Heat Exchanger

TECHNICAL FIELD

The present invention relates to a plate heat exchanger device having a contact-free distribution channel. The heat exchanger device comprises a plurality of cassettes, where a cassette constitutes a pair of heat exchanger plates permanently joined. The invention further relates to a heat exchanger comprising a plurality of heat exchanger devices.

BACKGROUND ART

Food manufacture is typically characterised by the need to process and treat highly viscous products, e.g. concentrates for carbonated beverages, juices, soups, dairy products and other products of fluid consistency. For natural reasons, the hygiene aspirations and expectations in this context are extremely high to enable the requirements of various authorities to be met.

Plate heat exchangers are used in the food industry for a number of different purposes. One problem in using plate heat exchangers for the food industry is that some products contain fibres and other solid materials mixed in the fluid. In most plate heat exchangers, the heat exchanger comprises one type of plate, which is mounted with every other plate rotated 180 degrees to form two different channels for the fluids, one channel for the cooling medium and one channel for the product that is to be cooled. Between each plate is a sealing provided. Such an arrangement is cost-effective and works for many applications, but shows some drawbacks when it comes to beverages and the like that comprises fibres and other solid materials, since the plates will bear on each other at some contact points. Each plate is provided with ridges and valleys in order to on one hand provide a mechanical stiffness and on the other hand to improve the heat exchange to the liquid. The plates will bear on each other where the patterns of the plates meet each other, which will improve the mechanical stiffness of the plate package. This is important especially when the fluids have different pressures. A drawback of the plates bearing on each other is that each bearing point will constitute a flow restriction where material contained in the liquid may be trapped and can accumulate. The accumulated material will restrict the flow further, causing more material to accumulate. This will somewhat resemble the formation of a river delta, where a small flow difference will deposit some material which in turn causes more material to deposit.

One solution to the problem with clogging of material in a plate heat exchanger is to use a heat exchanger where the product channel is contact-free. This type of heat exchanger reduces the accumulation of material in the product channel.

U.S. Pat. No. 4,403,652 describe a heat exchanger with a contact-free channel. The heat exchanger comprises specific, extruded heat panels having two sides connected by webs and specific header sections made by casting. When the panels are stacked to form a heat exchanger, contact-free channels are obtained. This solution is rather expensive and complicated, but may work for some applications.

In order to obtain a sufficient rigidity when using traditional heat exchanger plates for a contact-free plate heat exchanger, the plates are permanently joined together in pairs, e.g. by welding or brazing. In this way, two plates form a cassette with a plurality of contact points between the plates, where the contact points are joined together as well as the rim of the plate. The cassette will be rigid enough to handle some differences in pressure between the two fluids, thereby enabling the contact-free product channel. One plate heat exchanger having a contact-free channel is known from JP 2001272194. In this heat exchanger, two plates of the same type having longitudinal grooves are permanently joined to each other to form a cassette, in which longitudinal channels are formed for the heat exchange fluid. Such cassettes are stacked using gaskets, thereby forming a contact-free product channel between two cassettes.

Another heat exchanger having a contact-free product channel is disclosed in WO 2006/080874. In the disclosed heat exchanger, a corrugated and undulating pattern perpendicular to the flow direction is used in order to provide rigidity to the plates and also to improve the heat transfer between the two fluids. In order to achieve this, two different plate types are necessary. Two plates of a first plate type make up a first cassette, and two plates of the second plate type make up a second cassette. The patterns of the plates are adapted such that when the two cassettes are placed together, a product channel is formed where the plates do not bear on each other. Depending on the size of the heat exchanger, the distance between the plates in the contact-free product channel may be in the region of 2 to 12 mm. This type of heat exchanger reduces at least some of the accumulation of material in the product channel.

The heat exchanger disclosed in WO 2006/080874 is a so-called semiwelded plate heat exchanger, i.e. a heat exchanger comprising a number of cassettes formed by welding heat exchanger plates together in pairs. The weld seam normally runs along the side edges of the cassettes and around the portholes. A gasket is disposed between the respective cassettes and is normally made of a rubber material and situated in a groove of the heat exchanger plate. One fluid flows inside the cassettes, and another fluid between the cassettes. The flow channel inside the cassettes is used for the heating/cooling fluid and the flow channel between the cassettes is used for the fibrous fluid. Semiwelded plate heat exchangers tolerate relatively high pressures and make it possible to open the plate package and clean the spaces between pairs of welded heat exchanger plates. The welds which replace the gaskets in every second space between plates round the heat exchange surface of the heat exchanger plates reduce the need for gasket replacement and enhance safety.

