TECHNICAL FIELD OF THE INVENTION

The invention relates to a plate heat exchanger and a method for manufacturing of a plate heat exchanger according to the preambles of the independent claims presented below. The invention relates especially to a new way of arranging flows of the secondary side and the flow ducts of the secondary side of a plate heat exchanger.

BACKGROUND OF THE INVENTION

Heat exchangers are traditionally divided into plate structure and tube structure heat exchangers. Tube structure heat exchangers comprise a shell part inside which tubes, usually a bundle of tubes formed of several tubes, have been placed. The primary heat exchange medium is usually arranged to flow inside the tubes of the bundle of tubes and the secondary heat exchange medium in the shell. The distance between the tubes of a tube heat exchanger and the diameters of the tubes can be chosen rather freely. The heat exchange properties set limitations to the design and sizing of the tube heat exchanger. A round tube is not very advantageous in view of heat exchange because its heat exchange surface is the smallest possible as to its cross-sectional area. In order to intensify the heat exchange, surfaces of a tube have been equipped with various ribs. For example, so-called rib plates are attached perpendicular to the surface of the tube, or ribs are attached spirally around the tube.

Plate structured ribbed heat exchangers have been used for example in a radiator.

A plate heat exchanger of the Plate & Shell™ type consists of a plate pack formed by heat exchange plates and a shell surrounding it. The core of the heat exchanger is usually formed by a round plate pack that is composed of heat exchange plates that have been welded tightly together at the openings and/or perimeters in the heat exchange plates. The primary circuit of a heat exchanger is formed between the openings inside the plate pack and the secondary circuit between the connections of the shell surrounding the plate pack. In this way typically a primary heat exchange medium flows in every other plate space between two plates and a secondary heat exchange medium in the every other plate spaces.

The plates of a plate heat exchanger are usually corrugated. This is frequent both in Plate & Shell™ type and also in traditional rectangular plate heat exchangers equipped with rubber sealings. The corrugation, i.e. the grooves and the ridges between them, aims to improve heat exchange properties and produces e.g. a diamond shape to the plate spaces which improves heat transfer coefficients. A plate pack formed by corrugated plates in contact with each other endures well also pressure because the contact points of the ridges are very near to each other. When using plates that are corrugated at regular intervals, the flow ducts of the primary side and the secondary side are usually similar. In other words, the heat exchange plates are at equal distance from each other in the plate spaces of the primary and the secondary sides. This leads to the fact that heat exchangers often have to be oversized at some parts so that e.g. pressure losses would not rise too high at either side of the heat exchange plate. For example, in gas/liquid heat exchangers of Plate & Shell™ type, the heat exchange surface of the liquid side often has to be chosen to be unnecessarily large, if the plate spaces of the gas side are being optimized.

In some plate heat exchangers the size of the cross-sectional flow surface has been attempted to be changed in different flow ducts by making the corrugation of the plates more sparse e.g. by leaving every other groove away. With this kind of arrangement, it can be arranged to the gas side looser flow conditions than to the liquid side. The weaknesses in this kind of structure are the diminution of the pressure resistance due to direct plate surfaces, as well as limited possibilities to influence the ratio of the cross-sections of the flow ducts.

In some situations, a problem in the plate heat exchangers is the necking of the flow to a certain point of the plate space. In some situations, the flows are divided in an unbalanced way to the plate spaces of the secondary side. OBJECT AND BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art.

It is an object of the present invention to particularly provide a plate heat exchanger in which both the primary and the secondary sides can be designed and sized almost independently from each other. It is an object of the present invention to particularly provide a plate heat exchanger that resists pressure well.

An object of the present invention is particularly to provide a plate heat exchanger in which flows of the heat exchange medium in the plate spaces of the secondary side are controlled efficiently.

An object of the present invention is particularly to provide a plate heat exchanger with good heat exchange properties. One object of the present invention is to make the manufacturing of a plate heat exchanger more effective.

It is especially an object of the present invention to provide a plate heat exchanger, the manufacturing of which is inexpensive and easy.

