EP1966560A1

EP1966560A1 - Novel heat exchanger corrugations and applications thereof

Info

Publication number: EP1966560A1
Application number: EP06847185A
Authority: EP
Inventors: Sophie Deschodt; François LECLERCQ; Marc Wagner
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2005-12-22
Filing date: 2006-12-20
Publication date: 2008-09-10
Also published as: CN101341372A; US20080264616A1; FR2895493A1; FR2895493B1; WO2007074290A1

Abstract

The invention relates to a strip of corrugations (2) for brazed plate and fin heat exchangers of the type with partial offset, comprising a series of zones for brazing on a first separation sheet (1), a series of zones for brazing on a second separation sheet (1) adjacent to the first separation sheet (1) and a series of wings (13, 14), said wings forming the fins, of which at least one of the wings (14) of a corrugation is inclined without being perpendicular to the separation sheets (1) and of which at least one of the wings (13) has at least one section perpendicular to the separation sheets (1) and a brazed plate or fin exchanger comprising said corrugations.

Description

New heat exchange waves and their applications

The present invention relates to new heat exchange waves and their applications. The brazed plate and fin exchanger (EPAB) technique is commonly used to provide a large exchange surface in a very compact body.

The EPABs consist of a stack of embossed sheets, called "waves", separated by flat sheets called "separating plates" and closed on the sides by bars. The assembly constitutes a fluid passage layer.

These exchangers thus consist of several superimposed plates between which are inserted heat exchange waves or heat exchange fins, whose geometry is particularly varied. These constituent elements of the exchanger are usually aluminum. The assembly is carried out by soldering in a salt bath or under vacuum.

Each fluid flows in the space between two adjacent separation plates, called passage. The flows can be countercurrent, co-current or cross flow. The interest of these exchangers is to offer a large exchange area, in a rather small volume. These are very compact exchangers. An exchanger body may consist of a large number (more than one hundred) of solidarity layers. For large-scale processes, it is common for the exchanger to be composed of one or more parallel bodies mounted in batteries.

The waves inserted between the plates have the function of increasing the exchange surface and thus increase the overall transfer performance: integral with the primary surface by brazing, they transfer heat flow by conduction. The surface of the separation plates in direct contact with the fluid is the primary surface and the secondary surface constituted by the transfer waves, represents approximately 50% to 90% of the total exchange surface.

The waves play a dual role in EPABs. In addition to providing most of the heat exchange surface, soldered waves ensure the mechanical strength of the entire exchanger. Exchange waves based on folded flat product, perforated, punctured or stamped have given rise to a large number of variants.

One can quote the right wave, which is a simple embossed metal plate of generally crenellated form, the perforated wave, which is a straight wave realized with perforated bands (plates), and the partial offset wave ("serrated "). The partial shift wave is characterized by a waveform such that the legs of the waves are perpendicular to the separation plates and by a shift of the wavebands at regular intervals. The choice of the type of wave to be used in a heat exchanger depends on the required heat exchange and the maximum permitted pressure drops. However, a wave that has good thermal performance often generates high pressure losses; the best solution therefore generally involves a compromise between these two quantities. The wave most often used is the partial shift wave. Its manufacture is widespread and well controlled: it is made by folding and stamping sheet usually aluminum with appropriate tools.

Keeping all the other parameters constant, it can be seen that increasing the offset frequency improves the thermal performance while inducing greater pressure losses.

Including the extreme case of the right wave, the family of partial shift waves of the same density is a good example of the compromise to be found between thermal performance and pressure drop. The pattern of the partial shift wave is shown below in the figures.

At each shift line, the wave thickness creates a restriction for fluid flow. On the other hand, the edge of the fins creates a stopping point for the fluid. These two combined effects increase the pressure drop in the waves, especially since the offsets are frequent.

FR-A-2807828 proposes an improvement of these waves which consists of removing material over a short length at the beginning of the partial offset: The pressure drop is then lower and the heat exchange slightly degraded.

It would, however, be desirable to have brazed plate or fin exchangers having an improved exchange coefficient relative to the partial shift waves.