These solutions may function for some applications, but they still show some disadvantages. One disadvantage is that longitudinal fluid channels provide a relatively poor heat transfer which in turn requires a rather large heat exchanger. There is thus room for improvements.

DISCLOSURE OF INVENTION

An object of the invention is therefore to provide an improved heat exchanger having a contact-less product channel.

The solution to the problem according to the invention is described in the characterizing part of claim 1. Claims 2 to 6 contain advantageous embodiments of the heat exchanger device. Claim 7 contains an advantageous heat exchanger.

With a heat exchanger device, comprising a plurality of cassettes, where a first cassette comprises two plates of a first type and a second cassette comprises two plates of a second type, where each plate is provided with a corrugated pattern having a plurality of ridges and valleys with side walls there between, where the corrugated pattern comprises undulations parallel to the direction of the corrugated pattern, and where the cassettes are mounted adjacent each other at a predefined distance, the object of the invention is achieved in that the perpendicular distance (a₂) between the side walls (22, 23, 26, 27) of two adjacent cassettes (11, 21) is substantially constant over the width of the heat exchanger device.

By this first embodiment of the heat exchanger device, a product channel is obtained in which the flow restriction over the width of the heat exchanger is constant. Since the flow restriction caused by the distance between the side walls of the cassettes is constant over the width of the heat exchanger, there will be no regions in the heat exchanger where material will have a slower speed and thus there will be no region in which the material will start to accumulate.

This is advantageous in that the cassettes can be used in heat exchangers to heat or cool fluids containing particles or fibres without particles obstructing the fluid flow.

In an advantageous development of the invention, the corrugated pattern of the heat exchanger plates is substantially perpendicular to the main flow direction of the heat exchanger. This improves the heat exchanger properties of the heat exchanger further.

In another advantageous development of the invention, the difference in distance between the side walls of the first cassette and the side walls of the second cassette is less than 1/10 of the height of a ridge. The advantage of this is that the heat exchanger properties of the heat exchanger are improved. More precise, the difference in flow velocity of the fluid is reduced since the difference in flow resistance over the width of the cassette is reduced.

In an advantageous further development of the invention, the difference in distance between the side walls of the first cassette and the side walls of the second cassette is less than 1/50 of the height of a ridge. The advantage of this is that the heat exchanger properties of the heat exchanger are further improved.

In an advantageous further development of the invention, the difference in distance between the side walls of the first cassette and the side walls of the second cassette is less than 1/100 of the height of a ridge. The advantage of this is that the heat exchanger properties of the heat exchanger are further improved.

In an inventive heat exchanger, a plurality of heat exchanger cassettes is comprised. The advantage of this is that a heat exchanger for viscous fluids is obtained.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in greater detail in the following, with reference to the embodiments that are shown in the attached drawings, in which

FIG. 1 shows a prior art heat exchanger,

FIG. 2 shows a front view of a plate for the use in a heat exchanger according to the invention,

FIG. 3 shows a detail of a first embodiment of a heat exchanger according to the invention,

FIG. 4 shows a detail of two cassettes positioned adjacent each other in a heat exchanger according to the invention,

FIG. 5 shows cross-section A-A of the cassettes according to FIG. 4, and

FIG. 6 shows cross-section B-B of the cassettes according to FIG. 4.

MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims.

FIG. 1 shows a front view of a prior art cassette 1 as disclosed in WO 2006/080874. The cassette 1 comprises two heat exchanger plates 2 permanently joined together. The plates have four portholes constituting inlet and outlet ports 4, 5, 6, 7 and a heat transfer surface 8 with ridges 9 and valleys 10. The cassette 1 may be produced by welding or brazing the plates together, whereby the two plates 2 are joined together permanently along their periphery and around at least two of ports 4, 5, 6, 7. The plates are joined also in the heat transfer surface, where the pattern of one plate will bear on the pattern of the other plate. The plates may e.g. be joined along a few longitudinal lines reaching from one inlet/outlet side to the other inlet/outlet side.

A cassette is made from two plates of the same type. One plate is rotated by 180° around a centre axis 13 before the plates are joined. In this way, the pattern will interact such that the pattern of one plate will bear on the pattern of the other plate, creating a plurality of intermediate contact points. When all or at least some of these contact points are joined together, a stiff cassette that will withstand a certain overpressure is obtained.

