EP2446209A1

EP2446209A1 - 3 d heat exchanger

Info

Publication number: EP2446209A1
Application number: EP10709862A
Authority: EP
Inventors: Peter De Jaeger; Johan Hugelier
Original assignee: Bekaert NV SA
Current assignee: Universiteit Gent
Priority date: 2009-04-03
Filing date: 2010-03-25
Publication date: 2012-05-02
Also published as: WO2010112392A1

Abstract

A heat exchanger for motorised vehicles comprising a 3D configuration of the heat exchanger for better use of the available space in a motorised vehicle. The invention further being characterised by a split-up entry of the medium to be heat exchanged.

Description

3 D heat exchanger

Description Technical Field

[0001] The present invention relates to a heat exchanger for motorised vehicles which can be used for cooling, heating, ventilating and/or air conditioning modules.

[0002] The invention further relates to coolers in the automotive field, such as water or oil coolers, for e.g. turbo-chargers, which are cooled by the air which surrounds the motorised vehicle.

Background Art

[0003] Heat exchangers in the automotive field gradually need to fulfil more stringent demands with respect to heat exchanging capacity and efficiency, but also, among other things, to the amount of volume taken, weight, design freedom, strength and orientation.

[0004] A wide variety of automotive heat exchangers are already available on the market, e.g. fin type heat exchangers including offset fins, wave fins or louvered fins.

[0005] More recent developments show heat exchangers using open cell foams as e.g. in US 6,142,222 and WO 03/100339.

Disclosure of Invention

[0006] An aspect of the claimed invention provides a heat exchanger for a motor vehicle for a given volume with a given incoming flow surface. This heat exchanger comprises a plurality of heat-conducting tubes and heat exchange enlarging structures. The heat-conducting tubes are joined together by the heat exchange enlarging structures thereby forming at least two heat-exchanging stacks. In use, a first medium flows through the heat conducting tubes and a second medium flows through the heat exchange enlarging structures. The heat-exchanger comprises a first portion (A) and a second portion (B), wherein the second portion (B) is angled relative to the first portion (A), such that longer lengths of said heat exchanging stacks can be stowed in said volume. This increases the heat exchanging capacity for said volume with said given incoming flow surface. Air flowing into said volume through said given incoming flow surface is distributed across both of said first (A) and second (B) portions.

The heat exchanging stacks are further connected to first and second collecting tanks. The heat exchanger is fed through multiple first collecting tanks and released by at least one second collecting tank or fed through one first collecting tank and released by multiple second collecting tanks. [0007] In the automotive field, using the volume available might be an important factor in the increase of the heat exchanging capacity of a heat exchanger.

E.g. in a car, the volume available for cooling is limited and also the frontal surface or the incoming flow surface is limited to the frontal part of the car, i.e. where cooling airflow is coming to the car. [0008] The split up entry or exit of the fluid to be heat exchanged, i.e. the first medium, increases further the heat exchanging capacity of a given volume and incoming flow surface. [0009] In a preferred embodiment of the invention the first collecting tank is positioned in the angle of said first (A) and second (B) portions. [0010] In an even more preferred embodiment, there is only one second collecting tank which is positioned in the angle of said first (A) and second

(B) portions. [0011] Preferably, the angle of said first (A) and second (B) portions is between

10° to 90°. More preferably, the angle in between said first (A) and second

(B) portions is between 20° and 60°. [0012] The heat exchanger according to the invention is preferably made of metal, even more preferably the heat exchanging stack is made of a lightweight metal or a lightweight metal alloy. [0013] The first and second collecting tanks can be made of any suitable plastic or metal. [0014] The heat exchange enlarging structures can be any known fins, such as e.g. offset fins, wave fins or louvered fins. [0015] Preferably, the heat exchange enlarging structures are thermally conductive open cell porous media. This can be a carbon or graphite foam; a carbon or graphite containing metal foam; metal foam as described e.g. in EP1227908; a woven or knitted 3D textile in metal, graphite or carbon; a 3D wire structure made of metal, graphite or carbon, such as e.g. the Kagome structure or similar 3D-structures as described in WO2005/044483.

[0016] In a preferred aspect, the thermally conductive open cell porous medium has an amount of pores per inch (ppi) between 10 and 50 ppi. More preferably, the amount of pores per inch (ppi) is between 15 and 30 ppi, most preferably the amount of pores per inch (ppi) is 20 ppi.

