Patent Application
20110035942
The present invention relates to a method for producing a plate heat exchanger, and a plate heat exchanger produced on the basis of such a method of production.
Plate heat exchangers usually consist of a stack of plates defining passages for fluids.
In order to improve the heat exchange between the fluids, corrugated sheets, known as fins, may be sandwiched between said plates to form the heat exchanger. The resulting passages are closed at the sides by side bars. Having been put together in this way, the heat exchanger is then brazed to make the assembly rigid and ensure better thermal contact.
Plate heat exchangers can be made of aluminum or an aluminum alloy for good thermal conductivity and good mechanical strength.
Prior art heat exchangers, as described for example in FR-A-2 815 895 are capable of exchanging heat from many fluids, for example more than 5 fluids. The heat exchange fins, which are usually used, have both a thermal function of increasing heat exchange surface area and improving the thermal efficiency of the exchanger, and a mechanical function of maintaining the mechanical integrity of the heat exchanger during the brazing and preventing flexing of the passages. Thus it can happen that mechanical integrity is the determining aspect of the assembly. In particular, the fin is then no longer optimized thermally.
It is therefore known practice to replace said heat exchange fins with an improved coating on the separating plates. In some cases it can also be helpful to reduce the density of the fin, or even remove it completely to avoid masking the improved surface area of the plate with said fin.
It would therefore be advantageous to develop a method for producing a heat exchanger that makes it possible to maintain the mechanical integrity of said exchanger during the brazing step.
The object of the invention is to provide, particularly for the manufacture of plate heat exchangers, a method for producing said exchanger that is easy to carry out and maintains good mechanical integrity of said exchanger during the brazing step.
The invention thus provides a method for producing a plate heat exchanger of the type comprising a plurality of plates defining, with side bars arranged on the plates, paths for the flow of fluids, comprising at least the following successive steps:
a stack of a plurality of plates separated by side bars is provided, at least two of which plates are separated by side bars by a separation e;
at least one removable spacer piece is provided, comprising two first extremities spaced apart by a distance approximately equal to or greater than e and two second extremities spaced apart by a distance smaller than or approximately equal to e, the spacer piece being shaped in such a way as to permit a rotation between two plates spaced apart by a separation e about a longitudinal axis situated in the middle of the line joining said extremities;
said removable spacer piece is introduced between said plates which are spaced apart by a separation e in such a way as to present the thickness equal to the distance between the two second extremities so that said second extremities do not contact said plates simultaneously;
said removable spacer piece is rotated about said longitudinal axis in such a way that said first extremities of said removable spacer piece contact said plates;
said heat exchanger is brazed; and
said removable spacer piece is removed.
Advantageously, the introduction of at least one removable spacer piece between the two plates maintains sufficient mechanical integrity during brazing and/or handling of said heat exchanger.
Consequently, the removable spacer pieces are all withdrawn after the brazing step, thus vacating the space in the fluid flow path.
The introduction of the spacer piece between the preassembled plates offers a simple method: there is no need to position the spacer piece or pieces while stacking together the plates that will make up the exchanger because the spacer piece or pieces can be introduced in a subsequent step. The spacer piece or pieces are introduced without damaging the stack of plates separated by the side bars, and are easy to position by rotating them between the plates.
A method according to the invention may also involve one or more of the following optional features, considered individually or in any possible combination:
before the step in which the removable spacer piece is removed, the method includes a step in which said removable spacer piece is rotated about the longitudinal axis in such a way that the extremities of said removable spacer piece no longer contact the plates simultaneously;
the removable spacer piece is of essentially constant cross section along said longitudinal axis of the spacer piece and in that this cross section is essentially in the shape of a polygon, two points of said polygon forming the first extremities spaced apart by a distance approximately equal to e;
the polygon is a lozenge, of which one diagonal has approximately a length e and the other diagonal a length less than e;
the polygon is a hexagon with two parallel main sides and four small segments connected in pairs so that each forms a point at each extremity of the main sides; the distance between said points being approximately equal to or greater than e;
the removable spacer piece is of essentially constant cross section along the longitudinal axis of the spacer piece and this cross section is of essentially elliptical shape, the two extremities of the major axis of the ellipse forming the extremities which are spaced apart by a distance approximately equal to e;
a step in which the removable spacer piece is selected in such a way that it is made of one or more materials whose melting point is 900° C. or above.
A clearer understanding of the invention will be gained from reading the following description which is given purely by way of example.
For the purposes of the invention, “removable spacer piece” means a spacer piece which, after the step of brazing the exchanger, can be removed and reused without structural modification in another method of production according to the invention.
