Patent Application
20090120617
The present invention relates to a tube for a heat exchanger.
The invention has a particularly advantageous application in the field of flat tube heat exchangers. These exchangers are notably used as evaporators, condensers or forced air heaters in an air conditioning system of a motor vehicle, or as a radiator in the cooling circuit of such a vehicle.
Flat tube heat exchangers for motor vehicles are generally constituted by an array of flat tubes disposed parallel with each other in one or more rows, these tubes being intended for the circulation through the exchanger of a heat transfer fluid, such as water with added glycol in the case of radiators of engine cooling circuits. In cooling the devices of the engine, the water heats up and must in its turn be cooled. It is the role of the radiator to provide this function. For this purpose, the water with added glycol is circulated in the tubes of the radiator and is cooled by heat exchange with cool air coming from a propelling device, or fan, the heat exchange being favored by the presence of heat exchange elements disposed in the array of tubes. In the case of a forced air heater, the thermal energy dissipated in the air is retrieved in order to heat the passenger compartment of a motor vehicle via a ventilation, heating and/or air conditioning system which is known per se.
According to the heat exchanger assembly technology known as “by brazing”, the tubes are brazed onto heat exchange elements constituted by spacers or fins placed between the tubes. In general, these spacers are produced in the form of an undulating surface, the tubes being brazed onto the spacers at the peaks of the undulations. The assembly of the tubes and the spacers thus assembled by brazing is capped at each end by a collector box connected by pipes to the rest of the circuit.
The flat tubes can be obtained by various techniques, like extrusion, mechanized welding or folding. The invention applies to this latter technique in which each flat tube is produced by folding a metal sheet called a strip in order to define a circulation duct for the heat transfer fluid, water in this instance. The strip is constituted from a base material otherwise called the core, generally an aluminum alloy.
The international application No WO 03/046456 proposes in particular a flat tube with a separating partition, produced from a strip of which one end has been shaped such that the separating partition obtained after folding the strip has a curvilinear profile, substantially semicircular in shape.
However, despite all the advantages which it procures, the flat tube known from the international application No WO 03/046456 nevertheless has the disadvantage of offering only a low mechanical resistance to the inflation of the tube resulting from the pressure applied by the heat transfer fluid. In fact, its curvilinear arc-of-circle shape provides the separating partition with a certain flexibility favoring its opening up and therefore the inflation of the tube under the action of hydraulic pressure.
The opening up of the separating partition has the consequence of creating an asymmetry between the two circulation channels situated on either side of the partition, whereas the hydraulic cross-sections of the channels must be equal and remain so no matter what the operating phase of the heat exchanger may be.
Moreover, the inflation of the tube under pressure generates mechanical stresses at several places, notably along the radii of the tube and on the longitudinal weld at the junction between the two folded parts of the tube.
Finally, the repeated inflation/rest cycles accelerate the fatigue of the materials constituting the tube.
All of these phenomena consecutive to the inflation of the flat tube weaken the mechanical strength of the heat exchanger and lead to the appearance of leaks.
Therefore, one objective of the invention is to propose a tube for a heat exchanger which would make it possible to avoid the disadvantages related to the inflation under pressure of the tube described in the abovementioned international application, whilst retaining the advantages of this tube, such as being free of dimensional tolerance constraints in the width of the strip and/or the cladding with a brazing material on just one of the two faces of the core.
This objective is achieved, according to the invention, by means of a tube for a heat exchanger produced by folding a strip, one end of said strip being shaped in such a way as to constitute, after folding, a separating partition having a curvilinear profile, noteworthy in that said curvilinear profile is a looped profile, said separating partition being closed on itself. This feature is explained by the fact that the edge of the strip used in the separating partition is sandwiched in a U-shaped fold, which makes it possible to put the cladding in contact with the inside surface of the tube having no cladding and thus to widen the brazing in order to achieve a high level of resistance to inflation.
Thus, as will be seen in detail below, it is possible, with the looped curvilinear profile conferred by the invention on the separating partition, to carry out a first brazing of the partition on the inside surface of the tube in combination with a second brazing of the free end of the partition on itself. Because the invention prohibits by this fact any possibility of opening the partition, the mechanical resistance of the latter to inflation of the tube is thereby considerably increased.
It will be noted that this result is obtained whilst retaining the advantage of not having to clad both faces of the strip with brazing material. One clad face suffices for the implementation of the invention, the other face being able to receive a material limiting the corrosion on the inside surface of the tube.
According to one embodiment of the invention, said looped curvilinear profile comprises a first part of loop and a second part of loop ending inside the first part of loop.
In this particular embodiment, the invention makes provision for said first and second parts of loop to have substantially an arc-of-circle shape in which the thickness of the strip is constant.
