WO2002027257A1

WO2002027257A1 - A heat exchanger comprising plate elements with spiral ducts

Info

Publication number: WO2002027257A1
Application number: PCT/DK2001/000403
Authority: WO
Inventors: Erik Kristensen
Original assignee: Dantherm Hms A/S
Priority date: 2000-09-28
Filing date: 2001-06-12
Publication date: 2002-04-04
Also published as: DE10196671T1; AU2001273879A1

Abstract

The invention relates to a heat exchanger consisting of plate elements which are provided with a profile and arranged such that the profile produces spaced ducts or layers of ducts through which one or more fluids are conveyed. The plate elements (1) comprise at least two parts (2, 3), which have a plurality of substantially longitudinally extending grooves (4) provided with spiral profiles (5), so that the grooves together form tubular ducts (6) with spiral profiles. Spaced flow paths are achieved hereby, so that two or more fluids may be conveyed in these without getting into direct contact with each other. It is also ensured that the ducts may be made with different cross-sectional areas and geometry, thereby allowing the flow characteristics to be optimized individually.

Description

A heat exchanger comprising plate elements with spiral ducts

The invention relates to a heat exchanger comprising plate elements, said plate elements being provided with a profile and arranged such that the profile produces spaced ducts or layers of ducts through which one or more fluids are conveyed.

Heat exchangers of the plate type are known from DE19858652A1, wherein a plurality of plates manufactured with one and the same profile are arranged on top of each other to create two spaced flow paths for two fluids, each flow path consisting of a plurality of ducts. The two flow paths have different cross-sectional areas, which are produced in that the plates are stacked in a pattern: opposite - the same way - opposite - the same way - , etc. According to the specification the intention is to compensate for the fact that the two fluids have different viscosities, larger and smaller, respectively. According to the specification, the high viscosity fluid is passed through the flow path having the largest cross- sectional area, thereby reducing the flow resistance. The problem of this type of heat exchanger is the extremely great limitation in design which is due to the necessity of making the plates uniform, the reason being that the production costs get too high if the plates are to be different. This type of heat exchanger is typically mass- produced, and the price therefore changes considerably relative to the number of constituent components which are to be produced (i.e. more tools and machines), handled and assembled. Moreover, the efficiency is poor, as the ducts (the flow paths) are smooth, which is again dictated by the production method for this type of heat exchanger.

EP720720B1 discloses a plate heat exchanger which is con- structed by stacking of plates which are provided with one and the same profile to thereby create two spaced, parallel flow paths for two fluids, each flow path consisting of a plurality of ducts. The profile is trapezoidal and has an angle which is less than 90 degrees. When the angle is less than 90 degrees, it is ensured that the bottom of the trapezium is larger than the opening at the top. This solves a strength and sealing problem between the ducts in the individual layer, since a certain overlap is produced, which is suitable for seam or spot weld- ing the plates together - where- this is possible. The problem of this type of heat exchanger is the general design restraint to the trapezium shape, and that the plates have to be uniform to fit on top of each other at stacking. Further, the trapezium shape is not suitable as a cross-sectional shape to direct a flow. Particularly at the sharp corners of the trapezium where the angle is less than 90 degrees, zones are produced in which the flow resistance is great relative to other zones . This does not give a uniform flow, and the flow resistance therefore increases. This means that either the cross- section must be enlarged or the flow pressure must be raised to achieve a given flow. If the cross-section is increased, the volume of the heat exchanger increases . If the pressure is increased, thicker plates are required for greater rigidity, and greater demands are made on the welding of the joints.

GB2043867A discloses a special type of fluted tube for use in heat exchangers of the tube type. The tube is made from a profiled band which, under loading, is wound on a mandrel . Tube heat exchangers are usually constructed in that one or more tubes are wound in spiral shape or helical shape. One fluid is directed through the tube or tubes, while another fluid is caused to contact the external surface of the tube or tubes . Heat transfer hereby takes place between the fluids through the tube wall .

The problem of the wound type of tube, which is mentioned in the specification, is that the joining rim against rim merely consists of a compression. Thus, it can never be entirely tight and can only operate at relatively low pressures.

Moreover, US 4,248,179 discloses a type of tube for use in a tube heat exchanger, which is also provided with an internal profiled contour. The general problem is that tube heat exchangers are expensive to manufacture and require a great volume in order to provide a good effi- ciency, the reason being that there is no expedient flow of the fluid on the external side of the tubes. In this connection, a plate heat exchanger with closely spaced ducts will be preferable, as the flow of both fluids can be controlled here.

