Patent Application
20120324909
1. Field of the Invention
The present invention relates to a heat exchanger for exchanging heat between two media, as used, for example in a vehicle.
2. Description of the Background Art
The energy which is stored, for example, in the exhaust gas of a vehicle in the form of heat, is currently unused and discharged into the surroundings. To increase the efficiency of a system, e.g., a motor vehicle, and consequently reduce CO2 emissions during operation, a thermoelectric generator (TEG) may be implemented whose thermoelectric module (TEM) converts part of the heat to electrical energy and returns it to the system. The TEG is a heat exchanger which is provided with thermoelectrically active material. If this material is exposed to a temperature difference, the TEG generates electrical energy. The temperature difference is produced in the TEG by conducting a hot medium, e.g., exhaust gas, and a cold medium, e.g., a coolant, past each other. The TEG mat be accommodated at any location within the exhaust gas branch or in the exhaust gas recirculation system, producing different benefits.
Conventional TEGs are not very efficient, due to the elevated heat transfer resistance between thermoelectrically active materials and a heat source/heat sink. Integrating the TEM into a heat exchanger has also proven to be not very practical. Up to now, available connecting techniques have been, in part, unstable at high temperatures. In addition, only minimal heat transfer frequently exists on the contacting of the TEM in the heat exchanger on the gas side. According to the prior art, conventional TEMs are therefore not optimally suited for use in a TEG, due to their design and connecting techniques, and are also not very effective.
EP 1 475 532 A2, which corresponds to U.S. Pat. No. 7,100,369, describes a thermoelectric generator having a thermoelectric element which uses the exhaust gas from an engine as a high temperature heat source and an engine coolant as a low temperature heat source to generate electricity. A valve regulates the supply of the exhaust gas to the thermoelectric element according to the engine load.
It is therefore an object of the present invention to provide an improved heat exchanger for exchanging heat between two media.
An embodiment of the present invention is based on the finding that an optimization of the thermoelectric generator may be achieved by designing a heat exchanger, in particular, as a cross-flow heat exchanger. As an alternative to generating electrical energy from thermal energy, the heat exchanger according to the invention may also be used as a thermoelectric heater and cooler.
The present invention provides a heat exchanger for exchanging heat between two media in a vehicle, the heat exchanger having the following features: at least one tube, in particular a double-walled tube for guiding or conducting a first medium of a first temperature, a thermoelectric material being disposed between an inner wall of the tube and an outer wall of the tube or at least on an inner wall of the tube; and at least one guide sheet connected to the at least one tube for guiding a second medium of a second temperature, the at least one guide sheet being designed to guide the second medium to the outer wall of the at least one tube to enable the exchange of heat between the first medium and the second medium.
The heat exchanger may be a thermoelectric generator for generating electric current from a temperature difference between two media. Alternatively, the heat exchanger may also be a thermoelectric heater or cooler which provides a heating or cooling capacity, using electric current. A heat exchanger of this type may be used, for example, in vehicles. If the heat exchanger according to the invention is used as a thermoelectric generator, a coolant for cooling the engine or the battery of the vehicle, for example, may be used as the first medium, and an exhaust gas generated by an internal combustion engine of the vehicle may be used as the second medium. The tube may be designed, for example, as a flat tube or a round tube. In addition, the tube may be designed as a single-walled or double-walled tube. The double-walled tube is generally formed from an inner tube and an outer tube surrounding the inner tube. In this case, the thermoelectric material is disposed between the inner tube and the outer tube. The guide sheet may be a sheet strip, along which, for example, the exhaust gas from the internal combustion engine may be guided. The heat exchanger according to the invention may have a plurality of guide sheets disposed in layers and a plurality of tubes disposed in parallel. For example, each of the guide sheets may have openings through which the plurality of tubes is accommodated and held in such a way that the tubes and guide sheets are disposed largely orthogonally to each other. Accordingly, the first medium and the second medium may be carried in a cross current without the two media mixing. The first medium may generally be guided within the tube (for example, in an inner tube of a double-walled tube), and the second medium may be guided between main surfaces of the guide sheets and around the outer walls of the tubes. Alternatively, the second medium may also be guided within the at least one tube, and the first medium may be guided along the at least one guide sheet. The thermoelectric material may be, for example, differently doped semiconductor materials. According to the design of the heat exchanger proposed herein, the thermoelectric material between the favorably cross-flowing media of different temperatures may be disposed in such a way that the thermoelectric material is equally exposed to both media, so that a temperature gradient is as homogeneous and minimal as possible over the entire heat exchanger.