[0017] In another preferred aspect, the porosity of the thermally conductive open cell porous medium is ranging between 91 ,5% and 96,5%, more preferably between 92% and 96%, most preferably between 92,5% and 95,5%. This porosity provides an even more improved direct and immediate cooling of the metal piece. The porosity of the thermally conductive open cell porous medium can be tuned depending on the thermally conductive open cell porous medium used as known by the person skilled in the art. E.g. in the case of an open cell metal foam reference is made to EP 1604756.

[0018] In a further preferred aspect, the thermally conductive open cell porous medium is metal foam, preferably made of aluminium or an aluminium alloy. In another preferred aspect, the metal foam is made of copper or a copper alloy. In a more preferred aspect the metal foam is made of graphite or comprises graphite.

[0019] The use of such open cell porous media even increases the heat exchanging capacity of the heat exchanger because such open cell porous media are isotropic and thus indifferent to the direction of the incoming fluid flow.

[0020] In an even further preferred aspect, the thickness of the open cell porous medium is between 1 and 6 times the pore diameter. More preferably, the thickness of the open cell porous medium is between 1 ,5 and 5 times the pore diameter, even more preferably between 2 and 4 times the pore diameter. Some examples of pore diameters in relation to the ppi's and the porosity are shown in table 1. [0021] Table 1

[0022] Method of making a heat exchanger as in any of the previous claims.

[0023] This method comprises the following steps: first a plurality of heat- conducting tubes and heat exchange enlarging structures are provided. Thereafter the heat exchange enlarging structures are thermally attached to the heat conducting tubes so as to obtain at least two stacks of alternating tubes and heat exchange enlarging structures. Then collecting tanks are provided. The first and second collecting tanks are joined to the heat exchanging stacks, such that an angle α is formed between said at least two heat exchanging stacks 2 and a first or second collecting tank is in the angle α connecting those two heat exchanging stacks 2. The second or first collecting tanks, respectively, are then joined to the other ends of the heat exchanging stacks 2.

[0024] In a preferred aspect, the heat exchange enlarging structures are thermally attached to the heat conducting tubes by sintering, or via a thermally conductive means. The thermally conductive means can be formed by thermally conductive glue, thermally conductive epoxylayer, (soldering) paste, thermally conductive metal layer, e.g. brazing foil, and so on. Alternatively, in case a thermally conducting open cell porous medium is used as heat exchange enlarging structure, this can be attached by means of a co-casting method. Such method is described in DE19650613, second method. In a further alternative, the heat exchanging stack is produced integrally by casting the heat exchange enlarging structures together with the heat conducting tubes or by a method of rapid manufacturing. Every one of these attachment methods, reduce the thermal contact resistance and thus improves the thermal conductivity between the heat exchange enlarging structures and the heat conducting tubes.

[0025] Another aspect of the claimed invention provides use of a heat exchanger according to the invention for cooling, heating, ventilating and/or air conditioning.

[0026] Definitions

[0027] The term "porosity" is to be understood as the amount of air in the thermally conductive open cell porous medium expressed as a percentage of a same volume of dense material. [0028] The term "open cell porous medium" is to be understood as a porous medium with interconnecting porosity. Brief Description of Figures in the Drawings [0029] Example embodiments of the invention are described hereinafter with reference to the accompanying drawings in which [0030] - Figure 1 shows a top view of an exemplary embodiment of the present invention. [0031 ] - Figure 2 is a top view of another example embodiment of the present invention. [0032] - Figure 3 shows a top view of different test set-ups for an exemplary embodiment of the present invention. [0033] - Figure 4 shows the results of the test of figure 3. [0034] - Figure 5 shows in figure 5A a conventional, flat and finned heat exchanger and in figure 5B a comparable flat heat exchanger wherein the fins are replaced by open cell metal foam. [0035] - Figure 6 shows a second test for comparison. Figure 6A shows a top view of a conventional heat exchanger. Figure 6B shows a top view of another set up of the conventional heat exchanger of figure 6A. Figure 6C shows a top view of a heat exchanger according to a preferred embodiment of the present invention.

[0036] - Figure 7 shows 3-D views of the test of figure 6b and figure 6c respectively.

Mode(s) for Carrying Out the Invention

[0037] Examples of a heat exchanger and a method for producing such a heat exchanger will now be described with reference to Figures 1 to 7.

[0038] Figure 1 shows a top view of an exemplary embodiment of the present invention. Heat exchanger 1 is build up from two stacks 2 of heat conducting tubes which are interconnected via heat exchange enlarging structures. The heat exchanger further comprises first and second collecting tanks 3, 4. The heat exchanger comprises a first portion A and a second portion B, wherein portion A is angled with respect to portion B. The angle in between portion A and portion B is called α.