If an internal thickness of the tube is fixed in such a way as to impose a given hydraulic cross-section on the circulation channels, the dimensional characteristics of the separating partition must be adjusted accordingly.
The invention therefore provides for said separating partition to have along said loop a thickness less than the thickness of the tube, or again for said separating partition to have a first thickness less than the thickness of the tube over the first part of loop, and a second thickness less than the first thickness over the second part of loop.
The following description given with reference to the appended drawings, given as non-limiting examples, will give a good understanding of what the invention consists of and of how it can be embodied and will participate, if necessary, in the definition of the latter.
a is a partial cross-sectional view of a strip according to a first embodiment of the invention.
b is a partial cross-sectional view of a strip according to a second embodiment of the invention.
In
The tube 10 is obtained by shaping and folding a strip 11 produced from a base material, or core material, which is generally an aluminum alloy chosen from the series referenced 1xxx, 3xxx, 6xxx and 7xxx and whose melting temperature is between 630 and 660° C.
Before shaping and folding, the strip 11 receives, on a first face 111 which after folding constitutes the outside surface of the tube 10, a layer 21 of added material or cladding material, often call a “clad”, constituted by an aluminum alloy of the series 4xxx whose melting temperature is higher than 577° C. and lower than the melting temperature of the core metal. This layer 21 represents the actual brazing layer which, by melting the added material in a furnace, will provide the mechanical holding together of the heat exchanger whose components, flat tubes and spacers in particular, are previously assembled. This brazing layer 21 is shown in bold line in the figures.
On a second face 112 of the strip 11, that is to say the inside surface of the tube 10 after folding which delimits the internal volume of the tube, there is deposited a layer 22 of a material making it possible to reduce the speed of propagation of corrosion through the core metal of the strip 11. This material, notably based on aluminum and silicon, has a melting temperature higher than that of the brazing material or “clad”. This protective layer 22 is shown in dotted line in the figures.
As can be seen in
The separating partition 12 is closed upon itself in a looped curvilinear profile comprising a first part 12a of loop substantially having an arc-of-circle shape and a second part 12b of loop also substantially having an arc-of-circle shape ending inside the first part 12a of loop. The arcs of circle have a curvature of about 180°.
It is therefore possible to braze the partition 12 in two zones, namely a first zone centered about the point A where the partition is brazed on the inside surface 112 of the tube 10, and a second zone centered about the point B where the partition is brazed at the end of the second part 12b of loop onto the inside surface of the first part 12a of loop.
Starting from the outside surface of the tube, the separating partition comprises a first fold 41 at 45° towards the inside of the tube (clockwise direction) followed by a first flat section 42 and then a second fold 43 at 45° turned towards the outside of the tube (anticlockwise direction), after which there is a second flat section 44 which receives the edge of the strip not used in the separating partition. This second flat section 44 is an element of the first part of loop 12a turned through 180° towards the inside of the tube, followed by a third flat section 45 whose outside surface makes contact with the inside surface of the tube. This third flat section 45 is common to the first and to the second parts of loop 12a and 12b. The profile of the separating partition continues by the curvature of the second part of loop 12b turned through 180° towards the inside of the tube (clockwise direction) and ends at the edge of the strip 46 sandwiched between the second flat section 44 and the third flat section 45.
In this way there is obtained a very rigid separating partition 12 capable of resisting the pressure applied by the heat transfer fluid and therefore of opposing any inflation of the tube 10, notably by the opening of the profile of the partition, such as occurs for the known tube of the prior art. The hydraulic cross-section of the channels 31, 32 is maintained and no transmission of stress to other elements of the tube occurs.
If the hydraulic cross-section of the channels 31, 32 is fixed, the latter can be obtained by adjusting the thicknesses of the partition 12 over the first 12a and second 12b parts of loop.
According to a first embodiment, the partition 12 can have a constant thickness e2 along the loop (or the edge of the strip), this thickness being less than the thickness e1 of the tube 10. In this case, as shown in
According to a second embodiment, which is shown in
The thickness values are:
0.1 mm≦e1 ≦0.4 mm
0.05 mm≦e2 ≦0.4 mm
0.05 mm≦e3 ≦0.4 mm
If the hydraulic cross-section of the channels 31 and 32 is not fixed, then e1=e2=e3.
If the hydraulic cross-section of the channels 31 and 32 is fixed or imposed, then the thicknesses are adjusted as follows:
e
3
=e
2
<e
1 first embodiment
e
3
<e
2
<e
1. second embodiment
| Number | Date | Country | Kind |
|---|---|---|---|
| FR 07/07650 | Oct 2007 | FR | national |