According to an embodiment, the guide sheet may have at least one recess. The tube may be accommodated by the recess. According to such a design of the guide sheet and tube, a flow direction of the first medium may deviate from a flow direction of the second medium. For example, the first medium may flow largely orthogonally to the second medium. A flow relationship of this type permits better heat transfer between the first medium and the second medium than would be the case, for example, using a unidirectional flow (i.e., a flow in the same direction) of the two media. The guide sheet may also have a plurality of recesses for accommodating multiple tubes, in this case each tube being able to be accommodated in a separate recess.
According to another embodiment, at least one additional, in particular double-walled, tube may be disposed largely parallel to the tube on a first common plane, and at least one third, in particular double-walled, tube may be disposed on a second plane which is parallel to the first plane. The third tube may be disposed on the second plane in a position at which a passage between the tube and the additional tube is provided on the first plane. Such a non-aligned configuration of multiple tubes produces a meandering flow of the second medium around the tubes, which advantageously enlarges the heat transfer surface between the two media.
The inner wall of the tube may also form a guide channel for the first medium, the inner wall also being able to have protrusions into the guide channel. Additionally or alternatively, the outer wall of the tube may also have raised structures in the direction of a flow region for the second medium. Both the protrusions and the raised structures may be designed as filled or unfilled knobs, which may have different shapes. The protrusions and/or raised structures may act as a turbulence insert, for example to produce an swirling of a liquid medium. The protrusion and/or raised structures furthermore have the advantage that they may enlarge a heat transfer surface for the first medium and/or the second medium, which may improve the heat transfer coefficient.
According to another embodiment, the guide sheet may have a profiling. For example, the profiling may be designed in the form of a plurality of filled or unfilled knobs on a surface of the guide sheet. The knobs may have different geometries. The profiling may act as a spacer between the guide sheet and an adjacent guide sheet.
The profiling may be designed in the form of a plurality of elongated raised structures. The plurality of raised structures may be disposed on the guide sheet in such a way that a meandering guidance for the second medium around multiple tubes is made possible. For example the elongated raised structures may be designed as narrow, elongated knobs between two diagonally opposite tubes from two different rows of tubes disposed in parallel alignment. In this manner, the second medium may be advantageously guided or deflected along the outer wall of the tube, which makes it possible to achieve a better heat transfer with the first medium carried in the inner tube.
According to another embodiment, the guide sheet may have a profiling in the form of a plurality of protrusions. The guide sheet may be disposed adjacent to at least one additional guide sheet which has a profiling in the form of a plurality of protrusions, multiple protrusions of the profiling of the guide sheet being able to engage on the back with corresponding protrusions of the profiling of the additional guide sheet. A fixing of multiple, stacked guide sheets to each other, and thus also an improved hold for multiple tubes which engage with the stack of guide sheets, may thus be favorably provided.
Alternatively, the guide sheet may be disposed adjacent to at least one additional guide sheet having a profiling, the profiling of the guide sheet and the profiling of the additional guide sheet having the same structure and being able to face the same raising direction, the other guide sheet, however, being able to be rotated 180 degrees with regard to a normal to the guide sheet. According to this specific embodiment, therefore, the profiling of two adjacent guide sheets having identical profiling may be prevented from engaging with each other, since, for example, a distance between the guide sheets would thus be too small for certain applications or application scenarios of the heat exchanger. Since it is possible to dispense with the manufacture of differently profiled guide sheets, however, production costs may be reduced in this type of configuration of the guide sheets, since only guide sheets of the same type need to be manufactured.
