The present invention relates to 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 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:
- 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:
- 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:
- 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:
FIG. 1 is a cross-sectional view of a multiple port tube, with rectangular section ports;
FIG. 2 is a cross-sectional view of a multiple port tube, with trapezoid section ports according to the invention;
FIG. 3 is a cross-sectional view of a multiple port tube, with triangular section ports according to the invention;
FIGS. 4 and 5 are illustrative drawings showing the advantageous features of the tube according to the invention as compared with conventional tubes;
FIG. 6 shows the graph of a function f(α) related to the consumption of material for a tube with trapezoid ports, based on the angle α;
FIG. 7 shows the graph of a function h′(α) related to the saving of material for a tube with trapezoid ports, based on the angle α;
FIG. 8 is a perspective view of an end portion of a multiple-port tube according to the invention;
FIG. 9 is a cross-sectional view of a cylindrical distributor, to which a tube according to the invention has been assembled;
FIG. 10 is a sectional view in an enlarged scale of a detail in FIG. 9, taken on a plane parallel to that in FIG. 9, and intersecting the multiple-port tube;
FIGS. 11 to 13 are perspective views of different embodiments of multiple-port tubes according to the invention;
FIG. 14 is a cross-sectional view of a variant embodiment of a tube with approximately trapezoid section ports; and
FIG. 15 is a cross-sectional view of a tube with trapezoid section ports, which highlights several geometric characteristics of the tube.
With reference to FIG. 1, a cross section of a multiple-port tube 1 for a heat exchanger has been illustrated comprising a plate provided with a plurality of parallel flow ports 2, 3 suitable for one or more fluids to flow therein, depending on the use that will be made of the tube 1. The central ports 2 of the tube 1 in FIG. 1 have a rectangular section, whereas the peripheral ports 3 have a section depending on the configuration of the side ends of the plate of tube 1.
With reference to FIG. 2, a cross section of a multiple-port tube 10 for a heat exchanger has been illustrated, which comprises a plate 11 provided with a plurality of parallel flow ports 20, 30 suitable for one or more fluids to flow therein, depending on the use that will be made of the tube 10. The central ports 20 of the tube 10 in FIG. 2 have a trapezoid section, whereas the peripheral ports 30 have a section depending on the configuration of the side ends of the plate 11 of tube 10.
With reference to FIG. 3, another embodiment of the invention is illustrated, in which the central ports have a triangular section. In this embodiment, the same numerals have been used for those elements that correspond to those of the previous embodiments.
With reference to FIGS. 2 and 3, the plate 11 of the tube 10 is made from a single folded-up metal sheet, for example aluminum sheet. Preferably, this 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 (e.g., low-melting aluminum alloy) with a clad to core ratio c%, resulting from the ratio of the clad thickness to the overall thickness d, such as 5%≦c%≦15%.
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 FIG. 2 the partition structure 14 comprises base segments 14a, parallel to the opposite main walls 12a, 12b of the envelope 12 of the plate and in contact with either one of the latter, which base segments 14a are alternated with slanted connection segments 14b. The connection segments 14b thus interconnect the opposite walls 12a, 12b of the envelope and are interposed between adjacent flow ports. In the embodiment in FIG. 3, the partition structure 14 only comprises oblique connection segments 14b, as the base segments are reduced to the edges at which the connection segments are joined to each other, and which are in contact with either one of the opposite main walls 12a,12b of the plate envelope 12. The joints between base segments 14a and connection segments 14b (example in FIG. 2), or the joints between connection segments 14b (example in FIG. 3) can have a certain bending.
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 FIGS. 4 and 5, it is assumed to compare tubes having rectangular, trapezoid, and triangular ports, and to switch from one shape to another by rotating the vertical side of the rectangle about a point A, A′ positioned half-way along that side.
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:
- 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 FIG. 4, wherein, according to the above, B=2L, it is demonstrated that the wet perimeter of the triangular section is greater than the rectangular section 0<α<90°, i.e. the following relations holds true:
(2T+B)/(2L+H)>1 (1)
- 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 FIG. 5, wherein, for constructional reasons, c+α=2L, it is demonstrated that the wet perimeter of the trapezoid section is greater than that of the rectangular section 0<α<90°, i.e. the following relation holds true:
(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 FIG. 5, by rotating the vertical sides of the rectangle about the points A and A′ and given that: H/T=cosα, it is clear that the length increase Δ1 in the trapezoid side relative to the rectangle side can be expressed as follows:
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 FIG. 5, the reduction in the length Δb of the small base of the trapezoid relative to the rectangle base, which reduction can be intended as a reduction in the material of the trapezoid port as compared with the rectangular couterpart thereof, can be expressed as follows:
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 FIG. 6.
