GB2174488A

GB2174488A - Heat exchanger plate

Info

Publication number: GB2174488A
Application number: GB08510905A
Authority: GB
Inventors: Helmut Fischer
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-03-14
Filing date: 1985-04-30
Publication date: 1986-11-05
Also published as: GB2174488B; GB8510905D0

Abstract

A detachable plate heat exchanger has plates pressed from sheet metal. Central sections 1 of the plates, used for heat exchange, have numerous corrugated pressings 3 which run obliquely at angles alpha , alpha ' to the longitudinal axis of the plate and lie opposed to and intersect with the pressings of adjacent plates. The corrugated pressings are divided into numerous circular corrugated areas 2 which cover the central section of the plate in tightly-joined rows. For manufacturing the heat exchange plates, a press tool (Figure 5) comprises a base plate on which can be secured numerous circular stamps in such manner that the stamp can be rotated about its vertical axis so that the ribs used for pressing the corrugations form the required angle to the longitudinal axis of the heat-exchange plate <IMAGE>

Description

SPECIFICATION Heat exchanger plate The invention relates to plate-type heat exchangers. These may consist of a stack of heat exchanger plates pressed from sheet metal and joined together, the plates being clamped between two solid plates. The central areas of the heat exchanger plates, providing the heat exchange, may be provided with pressings which increase turbulance and hence heat transmission.

The objective of the invention is to provide a design for the central section of a heat-exchange plate which enables the heat exchange platee to provide any desired thermal length within a certain -range.

If it is assumed that the dimensions of the central section of the plate used for the heat transmission are established, i.e. its length and width, and the distance to the adjacent plate, the thermal length of this type of plate is determined by the design of the profile of the central section.

In many applications of plate-type heat exchangers, particularly in large installations used for cooling purposes, the entire heat transmission is required to take place along the length of one pass of a plate, i.e. in these installations, all the plates must be connected in parallel and both media must flow through the installation in opposite directions. If it is assumed that a specific pressure loss is also to take place within the heat exchanger, then, for a given set of conditions, the ideal thermal length of the heat exchanger or its plates is also predetermined. This length is provided when, at the predetermined pressure loss, the precise amount of liquid giving rise to the required temperature change flows through the plate duct.

If the thermal length of the type of plates used is too long, then, in order not to exceed the predetermined maximum pressure loss, more heat exchange plates must be installed in the plant than would be required for the thermal effect, with the result that the installation is over-dimensioned.

On the other hand, if the thermal length is too short, the throughput per plate duct must be reduced until the correct temperature range is obtained. However, the reduction in plate stress also gives rise to a reduction in the coefficient of heat transmission. This often means that heat exchangers used in this way require a much larger exchange area than those with the correct thermal length.

In order to counteract these known disadvantages, heat exchanger plates of the same size are being constructed with different profiles to enable them to approach the ideal thermal length more closely if required to do so. Most modern plates are provided, in their central section, with a profile which consists of corrugations running obliquely to the longitudinal axis, and hence also to the direction of flow, the corrugations of one plate intersecting the corrugation running in the opposite direction on an adjacent plate. The angles formed by these corrugations with the longitudinal axes of the plates lie in most cases between 35 and 650.

The angles are of crucial importance to the thermal length of the plate and may influence the length approximately in the ratio of 1:4. In this case the thermal length decreases with a reduction in the angle.

According to a known system, two types of plates with different corrugation angles are used, which corrugations, when each is used exclusively, provide flow ducts of either long or short thermal length. A combination, through alternate use of both types of plates, provides ducts of mean thermal length. It is obvious that this system only provides a rough graduation of the thermal lengths and cannot, therefore, be considered satisfactory.

According to another proposal, the central section of the plate is divided into several strip-like areas running transversely to the longitudinal axis, which areas are in turn provided with corrugations of varying angle of inclination to the longitudinal axis. The strip-like areas are formed by means of replaceable shaping parts in the press tool. By the simultaneous use of areas with a large angle and areas with a small angle, the thermal length of the plate can be varied. Although it is possible to come closer to the ideal length by this method, this design is also associated with certain disadvantages.

A profile with a small angle, under flow conditions in the turbulent range, gives a coefficient of heat transmission 50% below that obtained with a profile with a large angle, assuming both profiles are subjected to the same liquid flow rate. This results in an average coefficient of heat expansion which is below that obtained if a uniform profile is chosen with an angle which gives exactly the required thermal length of the plate duct.

The scope of the present invention is defined by the claims, to which reference should now be made.

