WO2008034749A1

WO2008034749A1 - Heat exchanger and method for producing a heat exchange element for such a heat exchanger

Info

Publication number: WO2008034749A1
Application number: PCT/EP2007/059576
Authority: WO
Inventors: Herveline Robidou; Fabien Chauvet; Yuji Yamamoto; Sylvain Moreau; Bruno Berthome
Original assignee: Valeo Systemes Thermiques
Priority date: 2006-09-19
Filing date: 2007-09-12
Publication date: 2008-03-27
Also published as: EP2064508A1; JP2010503818A; FR2906018A1; FR2906018B1

Abstract

Heat exchanger comprising at least one tube (10, 10') for the circulation of a first fluid in a given direction (F1), and at least one heat exchange element (20) in the form of a corrugated surface, with generatrices substantially perpendicular to the direction (F1) in which the first fluid is circulated, said generatrices defining a direction (F2) of circulation of a second fluid inside the heat exchange element (20). According to the invention, the corrugated surface that forms the heat exchange element (20) at least partially exhibits a plurality of holes (21) arranged in a lattice structure. Application to motor vehicle engine cooling radiators, heater matrixes and air conditioning evaporators.

Description

HEAT EXCHANGER AND METHOD OF MAKING HEAT EXCHANGE ELEMENT FOR SUCH A HEAT EXCHANGER

The present invention relates to a heat exchanger. The invention finds a particularly advantageous application in the field of heat exchange systems inside motor vehicles, including engine cooling radiators, cabin heating radiators and air conditioning evaporators.

In the automotive industry, heat exchangers are known which comprise a series of tubes for circulating a first fluid, arranged parallel to one another. These tubes can be constituted by tubes placed side by side in the same plane. Exchangers are also known whose tubes consist of plates.

In general, said first fluid must exchange heat with a second fluid through a heat exchange device.

By way of example, the first fluid considered here may be water containing glycol for cooling the engine and which must itself be cooled by air constituting the second fluid. The first fluid may also be a heat transfer fluid of an air conditioning system, such as freon, for cooling a second fluid constituted by the air circulating in the passenger compartment of a vehicle.

A known heat exchange device between the first and second fluids comprises a plurality of heat exchange elements, also called spacers, each heat exchange element being disposed between two consecutive tubes. These spacer elements are generally made by shaping a sheet of a heat conducting material, such as aluminum, into a corrugated surface in thermal contact with said circulation tubes at the level of the generatrices located at the apices of the corrugations of the surface. . The thermal contact is obtained by brazing the intermediate elements on the tubes or plates mentioned above.

The intermediate elements are arranged in the heat exchanger so that the generatrices of the corrugated surface are substantially perpendicular to the flow direction of the first fluid, the flow direction of the second fluid inside the intermediate elements being substantially parallel to said generators. In order to promote thermal exchanges in the intermediate elements, the sides of the corrugated surface constituting the intermediate elements are provided with slots transverse to the generatrices, affecting the shape of louvers whose orientation is variable in blocks along the generatrices, a block of n slots of a certain orientation being followed by another set of n slots of opposite orientation. The result of this arrangement is to impose the second fluid wave circulation in the direction of flow, the louvers to lengthen the path of said second fluid by creating obstacles in its path, When the proposed heat exchanger is an evaporator, there is the problem of the condensation of the water vapor contained in the air, which then constitutes the second fluid. Indeed, the air flowing along the intermediate elements is in contact with the first fluid, hypothesized colder, and therefore cools as it flows until its temperature drops below the temperature dew of water vapor. At this moment, the water vapor condenses to form drops which are deposited on the intermediate elements. However, even with slot spacers, as described above, gravity evacuation of the condensates is not effected effectively. As a result, the condensed water retained in the intermediate elements limits the passage of air and creates an additional pressure drop. The pressure drop of air between the inlet and the outlet of the spacers increases, which then forces to use blowers, or fans, more powerful. It was thus possible to measure that the pressure drop can increase by 40% with moist air. Also, an object of the invention is to propose a heat exchanger comprising at least one tube for circulating a first fluid in a given direction, and at least one wave-shaped heat exchange element, generators substantially perpendicular to the direction of flow of the first fluid, said generators defining a direction of circulation of a second fluid inside the heat exchange element, which would provide a good evacuation of condensates while ensuring the creation of a favorable regime for thermal exchanges, as explained above. In accordance with the invention, the aim is achieved by the fact that the corrugated surface forming the heat exchange element has at least partially a plurality of holes arranged in a grid structure.

The term "tube" for the circulation of a first fluid means any element or means making it possible to form at least one circulation duct for a fluid.

Thus, as said grid structure comprises a very large number of holes, gravity flow of the condensed water out of the exchanger is favored, which contributes to increasing the drainage capacity of the condensates and thus to limiting the fall of air pressure in the direction parallel to the intercalated heat exchange elements. On the other hand, the presence of said holes allows the air to cross the surface of the intermediate elements and thus to circulate from one intermediate element to another, thus promoting the formation of the desired turbulent regime. In addition, the heat exchanger according to the invention has many other advantages.

