JP2006514250A - Heat exchanger - Google Patents

Abstract

The invention comprises at least one heat transfer tube (3) for the passage of a first medium (1) and a tube (3 for the passage of a second medium (2) surrounding the tube (3). And a covering for the heat conductive porous structure (4) connected to the outside of the motor-driven vehicle heat exchanger.

Description

  The invention comprises at least one heat conducting tube for the passage of a first medium and a coating of a heat conducting porous structure surrounding the tube and connected to the outside of the tube for the passage of a second medium The present invention relates to a heat exchanger for a motor vehicle including a thing. The invention also relates to a motor vehicle equipped with such a heat exchanger. The invention further relates to a method for utilizing a heat exchanger located in a motor vehicle. The invention further relates to a method for producing such a heat exchanger.

  In order to achieve the maximum possible heat transfer between two media, it is known to provide a tube on the outside with fins and to flow a second medium around the outside (finned tube heat exchanger) Yes. Such heat exchangers are applied on a large scale in industrial, automotive and household applications. A characteristic of these structures is that the flow around the fins is laminar and the dimensions of these fins and the mutual distance between the fins are many times larger than the boundary layer thickness in the second medium. . It is known that the thickness of the boundary layer increases in the flow direction and this flow becomes turbulent at a certain point (Reynolds number> 300,000). For example, for atmospheric air and for example a gas flow velocity of about 10 m / s, a distance of about 0.5 meters is required here. In a tube for the first medium having a diameter and fin length less than this peripheral length, the flow is laminar and the thickness of the boundary layer in the second medium is about 0.1-0. 4 mm. The portion of the second medium outside this boundary layer has no interaction with the tubes or fins around which flow occurs, and therefore does not contribute to heat transfer. As a result, there is a fundamental limit to the amount of heat that can be transferred with the laminar flow around the tube or along the fins.

  In addition to the heat exchangers mentioned above, heat exchangers corresponding to the types described in the preamble are also known in the prior art. Such a heat exchanger is described in French patent FR 2 414 081 (UOP Inc.), in which the porous structure is formed by graphite foam. . Such a porous three-dimensional structure can be understood as a three-dimensional or hexagonal lattice, and the nodes are connected to each other by heat conducting wires. Due to the large number of wires in such a structure, the total heat exchange area generally increases very greatly. However, the heat exchanger known from the UOP patent has several drawbacks. A significant drawback of known heat exchangers is that heat is transferred from the first medium to the second medium (and vice versa) in a relatively inefficient manner. Because of the relatively small pore size, a significant portion of the second medium flows along the coating instead of passing through the coating, which generally reduces heat transfer significantly. In particular, when the flow rate of the second medium is low--generally true for motorized vehicles, but up to about 20 m / s--the heat transfer efficiency is approximately the same as the heat transfer efficiency of the conventional fin described above. It is.

  It is an object of the present invention to provide an improved heat exchanger for motorized vehicles that can achieve more efficient cooling of the prime mover.

  For this purpose, the present invention provides a heat exchanger of the type described in the preamble, wherein the number of pores per inch (ppi) of the porous structure is approximately 20 to 50 and the thickness of the coating is between 2 and 8 millimeters. More preferably, the number of pores per inch is between 25-30 ppi. The number of pores per inch is significantly reduced compared to the prior art, and as a result, the flow through the coating is better and therefore between the first medium and the second medium. Heat transfer becomes more efficient. Since the heat exchanger incorporated in the motor vehicle is exposed to free flowing gas flow at relatively low flow rates (up to about 20 meters / second), the optimum boundary layer thickness around the tube is , Between about 0.4 and 0.5 millimeters. If the pore diameter is greater than twice the boundary layer thickness, there will usually be no further increase in interaction between the second medium and the porous structure. Therefore, the pore diameter is preferably limited to 1.0 millimeter, which corresponds to about 25 ppi, and the pore diameter should preferably be no less than 0.8 millimeter, It corresponds to about 30 ppi. If the number of pores per inch is less than 20 or at least 25, the heat exchanger can be compared to a conventional fin structure. As in the UOP patent, at more than 50 ppi, the flow resistance increases and, as stated, a significant portion of the second medium flows around the porous structure instead of passing through the porous structure. Become. By adding a coating thickness between about 2-8 millimeters, an optimal configuration of the heat exchanger can be achieved, in which case the porous structure comprises a plurality of stacked pore layers. Assembled from.

