TUBE FOR A HEAT EXCHANGER AND A METHOD FOR MANUFACTURING THEREOF

Abstract

A tube for a heat exchanger including a tube structure made of lightweight metal alloy and having an inner surface and an outer surface. The tube further includes: a first layer of material on the outer surface of the tube structure, the first layer having different chemical composition than the tube structure, a second layer of material on the first layer of material, the second layer having different chemical composition than the tube structure and the first layer. The first layer includes metallic material having a lower galvanic potential than the tube structure. The first layer includes the deposition of zinc particles within the first layer. The deposition of zinc is not less than 3 g/m.sup.2 and not more than 7 g/m.sup.2. The second layer includes an aluminum silicon compound. The deposition of aluminum silicon compound within the second layer is not less than 14 g/m.sup.2 and not more than 16 g/m.sup.2.

Claims

1. A tube for a heat exchanger, comprising a tube structure made of lightweight metal alloy and including an inner surface and an outer surface, a first layer of material on the outer surface of the tube structure, the first layer having different chemical composition than the tube structure, a second layer of material on the first layer of material, the second layer having different chemical composition than the tube structure and the first layer, wherein the first layer includes metallic material having a lower galvanic potential than the tube structure, wherein the first layer includes the deposition of zinc particles within the first layer, wherein the deposition of zinc is not less than 3 g/m.sup.2 and not more than 7 g/m.sup.2, and in that the second layer includes at least an aluminum silicon compound, wherein the deposition of aluminum silicon compound within the second layer is not less than 14 g/m.sup.2 and not more than 16 g/m.sup.2.

2. The tube according to claim 1, wherein the deposition of zinc within the first layer is 5 g/m.sup.2.

3. The tube according to claim 1, wherein the tube structure is made of aluminum alloy and the first layer is applied directly onto said aluminum alloy.

4. The tube according to claim 1, wherein the aluminum silicon compound includes 12.6% of silicon.

5. The tube according to claim 1, wherein the deposition of aluminum silicon compound within the second layer is 15 g/m.sup.2.

6. The tube according to claim 4, wherein size of aluminum silicon particle is not smaller than 5 ?m and not greater than 15 ?m.

7. The tube according to claim 6, wherein the second layer includes a potassium aluminum fluoride flux and a binder.

8. The tube according to claim 7, wherein the deposition of potassium aluminum fluoride flux within the second layer is not less than 6 g/m.sup.2 and not more than 8 g/m.sup.2.

9. The tube according to claim 8, wherein the deposition of potassium aluminum fluoride flux within the second layer is 7 g/m.sup.2.

10. The tube according to claim 7, wherein the binder is an organic polymer, wherein the deposition of binder is not less than 4 g/m.sup.2 and not more than 6 g/m.sup.2.

11. The tube according to claim 10, wherein the deposition of organic polymer within the second layer is 5 g/m.sup.2.

12. A heat exchanger configured to heat exchange between fluids comprising at least one tube including a tube structure made of lightweight metal alloy and including an inner surface and an outer surface, a first layer of material on the outer surface of the tube structure, the first layer having different chemical composition than the tube structure, a second layer of material on the first layer of material, the second layer having different chemical composition than the tube structure and the first layer, wherein the first layer includes metallic material having a lower galvanic potential than the tube structure, wherein the first layer includes the deposition of zinc particles within the first layer, wherein the deposition of zinc is not less than 3 g/m.sup.2 and not more than 7 g/m.sup.2, and in that the second layer includes at least an aluminum silicon compound, wherein the deposition of aluminum silicon compound within the second layer is not less than 14 g/m.sup.2 and not more than 16 g/m.sup.2

13. The heat exchanger according to claim 13, wherein the heat exchanger further comprises manifolds, plurality of tubes including open ends received in said manifolds, and plurality of fins interlaced between the tubes, wherein at least one tube is fixed between the manifolds by brazing via second layer, so that the manifolds are fluidly connected.

14. The heat exchanger according to claim 13, wherein the first layer is located in-between the outer surface and the portion of the fin which is brazed to the tube.