In particular, the geometry of the intercalated heat exchange elements can be perfectly adapted to the desired performances.

This concerns in particular the pitch of the corrugations of the spacers which can be reduced thanks to the mechanical flexibility of the grid structure. As a result, the heat exchange surface between the second fluid and the spacers remains at least equivalent to that of traditional exchangers, this despite the presence of holes, which have the advantage of promoting the drainage of condensates. Other dimensional characteristics may also be adjusted, such as the pitch of the spacers which can be reduced to very small values, from 0.2 to 1.5 mm and preferably from 0.2 to 1 mm, which is not necessary. is not possible with louvered dividers, as well as the height of the spacer elements which can be between 3 and 7 mm. Preferably, the height will be less than 5 mm, and typically between 3 and 5 mm, without knowing the efficiency losses encountered with the slotted louvers, the latter being able to be formed for mechanical reasons only on a part of the flank of the corrugations and not on all, unlike the invention for which the holes of the grid can occupy the entire surface of the spacers. It has been shown that the heat exchangers produced according to the invention can increase by 18% the heat transfer coefficient at low air circulation speeds, this increase being even higher, up to 44%, for Finally, another advantage of the invention lies in the fact that the greater drainage capacity obtained avoids the phenomenon of splashing which occurs with conventional evaporators when the air flow entering the spacers increases abruptly, which results in the entrainment of drops of water inside the cabin. In order to provide a sufficient heat exchange surface between the spacers and the flow tube of the first fluid, the invention provides that said corrugated surface is free from holes on at least one defined band along a generator in contact with the first fluid. said tube for circulating the first fluid. On the other hand, a method of producing a heat exchange element for a heat exchanger according to the invention is remarkable in that said method comprises the following steps:

perforating a sheet of a heat conducting material in a set of parallel slots arranged according to said grid structure, stretching the metal sheet perpendicularly to the slots,

- To conform the stretched metal sheet into a corrugated surface.

It is understood that this method of production is simpler and less expensive than that to obtain interlayers slotted louvers. Advantageously, at least one sheet strip parallel to said slots is spared, the corrugated surface conformation being formed around said strip,

Finally, it is provided by the invention that said heat-conducting material is aluminum. The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the process consists of. invention and how it can be achieved.

Figure 1 is a side view of a tube heat exchanger according to the invention. Figure 2 is a perspective view of a pecan heat exchanger according to the invention.

FIG. 3 is a perspective view of a heat exchange element of the exchangers of FIGS. 1 and 2. FIG. 4 is a diagram giving the increase of the pressure drop due to the condensates as a function of the frontal speed of air circulation of an evaporator, (1) for inserts according to the invention and (2) for the spacers of the prior art.

FIG. 5 is a diagram giving the variations of the heat transfer coefficient, (1) for inserts according to the invention and (2) for the inserts of the prior art.

FIG. 6 is a diagram showing the steps of a method for producing the heat exchange element of FIG. 3.

FIG. 7 shows a variant of punched metal foil for implementing the method according to the invention.

FIG. 8 represents a schematic and partial view of the heat exchange element in which are detailed various parameters of a cell of said heat element according to a particular embodiment of the invention. In Figure 1 is shown a tube-type heat exchanger comprising a plurality of tubes 10 for circulating a first fluid, the tubes 10 are arranged side by side perpendicular to the plane of the figure. Said first fluid circulates for example in the direction of arrow F1.

FIG. 2 shows a variant of the exchanger of FIG. 1 in which the tubes 10 'of circulation are here in the form of plates 11' arranged parallel to one another

FIGS. 1 and 2 show that between two tubes 10, 10 'there is placed a heat exchange element 20 intended to allow the first fluid to exchange heat with a second fluid circulating in the elements 20 in which the direction of arrow F2.

In the case where the heat exchanger in question is a motor vehicle engine radiator, the first fluid is glycol-added water cooled by the second fluid which is then air. In the case of an air-conditioning evaporator, the first fluid is freon charged with cooling. [e second fluid, namely the air circulating in the passenger compartment of a motor vehicle.

Whatever the constitution of the tubes and the destination of the heat exchanger, the intermediate elements 20 have the shape, shown in FIG. 3, of a corrugated surface whose direction of the generatrices, which is also that of the circulation of the heat exchanger. second fluid, is substantially perpendicular to the flow direction of the first fluid.

In other words, the intermediate elements 20 comprise corrugations having aernernance of vertices 22 and recesses 23 brazed to the tubes. The vertices 22 and the recesses 23 are connected by means of plane zones

24. The vertices 22 and the recesses 23 are thus parallel to the transverse axis AT of the tubes 10 or 10 '.

The orientation of the intermediate elements 20, that is to say the fact that the vertices 22 and the recesses 23 are parallel to the transverse axis AT of the tubes 10 or 10 ', allows for losses of load equivalent to the losses of louvers interlayers of the prior art.