Furthermore, EP-A-1123763 discloses partial shift waves in which the wave legs are inclined relative to the separation plates and the length of each connection portion in the longitudinal direction of each waveband is less than or equal to to the thickness of the plate forming said strip to minimize the connection length between adjacent strips.

But after long research, the Applicant has discovered that by modifying the inclination of the legs of the waves of a classical partial shift geometry, waves are obtained allowing all the fluid to be involved in the heat exchange without leaving a zone. more weakly mixed and having a surface gain for low wave densities.

This is why the present application relates to a wave band for EPAB of the partial shift type comprising a series of zones intended to be brazed on a first separating plate, a series of zones intended to be brazed on a second plate separation member, adjacent to the first separation sheet, and a series of legs, said fin legs, characterized in that at least one of the legs of at least one wave is inclined without being perpendicular to the separation plates and at least one leg has at least one portion perpendicular to the separation plates.

In the present application and in the following, the angles indicated are those formed by a leg seen in cross-section with respect to the intended flow direction for a fluid. By convention the zero angle is the direction of the separating plates, shown horizontally in the figures below. The nature of the modifications is indicated by taking as a reference the conventional rectangular shape of a partial offset wave viewed in cross-section with respect to the intended flow direction for a fluid, and the shapes, unless otherwise indicated, are indicated by taking as a point of view the intended flow direction for a fluid and accordingly observing the section transversely to this direction of circulation.

We call "wave" the part of a waveband, analogous to the notion of "wavelength" in physics. Under preferred conditions of implementation of the invention, at least one of the legs of a wave is inclined at an angle of 43 ° to 80 °, preferably 45 ° to 75 °, preferably 50 ° to 75 °, especially 60 ° to 75 °, especially 60 ° to 70 °. Thus, the conventional rectangular shape of a wave and preferably each wave is modified to form a trapezoid with a right angle. This type of modification is called type 1.

Only part of the waves can have one of its legs which is inclined, but preferably at least 20%, especially at least 40%, especially at least 60% of the waves. Very advantageously, all the waves of a wave band have one of their legs which is inclined. Preferably only one of the legs of a wave is inclined, in particular always that located on the same side of the wave (left or right) of a waveband.

In other preferred conditions of implementation of the invention, the inclined leg of a wave comprises an additional folding. This type of modification, represented hereinafter, is called type 2. Advantageously, this additional folding is not performed parallel to the general direction of bending of the plates forming the waves, which is the general direction of flow intended for a fluid. This creates a vortex generation in the inclined part of the wave, which improves the heat transfer. This folding makes it possible to create a flow in 3 dimensions.

In still other preferred conditions of implementation of the invention, outward folding is provided on a vertical leg to form an inclined portion as shown in the figures below. This type of modification is called type 3. Preferably, a sloping leg and a vertical leg having an inclined zone are combined on the same wave.

In still other preferred conditions of implementation of the invention, bends are provided on one leg to form at least one step. This type of modification is called type 4. From preferably, one combines on the same wave an inclined leg and a bent leg to form a step.

The various folds above can advantageously be combined with each other on the same wave or on the waves of the same waveband.

The proposed patterns advantageously allow a junction between successive partial shifts to form a wave mat from folding a flat sheet and can be easily installed in a heat exchanger. In still other preferred conditions of implementation of the invention, the zones of a wave intended to be brazed on a first separating plate and the zones intended to be brazed on a second separation plate are parallel to each other, especially when they are brazed on their plates or separation plates. In still other preferred conditions of implementation of the invention, windows are provided in the sides of the waves according to the same principle as the windowed partial offset waves.

These new waves and wavebands can be made from flat products, by folding like the conventional partial shift wave, by modifying the profiles of the usual tools. The cuts and bends can be made in the same direction as with the tool for manufacturing conventional partial offset waves, the shape of the folding rules being different.

The waves and wavebands object of the present invention have very interesting properties and qualities. Recall that the partial shift wave is characterized in particular by a wave shift at regular intervals.

