MULTI-CHANNEL TUBE FOR HEAT EXCHANGERS, MADE OF FOLDED METAL SHEET
A tube for a heat exchanger comprises a plate provided with a plurality of parallel flow ports, wherein the plate is formed by a single folded-up metal sheet and consists of an envelope formed by a first portion of the metal sheet, and of a partition structure formed by a second portion of the metal sheet, which extends in an corrugated manner within the envelope so as to define said flow ports therewith, and wherein the partition structure has a substantially polygonal profile having connection segments interconnecting opposite walls of the envelope and being interposed between adjacent flow ports. The connection segments are slanted relative to the opposite walls of the envelope, thereby defining an angle a>0° relative to the normal to said walls.
The present invention relates to a tube for a heat-exchanger, comprising a plate provided with a plurality of parallel flow ports,
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- wherein said plate is formed by a single folded-up metal sheet and consists of an envelope formed by a first portion of the metal sheet, and of a partition structure formed by a second portion of the metal sheet, which extends in an corrugated manner within the envelope so as to define said flow ports along therewith, and
- wherein said partition structure has a substantially polygonal profile with connection segments interconnecting opposite walls of the envelope and being interposed between adjacent flow ports.
Tubes of this type are particularly used in the assembly of condensers for climatization systems, in the automotive or civil fields.
Generally, multiple port tubes for heat exchangers can be divided into three categories: electro-welded tubes with finned insert, folded-up tubes with inner fin and folded-up tubes with a single material.
The electro-welded tubes with finned insert suffer from the most serious drawbacks relative to the fabrication process; these problems are mainly due to:
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- the quality of the welding (seam), which is generally difficult to obtain and even more difficult to control;
- the difficulty in forcibly fitting the fin into the tube body. Different thicknesses are implied, the fin thickness should be as low as possible and a deformation at the ends thereof causes an irreparable obstruction to the coolant flowing therethrough;
- the difficulty in providing the contact between fin and tube to obtain the brazing between both parts;
- the tube-finned insert brazing, which is carried out in a controlled atmosphere and requires that each part of the heat exchanger has to be reached by the antioxidant flow, and consequently the tube interior, too;
- the production costs, as the finished product is the result of several operations (making of the tube, fin and assembly of both parts).
Folded-up tubes with inner fin suffer from the most serious problems in the fabrication process, which are mainly due to:
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- the junction of two (inner and outer) bodies, the first being made from a thinner material than the second, during the tube folding and forming operations;
- the fact that a static phase is reached, in which the two parts are in close contact to each other;
- the cutting of the tube on line with a fin previously fitted thereto (leading edge-trailing edge). This operation can cause a deformation of the fin at the ends thereof, which is then difficult to recover.
The best solution from the point of view of the process, quality and fabrication costs results to be that of using folded-up tubes with a single material.
Within this category, tubes with generally rectangular ports are known.
An object of the present invention is to provide a multiple port tube, of the folded-up type with a single material; which allows to achieve better thermal exchange performances as compared with conventional tubes. Another object of the present invention is to provide a multiple-port tube which further allows reducing the consumption of raw material for making the same.
This object is achieved according to the invention by means of a tube of the type as defined in the preamble herein, wherein said connection segments are inclined with respect to the opposite walls of the envelope, thereby defining an angle α>0° with respect to the normal to said walls.
With a tube according to this solution idea, significant improvements can be achieved as compared with conventional folded-up tubes, given that:
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- with the hydraulic diameter, and consequently the thermal exchange performance of the tube being the same, a lower number of ports can be made available as compared with a rectangular port tube;
- a lower number of ports corresponds to a lower amount of raw material used to obtain a finished tube.
Furthermore, in case the flow ports have a trapezoid section, within a determined range of values of the angle a, a material saving can be obtained as compared with a tube with rectangular ports, with the number of ports being the same.
Preferred embodiments of the invention are as defined in the dependent claims, which should be intended as an integral part of the present description.
Further characteristics and advantages of the tube according to the invention will be more apparent with the following detailed description of an embodiment of the invention, given with reference to the annexed drawings, which are provided by way of a non-limiting illustration thereof, in which:
With reference to
With reference to
With reference to
With reference to
The plate 11 consists of an envelope 12 formed by a first portion of the metal sheet, and of a partition structure 14 formed by a second portion of the metal sheet, which extends in an corrugated manner within the envelope 12 in order to define the flow ports 20, 30 therewith.
The corrugations of the partition structure 14 have a polygonal profile, whereby the whole separation structure 14 has also a polygonal profile. Particularly, in the embodiment in
In the examples illustrated herein, in order to seal the folded-up metal sheet, a first edge strip 17 of the metal sheet associated with the first portion of this sheet is welded to the outer side of the envelope 12, and a second edge strip 18 of the metal sheet, associated with the second portion of this sheet and adjacent to the partition structure, is welded to the inner side of the envelope 12. Particularly, the edge strips 17, 18 of the metal sheet are located at opposite ends of the plate.
