WO1997037188A1

WO1997037188A1 - Heat exchanger and method for the manufacturing thereof

Info

Publication number: WO1997037188A1
Application number: PCT/SE1997/000482
Authority: WO
Inventors: Lars Persson
Original assignee: Lars Persson I Skane Ab
Priority date: 1996-03-29
Filing date: 1997-03-21
Publication date: 1997-10-09
Also published as: SE509282C2; SE9601220L; AU2524697A; SE9601220D0

Abstract

The invention relates to a heat exchanger, as well as to a method for the manufacture thereof, and more specifically a heat exchanger (1) comprising a plurality of channel plates (2) defining channels for the circulation of a medium under pressure. The channel plates (2) are held together by two cover plates (3, 4) arranged at opposite sides of the channel plates (2) by means of clamping devices (6) connecting the cover plates. According to the invention, at least one of the cover plates (3, 4) is pre-bent to provide a compressing force onto the channel plates, to counteract a deflection of the plates and expansion of the central area of the heat exchanger which might otherwise be caused by the pressure of the circulating medium. Preferably, the pre-bending is adapted to the maximum working pressure of the circulating medium. It is preferred that both cover plates (3, 4) are pre-bent in a symmetrical fashion.

Description

TITLE OF INVENTION: HEAT EXCHANGER AND METHOD FOR THE MANUFACTURING THEREOF

FIELD OF INVENTION

The present invention relates to a heat exchanger as well as a method for the manufacture thereof, and, more specifically, an improved heat exchanger having the abil- ity to resist pressure without deflections of the heat exchanger. This is achieved through pre-bending the exte¬ rior cover plates in such a way that upon clamping them together, they will provide a compressing force to coun¬ teract the internal pressure.

STATE OF THE ART

Heat exchangers generally comprise a stack of exter¬ nal cover plates and internal channel plates . The channel plates define passages for the circulation of media under pressure. The heat exchanger is held together by the cover plates being clamped together, e.g. by means of bolts located along the edges.

One problem with the known heat exchangers is that the pressure of the medium will cause an expansion of the central region of the stack, due to the lack of support from the bolts in that area. As the stack expands, the channels located in the central region of the heat exchanger will also expand, and inter-channel leakage may occur, resulting in the flow of media through the heat exchanger becoming larger in the central region. This will cause an inferior exchange of heat between the media and a lower efficiency of the heat exchanger.

The present invention solves this problem by pre- bending at least one of the cover plates. The pre-bending will cause an inwardly directed compressing force on the channel plates, which is adapted to the working pressure of the circulating media. The pressure inside the heat exchanger can never exceed the pressure created by the cover plates, and the heat exchanger will thus retain its ideal, planar shape for all working pressures.

SUMMARY OF THE INVENTION

The present invention thus provides a heat exchanger comprising a plurality of channel plates defining pas- sages for the circulation of pressurised media. The chan¬ nel plates are kept together by two cover plates arranged on each side of the stack of channel plates with the aid of connecting means interconnecting the cover plates. In accordance with the invention, at least one of the cover plates is pre-bent to provide a compressing force on the channel plates. Preferably, the compressing force caused by the pre-bending is adapted to the maximum working pressure of the circulating media.

The invention further provides a method for the manufacture of a heat exchanger. The invention is defined in detail by the accompanying claims .

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below, with reference to the accompanying drawings, wherein:

Fig. 1 illustrates a heat exchanger according to the invention, clamped together with bolts, and

Fig. 2 illustrates an unloaded lower cover plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 illustrates a heat exchanger according to the present invention. When the heat exchanger is assembled and clamped together, its exterior appearance will not differ from heat exchangers of the prior art.

The heat exchanger 1 comprises a plurality of chan- nel plates 2 defining flow passages for the circulation of media. The channel plates 2 are arranged between an upper cover plate 3 and a lower cover plate 4. The upper cover plate 3 is provided with inlet and outlet connec¬ tions 5 for the media. The whole heat exchanger stack is held together by bolts 6, running through holes at the edges of the cover plates 3 and 4. Other arrangements for interconnecting the cover plates 3 and 4 are of course conceivable.