A method of production according to the invention can include the following successive steps:
a) said plate heat exchanger is assembled,
b) a plurality of removable spacer pieces is selected,
c) at least one removable spacer piece, preferably several, is or are introduced between the plates of said preassembled heat exchanger,
d) said heat exchanger is brazed,
e) said removable spacer pieces are removed from between the plates of the brazed heat exchanger.
The steps of assembly a) and brazing d) are well known to those skilled in the art. The brazing is done by introducing the exchanger into a furnace heated to a temperature suitable for carrying out brazing, for example 600° C.
Three embodiments of a spacer piece according to the invention are described below as non-restrictive examples.
In a first embodiment, in step b), a plurality of removable spacer pieces is selected whose cross section is approximately constant along their main axis and said cross section is lozenge-shaped.
“Lozenge” here means any simple polygon with four equilateral sides.
In this first embodiment, each spacer piece is selected in such a way that the long diagonal of its cross section has a length greater than or equal to the distance between the plates of the heat exchanger between which said spacer piece is intended to be introduced, and the short diagonal of its cross section has a length less than or equal to the distance between the plates of the heat exchanger between which said spacer piece is intended to be introduced.
Advantageously, the selection of such a spacer piece allows it to be placed between two plates of the exchanger in such a way that the area of contact between said spacer piece and the plate is less than or equal to 15% of the total surface area of said spacer piece, preferably less than or equal to 5% of the total surface area of said spacer piece.
The smaller the contact area between the spacer piece and the plates, between which said spacer piece is introduced, the less the risk of said spacer piece being welded to said plates during the brazing step.
In this first embodiment, the selected spacer pieces are placed between the plates of a preassembled heat exchanger.
This step of putting the spacer pieces in position may comprise two sub-steps. In the first, each spacer piece may be introduced between two plates with an orientation such that the long diagonal of the cross section of said spacer piece lies in a plane approximately parallel to the plane defined by the plates.
Advantageously, since the spacer piece has been selected in such a way that the short diagonal of its cross section has a length less than or equal to the distance between the plates of the heat exchanger between which said spacer piece is intended to be introduced, said spacer piece can be introduced without difficulty between the two plates.
In the second sub-step, once said spacer piece has been introduced between two plates of the exchanger, the spacer piece can be pivoted about its main axis so that the spacer piece is pushing against both plates.
Advantageously, in this position, the spacer piece maintains good mechanical integrity of the heat exchanger during the brazing step.
Also in this first embodiment, the method includes a step after the brazing step in which the removable spacer piece or pieces is or are removed from between the plates of the brazed heat exchanger.
Advantageously, the selected spacer pieces are not welded to the plates in the course of the brazing step, owing in particular to the fact that the contact area between said spacer piece and the plates is small.
In this first embodiment, each removable spacer piece can be removed by pivoting it about its main axis in such a way as to orient it such that the long diagonal of its cross section is in a plane approximately parallel to the plates.
Advantageously, this simplifies the step of removing the spacer pieces.
In a second embodiment, the cross section of the removable spacer piece is in the shape of a hexagon with two main sides, parallel to each other, forming the longer sides, and four short sides whose length is less than that of the long sides. The short sides each start at one end of a long side and meet in pairs to form a first extremity in the form of a point. The distance between the two first extremities in the form of points is greater than or equal to e while the distance between the two main sides forming the two second extremities is less than e.
In a third embodiment, in step b) a plurality of removable spacer pieces is selected, having an approximately constant cross section along their main axis and said cross section is in the form of an ellipse.
In this third embodiment, each spacer piece is selected so that the major axis of its cross section has a length greater than or equal to the distance between the exchanger plates between which said spacer piece is intended to be introduced and the minor axis of its cross section has a length less than or equal to the distance between the exchanger plates between which said spacer piece is intended to be introduced.
Selecting such a spacer piece has similar advantages to the first embodiment described. In particular, the contact area of said spacer piece, once positioned between the plates, can be less than or equal to 15% of the total surface area of the spacer piece, preferably less than or equal to 5% of the total surface area of said spacer piece.
The spacer pieces selected in a method according to the invention are preferably made of one or more materials whose melting point is above the brazing temperature, for example 900° C. or above, or even 1500° C. or above.
The selected spacer pieces may for example be made of stainless steel.
A method according to the invention can also include a step in which the selected spacer pieces are coated with a product that prevents or limits brazing during the brazing phase.
Advantageously, the use of such a product facilitates the step of removing the spacer pieces.
The invention is not limited to the embodiments described and should be interpreted without restriction so as to encompass any equivalent embodiment. In particular, the invention is applicable to any type of plate heat exchanger assembled by brazing. In particular, the method according to the invention can be carried out with spacer pieces having cross sections different from those of the embodiments described, such as other polygonal cross sections.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0852843 | Apr 2008 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR09/50757 | 4/24/2009 | WO | 00 | 10/18/2010 |