The inclinations of the legs periodically vary between the partial offsets, so as to periodically change the direction of the leading edge. The edges of attacks can be vertical, horizontal or inclined. The solution proposed by the invention, given the periodic change in the direction of the leading edges at each waveband allows to involve all the fluid in the heat exchange, without leaving a more weakly mixed zone. It also makes it possible to make the partial shift more efficient in the case of flow where the bonding does not have time to take place between two partial offsets: here the flow is intersected (and turbulence is created) in another plan. These new waves have a surface gain for low densities. The brazing surface is then reduced with respect to the partial shift wave. These waves are therefore of particular interest for medium or low pressure passages for which it is sought to reduce the pressure drop (where high and low density partial offset waves are usually used). The waves according to have a height of between 3 and 10 mm.

These properties are illustrated below in the experimental part. They justify the use of the waves and wavebands described above, in the manufacture of plate heat exchangers or brazed fins (EPAB).

They find applications in condensation or distribution, where its characteristics of low pressure losses can be important factors.

They find great use for di-phasic fluids in evaporation, or condensation.

This is why the present application also relates to a device comprising at least two parallel plates or separation plates between which are installed wavebands comprising waves as defined above, in particular a heat exchanger with brazed plates or fins. comprising waves as defined above.

Between two parallel separation plates, when for example the conventional shape of each partial offset is deformed to form a trapezoid comprising a right angle, at each partial shift, the pattern can be inverted and shifted. Thus the fluid approaches during its displacement leading edges successively inclined to the right and left.

The preferred conditions of implementation of the waves described above also apply to the other objects of the invention referred to above, in particular to wavebands, to devices comprising at least two parallel plates between which strips are installed. wave and brazed plate or fin exchangers as defined above. The invention will be better understood with reference to the accompanying drawings in which: Figure 1 shows a perspective view, partially in section and exploded, of a conventional brazed plate heat exchanger (EPAB); FIG. 2 represents a sectional view of three successive patterns of conventional partial offset waves; Figure 3 shows the leading edges encountered in the direction of fluid flow in a conventional partial offset wave exchanger; FIG. 4 represents a sectional view of six successive wave patterns according to the present invention, in which the left leg or the right leg of each wave is inclined such that each wave has a rectangular trapezoidal shape; Figure 5 is a view similar to that of Figure 3, but in the case of the wavebands of Figure 4; Fig. 6 is a perspective view of the series of wave patterns of Fig. 4; FIG. 7 shows a variant of a wave of FIG. 4, 5 or 6, in which the inclined leg of the wave comprises an additional folding to create a vortex effect; FIG. 8 represents a series of 9 wavebands comprising trapezoidal waves with a right angle, and waves of this same type but further comprising a profile in steps; the same sequence is resumed after the eighth band. FIG. 9 represents a view similar to those of FIGS.

3 or 5, but implementing the sequence of wave patterns of Figure 8; and finally, Figure 10 also shows a series of 7 wave patterns, all in accordance with the present invention. In Figure 1, there is a whole series of separating plates

1 planes and parallels, delimiting superimposed levels of passage of fluids. Between each pair of adjacent separating plates 1, there are exchange wave bands 2 brazed to the separating plates 1. In general, a whole series of bars 3 installed around the periphery of the exchanger, and generally soldered to the sheets, seal the assembly. The pipe system 4 comprising cylindrical distribution boxes, and the design of the assembly are made so that at least 2 fluids can flow so that each fluid flows at different levels. Figure 2 shows the shape of a conventional partial shift wave, as well as the lateral shift of the successive wave patterns. The top 11 and lower surfaces 12 of a waveband are soldered to upper and lower separation plates 1, not shown. The general rectangular cross-sectional shape of the conventional partial offset wave can be observed, as well as in FIG. 3 the succession of leading edges encountered by a fluid during its circulation. Each wave also has two lateral surfaces 13 and 14 perpendicular to the separation plates 1. The legs 13 and 14 of the waves are perpendicular to the separation plates 1 and the wavebands are shifted at regular intervals. FIG. 4 represents the modified profile of the waves according to the invention called type 1 waves. These have lost their rectangular shape, which has been modified to become a trapezoidal shape with right angles. On the band shown at the top of the drawing, it is observed that the right leg 14 is inclined at an angle α (alpha) at 45 ° with respect to the surface of the separating plates 1 not shown. The 45 ° angle corresponds to the opening angle of a leg, compared to the conventional rectangular shape of a conventional partial shift wave. The left leg is in its entirety perpendicular to the separation plates (angle α (alpha) equal to 90 °). It is observed that for successive wave bands, alternately the left leg and then the right leg is inclined to form, in cross section, a trapezium.