The object of the invention is. to provide a simple and inexpensive heat exchanger having an improved efficiency.

This may be achieved by the present invention, if the plate elements consist of at least two parts, said parts having on one side a plurality of substantially longitudinally extending grooves which are provided with spiral profiles, so that the grooves together form at least one tube-shaped duct with spiral profiles, and that the plate elements are provided with guide ribs at the ends .

In heat exchange there are situations where there is an almost unlimited resource of a first fluid, e.g. atmospheric air, and a limited resource of a second fluid, between which fluids heat transfer is to take place. It is therefore advantageous to give top priority to the efficiency of the limited resource. By constructing the heat exchanger from plate elements having longitudinally extending grooves which are provided with spiral profiles, it is ensured that spaced flow paths are created, so that two or more fluids may be conveyed in these without getting into direct contact with each other. It is moreover ensured that the ducts may be formed with different cross-sectional areas and geometry, thereby allowing the flow characteristics to be optimized individually. The use of tubular ducts with spiral profiles contributes to dividing the flow into a primary flow and a secondary flow. The primary flow takes place in the centre of the duct and is substantially laminar. The secondary flow occurs at the spiral profiles, where there are areas of higher flow rates, and where ball-shaped turbulent whirls are generated on the inner side of the tube wall. Ex- change and mixing of the two flows take place in the zone between the primary flow and the secondary flow. The result is that the fluid particles are in alternate contact with the inner wall of the tube and the main flow itself . This gives a very effective heat conduction transversely in the flow. The spiral geometry increases both the heat transfer area and serves as a 3D roughness element (rib shape) in the flow. This also affects the pressure loss through the tube because of the increased coefficient of resistance, which depends on the size (height and num- ber) , the shape, the pitch, etc. of the spiral profiles. These parameters are preferably selected so that the flow is not reduced considerably, and the prevailing flow type is laminar. The greater the pressure loss in the heat exchanger, the more energy has to be used for circulating the fluids. That is, an energy saving is achieved by keeping the pressure loss as low as possible, just as a further saving may be achieved by using a smaller and less expensive component for circulating the fluids.

The external side of the heat exchanger element, i.e. the external side of the spiral ducts, is given a larger effective flow area, where the external geometry of the spiral shape generates a partially whirling flow. This may be in the form of counter-flow or cross-flow exchange. The flow characteristics on the external side of the exchange element (between the exchange elements) is a combination of laminar and turbulent flow with a max. Re = 10000, which is a value twice as great as a smooth tube. The pressure loss may be increased to a smaller extent on the external side because of the geometrical shape of the ducts. This may be counteracted by increasing the cross-sectional area on the external side.

Providing the plate elements with guide ribs at the ends ensures both a lower flow resistance and a greater efficiency of the heat exchanger, as undesired turbulence of the fluids, which would otherwise occur at inlet and outlet, is prevented.

When, in cross-section, the grooves have the shape of a circle or a part of a circle, it is advantageously ensured that the geometry contributes to providing a laminar flow in the ducts. With other cross-sectional shapes, such as a part of an oval, a polygon or combinations of such, or combined with the circle shape, it is ensured that the fluids can perform other flows that can give a great heat transport transversely to the flow.

That the pitch of the spiral profiles is between 5 and 85 degrees and is between 60 and 75 degrees in a particularly preferred embodiment, contributes to a particularly good heat transmission in the ducts.

When, in cross-section, the spiral profiles have the shape of a part of a circle, it is advantageously ensured that the fluid or fluids may perform a ball-shaped rotation in the profile. With other cross-sectional shapes, such as a part of an oval, a polygon or combinations of such, or combined with the circular shape, it is ensured that the fluids may perform other.forms of rotations that can give a great heat transport transversely to the flow.

When the cross-sectional areas of the ducts are different, it is advantageously ensured that the efficiency of one flow may be given particular priority relative to the other.

When the fluids may be conveyed in the ducts in various directions, a particularly good efficiency may be achieved.

When the pitch of the spiral profiles may increase or de- crease in the longitudinal direction, it is advantageously ensured that the pressure loss may be diminished with retained efficiency. If e.g. the pitch is great at the inlet and diminishes toward the outlet, there may be a pitch at the outlet which is smaller than the one which would otherwise cause turbulence and thereby pressure loss. Smaller pitch results in greater mixing of the flow.