In order to achieve among others the objects mentioned above, the plate heat exchanger and the method and other objects of the invention are characterized by what is presented in the characterizing parts of the enclosed independent claims. The embodiments and advantages mentioned in this text relate, where applicable, both to the plate heat exchanger, the method as well as to the uses according to the invention, even though it is not always specifically mentioned. A typical plate heat exchanger according to the invention comprises a plate pack formed by heat exchange plates provided with openings and a shell surrounding the plate pack. In the plate heat exchanger

- inlet and outlet connections for a first and a second heat exchange medium have been arranged through the shell,

- heat exchange plates have been attached to each other as plate pairs, the inner parts of which have been arranged in connection to each other by means of connecting tubes that connect tightly the openings of the heat exchange plates,

- the inlet and outlet connections of the first heat exchange medium have been arranged in connection to inner parts of the plate pack, i.e. to inner parts of the plate pair, whereby a primary circuit of the plate heat exchanger is formed between the inlet and outlet connections of the first heat exchange medium, whereby there are plate spaces of the primary circuit inside the plate pairs,

- the inlet and outlet connections of the second heat exchange medium have been arranged in connection to the inside of the shell, i.e. the outside of the plate pack, whereby a secondary circuit of the plate heat exchanger is formed between the inlet and outlet connections of the second heat exchange medium, whereby there are plate spaces of the secondary circuit between adjacent plate pairs,

- to a plate space of the secondary side, in contact with the outer surface of the plate pair, is arranged at least one support element which is arranged as a pressure-proof support structure between plate pairs,

- the support element comprises openings, whereby the portion of the openings of the area of the support element is over 25 %.

A typical method according to the invention for manufacturing of a plate heat exchanger has at least the following steps:

- attaching heat exchange plates to each other in pairs as plate pairs, where each heat exchange plate has openings,

- arranging a number of plate pairs consecutively as a plate pack, - connecting the inner parts of the plate pairs, i.e. the inner part of the plate pack, in connection to each other by means of connecting tubes connecting tightly the openings of the heat exchange plates,

- arranging a shell around the plate pack and inlet and outlet connections through it for a first and a second heat exchange medium,

- arranging the inlet and outlet connections of the first heat exchange medium in connection with inner parts of the plate pack, whereby a primary circuit of the plate heat exchanger is formed between the inlet and outlet connections of the first heat exchange medium, whereby plate spaces of the primary circuit are formed inside the plate pairs,

- arranging the inlet and outlet connections of the second heat exchange medium in connection with the inside of the shell, i.e. the outside of the plate pack, whereby a secondary circuit of the plate heat exchanger is formed between the inlet and outlet connections of the second heat exchange medium, whereby plate spaces of the secondary circuit are formed between adjacent plate pairs,

- placing to a plate space of the secondary side, in contact with the outer surface of the plate pair, at least one support element for intensifying heat exchange in the plate space of the secondary side,

- arranging the support element as a pressure proof support structure between the plate pairs,

- forming openings to the support element, whereby the portion of the openings of the area of the support element is over 25 %. A typical support element according to the invention comprises a large number of openings. This kind of support element can be for example made of a perforated plate or a net-like material or a corresponding material. The portion of the openings of the area of the support element can be for example over 25 %, over 35 %, over 40 %, over 50 %, over 60 %, 25-75 % or 35-60 %. Through the openings, the heat exchange medium can pass through the support element. The size, the number and the location of individual openings in a support element can always be arranged as needed. One advantage of the invention is that a support element with openings can be arranged as an efficient turbulator of the secondary side heat exchange medium. A turbulator creates a turbulent flow. Heat exchange on the secondary side will be intensified as the turbulator decreases or prevents the laminar flow of the heat exchange medium of the secondary side. A support element with openings can also be arranged to level the flow of the heat exchange medium in a plate space, in this way for example the necking of the flow to a certain point of the plate space can be prevented. When the support elements are made of a material that has openings, the flow of the heat exchange medium can be divided more evenly to the different flow ducts of the secondary side. The flows of the heat exchange medium of the secondary side can thus be influenced with support elements.

