US20110036548A1

US20110036548A1 - Method Of Manufacturing A Plate-Type Heat Exchanger Using A Set Of Spacer Blocks

Info

Publication number: US20110036548A1
Application number: US12/989,221
Authority: US
Inventors: Frederic Crayssac; Sophie Deschodt; Jean-Pierre Tranier; Marc Wagner
Original assignee: 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: 2008-04-28
Filing date: 2009-04-08
Publication date: 2011-02-17
Also published as: WO2009136079A3; FR2930465A1; WO2009136079A2; EP2271456A2; FR2930465B1; JP2011519015A; ATE541663T1; EP2271456B1; CN102015183A

Abstract

A method of manufacturing a plate heat exchanger of the type comprising a plurality of plates defining paths for fluids to flow through, the plates being assembled to each other by brazing, and a heat exchanger produced by such a method is presented.

Description

The present invention relates to a method of manufacturing a plate heat exchanger of the type comprising a plurality of plates defining paths for fluids to flow through, the plates being assembled to each other by brazing, and a heat exchanger produced by such a method.
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 heat exchange fins, may be sandwiched between said plates that 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 integrity.
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 buckling 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 and that is easy to implement.
It is an object of the present invention to provide such a method of manufacture.
The invention provides a method of manufacturing a plate heat exchanger of the type comprising a plurality of plates which, together with side bars arranged on the plates, define paths for fluids to flow through, comprises at least the following successive steps:

- a stack of a plurality of plates separated by side bars is provided,
- at least one removable set of spacer blocks consisting of at least two spacer blocks, connected together by at least one connecting element, is introduced between plates of said heat exchanger,
- said heat exchanger is brazed, and
- the removable set of spacer blocks is removed
  said method being characterized in that the connecting element is shaped in such a way as to allow a rotary movement of the set of spacer blocks about the main axis of each of said spacer blocks, each spacer block having an essentially constant cross section along its main axis, and in that after the introduction step, a rotary movement is applied to all the spacer blocks of said set about their main axes, in such a way as to press each spacer block against said plates;
  after the brazing step, a rotary movement is applied to all the spacer blocks of said set about their main axes, in such a way as to release said spacer blocks and in which said removable set of spacer blocks is selected in such a way that either

i)

- said cross section is essentially polygonal in shape, and
- the length of at least one of the main diagonals of said cross section is greater than or equal to the distance between the plates of the heat exchanger between which said spacer block is intended to be introduced;
- or

ii)

- said cross section is essentially elliptical in shape, and
- the length of the major axis of said cross section is greater than or equal to the distance between the plates of the heat exchanger between which said spacer block is intended to be introduced.

Advantageously, the method according to the invention makes it possible to introduce and remove a plurality of spacer blocks between the plates of the heat exchanger easily and quickly.
As a consequence, the removable set of spacer blocks is withdrawn after the brazing step, thus freeing up space in the fluid flow path.
Introducing a removable set of spacer blocks connected together by a connecting element simplifies the method, as it can be tedious work introducing and later removing the spacer blocks individually.
In addition, there is no need when carrying out a method according to the invention to position the spacer blocks while the plates of the exchanger are being stacked, because the spacer blocks can be introduced at a later stage.
A method according to the invention may also include one or more of the optional features set out below, taken individually or in all possible combinations:

- a plurality of removable sets of spacer blocks, which are fixed together by fixing means, are introduced;
- a single removable set of spacer blocks is introduced between two plates of said heat exchanger;
- the method includes a step in which at least one removable set of spacer blocks is selected, in which the connecting element is shaped in such a way as to allow a rotary movement of the set of spacer blocks about the main axis of each of said spacer blocks;
- said removable set of spacer blocks is selected in such a way that:
  - each spacer block has an essentially constant cross section along its main axis,
  - said section being essentially polygonal in shape, and
  - the length of at least one of the main diagonals of said cross section is greater than or equal to the distance between the plates of the heat exchanger between which said spacer block is intended to be introduced;
- after the introduction step, a rotary movement is applied to all the spacer blocks of said set about their main axes, in such a way as to press each spacer block against said plates;
- after the brazing step, a rotary movement is applied to all the spacer blocks of said set about their main axes, in such a way as to release said spacer blocks;
- said removable set of spacer blocks is selected in such a way that:
  - each spacer block having a cross section essentially constant along its main axis,
  - said section being essentially elliptical in shape, and
  - the length of the major axis of said cross section being greater than or equal to the distance between the heat exchanger plates between which said spacer block is intended to be introduced,
- after the introduction step, a rotary movement is applied to all the spacer blocks of said set about their main axes, in such a way as to press each spacer block against said plates;
- after the brazing step, a rotary movement is applied to all the spacer blocks of said set about their main axes, so as to release said spacer blocks;
- the spacer blocks of said set of spacer blocks and the connecting elements that are selected are made of one or more materials whose melting point is 700° C. or above, preferably 900° C. or above (such as stainless steel);
- all the spacer blocks of said set have their main axes approximately parallel to each other.