When the cross-sectional area of the groove increases or diminishes in the longitudinal direction, the additional advantage is achieved that the pressure and the rate of the flow may be adapted in the longitudinal direction and thereby reduce turbulence and pressure loss. This in- creases the efficiency.

When the plate elements are made of a plastics material, it is advantageously ensured that the production process does not give any restraints in the design of the plate elements.

When the plastics material is polypropylene, it is advantageously ensured that the plate elements may be made sufficiently rigid and strong to withstand the pressure of the fluids, even with a low wall thickness.

List of figures

Fig. 1 shows a heat exchanger composed of plate elements.

Fig. 2 shows an example of flow directions in a heat exchanger.

Fig. 3 shows a section transversely through a heat exchanger, from which the structure of the construction with plate elements appears.

Fig. 4 shows a section longitudinally through a plate element .

Fig. 5 shows a plate element seen from above. Fig. 6 shows the flow longitudinally in a duct having a spiral profile.

Fig. 7 shows the flow in a duct having a spiral profile, seen in cross-section. - Fig. 8 shows examples of possible flow paths through a heat exchanger in an L-L-configuration. Fig. 9 shows examples of possible flow paths through a heat exchanger in a CC-I configuration. Fig. 10 shows examples of possible flow paths through a heat exchanger in an X configuration.

Fig. 11 shows examples of possible flow paths through a heat exchanger in a I-I configuration. Fig. 12 shows examples of possible flow paths through a heat exchanger in a I-C configuration. - Fig. 13 shows examples of possible flow paths through a heat exchanger in an L-C configuration. Fig. 14 shows examples of possible flow paths through a heat exchanger in a C-C configuration. Fig. 15 shows examples of possible flow paths through a heat exchanger in a C-I-C configuration.

Fig. 16 shows examples of possible flow paths through a heat exchanger in an elliptic I configuration. - Fig. 17 shows an example of possible flow paths through a heat exchanger in an elliptic X configuration.

Description of the drawing

Fig. 1 shows an example of an embodiment of a heat exchanger. A plurality of plate elements 1 are stacked on top of each other. Encapsulation and seals around the heat exchanger as well as supply and discharge of the heat exchanging fluids are not shown, since this basically does not differ from other heat exchangers and is thereby evident to perform for a skilled person. In the present context, fluids are taken to mean liquids, air, gas, etc. or combinations thereof.^'

Fig. 2 shows an example of flow directions through the heat exchanger in the form of counter-flow exchange. Co- flow exchange and cross-flow exchange may also be pro- vided, just as more than two fluids may be used.

Fig. 3 shows the plate elements which comprise lower parts 2 and upper parts 3. The lower and upper parts may be joined, e.g. by welding or gluing, if this is expedi- ent owing to the strength and rigidity of the plate elements relative to the dimensions and the pressure in the fluids . The longitudinally extending grooves 4 are provided with spiral profiles 5. The number of flutes in the profile as well as the size relative to the diameter of the duct is adapted to the desired flow characteristic. The grooves 4 are positioned opposite each other so as to form tubular ducts 6 in which one fluid is conveyed. Also formed are the ducts 7 which are intended for the other fluid. The fluids are separated by the upper and lower parts of the plate elements. It will be seen that the cross-sectional area of the ducts 6 may be selected to be considerably smaller than the cross-sectional area of the ducts 7. The ratio of the cross-sectional areas may be changed in several ways, inter alia by changing the spac- ing between the plate elements 1 and by changing the diameter and the number of the ducts 6.

Fig. 4 shows a section through a plate element. The upper and lower parts can substantially be mirror images of each other with their common engagement face as a mirror face. Therefore only the one part is shown. In addition to the grooves 4 and the spiral profiles 5, the part is provided with guide ribs 8. The grooves 4 are depres- sions, while the guide ribs 8 are local elevations which form barriers to the flows and guide these at the inlet and outlet. Also shown is a joint 10 of the lower part 2 and the upper part 3. The lower and upper parts are joined at several places inter alia between the grooves to make the ducts 6 tight. This is not shown in the figure.

Fig. 5 shows a plate element from above. The figure shows a face 10.1 which is an elevation that forms a boundary when engaged with the next plate element, so that a closed flow path is achieved. Relative to fig. 4, the profile is terminated conversely. This means that the grooves 4 in fig. 5 are elevations, while the guide ribs 8 are depressions. Hereby the guide ribs only affect the flow, which is to pass transversely to these, to a limited extent .