  The heat conducting structure is preferably formed from a metal foam. Metal foam has the advantage of being exceptionally thermally conductive, thereby maximizing heat exchange between the first medium and the second medium. In one particularly preferred embodiment, the metal foam is made from at least one of the following metals: copper, nickel and aluminum. Furthermore, it is possible to envisage the production of metal foam from alloys. The coating is preferably provided with a corrosion resistant metal or metal oxide to prevent or at least combat the deterioration of the heat exchanger so as to increase the durability of the heat exchanger.

  In a preferred embodiment, the wire thickness of the porous structure is at least approximately between 15 and 90 micrometers, in particular between 20 and 70 micrometers, more particularly between 30 and 60 micrometers. It is in. With such a wire thickness, the efficiency of heat transfer between the first medium and the second medium can be further increased.

  In another preferred embodiment, the hydraulic external diameter of the tube reaches up to 10 millimeters. Since we are only referring to the hydraulic diameter, the tubes can take a great variety of geometric shapes. Thus, in addition to cylindrical tubes, fin-like tubes or tubes formed in other ways are possible, in which case the hydraulic diameter does not exceed the limit of 10 millimeters.

  The side of the coating directed to the tube is preferably in at least almost complete thermal contact with the tube. In this way, the heat transfer between the tube and the porous structure or between the first medium and the second medium can be optimized.

  In a preferred embodiment, the coating is connected to the tube via heat conducting means. The heat transfer means can be very diverse in nature. The heat conducting means can be formed by, for example, a heat conducting adhesive, a (for solder) paste, a heat conducting metal layer or the like. The heat transfer means can be arranged in various ways, for example by vapor deposition or by an electro-deposition process.

  In another preferred embodiment, the coating consists of at least one strip of material arranged in a spiral around the tube. It is therefore possible to make use of relatively narrow metal strips that can be arranged around the tube in a relatively simple manner.

  The heat exchanger preferably includes a plurality of interconnected tubes to increase overall heat transfer. In one particular preferred embodiment, the tubes are positioned away from each other, in which case a guide member is arranged between the tubes to guide the second medium to the coating. Here, the guide members can be very diverse.

  The invention also relates to a motor vehicle equipped with such a heat exchanger.

  The invention further relates to a method of using such a heat exchanger located in a motor vehicle, the method comprising: A) transferring a relatively warm first medium through a tube; Transferring a relatively cool second medium through the coating to cool one medium. In a preferred embodiment, the relatively cool second medium is formed at least substantially by a gas flow, in particular an air flow. In one particularly preferred embodiment, the transfer of the relatively cold gas flow through the coating as described in step B) is performed at a flow rate that is at least substantially between 0 and 20 meters / second. Is called.

  Furthermore, the present invention relates to a method for manufacturing such a heat exchanger, A) a step of placing solder outside the tube, and B) a step of placing a coating around the tube surrounding the solder. C) melting the solder, and D) solidifying the solder. The actual adhesion between the tube and the porous structure takes place according to step D) while the melted solder solidifies, in this case the tube and the side of the porous structure directed to the tube. The contact between can be maximized.

  In a preferred embodiment, the melting of the solder described in step C) is performed by heating the solder. Such heating can be performed indirectly, for example, by applying a voltage, preferably quickly and for a very short time, but also directly by increasing the ambient temperature of the solder. be able to. However, it is also possible to envisage the application of other methods that result in the mutual adhesion of the tube and the porous structure, such as induction soldering or chemical soldering.

  The present invention further relates to a method for manufacturing such a heat exchanger, the method comprising: A) contacting the tube with a porous structure; and B) electrical and / or chemical (galvanic). Adhering the tube and the porous structure to each other through a deposition process.

  The invention will be elucidated in connection with the non-limiting embodiments shown in the following figures.