[0039] The illustrated example of figure 2 comprises a further exemplary embodiment of the present invention. Heat exchanger 1 is build of two stacks 2, which are made of 2 parallel first stacks which are attached to one another. The two stacks are further bent in an angle β and an angle δ. Angle β and δ might be equal to one another and might be equal to or different of angle α. Preferably, the angles α, β and δ are all equal to one another. This provides an equal division of the incoming fluid flow over the front surface of the heat exchanger, as a result of the even pressure build up over the depth of the heat exchanger.

[0040] Figure 3 shows different set ups of fluid flow in the heat exchanger of figure 2. In figure 3a hot liquid was fed into the heat exchanger 1 at the sides and released in the center of the heat exchanger 1. Cooling air was blown through heat exchanger 1 with a constant airflow. In figure 3b hot liquid was fed into the heat exchanger in the center and released at both sides. Again cooling air was blown as in the test of figure 3a, with the same test conditions. In figure 3c the center collecting tank was closed and all hot liquid was fed at one side and released at the other side of heat exchanger 1. All tests were done under same test conditions. [0041] Figure 4 shows the results obtained in the test of figure 3, they are expressed as a percentage of the heat exchange coefficient ε of the best performing heat exchanger in the test. As can be seen, the heat exchanger of figure 3a is the best, whereas the heat exchanger of figure 3b is only performing at 98% in comparison with the heat exchanger of figure 3A and the heat exchanger of figure 3c is performing at 64% in comparison with the heat exchanger of figure 3a. This clearly demonstrates that a split up entry and/or exit of the liquid to be heat exchanged increases the heat exchanging performance of the heat exchanger.

[0042] Figures 5a and 5b show flat heat exchangers with only one entry and one exit of fluid to be heat exchanged, i.e. the first medium. The heat exchanger of figure 5a is a conventional finned heat exchanger; the heat exchanger of figure 5b is the same conventional finned heat exchanger wherein the fins are replaced by open cell metal foam of 20 ppi. These heat exchangers were tested in a wind tunnel with air speeds of 15m/s at an angle of 90° (frontal) and hot water at 80⁰C at a speed of 0,75m/s flowing through the heat conducting pipes of both heat exchangers. The measured heat exchanging power of the metal foam flat heat exchanger of figure 5b amounts up to 98% of the heat exchanging power of the conventional finned flat heat exchanger of figure 5a.

[0043] Figure 6 shows another test on heat exchanging capacity of a heat exchanger with respect to the flow direction and the incoming flow surface. Figure 6a shows a conventional heat exchanger build up of a stack of heat conducting tubes which are interconnected by heat exchange enlarging louvered fins. The heat exchanger is set up under an angle of 90° with respect to the incoming cooling air. The incoming flow surface in this test was as large as the surface of the straight conventional heat exchanger of figure 6a. Figure 6b shows the same conventional heat exchanger as used in figure 6a which was set under an angle of 12° with respect to the incoming cooling air. The fins in this heat exchanger are also under an angle of 12° with respect to the incoming cooling air. Accordingly, the incoming flow surface is the length of the heat exchanger multiplied with sin(12°). Figure 6c shows an exemplary heat exchanger according to the present invention wherein the heat conducting tubes are interconnected with open cell aluminium foam of 20 ppi. All angles α, β and δ are equal to 12°. Tests were done with a first medium flow of 0,75m/s, entry of the first medium at angle a (in the center) and exit at collecting tanks 4 (as shown in fig.2).

[0044] Figure 7 shows 3-dimensional views of the test of figure 6. The set up of figure 6B is shown in figure 7A and the set up of figure 6C is shown in figure 7B for clarification of the results.

[0045] Table 2 shows the test results of the examples in figure 6 and 7.

[0046] The results in table 2 show a clear increase in heat exchanging power per incoming flow surface 8 for a given volume 6. Using a heat exchanger in a volume rather than in the frontal way, already increases the heat exchanging power dramatically. By using a volume together with the split up entrance and/or exit of the fluid to be heat exchanged, a further increase in heat exchanging power of the heat exchanger can be obtained

(see results (heat exchanging power /AFRONT) V and heat exchanging power in W-shape

(calculated for comparison for a length of 0,95 m)). An even more increased heat exchanging power can be obtained by using open cell metal foam, which is, due to its isotropic properties, less dependent on the direction of the incoming flow of fluid.