Figs . 6 and 7 show the flow in a duct with a spiral profile. At the tube wall, the spiral profiles contribute to dividing the flow into a primary flow and a secondary flow. The primary flow takes place in the centre of the duct and is substantially laminar. The secondary flow occurs at the spiral profiles, where there are areas with higher flow rates, and where ball-shaped turbulent whirls are formed on the inner side of the tube wall. Exchange and mixing of the two flows take place in the zone between the primary flow and the secondary flow. The result is that the fluid particles are alternately in contact with the inner wall of the tube and the main flow itself. This gives a very effective heat conduction transversely in the duct.

Figs . 8 - 17 show examples of various selections of flow paths through heat exchangers according to the invention. Of course, the illustrated flow paths may be selected freely, as desired, for the first, second, etc. fluid, or they may be turned oppositely.

Claims

Patent Claims

1. A heat exchanger comprising plate elements (1), said plate elements being provided with a profile and arranged such that the profile produces spaced ducts (6, 7) or layers of ducts in which one or more fluids are conveyed, characterized in that the plate elements (1) comprise at least two parts (2, 3), said parts having on one side a plurality of substantially longitudinally extending grooves (4) which are provided with spiral profiles (5) , so that the grooves together form at least one tubular duct (6) with spiral profiles.

2. A heat exchanger according to claim 1, characterized in that the parts (2, 3) are provided with guide ribs (8) at least on one side .

3. A heat exchanger according to claim 2, characterized in that the guide ribs (8) are parallel with the substan- tially longitudinally extending grooves (4) .

4. A heat exchanger according to claim 2, characterized in that the guide ribs (8) are angled relative to the substantially longitudinally extending grooves (4) .

5. A heat exchanger according to one or more of claims 2

- 4, characterized in that guide ribs (8) on the one part (2) of the plate elements when contacted with its at least one cooperating part (3) form completely or partly closed guide ducts.

6. A heat exchanger according to one or more of claims 2

- 5, characterized in that guide ribs (8) on a first plate element (1) when contacted with a second plate element form completely or partly closed guide ducts .

7. A heat exchanger according to one or more of claims 2 - 6, characterized in that guide ribs (8) on one side of a part (2) have a first height and guide ribs (8) on the opposite side of the part (2) have a second height, so that guide ducts on opposite sides of the part have a first cross-sectional area and a second cross-sectional area, respectively.

8. A heat exchanger according to one or more of claims 5

- 7, characterized in that the total cross-sectional areas of the guide ducts are preferably larger than the to- tal cross-sectional areas of the tubular ducts (6) with which they cooperate, so that the flow resistance is the same in the guide ducts as in the tubular ducts or smaller.

9. A heat exchanger according to one or more of claims 5

- 8, characterized in that closed guide ducts are preferably positioned so as to cooperate with the tubular ducts (6) .

10. A heat exchanger according to one or more of claims 1 - 9, characterized in that the pitch of the spiral profiles (5) is between 5 and 85 degrees, and is between 60 and 75 degrees in a particularly preferred embodiment.

11. A heat exchanger according to one or more of claims 1 - 10, characterized in that in cross-section the spiral profiles (5) have the shape of a part of a circle, an oval, a polygon or combinations of such.

12. A heat exchanger according to one or more of claims 1 - 11, characterized in that the cross-sectional areas of the ducts (6, 7) are different.

13. A heat exchanger according to one or more of claims 1 - 12 , characterized in that fluids are conveyed in the ducts (6, 7) in different directions.

14. A heat exchanger according to one or more of claims 1- 13, characterized in that the pitch of the spiral profiles (5) increases or decreases in the longitudinal direction.

15. A heat exchanger according to one or more of claims 1 - 14, characterized in that the cross-sectional area of the grooves (4) increases or decreases in the longitudinal direction.

16. A heat exchanger according to one or more of claims 1 - 15, characterized in that the plate elements (1) are made of a plastics material.

17. A heat exchanger according to claim 16, characterized in that the plastics material contains polypropyl- ene.

18. A heat exchanger according to one or more of claims 1 - 17, characterized in that the wall thickness of the parts (2, 3) is preferably smaller than 1 mm, and is smaller than 0.5 in a preferred embodiment, and is between 0.05 and 0.3 mm in a particularly preferred embodiment.