The pattern of the plate is configured in such a way that there will be no contact points between the cassettes at the heat exchange surface when the cassettes are assembled in a heat exchanger. The plates are further so designed that the intermediate contact points for necessary mechanical support are created substantially only inside the cassette, in the cooling media channel, when two plates are joined to form a cassette. In contrast, at portholes 6 and 7 the plates abut completely against one another and are joined together permanently so as to form a seal against the fluid which is intended to flow through the portholes. Portholes 4 and 5 constitute the inlet and outlet to the cassettes.

The cassettes are mounted to each other with a sealing gasket. The gasket, which is preferably made of an elastic material, e.g. rubber material, is disposed in a groove which extends along the periphery of the constituent plates of the cassette and around ports 6 and 7. There is a ring gasket round ports 4 and 5. The purpose of the gasket is to seal the space between two cassettes, thereby creating a product channel.

FIG. 2 shows a front view of a cassette 11 for the use in a heat exchanger according to the invention. The cassette 11 comprises two heat exchanger plates 12 permanently joined together. The plates have at least four portholes constituting inlet and outlet ports 14, 15, 16, 17 and a heat transfer surface 18 with ridges 19 and valleys 20. The cassette 11 may be produced by welding or brazing the plates together, whereby the two plates 12 are joined together permanently along their periphery and around at least two of ports 14, 15, 16, 17. Preferably, the plates are joined also in the heat transfer surface, where the pattern of one plate will bear on the pattern of the other plate. The plates may e.g. be joined along a few longitudinal lines reaching from one inlet/outlet side to the other inlet/outlet side. In the description, the centre axis 13 is also referred to as the transverse axis or the x-axis, and the longitudinal axis or the y-axis is the axis extending along the length of the heat exchanger plate.

A first cassette is made from two plates of the same type. One plate is rotated by 180° around a centre axis 13 before the plates are joined. In this way, the pattern will interact such that the pattern of one plate will bear on the pattern of the other plate, creating a plurality of intermediate contact points. When all or at least some of these contact points are joined together, a stiff cassette that will withstand a certain overpressure is obtained.

The inventive plate heat exchanger comprises two different types of cassettes. The first cassette is described above. A second cassette is made in the same way, using two plates of the same type and with one plate rotated by 180° around a centre axis 13. The plates for the second cassette have the same pattern as the plates for the first cassette, but with the pattern rotated compared with the plates for the first cassette.

The patterns of the first and second cassettes are configured in such a way that there will be no contact points between the cassettes at the heat exchange surface when the cassettes are assembled in a heat exchanger.

The cassettes are mounted to each other with a sealing gasket. The gasket, which is preferably made of an elastic material, e.g. rubber material, is disposed in a groove which extends along the periphery of the constituent plates of the cassette and around ports 14 and 15. There is a ring gasket round ports 16 and 17. The purpose of the gasket is to seal the space between two cassettes, thereby creating a product channel.

According to the invention, the plates are also so designed that contact points for necessary mechanical support occur largely only on the inside, between two plates which are to be joined together to form a cassette, by opposite ridges abutting against one another. In contrast, at portholes 14 and 15 the plates abut completely against one another and are joined together permanently so as to form a seal against the fluid which is intended to flow through the portholes. Portholes 16 and 17 constitute the inlet and outlet to the cassettes.

FIG. 3 shows a detail of the pattern of the plates. The pattern comprises corrugations with ridges 19 and valleys 20. The corrugations are wave shaped creating undulations across the plate surface, parallel to the centre axis 13 and thus perpendicular to the direction of flow through the channels in the heat exchanger. The main flow direction through a flow channel is in the longitudinal direction of the heat exchanger, i.e. along the y-axis. This will be referred to as the flow direction of the heat exchanger.

The purpose of the undulations is to enlarge the heat exchange surface and to create a somewhat larger pressure drop for the fluid flowing through the flow channel. The undulations may have different shapes. In the shown example, an undulating pattern that has proved to be successful is used. This undulating pattern comprises straight sections parallel to the transverse direction of the heat exchanger plate, with angled sections interconnecting the straight sections. In this case, the direction of the undulating pattern follows the straight sections, i.e. the transverse direction. In the shown example, the direction of the corrugated pattern is also in the transverse direction.

It is also possible to incline the corrugated pattern together with the undulations with respect to the transverse direction. The direction of the pattern may be inclined with up to 30 degrees with respect to the transverse axis. The undulating pattern will have the same inclination angle as the corrugated pattern.