One advantage of the invention is that a support element can function as a heat exchange rib improving the heat exchange.

One advantage of the invention is that with the help of a support element, the size of the plate spaces of the secondary circuit can be chosen as desired by placing a support element of desired size to a plate space of the secondary side. The support element can vary rather widely as to its external appearance. The profile of the cross-section of the support element can for example be saw blade like or toothed so that no sharp peaks appear. This kind of so-called corrugated or grooved support element models are advantageous from the point of view of pressure losses, because the flow is arranged to be along the grooves in the counter-flow, forward flow or cross-flow carriers. For example, if the support element is desired to be manufactured of a solid plate, the supporting points can be shaped as cup-like. An opening can be made to the bottom of these cups. Also depressions of different shapes, perforating the support plate, can be used. A weakness of a support element made of solid plate is an inferior penetrating power of the heat exchange medium, such as a gas or a liquid, because the area of the openings easily remains small. One advantage of the invention is that with the help of support elements, a supporting structure can be formed between the heat exchange plates. Due to the support elements functioning as a supporting structure between the plate pairs, the plate pack of the heat exchanger according to the invention can be made to resist pressure well. A plate type support element can for example be made of a material that is at least two times as thick as the actual heat exchange plates. The thicker and stronger the material that is used for making the support element, the more robust it is possible to be made and the better it can be made to conduct heat. Naturally, the heat exchange coefficient is material-specific, for example the differencies between the different metals can be over tenfold. With the help of the support elements according to the invention, the heat exchanger can be dimensioned to endure a pressure difference between the primary and the secondary side of for example over 10 bar, 10-100 bar, 15-100 bar, over 30 bar, over 50 bar or over 80 bar.

The heat energy travels in the support element by conduction. A possible problem in view of heat transfer is formed by the contact point of the support element and the actual heat exchange plate. A good contact point is achieved, if the support element and the heat exchange plate are one and the same piece. The heat exchange properties of the contact point can be improved also for example by increasing the area of the contact point or by soldering or welding e.g. spot welding or laser welding to each other the support element and the heat exchange plate that are separate from one another. Other factors affecting the efficiency of the heat exchange are among others the flow conditions, the temperature, the pressure, the corrosion tolerance.

The support element can be for example a solid plate, a perforated plate, a lattice structure mounted of separate ribs, or a plate made of a net-like material, such as a steel wire net. In an embodiment of the invention, the plate-like support element is grooved plate having a diameter of the size of the heat exchange plates, in which element there are openings at the openings of the heat exchange plates. It can be arranged more openings to the plate-like support element, always appropriately for each situation. The support element can be made of the same or a different metal as compared to the heat exchange surfaces, e.g. of steel, copper or aluminium. In an application of the invention, both the heat exchange plates and the support element have corrugations that form ridges and grooves in between them.

The heat exchange plates according to the invention can for example be shaped approximately as circles, the diameter of which is for example 0.2-1.5 meters. The support elements according to the invention can for example be shaped approximately as circles, the diameter of which is for example 0.2-1.5 meters. In an application of the invention, the heat exchange plates of the same plate pack and the support elements arranged to it are mainly congruent in shape so that the edges of the heat exchange plates and those of the support elements are at least mainly approximately in a same plane. In an application of the invention, the diameters of the circular shaped heat exchange plates and support elements are mainly the same. The plate heat exchanger according to the invention can for example be shaped as a substantial circular cylinder, the length of which can for example be 0.5-3 meters and the diameter 0.2-1.6 meters.

The heat exchange plates according to the invention can be made of steel or another suitable material for example by cold working. The cold working reinforces the heat exchange plates, whereby thinner plates than before can be used, and thus a better heat transfer than before is achieved. The thickness of a heat exchange plate can for example be 0.5-1.5 mm. The thickness of a support element can for example be 0.5-5 mm or 0.5-10 mm.