15. A method of manufacturing a tube for a heat exchanger comprising: providing a lightweight metal alloy tube structure, depositing a first layer of material directly onto an outer surface of the tube structure by zinc arc spraying method, wherein liquid zinc is sprayed onto the outer surface to deposit about 5 g/m.sup.2 of zinc, so that the complete coverage of the outer surface and even distribution of the zinc is provided, drying the first layer, depositing a second layer onto the first layer, drying the second layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Examples of the invention will be apparent from and described in detail with reference to the accompanying drawings, in which:

[0030] FIG. 1 shows a cross-section view of the tube, according to the first example;

[0031] FIG. 2 shows a cross-section view of the tube, according to the second example

[0032] FIG. 3 shows a schematic view of the heat exchanger comprising the at least one tube depicted in FIG. 1 or 2;

[0033] FIG. 4 shows a cross-section view of the tube-manifold assembly;

[0034] FIG. 5 a cross-section view of the tube-fin assembly; and

[0035] FIG. 6 shows a process of manufacturing the tube of FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The invention refers to tube for a heat exchanger. In particular, the invention relates to tube suitable for heat exchanger such as condenser, evaporator, gas cooler, chiller, and other. It is to be noted that the invention can also refer to other type of tube for the heat exchanger, for example radiator and alike.

[0037] FIGS. 1 and 2 show an exemplary cross-section view of tube 4 comprising a tube structure 4a. The tube structure 4a can refer both to extruded and folded types of tubes. The tube structure 4a can comprise an axis of elongation. The cross-sections shown in FIGS. 1 and 2 and are selected in a plane perpendicular with respect to the main axis of elongation of the tube structure 4a. At least one tube structure 4a can comprise an inner surface 4b and an outer surface 4c. The inner surface 4b of the tube 4 can be defined as the surface of the channel or channels within the tube structure 4a. In FIG. 1, the inner surface 4b is depicted as the surface of the single channel for the fluid, whereas the tube 4 depicted in FIG. 2 comprises multiple channels for the fluid, thus it comprises plurality of inner surfaces 4b. The outer surface 4c of the tube structure 4a is the portion of the tube 4 which provides at least one wall fluidly insulating one fluid from the other, during the operational mode of the tube 4. Term operational mode can be defined based on the existence of the fluid for heat exchange within the channel or channels of the tube 4.

[0038] It is to be noted that term tube structure can refer to the tubes made in process of extrusion, as well as the tubes made in different process, e.g. folding, etc.

[0039] As further shown in FIGS. 1 and 2, the tube 4 can further comprise at least one first layer 100 of material configured to cover entire outer surface 4c of the tube 4. Further, the first layer 100 can adhere to the outer surface 4c of the tube structure 4a to ensure complete coverage of the outer surface 4c of the tube structure 4a and compensate the uneven distribution of the material.

[0040] The tube structure 4a can be made of lightweight metal alloy, for example, aluminum alloy. The first layer 100 can have different chemical properties than the tube structure 4a. In other words, the first layer 100 can be made of material having different chemical properties than the material of the tube structure 4a. The first layer 100 can comprise a metallic material having a lower galvanic potential than the tube structure 4a. In other words, the first layer 100 of material is configured to prevent the corrosion of at least outer face 4b of the tube structure 4a. For example, the first layer 100 can be made of metallic material such zinc, Zn.

[0041] In order to give anticorrosion protection to the tube structure 4a the deposition of Zn on the first layer 100 can be not less than 3 g/m.sup.2 and not more than 7 g/m.sup.2.

[0042] The best anticorrosion feature can be observed when the deposition of Zn is the median value of the range presented in previous paragraph, i.e. when the deposition of zinc on the first layer 100 is around 5 g/m.sup.2. In particular, the deposition of zinc on the first layer 100 can be 5.04 g/m.sup.2.

[0043] As further shown in FIGS. 1 and 2, the tube 4 can comprise a second layer 200 of material configured to cover entire first layer 100 of material. In other words, the second layer 200 is applied on the surface created by the first layer 100. Since the second layer 200 can comprise several components, the second layer 200 can comprise different chemical properties than the tube structure 4a and the first layer 100. The purpose of applying the second layer 200 of material is to provide a surface which would allow fixing the tubes 4, for example, to the manifolds of the heat exchanger 1, as well as fixing the fins in-between the plurality of tubes 4. The examples of fixation means are discussed in further paragraphs.