FIG. 4 shows a detail of the first cassette 11 and the second cassette 21 when they are assembled in a heat exchanger. The first cassette 11 is provided with ridges 19 and valleys 20 having inclined side walls 22, 23 there between. The second cassette 21 is likewise provided with ridges 24 and valleys 25 having inclined side walls 26, 27 there between.

FIG. 5 shows a cross-section of plane A-A. In this figure, the distance between the two ridges 19 and 24 is denoted a₁, the distance between the two side walls 22 and 26 is denoted a₂, the distance between the two valleys 20 and 25 is denoted a₃, and the distance between the two side walls 23 and 27 is denoted a₄. The distance between the ridges, valleys or side walls is measured perpendicular to the surfaces. The volume between the first cassette 11 and the second cassette 21 constitutes the product flow channel for the fluid that is to be cooled or heated. Arrows 31 indicate the direction of flow for the fluid. The volume between the cassettes comprises cavity 28 between the ridges 19 and 24, cavity 29 between the side walls 22 and 26 and cavity 30 between the valleys 20 and 25. Distances a₁and a₃are preferably substantially the same, as are distances a₂and a₄. Distance b is the height of a ridge measured from a valley. This value is the pressing depth of a plate.

FIG. 6 shows a cross-section of plane B-B. In this figure, as in FIG. 5, the distance between the two ridges 19 and 24 is denoted a₁, the distance between the two side walls 22 and 26 is denoted a₂, the distance between the two valleys 20 and 25 is denoted a₃, and the distance between the two side walls 23 and 27 is denoted a₄. The distance between the ridges, valleys or side walls is measured perpendicular to the surfaces. The volume between the first cassette 11 and the second cassette 21 constitutes the product flow channel for the fluid that is to be cooled or heated.

Due to the fact that the distance between the side walls is smaller than the distance between the ridges and the valleys, i.e. distance a₂is smaller than distance a₁and a₃, the side walls and thus the cavity 29 will constitute a flow restriction for the fluid. By keeping this flow restriction constant over the width of the heat exchanger, the problem with clogging and accumulation of material in the product channel is minimised. By keeping the flow restriction constant, there will be no position in the flow channel where material may start to accumulate, since the speed of flow will be substantially the same over the whole width of the heat exchanger.

In the inventive heat exchanger, the distance between the side walls, i.e. distance a₂, is held substantially constant over the complete heat exchanger. By substantially constant is meant that the variation of the distance between the side walls lies within the tolerances achieved in the manufacturing of the heat exchanger plates. Preferably, the tolerance for the pressed plates used for the cassettes is smaller than 1/10 of the pressing depth of the plate. More preferably, the tolerance for the pressed plates used for the cassettes is smaller than 1/50 of the pressing depth of the plate. More preferably, the tolerance for the pressed plates used for the cassettes is smaller than 1/100 of the pressing depth of the plate. Tolerances in these regions are possible and economical to achieve when pressing heat exchanger plates. This means that a typical tolerance for plates having a pressing depth in the region of 10 mm may be in the region from 1 mm down to 0.1 mm.

To achieve a substantially constant distance between the side walls of two adjacent cassettes, the patterns of the two plate types used for the first and the second cassette are made asymmetric with regard to the width of the valleys and ridges. In the described embodiment, this means that the width of valley 20, i.e. the distance between the lower part of the side walls 22, 23, is greater for the straight section of the undulating pattern, i.e. when the valley is directed in the transverse direction, perpendicular to the direction of flow (see FIG. 5) than for the angled section of the undulating pattern, i.e. when the direction of the valley is angled with respect to the direction of flow (see FIG. 6).

The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims. In one example, a different plate pattern may be used for the heat exchanger cassettes.

Reference Signs

Prior Art:

1: Cassette

2: Plate

3: Centre axis

4: Port

5: Port

6: Port

7: Port

8: Heat transfer surface

9: Ridge

10: Valley

11: Cassette

12: Plate

13: Centre axis

14: Port

15: Port

16: Port

17: Port

18: Heat transfer surface

19: Ridge

20: Valley

21: Second cassette

22: Side wall

23: Side wall

24: Ridge

25: Valley

26: Side wall

27: Side wall

28: Cavity

29: Cavity

30: Cavity

31: Flow direction

Heat Exchanger

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Priority Claims (1)

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