Thus, the central section of the plate may be provided with numerous circular sections, joined together, with corrugated shapings. The corrugations are directed obliquely to the longitudinal axis of the plates. For manufacturing the plate, a press tool may be used in whose central section are inserted disc-shaped stamps whose upper sides have a profile suitable for stamping the corrugations.

The stamps themselves are rotatable in the tool so that the angle formed by the corrugations to the longitudinal axis of the press tool, and hence the heat exchange plate, can be varied. By this method it is possible to give the heat exchange plate the exact profile required to obtain the desired thermal length.

Embodiments of the invention are described below with reference to the drawings, in which: Figure 1 shows, in a front view, a heat exchange plate whose central section is provided with pressings arranged symmetrically in relation to the transverse axis CD; Figure 2 shows a portion of the central section of another plate which has a different angle of corrugation; Figure 3 shows the same central portion but of a plate with a different grouping of the corrugations; Figure 4 shows the central portion of a plate having corrugations arranged asymmetrically in relation to the transverse axis CD; Figure 5 shows, in section, a stamp for manufacturing a circular corrugated area and, in section, a portion of a press tool; and Figure 6 shows the stamp of Figure 5 in elevation.

Figure 1 shows a front view of the heat exchange plate. In its central section 1 are pressed numerous circular areas 2, which consist of corrugations 3, represented in the drawing as strokes. In order to clarify the representation, the corrugated areas are surrounded in the drawing by circular lines 4. The areas remaining between the circular areas are provided with corrugations 5. Areas in the central section, which for constructional (geometrical) reasons are too small for areas 2 to be provided, can be provided with circular areas 6 of suitably smaller dimensions and also provided with corrugations 7.

The corrugations 3 of the upper half of the central section form a certain angle or to the central axis AB. In the lower half (a mirror image of the upper half) the corrugations form an angle d of the same magnitude. In the drawing the angles a, a' are 300. The central section of an adjacent plate (not shown) is rotated through 1800 relative to the plate of Figure 1 about a central axis perpendicular to the plane of the plate shown, so that the corrugations of the two plates cross, with one corrugated area covering the other. The angle of intersection of the corrugations is then 2a, i.e. 600.

This angle would give a flow duct of short thermal length.

Figure 2 shows the central region of a heat exchange plate of design similar to th plate of Figure 1 but where the angle a is 600. The angle of intersection between two plates of this design is 1200 which corresponds to a profile with a long thermal length.

Figure 3 shows a central section whose corrugated areas 2 exhibit a constantly-changing direction of corrugation in each horizontal rows. When two adjacent plates are placed one above the other, the corrugations intersect, and therefore produce the same effect as the plate in Figure 1.

Figure 4 shows a central section in which corrugated areas 2 are not mirror inverted in relation to the transverse axis CD, but are staggered in relation to each other. The result of this is that in the case of two successive plates whose central sections are rotated 1800 to each other about a central axis perpendicular to the plane of the plate, corrugated areas 2 overlap corrugations 5 located in the small intermediate zones. This provides a particularly homogeneous design of flow duct.

Figure 5 represents in section a stamp 8 for manufacturing a corrugated area 2. Figure 6 shows the stamp 8 in elevation. This circular tool component is fitted into a main plate 9 of a press tool and is secured with a central screw 11. This design enables the stamp to be rotated, and therefore to provide any variation of the direction of a series of ribs 10 provided on the press tool. If the tool section shown is regarded as the bottom, then the top may be designed similarly as a counter-mould.

However, it is also possible to design one of the two tool halves as a rubber cusion press mould.

The plate press tool design according to the invention not only enables the heat exchange plate to be given any thermal length within certain limits but also provides the possibility of manufacturing special plates whose central section exhibits a gradually varying flow characteristic. For example, the central section may begin in its upper region with a number of areas with a large angle a and terminate in its lower region with a small angle a when the angle has been gradually reduced row by row. Such plates are suitable for the thermal exchange of substances whose viscosity varies considerably with temperature. The area with the small angle a, i.e. the area with the profile which offers less flow resistance, is then used on the side where the flow medium exhibits the higher viscosity. A further area of application of these special plates is in plate-type evaporators, where a considerable increase in volume occurs due to partial evaporation of liquid in the plate duct. In this case the medium to be evaporated is allowed to flow in at the plate end where the profile offers the greatest flow resistance.