The invention also relates to a plate-type heat exchanger of the type comprising a plurality of plates made of a brazable material, which exchanger is noteworthy in that it can be produced by the method according to the invention.
For the purposes of the invention, “removable set of spacer blocks” means a set of spacer blocks which, after the step of brazing the exchanger, can be removed and reused without requiring structural modification.
The invention consists in using a removable set of spacer blocks to mechanically support the heat exchanger during the brazing step. The reason for this is that, in order to improve the brazing step, it is known practice to apply pressure to the heat exchanger during said brazing step. The set of spacer blocks ensures that the plates forming the heat exchanger do not buckle under the pressure.
The use of a set of spacer blocks reduces the number of operations to be carried out during manufacture of the heat exchanger.
In a first embodiment of the invention, the method also includes a step in which the removable set of spacer blocks is selected in such a way that each spacer block is of essentially constant cross section along its main axis:

- said cross section being square in shape, and
- the length of the side of the square being equal to the distance between the heat exchanger plates between which said spacer block is intended to be introduced.

The spacer blocks of the selected set are connected together, for example by means of connecting bars distributed at regular intervals along the spacer blocks of the set. The connecting bars may be welded to the spacer blocks.
Advantageously, such a set is easy to use and makes it very easy to arrange a plurality of spacer blocks between two plates of the heat exchanger, since all that is required is to slide the set of spacer blocks between the plates of the exchanger.
After the brazing step, the set of spacer blocks can easily be removed, and this operation again is made easy by the connecting elements.
In one embodiment of the invention, the method also includes a step in which the removable set of spacer blocks is selected in such a way that:

- each spacer block has an essentially constant cross section along its main axis,
- said cross section being lozenge-shaped,
- the length of the long diagonal of said cross section is greater than or equal to the distance between the heat exchanger plates between which said spacer block is intended to be introduced, and
- the length of the short diagonal of said cross section is less than the distance between the heat exchanger plates between which said spacer block is intended to be introduced.

The word “lozenge” is used to mean any simple polygon with four equilateral sides.
The connection between the spacer blocks can be provided by connecting elements, connected to the spacer blocks, by welding for example.
The connecting elements may comprise a mechanical device such as a hinge, spring, drive, or rod that makes it possible to apply to all the spacer blocks a movement, e.g. a rotary movement about the main axis of each of the spacer blocks of the set of spacer blocks.
Advantageously, the selection of such a removable set of spacer blocks makes it possible to position the set of spacer blocks between at least two plates of the heat exchanger in such a way that the contact area of each of the spacer blocks with the plates is less than or equal to 15% of the total surface area of each spacer block, preferably less than or equal to 5% of the total surface area of each spacer block.
The smaller the contact area between each spacer block and the plates between which the spacer blocks are introduced, the less the risk that the spacer blocks will be welded to said plates during the brazing step. In this embodiment, the selected set of spacer blocks is positioned between the plates of a pre-assembled heat exchanger.
This step of putting the spacer blocks in position may comprise two sub-steps. In the first, each set of spacer blocks may be introduced between two plates with an orientation such that the long diagonal of the cross section of each spacer block lies in a plane approximately parallel to the plane defined by the plates.
Advantageously, since the set of spacer blocks has been selected in such a way that the short diagonal of the cross section of each spacer block has a length less than or equal to the distance between the plates of the heat exchanger between which the set of spacer blocks is intended to be introduced, each spacer block can be introduced without difficulty between the two plates.
In the second sub-step, once the set of spacer blocks has been introduced between the two plates of the exchanger, a movement can be applied, by means of the connecting element, to all of the spacer blocks, causing each spacer block to pivot about its main axis so that each spacer block is pushing against the two plates.
Advantageously, in this position, the set of spacer blocks maintains good mechanical integrity of the heat exchanger during the brazing step.
Also in this embodiment, the method includes a step after the brazing step in which the removable set of spacer blocks is removed from between the plates of the brazed heat exchanger.
Advantageously, the spacer blocks of the removable set of selected spacer blocks are not welded to the plates in the course of the brazing step, owing among other things to the fact that the contact area between each of the spacer blocks and the plates is small.
In this embodiment, the removable set of spacer blocks can be removed by pivoting each spacer block 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. All the spacer blocks forming the set of spacer blocks can be pivoted at the same time by means of the connecting element.
Advantageously, this simplifies the step of removing the spacer blocks.
In another embodiment of the invention, the method also includes a step, the removable set of spacer blocks is selected therefrom in such a way that:

- 1) each spacer block is of essentially constant cross section along its main axis,
- 2) said cross section is in the shape of an ellipse,
- 3) the length of the major axis of said cross section is greater than or equal to the distance between the heat exchanger plates between which said set of spacer blocks is intended to be introduced, and
- 4) the length of the minor axis of said cross section is less than or equal to the distance between the heat exchange plates between which said removable set of spacer blocks is intended to be introduced.

Spacer blocks for the selected removable set of spacer blocks are connected to each other by a connecting element, such as a rigid bar welded to each spacer block, or a bar connected to each spacer block by means of a mechanical device such as a hinge, spring, drive or rod, that allows a rotary movement to be applied to each spacer block of the removal set of spacer blocks about their main axes. Selecting such a set of spacer blocks has advantages similar to the previous embodiment.
In particular, the contact area of each spacer block, once positioned between the plates, can be less than or equal to 15% of the total surface area of said spacer block, preferably less than or equal to 5% of the total surface area of said spacer block.
The spacer blocks of the removable sets of spacer blocks selected during 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 1500° C. or above. The spacer blocks of the sets of selected spacer blocks may for example be made of stainless steel.
A method according to the invention can also include a step in which each spacer block of the selected sets of spacer blocks is covered with a product that prevents or limits brazing during the brazing phase, such as STOP OFF®.
Advantageously, the use of such a product eases the step of removing the sets of spacer blocks of cross sections that differ from the embodiments described, such as hexagonal cross sections according to the invention.
The invention is not limited to the embodiment described and can be interpreted non-restrictively so as to encompass any equivalent embodiment.
In particular, the invention is applicable to any type of plate-type heat exchanger assembled by brazing. In particular, the method according to the invention can be carried out with sets of spacer blocks in which the spacer blocks have cross sections different from the embodiments described, such as hexagonal cross sections.

Claims

1-6. (canceled)

7. A method of manufacturing a plate heat exchanger of the type comprising a plurality of plates which, together with side bars arranged on the plates, define paths for fluids to flow through, comprising at least the following successive steps:

providing a stack of a plurality of plates separated by side bars,

introducing at least one removable set of spacer blocks consisting of at least two spacer blocks, connected together by at least one connecting element, between plates of said heat exchanger, wherein the connecting element is shaped in such a way as to allow a rotary movement of the set of spacer blocks about the main axis of each of said spacer blocks, each spacer block having an essentially constant cross section along its main axis;

brazing said heat exchanger, and

removing the removable set of spacer;

applying a rotary movement to all the spacer blocks of said set about their main axes, in such as away as to press each spacer block against said plates, after the introduction step;

applying a rotary movement to all the spacer blocks of said set about their main axes, in such a way as to release said spacer blocks, after the brazing step, wherein;

removable set of spacer blocks is selected in such a way that either

i)

said cross section is essentially polygonal in shape, and

the length of at least one of the main diagonals of said cross section is greater than or equal to the distance between the plates of the heat exchanger between which said spacer block is intended to be introduced; or

ii)

said cross section is essentially elliptical in shape, and

the length of the major axis of said cross section is greater than or equal to the distance between the plates of the heat exchanger between which said spacer block is intended to be introduced.

8. The method of claim 7, wherein a plurality of removable sets of spacer blocks, which are fixed together by fixing means, are introduced.

9. The method of claim 8, wherein a single removable set of spacer blocks is introduced between two plates of said heat exchanger.

10. The method of claim 7, wherein the spacer blocks of said set of spacer blocks and the connecting elements that are selected are made of one or more materials whose melting point is 700° C. or above.

11. The method of claim 7, wherein the spacer blocks of said set of spacer blocks and the connecting elements that are selected are made of one or more materials whose melting point is 900° C. or above.

12. The method of claim 11, wherein said material is stainless steel.

13. The method of claim 7, wherein all the spacer blocks of said set have their main axes approximately parallel to each other.

14. A plate-type heat exchanger of the type comprising a plurality of plates made of a brazable material, which exchanger is characterized in that it can be produced by the method according to claim 7.