By the thickness of the support element, it is meant its total measure in a perpendicular angle to the diameter. For example, if the support element is corrugated, by its thickness it is meant the distance of the planes formed by the peaks of the ridges of its two sides from each other. In other words, the thickness of the support element depicts how big plate space of the secondary side can be filled with the support element. The thickness of the support element can be defined based on the thermal calculations and strength calculations to suit each situation. If the thickness of the support elements is standardized to only have certain values, the gradation can be e.g. 3, 5, 10, 15 and 20 mm. In an application of the invention, the support element has been arranged in contact with the outer surface of the plate pairs on both sides of the plate space. In this way, the heat transfer is intensified. At the same, the plate space can be, if so desired, arranged to have precisely the size of the thickness of the support element. Such support element functions also as a good support structure.

In an application of the invention, the corrugations of the heat exchange plates and of the support elements have been formed to be suitable for each other so that the corrugation ridges can be arranged inside the grooves of the heat exchange plates, even against the bottoms of the grooves. It is the most advantageous to form the corrugations of the support elements such that the structure becomes as strong as possible. The corrugations of the support elements and of the heat exchange plates thus will at least to some extent be nested. The ridges of the support elements will thus be supported to the inner surfaces of the grooves of the heat exchange plates, for example to the bottoms of the grooves. The grooving can be designed so that the groove pitch in the support element, i.e. the distance of adjacent grooves from one another, is two, three, four, five or another integer times the groove pitch of the heat exchange plates. Then the ridges of the support element will hit every other, every third, every fourth, every fifth, etc. groove of the heat exchange plate or less often. In this way, the heat exchange properties and the flow properties can be chosen as desired. The contact points between such suitably to each other corrugated heat exchange plates and support elements can be arranged as linear. By shaping the ridges of the support elements to more or less conform to the shape of the grooves of the heat exchange plates, the contact points can be made to have areas of desired size and thus, the heat transfer can be adjusted as desired.

In an application of the invention the corrugation ridges of the support element have been arranged against the corrugation ridges of the heat exchange plates so that the corrugations of the support elements and of the heat exchange plates will not be within each other. The ridges of the support elements are thus supported against the ridges of the heat exchange plates. If support elements are used the direction of the ridges of which is different from that of the ridges of the heat exchange plates, the groove pitch and the shape of the grooves can be chosen freely. In this kind of structure, the contact points can be almost point-form. The heat exchange medium can flow on almost all of the surface of the heat exchange plate, which for its part improves the heat exchange properties. On the other hand, the point-form contact points allow only little heat exchange between the heat exchange plate and the support plate.

Also a support element mounted of originally separate ribs that have been attached together, for example a lattice structure, can be supported either to the bottoms of the grooves or to the ridges. In a support element assembled of separate ribs, the ribs can be partly interleaved with each other. In this case, structures are achieved in which flows are turbulent already at low speeds. The size and the shape of the ribs can be chosen to suit each situation.

Support elements according to the invention are not necessarily attached to the rest of the plate pack. Support elements that are separate from the heat exchange plates can be made to remain in the plate pack for example by means of friction.

In an embodiment of the invention the connecting tubes have been formed of a cup deepdrawn from the material of the heat exchange plate blank that was at the opening of the heat exchange plates and to the bottom of which cup an opening has been formed. In this kind of solution, no separate connecting tubes are needed. Also, the amount of welding needed decreases.

In an embodiment of the invention, the heat exchange plate blanks are left intact at the openings in the cold working stage. At the openings, cups are deepdrawn, to the bottoms of which cups openings are made. In an embodiment of the invention, the depth of the grooves of the heat exchange plates of the primary flow side is chosen as desired on the basis of the heat exchange medium of the primary side, such as properties of the fluid and the flow rates. In an embodiment of the invention, the thickness of the support elements of the secondary flow side is chosen as desired as defined by the heat exchange medium, such as gas.

In an embodiment of the invention, groove depths of the heat exchange plates used in the manufacturing process of the heat exchangers are standardized. In an embodiment of the invention, groove depths of the support elements used in the manufacturing process of the heat exchangers are standardized. For example, there can only two, three or four different groove depths or support plate thicknesses, whereby the manufacturing, the maintenance and the repair of the heat exchangers becomes easier.