Claims

1. A heat exchange plate for a heat exchanger of the detachable plate type, the plate having a corrugated, heat exchange region, the corrugations being inclined to the longitudinal axis of the plate and being arranged in a plurality of closely-spaced circular areas which extend over at least a portion of the corrugated region of the plate.

2. A plate according to claim 1, in which the circular areas form transverse rows, the corrugations of alternate circular areas of each row being oppositely inclined.

3. A plate according to claim 1 or 2, in which at least some of the circular areas form a hexagonally close-packed array.

4. A plate according to any preceding claim, in which the corrugations of the heat exchange region have a median mirror plane of symmetry extending perpendicularly to the longitudinal axis.

5. A plate according to claim 3, in which the corrugations of the circular areas of the closepacked array lying to respective sides of a median line of the array extending perpendicularly to the longitudinal axis are oppositely-inclined at equal angles to the longitudinal axis.

6. A plate according to any preceding claim, in which at least portions of at least some interstitial areas of the heat-exchange region not constituting the said circular areas are corrugated.

7. A plate according to claim 6, in which the corrugations of at least some of the interstitial areas comprise corrugations arranged in further, smaller circular areas.

8. A plate according to claim 7, in which the corrugations of at least some of the smaller circular areas are inclined oppositely to the corruga tions of at least some of the larger circular areas.

9. A plate according to claim 8, in which the respective said inclined corrugations are inclined at equal angles to the longitudinal axis.

10. A plate according to any preceding claim, in which the circular areas are arranged in a series transversely-extending rows, the corrugations of the row of the series at one end of the heat-exchange region being inclined at a larger angle to the longitudinal axis and the angle of inclination being reduced row by row to a smaller angle at the opposite end of the heat-exchange region.

11. A plate according to any preceding claim, in which the heat-exchange region is a central region of the plate.

12. A detachable-plate heat exchanger having a plurality of plates each according to any one of claims 1 to 11, the corrugations of each plate facing oppositely-inclined corrugations of its neighbouring plate.

13. A heat exchanger according to claim 12, in which the larger circular areas of at least one plate face interstitial areas of a neighbouring plate.

14. A press tool for manufacturing a heat exchange plate for a heat exchanger of the detachable plate type, the tool comprising a support member on which is mounted an array of corrugating elements each having a corrugating surface and each being rotatable about an axis extending perpendicularly to its corrugating surface for selective adjustment of the orientation of the corrugating surface.

15. A press tool for manufacturing a heat exchange plate according to any one of claims 1 to 11, the tool comprising a base member to which are secured a plurality of circular corrugating elements each having a corrugating surface and each being rotatable about an axis extending perpendicularly to its corrugating surface for selective adjustment of the orientation of the corrugating surface.

16. A press tool according to claim 14 or 15, including a cushioning member having a cushioning surface between which and the corrugating surfaces of the corrugating elements a sheet of material can be corrugated by relative movement towards each other of the cushioning surface and the corrugating surfaces.

17. A press tool according to claim 14 or 15, including a counter press member having secured thereto a plurality of circular corrugating counterelements arranged in a corresponding array to the corrugating elements of the base member and each having a complementary corrugating surface, the counterelements each being rotatable about an axis extending perpendicularly to its corrugating surface and being movable relative to the base member for corrugation therebetween of sheet material when the corrugating surfaces of the corrugating elements and counterelements are co-operatively oriented.

18. A press tool substantially as hereinbefore described with reference to Figures 5 and 6 of the drawings.

19. A heat exchanger plate for a heat exchanger of the detachable plate type, the plate having been manufactured by use of a press tool according to any one of claims 14 to 18.

20. A method of manufacturing a heat exchange plate for a heat exchanger of the detachable plate type, comprising the steps of calculating the thermal length of the heat exchange plate necessary to produce a desired exchange of heat, calculating the thermal length of the heat exchange plate necessary to produce a desired exchange of heat, calculating awn angle or a series of angles at an inclination of which corrugations or successive rows of corrugations of the heat exchange plate will produce the desired exchange or heat, corrugating a plurality of plates at the calculated angle or series of angles and assembling a heat exchanger by arranging the corrugated plates with the corrugations of each plate facing and being inclined oippositely to those of a neighbouring plate and to the flow direction of the heat exchanger.

21. A method of manufacturing a heat exchange plate, the method being substantially as hereinbefore described with reference to the drawings.

22. A heat exchange plate manufactured by the method of claim 21 or 22.

23. A heat exchanger plate substantially as hereinbefore described with reference to any one of Figures 1 to 4 of the drawings.