  As an example, FIG. 1 shows a part of a pipe 3 through which a first medium 1 such as water flows. The tube 3 has a second medium 2 such as air flowing around it. The tube 3 is itself covered with a heat conductive three-dimensional structure 4 such as a known metal foam. Here, the metal foam takes the form of strips 8 spirally wound around the tube. The connection between the tube and the metal foam is made by means known in the art, for example by means of a thermally conductive adhesive, a thermally conductive paste, a soldering process or by the deposition of adhesive and thermally conductive metal layers or a galvanic deposition process. be able to. What is important here is to provide sufficient thermal contact between the three-dimensional structure and the tube wall. It is preferable to use a thermally conductive metal compound on a nickel, copper or aluminum base. Depending on the application, a corrosion-resistant metal or metal oxide layer can also be added to the coating 4. The metal foam is preferably made of nickel, copper or aluminum or an alloy thereof. A metal foam can be comprised from the laminated | stacked combination of the said metal as needed. The volume porosity of the metal foam is 90% or more. The metal foam has a ppi (pores per inch) between 20 and 63, with 35 being preferred.

  FIG. 2a shows the boundary layer in a conventional heat exchanger. The laminar boundary layer is shown here by the dashed line 9. The boundary layer has a thickness of 0.1 to 0.4 mm.

  In FIG. 2 b, the de facto boundary layer is schematically indicated by the dashed line 10, which almost coincides with the outer periphery of the three-dimensional structure 4. Therefore, the thickness of this de facto boundary layer can be changed by changing the thickness of the coating. The limiting factor here is the thermal conductivity in and through the coating structure. By appropriately sizing the structure (ppi, type and amount of metal), it is possible to increase heat transfer by a factor of 5-10 with respect to laminar flow around the tube. Since the size of the opening in the three-dimensional structure is the same size as the boundary layer, the space taken by this structure is optimally used for heat transfer, so that the diameter of the coated tube is the same as the heat transfer The space occupied by the use of fins is smaller. Thus, a space saving of 25-50% is realized compared to conventional heat exchangers. The table below shows an example of an increase in heat transfer from a single, thin-walled aluminum tube (300 x 7 mm) through which a water (F) stream flows, to the air stream, which is Is coated with a 2 mm thick copper foam layer with a volume porosity of 96% and a structure of 35 ppi.

The table shows that for tubes coated with metal foam according to the invention at the same air velocity (v), the result is a heat transfer from the first medium (water) to the second medium (air) (G tot) shows a significant improvement.

  FIG. 3 shows a typical configuration of several parallel tubes 3 coated according to the invention and arranged between two manifolds 3a and 3b for a first medium such as water. Since these tubes 3 occupy less space, it is efficient to arrange between the tubes 3 guide members 7 that guide a second medium such as air along the porous metal coating.

FIG. 4 shows the heat exchange according to the invention with a conventional fin structure (line a) at different flow rates of gas (v-gas) as the second medium flowing along or through the heat exchanger. A graphical comparison of heat transfer (G) to the vessel (line b) is shown. A conventional fin structure is composed of a cylindrical tube having an outer diameter of 7 millimeters and a length of 1 meter. Here, the tube is provided with 870 fins of 18.5 × 11.5 millimeters according to the heat exchanger used in existing vehicles (particularly made by Volkswagen). In the present embodiment, the heat exchanger according to the present invention is composed of the same cylindrical tube having an outer diameter of 7 millimeters and a length of 1 meter. Around the tube, a copper foam coating having a thickness of 5 millimeters and a density of 2 kg / m ² is arranged. Here, the copper foam has about 35 ppi. The gas flow rate in the displayed graph is the flow rate along the fins and through the copper foam, not the free flow rate of gas. The moving direction of the gas here is at least approximately perpendicular to the moving direction of the liquid (for cooling) through the tube. The graphical representation clearly shows that the heat transfer of the heat exchanger according to the invention is significantly higher than that of the conventional fin structure. The graph diagram is particularly focused on relatively low gas flow rates because the heat exchanger is intentionally applied to a vehicle. It is at such relatively low gas flow rates that the vehicle engine can be cooled much better and more efficiently by the heat exchanger according to the invention than by conventional fin structures. Line b is optimal at gas flow speeds between 1 and 2 m / s, so that a vehicle running very slowly, unlike the prior art, is relatively It can be cooled in an efficient manner. Efficient and easy cooling of the engine of a vehicle running very slowly has been generally recognized as a (large) problem.