The different embodiments of the invention are applicable for use in connection with different heat exchangers, for example in air condition technology and processing industry, in different coolers, heat recovery devices and flue gas boilers. Heat exchangers according to the invention can be used for example in conditions where the volume flow of the secondary heat exchange medium differs considerably from the other heat exchange medium. E.g. liquid/gas exchangers are like this. Due to the weaker heat exchange properties of gases, the gas ducts have to be dimensioned considerably larger than on the liquid side to reduce the pressure loss. A heat exchanger according to the invention is also applicable to a situation in which a phase transition occurs in the secondary heat exchange medium. Also for example in evaporators and condensers benefit is gained when the vapour side is dimensioned looser. The invention is well suited also for gas/gas heat exchangers. The use of support elements separate from the heat exchange plates is advantageous also in different applications suffering from problems of contamination and/or viscosity.

According to an embodiment of the invention, a plate heat exchanger comprises a plate pack formed of heat exchange plates, connecting tubes and support elements, a shell surrounding the plate pack, the ends of the shell as well as necessary connections for heat exchange media.

According to an embodiment of the invention, the plate heat exchanger is a plate heat exchanger according to the so-called Plate & Shell™ technology developed by the applicant, which plate heat exchanger comprises a pack of plates formed by heat exchange plates and a shell surrounding it. The plate pack is made up of several plate pairs. Each plate pair is typically formed of two heat exchange plates that are welded together at least at their outer periphery. Each heat exchange plate has at least two first openings for the flow of the first heat exchange medium. Adjacent plate pairs are attached together by welding or by otherwise combining the first openings of two adjacent plate pairs to each other. Thus the first heat exchange medium can flow from a plate pair to another via the first openings. The second heat exchange medium is arranged to flow inside the shell in the spaces between the plate pairs. Inlet and outlet connections for the first as well as for the second heat exchange medium have been arranged through the shell of the Plate & Shell™ plate heat exchanger. The inlet and outlet connection of the first heat exchange medium has been arranged in connection with the inner parts of the plate pack. The primary circuit of the plate heat exchanger is thus formed between the inlet and outlet connection of the first heat exchange medium. The inlet and outlet connections for the second heat exchange medium have been arranged in connection with the inner side of the shell, i.e. with the outer side of the pack of plates. In other words, the secondary circuit of the plate heat exchanger is formed between the inlet and outlet connection of the second heat exchange medium, inside the shell, in the spaces between the plate pairs. Typically, the primary and secondary circuits are separate from each other, i.e. the first heat exchange medium flowing in the inner part of the plate pack cannot get mixed with the second heat exchange medium flowing in the shell, i.e. outside the plate pack. Thus, the first primary side heat exchange medium flows in every other plate space and the second secondary side heat exchange medium flows in every other plate space of an advantageous plate heat exchanger according to the invention. Heat exchangers according to the invention can be manufactured for example as follows. The heat exchange plates are pressed with a flat press tool or the like as cold from a plate blank. The heat exchange plates of adjacent plate pairs are attached to each other at their openings, with tubes fitted to them. The tubes are welded at their ends to the perimeters of the openings of the plates. The support elements can be fitted between the heat exchange plates before welding the other end of the tubes. The connecting tubes can also be formed at least partly by deepdrawing from the plate material. Then, it is not necessary to use separate connecting tubes but instead, an intact plate remains in the blank of the heat exchange plate at the openings to be connected to each other, to which plate a cup is deepdrawn by means of a deepdrawing tool. To the bottom of the cup an opening is made, and the plate pairs are welded together at the cups of the opposite heat exchange plates. The opposite cups thus form a connecting tube between the plates.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described in more detail below with reference to the enclosed schematic drawing, in which

Figure 1 shows a first embodiment of the heat exchanger according to the invention,

Figure 2 shows a cross-section of the heat exchanger of Figure 1 ,

Figure 3 shows a second embodiment of the heat exchanger according to the invention,

Figure 4 shows a cross-section of the heat exchanger of Figure 3,

Figure 5 shows a part of one plate pack according to the invention,

Figure 6 shows a part of another plate pack according to the invention, and Figure 7 shows a support element formed of steel wire net, and

Figure 8 shows a support element formed of perforated plate.

