WO1994007102A1

WO1994007102A1 - Ribbed heat exchanger

Info

Publication number: WO1994007102A1
Application number: PCT/SE1993/000745
Authority: WO
Inventors: Kjell NORRMÉN
Original assignee: Senea Heat Ab
Priority date: 1992-09-14
Filing date: 1993-09-14
Publication date: 1994-03-31
Also published as: SE9202638L; SE9202638D0

Abstract

A ribbed heat exchanger which comprises a plurality of mutually parallel plates which define therebetween passageways for the two media between which a heat exchange shall be effected, wherein each plate, with the exception of the outermost plates, forms a defining surface or limitation between two mutually adjacent passageways. The invention is characterized in that each alternate plate (3) has upwardly folded opposing first edges (7, 8) and each other alternate plate (2, 4) has the two remaining, second edges (5, 6) upwardly folded, wherein the upwardly folded parts (5-8) of each plate are intended to abut an adjacent plate, in that U-shaped strips (9-11) are fitted over each upwardly folded part (5-8), with the inner surfaces of the two limbs (12, 13) of each U-shaped strip (9-11) abutting the mutually remote surfaces of two adjacent plates so as to form mutually parallel passageways (19, 20), of which each alternate passageway extends in one direction and each other alternate passageway extends in a direction at right angles to the first-mentioned passageways, and in that each U-shaped strip (9-11) is sealed against the upwardly folded part (5-8) and the adjacent plate concerned with an elastic adhesive.

Description

Ribbed Heat Exchanger

The present invention relates to a ribbed heat ex¬ changer.

Such heat exchangers are used in many different con¬ texts. A characteristic feature of a heat exchanger is that flat plates are mounted so as to form passageways in which the two media between which heat exchange shall be effected flow on mutually different sides of the plates.

Although the present invention is not restricted to any particular area of use, it is primarily intended for application in relatively large heat exchangers of the type used in heating plants for heat exchange between flue gases and another medium. The plates of such heat exchangers may measure 4,000 x 1,000 milli¬ meters and the total plate surface area may reach 4,000 square meters for instance.

In the manufacture of conventional flue-gas heat exchangers of this kind, parallel plates are welded to beams at their upper and lower edges, so as to hold the plates in place. Side pieces are welded to the plates to obtain a tight join between mutually adja¬ cent passageways defined by the plates. In order to maintain the plates in spaced relationship over the whole of the plate area, the plates are embossed with a large number of knobs over their respective surfaces, these knobs lying against adjacent plates.

The plates are normally made of stainless steel, and in order to enable the plates to be welded, they must have a smallest plate thickness of 1 millimeter. A smaller plate thickness would result in lower material costs and also in improved heat transfer. Such known heat exchangers are expensive to produce, partly because of the time taken to weld the plates and partly because of the cost of the materials used.

The present invention relates to a heat exchanger which is much cheaper to produce and which provides better heat transfer between the two media involved in the heat exchange.

The present invention thus relates to a ribbed heat exchanger which comprises a plurality of mutually parallel plates which define therebetween passageways for the two media between which heat shall be exchang¬ ed, wherein each plate, with the exception of the outermost plates, forms a defining surface or limita¬ tion between two mutually adjacent passageways, said heat exchanger being characterized in that each alter¬ nate plate has upwardly folded opposing first edges and each other alternate plate has the two remaining, second edges upwardly folded, wherein the upwardly folded parts of each plate are intended to abut an adjacent plate; in that U-shaped strips are fitted over each upwardly folded part, with the inner surfac¬ es of the two limbs of each U-shaped strip abutting the mutually remote surfaces of two adjacent plates so as to form mutually parallel passageways of which each alternate passageway extends in one direction and each other alternate passageway extends in a direction at right angles to the first-mentioned passageways; and in that each U-shaped strip is sealed against the upwardly folded part and the adjacent plate concerned with an elastic adhesive.

The invention will now be described in more detail partially with reference to an exemplifying embodiment thereof shown in the accompanying drawings, in which - Figure 1 is an exploded view of a heat exchanger, said view being intended to facilitate an under¬ standing of the construction of the heat exchanger; Figure 2 illustrates an inventive heat exchanger as seen in the intended flow direction of one medium; Figure 3 shows the heat exchanger according to Figure 2 from above; and - Figure 4 illustrates a heat exchanger constructed in accordance with the principle shown in Figures 1 to 3, and also illustrates the flow of the two heat-exchange media.

Figure 1 illustrates the construction of an inventive ribbed heat exchanger. The heat exchanger comprises a plurality of mutually parallel plates 1-4 which define passageways for the two media between which heat exchange shall take place, wherein each plate forms a limitation between two mutually adjacent passageways, with the exception of the two outermost plates 1, 4.

According to the invention, each alternate plate 2, 4 has upwardly folded, mutually opposing first edges 5, 6, and each other alternate plate 1, 3 has the two remaining, second edges 1 , 8 folded upwards, wherein the upwardly folded parts of each plate are intended to abut an adjacent plate. The plates are shown in an exploded view in Figure 1. In the assembled state of the heat exchanger, the edges 5-8 lie against respec¬ tive overlying plates.