As was mentioned before, the pressure of the circu¬ lating media will cause the central area of the heat exchanger to expand, as the clamping forces of the heat exchangers according to the prior art are only applied at the edges of the cover plates. This will result in a higher flow of the media in the central region of the heat exchanger as the passages in this area of the chan- nel plates 2 expand, entailing the disadvantages stated above.

According to the present invention, a pre-bending is provided of at least one of the cover plates 3 and 4. Fig. 2 shows the lower cover plate 4 in an unloaded con- dition. When the cover plate is clamped together with the other plates of the heat exchanger into a flat or planar condition, said cover plate 4 will cause an additional force, having a maximum at the centre of the heat exchanger and decreasing toward the edges. The additional force is added to the force of the bolts and is intended for counteracting the internal pressure caused by the circulating media.

Preferably, the pre-bending of the cover plate is adapted to the maximum working pressure at which the heat exchanger is expected to operate. In this way, the internal pressure in the heat exchanger can never cause any deflection of the plates. At lower working pressures, the additional compressing force is counteracted by the channel plates themselves, even without any overpressure at all in the circulating media, and the heat exchanger will remain planar also at lower working pressures than the maximum working pressure.

The invention functions well with only one pre-bent cover plate, but the most favourable effect is achieved if both cover plates are pre-bent in a symmetrical fashion.

It should be noted that the pre-bending illustrated in Fig. 2 is exaggerated for the sake of clarity. In reality, the deviation from flatness lies at about 1,5 mm for a plate of normal size, having a thickness of about 30 mm. The authority norm for flatness lies at about 3 mm, and from this aspect, the pre-bent cover plate is still "flat". During the manufacture of the heat exchanger, it is favourable to produce the cover plates to a finished state, complete with holes, folds and other details, before pre-bending them in a special pressing tool. The bending radius of the plates will easily be calculated to a suitable value by somebody skilled in the ar . The invention is only limited by the following claims.

Claims

CLAIMS :

1. A heat exchanger (1) comprising a plurality of channel plates (2) , defining channels for the circulation of media under pressure, said channel plates (2) being held together by two cover plates (3, 4) arranged at opposite sides of the channel plates (2) by means of clamping devices (6) connecting the cover plates, c h a r a c t e r i s e d i n that at least one of said cover plates (3, 4) is pre-bent in order to provide a compressing force acting on the channel plates .

2. A heat exchanger according to claim 1, c h a r a c t e r i s e d i n that the compressing force caused by the pre-bending is adapted to the maximum working pressure of the circulating medium.

3. A heat exchanger according to claim 2, c h a r a c t e r i s e d i n that the compressing force caused by the pre-bending is lower than, or equal to, the maximum working pressure in the circulating medium.

4. A heat exchanger according to any one of the previous claims, c h a r a c t e r i s e d i n that both cover plates (3, 4) are pre-bent.

5. A method for the manufacture of heat exchangers (1) comprising a plurality of channel plates (2) , defining channels for the circulation of media subjected to pressure, said channel plates (2) being held together by two cover plates (3, 4) arranged at opposite sides of the channel plates (2) by means of clamping devices (6) con¬ necting the cover plates (3, 4) , c h a r a c t e r i s e d i n that at least one of said cover plates (3, 4) is pre-bent in order to provide a compressing force acting on the channel plates.

6. A method for the manufacture of heat exchangers according to claim 5, c h a r a c t e r i s e d i n that the pre-bending is performed so as to provide a com- pressing force adapted to the maximum working pressure of the circulating medium.

7. A method for the manufacture of heat exchangers according to claim 6, c h a r a c t e r i s e d i n that the pre-bending is performed so as to provide a com¬ pressing force lower than, or equal to, the maximum work¬ ing pressure of the circulating medium.

8. A method for the manufacture of heat exchangers according to any one of claims 5-7, c h a r a c t e r i s e d i n that the pre-bending is performed after producing the holes in the cover plates, in a pre-bending pressing device.