[0044] As further shown in FIGS. 1 and 2, the tube 4 can comprise at least one second layer 200. The second layer 200 can comprise at least an aluminum silicon (AlSi) compound. The aluminum silicon compound can enhance fixing the tube 4 to other sub-components, for example, by means of brazing. More specifically, the aluminum silicon can serve as a filler during brazing process.

[0045] In order to provide a robust, fluid tight connection between the tube 4 and other sub-components, the AlSi12.6 compound can be selected. AlSi12.6 should be regarded as AlSi compound which comprises less than 12.6% of silicon. This feature prevents the tube structure 4a defects that can be caused by big silicon particles or agglomeration of silicon particles as AlSi12.6 particles are spheroidal and they are softer than regular silicon particles.

[0046] It is to be noted that the tube structure 4a, first layer 100 and the second layer can comprise the thickness, wherein each individual thickness can be measured in a direction perpendicular to the axis of elongation of the tube structure 4a. The thickness of the tube structure 4a can thus be indexed as Ts. The thickness of the first layer 100 can be indexed as T1. The thickness of the second layer 200 can be indexed as T2. The total thickness Tt can thus be defined as the sum of the thickness of the tube structure 4a Ts, the thickness of the first layer 100 T1 and the thickness of the second layer 200 T2. The thickness of the tube structure Ts can be greater than the sum of the thickness of the first layer 100 and the second layer 200.

[0047] Further, the amount of AlSi12.6 compound within the second layer 200 can not be less than 14 g/m.sup.2 and not more than 16 g/m.sup.2. Preferably, the amount of AlSi12.6 compound within the second layer 200 is in particular 15 g/m.sup.2. Further, the size of aluminum silicon particle is not smaller than 5 ?m and not greater than 15 ?m, i.e. 5-15 micrometers, so that AlSi aluminum silicon particle size is not greater than the thickness of the first layer T1.

[0048] In order to further facilitate brazing ability of the tube 4, the second layer 200 can comprise potassium aluminum fluoride flux (KAlF4) and a binder. The potassium aluminum fluoride flux (KAlF4) enhances soldering and brazing of aluminum, whereas the binder facilitates adhering the solid composition on the surface of the tube 4.

[0049] In order to achieve aforementioned effects, it can be preferred that the deposition of aluminum fluoride within the second layer 200 is not less than 6 g/m.sup.2 and not more than 8 g/m.sup.2. In particular, the deposition of aluminum fluoride within the second layer 200 can be in particular 7 g/m.sup.2. Even more precisely, the deposition of aluminum fluoride within the second layer 200 can be 7.04 g/m.sup.2.

[0050] Further, it can be preferred that the deposition of the binder which can be in form of an organic polymer is not less than 4 g/m.sup.2 and not more than 6 g/m.sup.2. In particular, the deposition of organic polymer within the second layer 200 can be in particular 5 g/m.sup.2. Even more precisely, the deposition of the binder can be in particular 5.15 g/m.sup.2.

[0051] FIG. 3 shows a schematic view of a heat exchanger 1 configured to heat exchange between fluids comprising at least one tube 4. The first fluid such as refrigerant, for example, R134a, R1234yf, R744 or R290, can be circulating within the heat exchanger 1 whereas the second fluid, for example ram air, can be delivered to cool down the first fluid.

[0052] The heat exchanger 1 can comprise the manifolds 2, 3 and plurality of tubes 4 comprising open ends received in manifolds 2, 3. The tubes 4 can extend along their general axis of elongation so that their open ends can be introduced into respective manifolds 2,3 in order to provide the fluidal communication between these sub-components. The heat exchanger 1 can also comprise fins 5 interlaced between the tubes 4. Usually, the manifolds 2, 3 can be fluidly connected with inlet and/or outlet, however, these sub-components have been omitted for the sake of clarity of the drawings.

[0053] FIG. 4 shows a cross sectional view of the tube 4 and manifold 2, 3 assembly.

[0054] As shown in FIGS. 3 and 4, at least one tube 4 can be fixed between the manifolds 2, 3 by the means of brazing via second layer 200, so that the manifolds 2, 3 are fluidly connected to each other.

[0055] As further shown in FIG. 4, the first layer 100 can be located in-between the outer surface 4c of the tube structure 4a and the portion of manifold 2, 3 which is brazed to the tube 4. Thanks to previously discussed specific zinc deposition, the first layer 100 does not deteriorate by e.g. diffusion after the brazing process.