The illustrated heat exchanger also includes U-shaped strips 9-11 which are fitted over each upwardly folded part 5-8. Figure 1 shows only U-shaped strips that are intended for one short side and one long side of the plates respectively, for the sake of clarity. It will be understood, however, that similar strips are also provided for the other short sides and long sides respectively.

The inner surfaces of the two limbs of each U-shaped strip 5-8 abut the mutually remote surfaces of two adjacent plates, as illustrated by the arrows in Figure 1, these arrows indicating how plates and strips are mutually assembled. Thus, the inner surface of the upper limb 12 of the strip 11 abuts the upper surface of the plate 2 , whereas the inner surface of the lower limb 13 of the strip 11 abuts the undersur- face of the plate 3. Furthermore, the inner surface of the upper limb 14 of the strip 9, for instance, abuts the upper surface of the plate 1, whereas the inner surface of the lower limb 15 abuts the undersurface of the plate 2. This arrangement results in the formation of mutually parallel passageways of which alternate passageways extend in a first direction 16 and the other alternate passageways extend in a second direc¬ tion 17 which is perpendicular to the first mentioned passageway direction.

For the sake of clarity. Figure 1 shows only four plates, of which the two plates referenced 1, 4 are the two outermost plates. It will be understood, however, that a heat exchanger may consist of a large number of plates, for instance hundreds of plates. In this regard, all plates are configured in the same way as the intermediate plates 2, 3, with the exception of the outermost plates.

According to the invention, each U-shaped strip 9-11 is sealed against its associated upwardly folded part and adjacent plate with an elastic adhesive.

In the present description and Claims, by adhesive is meant an actual glue but alternatively a sealing com¬ pound. However, the term adhesive is used.

According to one preferred embodiment of the inven- tion, the adhesive, or sealing compound, is a silicone adhesive. Silicone adhesives are insoluble in their cured state in those environments in which a heat exchanger of the type concerned is used. One adhesive which has been found suitable for use in this respect is an adhesive retailed by Bostic AB, Helsingborg, Sweden, under the name Bostic Silikon Industri 2695.

In actual fact, it is not always necessary to use an adhesive to hold the construction together, since the actual need is for a sealing compound. In normal cases, the construction is held together by a frame structure or the like fitted externally to the heat- exchanger. Small heat exchangers can be held together by a surrounding box-like structure. In certain cases, however, it can be beneficial to glue each part so as to obtain a self-supporting construction.

According to one preferred embodiment of the inven- tion, the edges 5-8 are folded up and over to form U- shaped parts in cross-section. The distance between the inner surfaces of the limbs of respective U-shaped strips 9-11 will correspond to the height of the over- folded edges 5-8 together with the combined thickness of the two mutually adjacent plates embraced by the U- shaped strip concerned. The distance between two mutually adjacent plates will therefore be well defined, and large gluing and/or sealing surfaces are obtained.

According to the invention, spacer elements 18 are distributed uniformly over the plate surfaces, so as to maintain the plates in mutually spaced relation¬ ship.

According to one preferred embodiment of the inven¬ tion, the spacer elements are comprised of plastic inserts, preferably made from PVC material. The in¬ serts are glued to the plates, preferably with a silicone adhesive.

The inserts 18 are suitably placed in rows equidistant from one another. When the inserts have a diameter of about 10-15 millimeters, a suitable spacing is about 10-15 centimeters. The distance between two adjacent rows is suitably 10-15 centimeters. Preferably, the inserts in two mutually adjacent rows will be offset longitudinally in relation to one another, so that an insert in one row will lie opposite the space between two adjacent inserts in the other rows, as illustrated in Figure 1. This positioning of the inserts results in favourable turbulence of the media flowing through the heat exchanger, which increases the heat transfer.

According to a further preferred embodiment, the plates have a thickness of less than 1 millimeter, and preferably a plate thickness of about 0.5 millimeter.

Because the plates and the strips are glued together, plates used may be much thinner than the plates of conventional heat exchangers, in which the plates are welded. Thinner plates results in lower material costs and also in more effective heat transfer. The inven- tive heat exchanger is thus less expensive, lighter in weight and more effective than corresponding known heat exchangers.

With regard to manufacturing costs, the task of weld- ing the plates is highly time-consuming and therewith expensive. It has been found that the working costs entailed in the manufacture of an inventive heat exchanger are roughly half the working costs entailed with a conventionally manufactured heat exchanger.

Figures 2 and 3 illustrate schematically an inventive heat exchanger in which only a few plates have been included. It will be understood, however, that a heat exchanger will normally comprise hundreds of plates. The heat exchanger shown in Figure 2 is seen from the right in Figure 1 in the direction 17, whereas in Figure 3, the heat exchanger is seen in the direction 16 in Figure 1. The heat exchanger thus includes a plurality of passageways 19 for a first medium and a plurality of passageways 20 for a second medium. The passageways may have different or the same widths. The width of the passageways is determined by the heights of the inserts and the U-shaped strips are adapted to the passageway width concerned.