  It will be apparent that the invention is not limited to the embodiments shown and described herein, and that many modifications will be apparent to those skilled in the art within the scope of the appended claims. Let's go.

1 schematically shows a tube of a heat exchanger according to the invention coated with strips of metal foam. 2 shows a boundary layer of a second medium in a conventional heat exchanger and a heat exchanger according to the invention. 2 shows a boundary layer of a second medium in a conventional heat exchanger and a heat exchanger according to the invention. 2 shows further development of the heat exchanger according to the invention. 2 shows a graphical comparison of heat transfer between a conventional fin structure and a heat exchanger according to the present invention.

Claims (20)

At least one heat transfer tube (3) for the passage of the first medium (1);
A coating of a thermally conductive porous structure (4) connected to the tube (3) outside the tube (3) for the passage of a second medium (2) surrounding the tube (3) When,
A heat exchanger for a motor vehicle including a motor,
The number of pores per inch (ppi) of the porous structure (4) is between approximately 20-50 and the thickness of the porous structure is approximately between 2-8 millimeters; A heat exchanger characterized by   2. A heat exchanger according to claim 1, characterized in that the heat conducting structure (4) is formed by a metal foam.   The heat exchanger according to claim 2, characterized in that the metal foam is manufactured from at least one of the following metals: copper, nickel and aluminum.   The heat exchanger according to claim 1 or 2, wherein the covering is provided with a corrosion-resistant metal.   The heat exchange according to any one of the preceding claims, characterized in that the wire thickness of the porous structure (4) is at least substantially between 15 and 90 micrometers. vessel.   6. A heat exchanger according to any one of the preceding claims, characterized in that the hydraulic diameter of the tube (3) reaches a maximum of 10 millimeters.   Heat according to any one of the preceding claims, characterized in that the side surface of the covering directed to the tube (3) is in at least almost complete thermal contact with the tube (3). Exchanger.   The heat exchanger according to any one of claims 1 to 7, characterized in that the covering is connected to the tube (3) via heat conduction means.   9. The coating according to any one of the preceding claims, characterized in that the covering is composed of at least one strip of material (8) arranged in a spiral around the tube (3). The described heat exchanger.   A heat exchanger according to any one of the preceding claims, characterized in that the heat exchanger comprises a plurality of mutually coupled tubes (3).   The tubes (3) are positioned away from each other and a guide member (7) is disposed between the tubes (3) to guide the second medium (2) to the covering. The heat exchanger according to claim 10, wherein   A vehicle with a prime mover provided with the heat exchanger according to any one of claims 1 to 11. A method for using a heat exchanger according to any one of claims 1 to 11 arranged in a motor vehicle.
A) transferring the relatively warm first medium (1) through the tube (3);
B) transferring a relatively cool second medium (2) through the coating to cool the first medium (1);
A method comprising the steps of:   14. Method according to claim 13, characterized in that the relatively cool second medium (2) is formed at least substantially by a gas flow, in particular an air flow.   The transfer of the relatively cold gas flow through the coating according to step B) is performed at a flow rate that is at least substantially between 0 and 20 meters / second. The method according to claim 14. A method for manufacturing a heat exchanger according to any one of claims 1 to 11, comprising:
A) placing solder on the outside of the tube (3);
B) placing the covering around the tube (3) while enclosing the solder;
C) melting the solder;
D) solidifying the solder;
A method comprising the steps of:   The method according to claim 16, wherein the melting of the solder according to step C) is performed by heating the solder.   The method according to claim 17, wherein the heating of the solder is performed indirectly by applying a voltage.   The method according to claim 17, wherein the heating of the solder is performed directly by increasing the ambient temperature of the solder. A method for manufacturing a heat exchanger according to any one of claims 1 to 11, comprising:
A) contacting the tube with the porous structure;
B) adhering the tube and the porous structure to each other via an electrical and / or chemical deposition process;
A method comprising the steps of:

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