DETAILED DESCRIPTION OF THE EXAMPLES OF THE FIGURES

For the sake of clarity, the same reference numbers are used for corresponding parts in different embodiments. Figures 1 to 4 show Plate & Shell™ plate heat exchangers 1 according to the invention. A plate heat exchanger 1 comprises a plate pack 5 formed by heat exchange plates 2, connecting tubes 3 and support elements 4. The plate pack 5 is surrounded by a shell 6 that is composed of a circular cylindrical shell part 6a and ends 6b. The inlet connection 7a and outlet connection 7b for the first heat exchange medium lead through the end 6b to the inside of the plate pack 5. The inlet connection 8a and outlet connection 8b of the second heat exchange medium lead through the shell part 6a to the inside of the shell 6. The heat exchange plates 2 have openings 9 for the primary side flow. The heat exchange plates 2 have been welded at their perimeters 10 to each other as plate pairs 11. The adjacent plate pairs 11 have been attached to each other at the openings 9 with connecting tubes 3. To each secondary flow duct between plate pairs, i.e. secondary plate space 12, support elements 4 have been arranged. The thickness T of the support element 4 is approximately equal to the length of the connecting tube 3. In this way, the connecting tubes 3 and the support elements 4 support the plate pack 5. The space between the shell 6 and the plate pack 5 is partly closed with the sealings 13 shown in Figure 2. With the sealings 13, the flow of the secondary side is guided in its entirety between the plate pairs. The connecting tubes 3 of Figures 1 and 2 are originally separate tubes that are welded tightly at their both ends to the perimeters of the openings 9 of the heat exchange plates. Figures 3 and 4 show an embodiment of the invention in which the tubes to be fitted to the openings 9 of the heat exchanger plate have been replaced with cups 3a deepdrawn at the openings from a plate blank of the heat exchange plates 2. To the bottoms of the cups 3a, openings 3b shown in Figure 4 have been formed, and the opposite cups have been welded to each other at their ends. The cups 3a welded to each other thus form the connecting tube 3. Otherwise, the embodiments of Figures 1 and 2 and those of Figures 3 and 4 correspond to each other.

Figure 5 shows two adjacent plate pairs 11 and the connecting tubes 3 between them. A support element 4 has been arranged between plate pairs, i.e. to a plate space 12 of the secondary side, the support element being composed of two corrugated plates 4a and 4b that have been welded to each other. The corrugation ridges 14 of the support element have been arranged to the bottom 15 of the grooves of the heat exchange plates. The thickness of the support element is marked with letter T.

Figure 6 shows two adjacent plate pairs 11 and the connecting tubes 3 between them. A support element 4 has been arranged between plate pairs 11 , i.e. to a plate space 12 of the secondary side, the support element being composed of two corrugated plates 4a and 4b that have been welded to each other. The corrugation ridges 14 of the support element and the corrugation ridges 16 of the heat exchange plates are opposite to each other. The support elements of Figures

5 and 6 have the same thickness T. By comparing the examples of Figures 5 and

6 it is noticed that with a support element 4 with equal thickness, plate spaces 12 of the secondary side of different sizes can be achieved.

Figure 7 shows a principle view of a support element 4 formed of steel net. Figure 8 shows a principle view of a support element 4 formed of perforated plate. The support elements have openings 9 for the connecting tubes between the plate pairs.

All described examples can be applied as well by using separate connecting tubes as by using connecting tubes formed of deepdrawn cups.

The figures show only a few preferred embodiments according to the invention. The figures do not specifically show matters that are of secondary importance in view of the main idea of the invention, known as such or obvious as such for someone skilled in the art. It is obvious to someone skilled in the art that the invention is not limited merely to the above-described examples, but the invention may vary within the scope of the claims presented below. The dependent claims present some possible embodiments of the invention, and they are as such not to be considered to restrict the scope of protection of the invention.