefore, as a first approximation, for similar batteries, proportional to the cube of the number of passes. The configurations of the type of those shown in fig. 3 with a very high number of passes are therefore not satisfactory.

We could then think of adding, as shown in FIG. 4, intermediate connection boxes 16 and 17 similar to the boxes 13 and 14 of the battery of FIG. 3 to return to the initial number of passes, that is to say four in the example shown in FIG. 1. However, this configuration is also not satisfactory because the connection boxes being relatively long (their length is equal to the width of the battery), therefore distributing the internal fluid to a relatively large number of tubes, must be relatively thick. Consequently, the presence of contiguous boxes such as boxes 16 and 17 does not allow, if a satisfactory flow of the internal fluid is desired, to maintain between two contiguous beds supplied one by a box and the other by another box ., the normal spacing between the beds due to the thickness of these boxes, which is harmful from the thermal, aeraulic and technological points of view. In addition, the relative movement of fluids, which consists in the situation in series in the air flow of several sub-batteries operating according to a mixed cross-current / counter-current system, is not favorable from the thermal point of view.

There is shown in FIG. 5 a heat exchanger according to the invention which differs fundamentally from the known heat exchangers with tube batteries or from those which could be designed from known heat exchangers.

This exchanger conventionally comprises a battery of straight tubes 1 staggered in accordance with superimposed horizontal beds. The external fluid is introduced under the battery and circulates upwards according to arrow A. Water is sprayed above the battery and trickles on the tubes according to arrow E.

The battery comprises at one of its ends a series of connection boxes 18a and 18b respectively for supplying the internal fluid and for discharging this internal fluid. Thus, the internal fluid enters a connection box 18a according to arrow I and leaves a connection box 18b according to arrow J. These boxes are narrow and extend in the vertical direction over the entire thickness of the battery. . They are connected only to two successive vertical rows of tubes 1 staggered.

Between the boxes 18a and 18b two successive vertical rows of tubes are connected to the next two vertical rows by the horizontal bent tubes 19, the connection being thus made between the tubes of the same bed.

At the other end of the battery, two successive vertical rows of tubes are also connected to the next two vertical rows by horizontal bent tubes 19.

Thus, the connection boxes 18a and 18b serve only to bring in and evacuate the internal fluid, the connection of the tubes from one pass to the other being carried out only by the horizontal bent tubes 19. The alignment of the successive passes, with the arrangement according to the present invention, is horizontal, contrary to what exists for the arrangements described previously.

The internal fluid entering the battery through a connection box 18a thus makes four passes before coming out of the connection box 18b.

With this arrangement, it is possible to arrange in the direction of the width of the battery a succession of elementary exchangers (by elementary exchanger denotes the part which goes from a box 18a for supplying the internal fluid to the corresponding box 18b fluid discharge).

Compared to the configuration of FIG. 4, there are a greater number of boxes, shorter and consequently narrower. The contiguous boxes (18b, 18a) no longer interfere with each other when it is desired to respect over the entire thickness and width of the battery a longitudinal pitch and a single transverse pitch between the tubes.

On the other hand, compared to the known arrangement of FIG. l, the speed of the internal fluid is preserved and the hydraulic pressure drop is not substantially modified, that of the tubes themselves is identical, as shown in formula I, since the arrangement according to the invention has neither modified nor Nb, neither Nt, neither Nl, nor Np, and that of the hydraulic connections is rather reduced because the elbows and the narrow and elongated connection boxes ensure a more regular circulation of the fluid.

Instead of supplying the battery with all the tubes of the first beds, as is known, supplying according to the invention takes place on the first or the first tubes (preferably the first two) of the set of beds.

• - le problème de la tenue à la pression des boites de connexion est beaucoup moins complexe:
• - la détection et la réparation des fuites du fluide interne aux raccordements des tubes sont beaucoup plus aisés:
• - les problèmes de dilatation sont ^pratiaue- ment inexistants: alors que la dilatation est particulièrement appréciable en ce qui concerne l'effet différentiel dû aux différences de température entre les tubes de passes différentes, dans la présente invention les tubes pouvent se dilater librement par suite de l'absence des grandes plaques tubulaires.

The arrangement according to the invention also has the following advantages:

• - the problem of the pressure resistance of the connection boxes is much less complex:
• - detection and repair of internal fluid leaks at the tube connections are much easier:
• - expansion problems are ^p ratiaue- ment nonexistent: while the expansion is particularly advantageous with regard to the differential effect due to the temperature differences between the different passes of tubes, in the present invention the pouvent tubes expand freely by due to the absence of large tubular plates.

There is shown in FIG. 6 a variant of the exchanger shown in FIG. 5.

Instead of being connected on the same side of the battery as on the Fiq. 5, the connection boxes 18a intended to bring the internal fluid are connected to one of the sides, while the connection boxes 18b intended to evacuate the internal fluid are connected to the other side.

As with the battery shown in Fia.5, the tubes are connected from one pass to the other using horizontal bent tubes 19. With such a layout. the number of passes is odd, while it is even when all the boxes are on the same side of the battery. In the case shown in FIG. 6 the number of passes is three.

In variants. the bent tubes connecting two successive tubes of the same l _i t can be replaced by small connection boxes horizontally connecting two successive tubes of the same bed.

Claims (5)

1. Heat exchanger between a fluid and at least atmospheric air of the type comprising: a) a battery of very long tubes (1) arranged in a set of superimposed tube beds, each bed consisting of a set of parallel tubes, said fluid circulating inside the tubes and atmospheric air circulating at the outside of the tubes perpendicular to the tube beds, b) connection boxes (18a, 18b) connected to the ends of some of these tubes and intended to bring said fluid to these tubes or to evacuate it, and c) means for connecting the other ends of the tubes together so as to allow the passage of said fluid successively inside at least two tubes,
characterized in that the connection boxes (18a, 18b) are connected only to the ends of a row of tubes extending in the direction perpendicular to the beds or to the ends of a limited number of such successive rows of tubes and in that that the means for connecting the other ends of the tubes together consist of substantially horizontal connecting elements which connect two successive tubes of the same bed. 2. Heat exchanger according to claim 1, characterized in that the connecting elements consist of bent tubes (19). 3. Heat exchanger-according to claim 1, characterized in that the connecting elements consist of small water boxes. 4. Exchanger according to any one of claims 1 to 3, characterized in that the connection boxes (18a, 18b) are arranged on the same side of the battery. 5. Exchanger according to any one of claims 1 to 3, characterized in that the connection boxes (18a) intended to bring the first fluid are arranged on the same side and the connection boxes (18b) intended to evacuate the first fluid are arranged on the other side of the battery.

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