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 FIG. 7.
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 FIGS. 8 to 10, which show an end portion 40 of the tube 10 according to the invention, and a distributor 50 to which the tube 10 is assembled. In order to allow for the coupling of the tube 10 to the distributor 50, a slot 51 is provided on the outer wall of the latter for fitting the end portion 20 of the tube 10.
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 FIG. 10) which is suitable to be engaged by the abutment length 46 of the end portion 40 of the tube 10, at which the slot 51 has bevelled edge side faces or, more generally, it has a section widthwise tapered inwardly of the distributor. This coupling portion can be obtained, for example, by means of cutting.
The end portion 40 of the tube 10 as shown in FIG. 8 can be obtained by means of stock removal processing, wherein a tool, for example a laser beam or finger bit, processes the side edges of the multiple-port tube 10 such that the desired profile is obtained.
According to other embodiments, as shown in FIGS. 11 to 13, formations provided on the envelope 12 of the tube 10 act as abutment and rotation-restraining elements. In FIG. 11, these formations consist of point bosses 46′ provided on both main faces of the envelope 12 and projecting outwards from the surface of this envelope, which provide slanted surfaces suitable to engage corresponding coupling portions provided on the edge of the slot 51. In FIG. 12, the abutment and anti-rotation formations consist of linear bosses 46″ provided on the two main faces of the envelope 12, which are transversally extended relative to the tube 10 and outwardly project from this tube envelope surface. Similarly to the point bosses 46′, the linear bosses 46″ provide slanted surfaces which are suitable to engage corresponding coupling portions which are provided on the slot 51 edge. According to a further embodiment, not illustrated herein, the abutment and anti-rotation function can be provided by a collar surrounding the entire tube section. In FIG. 13, the abutment and anti-rotation formations consist of linear grooves 46′″ provided on the two main faces of the envelope 12, which are transversally extended relative to the tube 10 and inwardly recessed within the tube. The linear grooves 46′″ provide slanted surfaces which are suitable to engage corresponding coupling portions which are provided on the slot 51 edge. In this case, it is provided that, during the assembly step the slot 51 edge is elastically deformated to allow for the tube being fitted into the slot 51 to the position of the linear grooves 46′″.
With reference to FIG. 14, a preferred variant embodiment of the multiple port tube with trapezoid section ports will be now described, wherein the base segments 14a of the separation structure 14 have an corrugated transversal profile, instead of being substantially flat. Particularly, each of these base segments 14a having an corrugated profile has, at the side ends thereof, respective ridge portions 14c which join each base segment 14a to the connection segments 14b adjacent thereto, and a depression portion 14d interposed between the ridge portions 14c, and defining a recess in the transversal direction relative to the ridge portions. For each base segment 14a the ridge portions 14c thus provide two points of contact with the wall of the envelope 12, thereby improving the brazability of this envelope segment. In the meanwhile, the depression portion 14d cooperates with the envelope 12 wall to form a cavity suitable to collect the plating material melted during the brazing process. Preferably, the pitch Po of the corrugations is such that 1 mm≦Po≦5 mm, the distance Pc between the ridge portions 14c of a base segment 14a is such that 0.241 mm ≦Pc≦1.205 mm (Pc being approximately 0.241 Po), and the depth g of the depression portion 14d is such that 0.05 mm≦g≦0.20 mm.
With reference to FIG. 15, a solution will be now described to provide a greater contact area between the corrugation ridges of the partition structure 14 and the envelope 12 wall of the tube 10, and thereby improve the efficacy of the brazing process. This solution consists in providing that the height h of the corrugations of the partition structure 14, intended as the difference in height between the corrugation maximum and minimum points, before the envelope 12 is closed on said structure, is greater than the separation distance H between the main walls 12a and 12b of the envelope 12 after it has been closed. The compressive elastic strain of the partition structure corrugations creates a “spring effect” which provides for a greater contact area between the ridges of the partition structure 14 corrugations and the wall of the envelope 12 of the tube 10. The dotted line S in FIG. 15 represents the virtual profile that the tube would have due to the height h of the partition structure 14 corrugations if the compression of the tube were not operated in the direction perpendicular to the walls 12a and 12b of the envelope, and accordingly it gives a qualitative measure of the spring effect that is obtained when the tube 10 is closed. The solution for obtaining the above-described elastic effect can be applied to any profile of the corrugations of the tube separation structure according to the invention.
Patent Application
20130213623