[0056] FIG. 5 shows a cross sectional view of the tube 4 and fin 5 assembly.

[0057] A shown in FIG. 5, at least one fin 5 can fixed by the means of brazing via second layer 200 in-between proximal pair of tubes 4. Further, the first layer 100 can be located in-between the outer surface 4c of the tube structure 4a and the portion of the fin 5 which is brazed to the tube 4.

[0058] As discussed in previous paragraphs, in order to give anticorrosion protection to the tube structure 4a the deposition of Zn on the first layer 100 can be not less than 3 g/m.sup.2 and not more than 7 g/m.sup.2. Further, the deposition on zinc in this particular range prevents fins 5 interlaced in-between the tube structure 4a from mechanical destruction of the heat exchanger 1 due to stress accompanying fixation of tubes 4 to the manifolds 2, 3, for example during brazing of these sub-components. The aforementioned range of zinc deposition is therefore optimal to give enough corrosion resistance and the mechanical resistance of the structure of the heat exchanger 1 is also ensured.

[0059] Further, the aforementioned AlSi12.6 particles allow removing the clad from the fin 5 and they allow creating a direct brazing joint either with fin or with manifold 2, 3.

[0060] Therefore, the flux prevents the oxidation of the aluminum surfaces during brazing and allow good wettability of the AlSi12, whereas the binder allows to keep the composition of the second layer 200 on the tube 4.

[0061] The object of the invention aims to define a method for bringing filler metal and corrosion protection on the tube structure 4a for the heat exchanger 1 which is usually brazed under controlled atmosphere. With respect to extruded tubes, the metallurgical extrusion process does not allow bringing filler metal in known aluminum rolling process. The method described below defines a corrosion protection solution for the tube structure 4a.

[0062] The method can comprise several steps as shown in FIG. 6 and as described in further paragraphs.

[0063] Initially, the first step can be providing 1000 at least one aluminum extruded tube structure 4a for heat exchanger 1.

[0064] Next, the first layer 100 of material can be deposed 2000 directly onto the outer surface 4c of the tube structure 4a. The deposition of first layer can be carried out by means of zinc arc spraying (ZAS) method. During zinc arc spraying, the tube structure 4a can be shot blasted to certain grade which provides an adequate surface for the zinc to adhere to. After shot blasting the zinc protective coating can be applied. This process involves two zinc wires being fed into a pistol which get electrically charged, one positive and one negative. The wires are forced together which forms an electric arc, melting the wire. Compressed air is then passed through a nozzle which atomises the molten metal and sprays it onto the outer surface 4c of the tube structure 4a. Upon contact, the particles flatten onto the surface, freeze and mechanically bond, firstly onto the outer surface 4c and then onto each other as the coating thickness increases.

[0065] The liquid zinc is sprayed to the surface of the tubes to deposit about 5 g/m.sup.2 of zinc, so that the complete coverage of the outer surface 4c and even distribution of the zinc is provided. It is to be noted, that first layer 100 covers the whole outer surface 4c between the open ends of the tube 4. The first layer 100 sprayed on the outer surface 4a is initially hot. Before applying the second layer 200, the first layer 100 can be cooled down to room temperature. Thus, the first layer is dried 2500 in order to obtain maximal corrosion protection of the tube 4.

[0066] Next, the second layer 200 of material can be deposed 3000 onto the first layer 100. The second layer can comprise mixture of AlSi (10-14%) being close to the composition of the eutectic AlSi12.6%, KAlF4 flux, and a binder to fix the coating onto the first layer 100. The second layer 200 comprising the filler metal and flux allow the brazing of the tube 4 in the controlled atmosphere. Optionally, the second layer 200 can comprise a surface tension additive to promote the homogeneity of the second layer 200. The second layer 200 can then be dried 3500 in order to obtain maximal brazing ability of the tube 4.

[0067] The tube 4 comprising layers 100, 200 can further be cut to desired length, and stacked between the manifolds 2, 3 so that the heat exchanger 1 can be assembled. In order to provide better heat exchanger between the fluids, the fins are interlaced with tubes 4 before forming a stack of tubes.

[0068] To finalize the heat exchanger 1 production process, the second layer 200 of the tube 4 can be brazed to the manifolds 2, 3 and at least a portion of the fins 5, so that the heat exchanger 1 is ready for operation.

[0069] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to the advantage.