It is now demonstrated that the tubes 10 according to the invention, which have either triangular or trapezoid ports, allow to obtain a desired hydraulic diameter Øi (Øi=4S/P, where S=gas flow inner area and P=wet inner perimeter) with a lower number of port than they would require if they had a rectangular geometry.
With reference to
With reference to the figures, from the construction method there results that 2L=a+c=B, where L is the length of the rectangle base, a is the length of the trapezoid large base, c is the length of the trapezoid small base, and B is the length of the triangle base.
The following assumptions are also made during the comparison:
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- the tubes involved in the comparison have equal overall height and width;
- the tubes involved in the comparison have the same number of ports;
- the tubes involved in the comparison are obtained from an equally thick coil;
- finally, referring to the angle α as indicated in the figures, with reference to the normal to the main walls 12a, 12b of the plate, it is also assumed to work in the interval 0<α<90°.
As to the central ports 20, it is now demonstrated that the wet perimeter is increased when switching from the rectangular to the triangular shape, while the passage area is unchanged. As to the side ports 30, it is assumed that the differences between perimeter and area are neglectable.
With reference to
(2T+B)/(2L+H)>1 (1)
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- where T is the length of the triangle hypotenuse, and H is the height that is assumed equal both for triangle and rectangle.
In fact, given B=2L (hypothesis),
and also given H/T=cosα, from which: T=H/cosα,
there results T>H being:
cosα<1 within the interval 0<α<90°.
According to the above, therefore: 2T>2H, per 0<α<90°, which demonstrates the expression (1).
With reference to
(2T+c+a)/(2L+2H)>1 (2)
where H is the height that is assumed equal for both trapezoid and rectangle.
In fact, given c+a=2L (hypothesis),
and further given H/T=cosα, from which: T=H/cosα,
there results T>H, being:
cosα<1 within the interval 0<α<90°.
According to the above, therefore: 2T>2H, for 0<α<90°, which demonstrates the expression (2).
It will be now demonstrated that the port passage area remains unchanged. Assuming that the differences in the side port 30 areas are neglectable, it is clear that the rectangular port 2 areas coincide with the triangular port 20 areas. In fact, given B=2L;
Triangle area=(B*H)/2=(2L*H)/232 H*L=rectangle area (QED)
This assumption holds true also for the trapezoid ports 20; in fact, given the sum of the small base and large base of the trapezoid is 2L, then:
Trapezoid area=((a+c)*H)/2=(2*L*H)/2=H*L=rectangle area (QED)
It will be now demonstrated that, for multiple-port folded-up tubes with trapezoid section ports the consumption of material (coil) for slanting α the connection segments 14b of the partition wall 14 ranging between 0 and arccos(⅗), i.e. about 53.13° can be reduced.
With reference to
Δ1=T−H=T−Tcosα=T*(1−cosα)
The increase in the material of the trapezoid port, as compared with the rectangular port, can be thus expressed as follows:
Material increase=2T*(1−cosα) (3)
With further reference to
Material reduction=Δb=Tsenα (4)
In order that the switching beween rectangular sections to trapezoid sections results in a reduction in the coil consumption, the following inequality shall be proved:
Using the expressions (3) and (4), the inequality becomes:
By diagramming the function f(α)=senα/(2*(1−cosα)) in the interval 0<α<90°, it is obtained that this function is greater than 1 for α between 0 and arccos(⅗), as highlighted in the diagram in
N being the number of ports, the material saving obtained in the central ports when a trapezoid section is used instead of a rectangular section can be thus expressed as follows:
The function h(α) shows that the reduction in the material consumption (resulting from the use of trapezoid ports instead of rectangular ports) is directly proportional to the number of ports and tube height. This reduction further depends on the function h′(α) as defined below:
h′(α)=tgα−2/cosα+2
This function becomes zero at the angle α=0 (i.e. when the trapezoid is collapsed into the rectangle) and α=arccos(⅗) (which is the angle at which the function f(α) is 1, i.e. the angle beyond which the trapezoid geometry is no longer convenient in terms of material saving as compared with the rectangular geometry) and has a peak about the angle α=30° approximately, as shown in
The above-described tube is intended to be assembled, at each end thereof, to a heat exchanger distributor or collector. This assembly is carried out by fitting the end of the tube into a corresponding slot provided on the distributor outer wall.