Figure 6 is a perspective view of such a sequence, wherein the wave band shown in the foreground corresponds to that shown at the top of Figure 4, and successively. In FIG. 5, it can be observed that when the fluid flows between two separator plates provided with such a succession of wavebands, the leading edges are not only perpendicular, as in the offset wavebands. classical partial, but also inclined in the model represented at 45 °. An increase of almost 15% of the surface secondary is thus obtained with respect to the serrated wave of the same height, thickness and density.

In Figure 7, it is observed that the inclined leg 14 of a wave of Figures 4, 5 and 6 includes an additional fold. Thus, the right leg 14 of the wave shown in Figure 7 consists of two plates 15 and 16. In addition, the folding between the strips 15 and 16 is not made parallel to the folding made between the strip 16 and the upper surface 11 or between the upper surface 11 and the leg 13. As a result, during the circulation of the fluid, a vortex effect is obtained. This type of modification has been called type 2. In FIG. 8, it can be observed that the wave patterns A, C, D, F and H are of type 1, whereas the wave patterns B, E and G are wave patterns of the same type, but in which the leg 13 perpendicular to the separating plates 1 comprises two folds which give this leg 13 a staircase profile thus comprising two portions perpendicular to the separating plates 1.

The leading edges encountered by the fluid during circulation between two separating plates 1 provided with such a succession of such wave patterns is shown in FIG. 9.

In FIG. 10, it can be observed that the waveband C comprises left and right lateral legs, each provided with an additional fold, such that each of the lateral legs comprises a portion perpendicular to the separating plates 1, and an inclined part. Such a leg is inclined without being perpendicular to the separation plates and at the same time has a portion perpendicular to the separation plates. Finally, in FIGS. 8 and 10, the dotted arrows represent the lines according to which successive wave legs are interconnected, thus enabling them to be manufactured from a flat sheet.

In the present invention, and in general, it will be advantageous to choose the profiles of the wavelength legs, as well as their sequences, so that the shaping of the wave is possible from a flat sheet both for the legs and for the legs. the upper and lower surfaces of the wavebands.

Claims

1. A wave band (2) for partial-shift-type brazed plate and fin exchangers comprising a series of zones for brazing on a first separating plate (1), a series of zones to be soldered on a second separating plate (1), adjacent to the first separating plate (1), and a series of legs (13, 14), said legs forming fins, characterized in that at least one of the legs (14) at least one wave is inclined, without being perpendicular to the separation plates (1), and in that at least one of the legs (13) comprises at least a portion perpendicular to the separation plates (1).

2. A waveband according to claim 1, characterized in that at least one of the legs (14) of a wave is inclined at an angle of 43 ° to 80 °.

3. A waveband according to claim 1 or 2, characterized in that at least 60% of the waves have at least one of their legs (14) which is inclined.

4. A waveband according to one of claims 1 to 3, characterized in that only one leg (14) of a wave is inclined.

5. A waveband according to one of claims 1 to 4, characterized in that the inclined leg (14) of a wave comprises an additional fold (15, 16).

A waveband according to claim 5, characterized in that the waves are formed by folding plates and that the additional folding (15, 16) is not made parallel to the general direction of folding the plates. forming the waves.

7. A waveband according to one of claims 1 to 6, characterized in that the same wave comprises an inclined leg (14) and a vertical leg having an inclined zone.

8. A waveband according to one of claims 1 to 7, characterized in that bends are provided on a leg of at least one wave to form at least one step.

9. A waveband according to one of claims 1 to 8, characterized in that different bends are combined with each other on the same wave or on the waves of the same waveband.

10. A brazed plate or fin exchanger comprising waves as defined in one of claims 1 to 9.