It can also be seen in Figure 3 that the surface of the spacer element 20 has a plurality of holes 21 arranged in a grid structure. Thus and unlike the spacers provided with louvers of the prior art, no element exceeds planar zones 24. In other words, the plurality of holes 21 allows the definition of a grid at least at the level of the flat zone 24, the maiϋage said grilies being entirely included in the plane of the planar zone 24. In other words, the mesh of the grid allows the definition of cells. As explained above, this type of spacer element has the advantage of creating in the second fluid a more favorable regime for heat exchange.

In addition, in the case of an evaporator, the multiplicity of holes allows efficient drainage of water from the condensation of water vapor contained in the air flowing along the spacers. The pressure drop of the air between the inlet and the outlet of the spacers is diminished and maintained substantially constant with respect to the slotted interleaves, as can be seen in FIG. 4.

Furthermore, the grid structure gives the interlayers 20 a mechanical flexibility to tighten ripples and therefore to increase the developed surface of the spacers. It is thus possible to compensate the losses in terms of heat exchange due to the presence of the holes. FIG. 5 shows that a better heat transfer coefficient can be obtained with the inserts according to the invention than with conventional inserts with louvered slots.

The dimensions of the holes of the grill are chosen according to the final performances sought. The pitch between each hole or cell 21 may be between 0.5 and 3 mm. In other words, this pitch between each hole corresponds to the material separating two adjacent holes or cells. The pitch of the intermediate element 20 is between 0.2 to 1.5 mm and preferably between 0.2 and 1 mm, and especially between 0.4 and 0.9 mm or between 0.5 and 0.8. mm.

The height of the intermediate element 20 is between 2.5 and 8 mm and preferably between 3 and 7 mm. Preferably, the height will be less than 5 mm and preferably between 3 and 5 mm.

Figure 6 illustrates the steps of a method of making the heat exchange elements according to the invention.

An aluminum foil with a thickness of in particular between 0.04 and 0.1 mm is cut (a), then perforated (b) to obtain a network of slots arranged according to the desired grid structure, and finally stretched (c) over a distance that depends on the desired height for the holes. The sheet is then shaped into corrugations to obtain the interlayer 20 of FIG.

One embodiment provides that the blank (a) described above is made. after the perforation (b) and stretching (c) steps.

FIG. 7 illustrates a variant of the method of FIG. 6 in which strips 22 of the aluminum foil are spared during perforation of the slots. These hole-free strips are intended to improve the thermal contact between the spacers and the tubes or plates of the exchanger, as well as to serve as brazing surfaces. The conformation of the corrugated surface sheet is performed around each of the strips 22.

FIG. 8 shows a particular embodiment of an intermediate element 20. In this embodiment, the grid structure of the intermediate element 20 is formed by a plurality of cells 30 which here have a quadrilateral shape and in particular of rhombus. The dimensions of the cells can be defined in particular by two diagonals a and b which are perpendicular to each other. According to a particular embodiment, the length of the diagonal has a long diagonal is between 0.8 and 3.3 mm and preferably between 1 and 2.8 mm. According to another particular embodiment, the length of the diagonal b said small diagonal is between 0.7 and 2 mm and preferably between 1 and 1, 8 mm.

The cells thus comprise four sides or branches. These sides are formed by a strip of material which, according to one embodiment, has a width of between 0.11 and 0.45 mm and preferably between 0.15 and 0.35 mm.

Claims

1. Heat exchanger comprising at least one tube (10, 10 ') for circulating a first fluid in a given direction (F1), and at least one wave-shaped heat exchange element (20), of generatrices substantially perpendicular to the direction (F1) of circulation of the first fluid, the generatrices defining a direction (F2) of circulation of a second fluid inside the element (20) of heat exchange, characterized in the corrugated surface forming the heat exchange element (20) has at least partially a plurality of holes (21) arranged in a grid structure,

2, exchanger according to claim 1, wherein the pitch of the heat exchange element (20) is between 0.2 to 1 mm.

3. Exchanger according to claim 1 or 2, wherein the height of the intermediate element (20) is between 3 and 7 mm.

4. Heat exchanger according to one of the preceding claims, wherein IΘ not between each hole (21) is between 0.5 and 3 mm.

5, heat exchanger according to one of the preceding claims, wherein said corrugated surface is free from holes on at least one strip (22) defined along a generatrix in contact with the tube (10, 10 ') of circulation of first fluid.

6, heat exchanger according to one of the preceding claims, wherein the element (20) of heat exchange is aluminum.

7. A method of producing a heat exchange element for a heat exchanger according to one of the preceding claims, characterized in that said method comprises the following steps;

perforating a sheet of heat-conducting material into a set of parallel slots arranged according to said grid structure,

stretching the metal sheet perpendicular to the slits,

- To conform the stretched metal sheet into a corrugated surface.

8. Method according to the preceding claim, wherein at least one strip (22) of sheet parallel to said slots is spared, the corrugated surface conformation being formed around said strip (22).

The method of one of claims 7 or 8, wherein said heat conductive material is aluminum.