To the purpose, a preferred embodiment of the invention is illustrated in
Particularly, the end portion 40 of the tube 10 comprises in order, from the axial end to the center of the tube, a fitting length 42, a sealing length 44 and an abutment length 46. At the fitting length 42, the end portion 40 of the tube 10 has bevelled side edges or is, more generally, widthwise tapered towards the axial end of the tube, in order to facilitate fitting the portion 40 into the slot 51. The sealing length 44 of the end portion 40 of the tube 10 is, on the contrary, suitable to engage the edge of the slot 51. At the abutment length 46, the end portion 40 of the tube 10 has bevelled side edges or is, more generally, widthwise tapered towards the axial end of the tube. This length 46 defines an abutment position for fitting the end portion 40 into the slot 51, and simultaneously provides slanting surfaces in order to compensate for any clearance between the tube 10 and the slot 51 and to prevent (by friction) any relative rotation between the distributor and the tube which can occur during the brazing process. To the purpose, the slot 51 edge is provided with a matching coupling portion 53 (seen in
The end portion 40 of the tube 10 as shown in
According to other embodiments, as shown in
With reference to
With reference to
Claims
1-12. (canceled)
13. A tube for a heat exchanger, comprising a plate provided with a plurality of parallel flow ports,
- wherein said plate is formed by a single folded-up metal sheet and consists of an envelope formed by a first portion of the metal sheet, and of a partition structure formed by a second portion of the metal sheet, which extends in a corrugated manner within the envelope so as to define said flow ports along therewith, and
- wherein said partition structure has a substantially polygonal profile having connection segments interconnecting opposite walls of the envelope and being interposed between adjacent flow ports, and
- wherein said connection segments are inclined with respect to the opposite walls of the envelope, thereby defining an angle α>0° with respect to the normal to said walls.
14. The tube according to claim 13, wherein at least the central ports of said flow ports have an approximately trapezoid section, and said partition structure further comprises base segments alternated with said connection segments, approximately parallel to the opposite walls of said envelope, and in contact to either one thereof, wherein said base segments have a corrugated transversal profile, thereby each of said base segments has, at the side ends thereof, respective ridge portions which join each base segment to the connection segments adjacent thereto, and a depression portion interposed between said ridge portions, and defining a recess in the transversal direction relative thereto.
15. The tube according to claim 13, wherein said partition structure defines a plurality of corrugations, whose height h before closing the envelope on said structure, intended as the difference in height between the maximum and minimum height points of the corrugations, is greater than the separation distance H between the opposite walls of said envelope after the latter has been closed.
16. The tube according to claim 13, said tube being intended to be coupled to a distributor for a heat exchanger, and having an end portion suitable to be inserted into a corresponding slot that is provided on a wall of the distributor, wherein said end portion is provided with abutment means suitable to define a stop position for fitting said tube into the slot, said abutment means further providing slanted surfaces relative to the outer surface of the tube envelope, which are suitable to engage corresponding coupling portions provided on the edge of the slot.
17. The tube according to claim 16, wherein said abutment means comprise one or more projections and/or grooves provided on said envelope.
18. The tube according to claim 16, wherein said abutment means comprise an abutment length of said end portion of the tube, at which the end portion of the tube is widthwise tapered towards the axial end of the tube.
19. The tube according to claim 16, wherein said end portion of the tube further comprises a fitting length, at which the end portion of the tube is widthwise tapered towards the axial end of the tube, in order to facilitate the fitting of the end portion into the slot.
20. The tube according to claim 18, wherein said tube end portion comprises in order, from the axial end towards the center of the tube, a fitting length, at which the end portion of the tube is widthwise tapered towards the axial end of the tube, in order to facilitate the fitting at the end portion into the slot, a sealing length and said abutment length, said sealing length being suitable to engage the edge of the slot.
21. The tube according to claim 13, wherein at least the central ports of said flow ports have an isosceles trapezoid cross section, said connection segments defining an angle 0<α≦arccos(⅗) relative to the normal to the opposite walls of the envelope.
22. The tube according to claim 13, wherein a first edge strip of the metal sheet associated with the first portion of said sheet is welded to the outer side of the envelope, and a second edge strip of the metal sheet associated with the second portion of said sheet, adjacent to the separation structure, is welded to the inner side of the envelope.
23. The tube according to claim 22, wherein said edge strips of the metal sheet are positioned at opposite side ends of the plate.
24. The tube according to claim 13, wherein said metal sheet has an overall thickness d such as 0.2 mm≦d≦0.35 mm, and has, on each face of the sheet, a clad of brazing filler metal with a clad to core ratio c%, resulting from the ratio of the clad thickness to the overall thickness d, 5%≦c%≦15%.
Type: Application
Filed: Nov 4, 2011
Publication Date: Aug 22, 2013
Inventors: Davide Perocchio (Poirino), Giandomenico Cappello (Poirino), Giuseppe Tiziano (Poirino)
Application Number: 13/882,729
International Classification: F28F 3/12 (20060101);