Angled strips 21 can be glued onto the corners of the illustrated heat-exchanger package, in order to seal the corners.

Figure 4 illustrates an example of the use of an inventive heat exchanger. In the illustrated case, the heat exchanger is used to moisturize combustion air in a heating plant. The heat-exchanger package is en- closed in a box-like structure comprised of sheet- metal walls 22 and is surrounded by a frame structure 23 which exerts pressure against the plates in a direction normal thereto. The entire heat-exchanger package is held compressed in this way, so as to essentially eliminate any play. The intention is also to relieve the glue joints of tensile stresses.

In the Figure 4 illustration, the passageways which extend vertically are connected to combustion-air pipes 24, 25. Cold air flows from beneath and upwards.

The passageways which extend horizontally in the upper part of the heat-exchanger package are connected to a hot flue-gas pipe 26. The remainder of that side of the heat exchanger referenced 27 is covered by a sheet-metal wall. Correspondingly, the opposite lower part of the heat-exchanger package is connected to a flue-gas exhaust pipe 28. The hot flue gases thus flow through the heat exchanger from its upper vertical part to its lower vertical part.

Curved walls are provided in the passageways so as to guide the flow of flue gas into contact with the walls of the entire heat exchanger, these curved walls being illustrated in dotted lines 29. According to one preferred embodiment of the invention, the walls are formed by steel rounds having a diameter which corres¬ ponds to the distance between the walls of the pas- sageways, said rounds being bent to a desired shape to achieve a desired flow. The rounds are suitably glued to the walls by means of silicone glue.

Thus, in the case of the Figure 4 example, the flue gases deliver heat to the combustion air, which is moisturized by spraying water into the pipe 25 through nozzles 30. The moisturized flue gases are passed to a boiler. It will be understood, however, that this represents only one example of use. It is obvious that an inventive heat exchanger can be used in all applications.

It will be evident from the aforegoing that an inven¬ tive heat exchanger is more effective and less expen- sive than conventional heat exchangers.

Although different exemplifying embodiments have been described above, it will be obvious that the heat exchanger can be modified with respect to the shape of the plates, the configuration of the spacer elements and with regard to the sealing compound or the adhe¬ sive used.

The invention shall not therefore be considered limit- ed to the aforedescribed and illustrated exemplifying embodiments thereof, since modifications can be made within the scope of the following Claims.

Claims

1. A ribbed heat exchanger which comprises a plurali¬ ty of mutually parallel plates which define therebe- tween passageways for the two media between which a heat exchange shall be effected, wherein each plate, with the exception of the outermost plates, forms a defining surface or limitation between two mutually adjacent passageways, c h a r a c t e r i z e d in —that each alternate plate (3) has upwardly folded opposing first edges (7, 8) and each other alternate plate (2, 4) has the two remaining, second edges (5, 6) upwardly folded, wherein the upwardly folded parts (5 - 8) of each plate are intended to abut an adjacent plate; in that U-shaped strips (9-11) are fitted over each upwardly folded part (5 - 8) , with the inner surfaces of the two limbs (12, 13) of each U-shaped strip (9 - 11) abutting the mutually remote surfaces of two adjacent plates so as to form mutually parallel passageways (19, 20) of which each alternate passage¬ way extends in one direction and each other alternate passageway extends in a direction at right angles to the first-mentioned passageways; and in that each U- shaped strip (9 - 11) is sealed against the upwardly folded part (5 - 8) and the adjacent plate concerned with an elastic adhesive.

2. A ribbed heat exchanger according to Claim 1, c h a r a c t e r i z e d in that said edges (5-8) are folded-up and folded-over to form parts of U- shaped cross-sections; and in that the U-shaped strips (9-11) have a measurement between the inner surfaces of the limbs (12, 13) which corresponds to the height of the over-folded edges (5-8) plus the combined thickness of the two adjacent plates embraced by the U-shaped strip concerned.

3. A ribbed heat exchanger according to Claim l or 2, c h a r a c t e r i z e d in that the heat exchanger is surrounded by a frame structure (23) which exerts a force on the plates (1-4) in a direction normal to the plates.

4. A ribbed heat exchanger according to Claim 1, 2 or 3, c h a r a c t e r i z e d in that the adhesive is a silicone glue.

5. A ribbed heat exchanger according to any one of Claims 1, 2, 3 or 4, c h a r a c t e r i z e d by spacer elements (18) that are distributed uniformly over the surfaces of the plates (1-4) so as to maintain the plates in mutually spaced relationship.

6. A ribbed heat exchanger according to Claim 5, c h a r a c t e r i z e d in that the spacer elements (18) have the form of inserts of a plastic material, preferably a PVC material; and in that the inserts (18) are glued to the plates (1-4), preferably with a silicone glue.

7. A ribbed heat exchanger according to any one of Claims l, 2, 3, 4, 5 or 6, c h a r a c t e r i z e d in that the thickness of the plates (1-4) is less than 1 millimeter and that the thickness preferably is about 0.5 millimeter.