[0047] Another example of a heat exchanger according to the present invention has heat conducting tubes with height of 10 mm and width of 30 mm, which are interconnected with Kagome structure with a porosity of 96,5% . Angle α is equal to 12°, angles β and δ are equal to 20°. The first medium flow has its entry at the sides (collecting tanks 4) and exits the heat exchanger at collecting tank 3 (center).

[0048] A still further example of a heat exchanger according to the present invention has heat conducting tubes with height of 8 mm and width of 25mm, which are interconnected with metal foam of 30ppi and porosity of 95,8%. There is only one angle α of 60°. The first medium enters the heat exchanger at the sides (collecting tanks 4). Thus there has been described a heat exchanger for motohsed vehicles comprising a 3D configuration of the heat exchanger for better use of the available space in a motohsed vehicle. The invention further being characterised by a split-up entry of the medium to be heat exchanged.

Claims

1. A heat exchanger (1 ) for a motorised vehicle, for a given volume with a given incoming flow surface, said heat exchanger (1 ) comprising a plurality of heat-conducting tubes for passage of a first medium and heat exchange enlarging structures for passage of a second medium, said heat-conducting tubes being joined together by said heat-exchange enlarging structures thereby forming at least two heat-exchanging stacks (2), said heat exchanger comprising a first portion (A) and a second portion (B), said second portion (B) being angled relative to said first portion (A) such that longer lengths of said heat exchanging stacks (2) can be stowed in said volume, thereby increasing the heat exchanging capacity for said volume with said given incoming flow surface (8), and wherein said second medium coming into said volume through said given incoming flow surface (8) is distributed across both of said first (A) and second

(B) portions, said heat exchanging stacks (2) further being connected to at least one first (3) and at least one second (4) collecting tanks, characterised in that said heat exchanger is fed with said first medium through multiple first collecting tanks (3) and released by at least one second collecting tank (4) or fed with said first medium through one first collecting tank (3) and released by multiple second collecting tanks (4).

2. A heat exchanger as claimed in claim 1 , wherein a first (3) or second (4) collecting tank is positioned in the angle of said first (A) and second (B) portions.

3. A heat exchanger as in claims 1 or 2, characterised in that said at least one heat exchanging stack (2) is permanently bent in an angle.

4. A heat exchanger according to any of the previous claims, wherein said heat exchanging stacks (2) are made of metal.

5. A heat exchanger according to any of the previous claims, wherein said heat exchanging stacks (2) are made of a lightweight metal or a lightweight metal alloy.

6. A heat exchanger according to any of the previous claims, wherein the collecting tanks (3, 4) are made of plastic.

7. A heat exchanger according to any of the previous claims, wherein the collecting tanks (3, 4) are made of metal.

8. A heat exchanger as in any of the previous claims, wherein said heat exchange enlarging structures are made of an open cell porous medium.

9. A heat exchanger as in any of the previous claims, wherein said heat exchange enlarging structures are made of open cell metal foam.

10. Method of making a heat exchanger as in any of the previous claims, said method comprising following steps:

- providing a plurality of heat exchanging tubes;

- providing heat exchange enlarging structures;

- providing first and second collecting tanks;

- joining together said plurality of heat exchanging tubes with said heat exchange enlarging structures in sandwich-like configuration thereby obtaining at least two heat exchanging stack;

- joining the first and second collecting tanks to the heat exchanging stacks, such that an angle α is formed between said at least two heat exchanging stacks (2) and a first or second collecting tank is in the angle α connecting those two heat exchanging stacks (2).

11. A method of heat exchanging in motohsed vehicles, said method comprising the steps:

- providing a volume (6) wherein heat can be exchanged;

- providing a heat exchanger (1 ) in 3-D format;

- said heat exchanger (1 ) having first (3) and second (4) collecting tanks and being a combination of at least two stacks (2) of heat conducting tubes alternated with heat exchange enlarging structures;

- said heat conducting tubes adapted for passage of a first medium, said heat exchange enlarging structures adapted for passage of said second medium;

- said at least two stacks being angled relative to one another;

- said volume filled with said heat exchanger;

- feeding said heat exchanger with said first medium through multiple first collecting tanks and releasing said heat exchanger through at least one second collecting tank or feeding said heat exchanger through a single first collecting tank and releasing by multiple second collecting tanks and passing said second medium through said heat exchange enlarging structures.

12. A method according to claim 11 , wherein said heat exchange enlarging structures are open cell metal foam.

13. Use of a heat exchanger as in any of the claims 1 to 9, for cooling, heating, ventilating and/or air conditioning.