The guide sheet may also be disposed adjacent to at least one additional guide sheet having a profiling, the profiling of the guide sheet and the profiling of the additional guide sheet being able to face each other. In a stack of guide sheets, therefore, two surfaces having profiling and two upper sides not having profiling may each alternately face each other. This provides the advantage that the raised structures of the profiling of both guide sheets may touch each other and thereby ensure a greater distance between the two guide sheets. For certain application scenarios, in particular for two media of higher viscosity, such a greater distance between the guide sheets may be helpful to ensure a lower resistance of the second medium between the guide sheets.
According to another embodiment, the at least one guide sheet may be uneven in the area of the passages in the tube or uneven in the area of the at least one recess. For example, the guide sheet may be corrugated in the area of the recesses. This specific embodiment of the guide sheet offers the advantage, on the one hand, that an improved hold for the at least one tube may be achieved without additional components, since a larger area of the tube is contacted and held by the guide sheet, due to the uneven form. On the other hand, an improved heat transfer may be made possible between the guide sheet and the tube, since a greater contact line exists between the uneven guide sheet and the tube.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
In the following description of the exemplary embodiments of the present invention, identical or similar reference numerals are used for the elements illustrated in the different drawings and having a similar function, these elements not being described repeatedly.
The heat exchanger according to the invention may be used, for example, as a thermoelectric generator (TEG) for generating electricity in a vehicle.
In a TEG according to exemplary embodiments of the invention, two media of different temperatures may be conducted past each other in a cross flow along a heat transfer route, so that heat may be transferred from the warm medium to the cold medium. The two media are separated to prevent mixing from occurring. The hot medium is, for example, exhaust gas, and the cold medium is, for example, a water/Glysantin mixture, which may be used as a coolant. The exhaust gas comes from, for example, an internal combustion engine; the water/Glysantin mixture comes from a coolant circuit for cooling different engine, air-conditioning or battery components.
The TEG may largely comprise, for example, the following components: a possible holder, a thermoelectric module (TEM), at least one profiling, at least one base, a housing, diffusers or collectors as well as a possible turbulence insert.
According to the approach presented herein, a thermoelectric material, which forms the thermoelectric module (TEM) of the heat exchanger, is disposed on an inside of the plurality of tubes of the heat exchanger. If the heat exchanger is used as a TEG, the TEM is used to generate electricity from exhaust gas heat.
In the TEM illustrated herein, for example, a heat source based on a second medium is located on one side, and a heat sink based on a first medium is located on the other side, so that heat is transported from the warm side to the cold side due to the different temperatures of the two media. As a result the TEM produces electricity in the presence of the temperature difference according to the Seebeck effect.
The TEM is generally designed in such a way that a plurality of thermoelectrically active materials, e.g., n-doped and p-doped semiconductors, are alternately connected to each other via electric conductors. The geometric orientation of the thermoelectrically active materials is in the direction of the heat flow from the warm side to the cold side. For example, PbTe, BiTe, SiFe, SiMn or SiMg may be used as the material of the thermoelectrically active materials.
The separating plane or surface between the hot and cold sides favorable represent the TEM. This means that one side of the TEM is in direct or indirect contact with a hot source, and the other side is in direct or indirect contact with a cold area. The temperature difference provided hereby between the one side and the other side of the TEM produces thermal diffusion flows within the thermoelectrically active (TE-active) materials in the TEM, which results in an electric voltage. This phenomenon is known as the Seebeck effect. TE-active materials may be, for example, semiconductor materials. The electric voltage may be tapped in the form of electric current. For this purpose, the electric current is supplied to an electric load or an electric storage unit outside the TEM via electric lines which lead to the TEM and are connected thereto.
The TE-active materials do not touch each other, for which reason a space is provided between the TE-active materials. For efficiency reasons, a ratio between a volume of TE-active materials and a volume of space should, in principle, be as high as possible.
To set the desired electric voltages and current flows, the semiconductor conductor material integrated into the TEM may be connected in alignment or in parallel. This also applies to the electric interconnection of multiple TEMs.
The TEM or TEG construction may be executed in such a way that the TEM is designed to be media-tight. As a result, neither the first medium nor the second medium enters the interior of the TEM and thus reaches the TE-active materials.
During the course of the following description, the term “TEM tubes” is used for the tubes of the heat exchanger presented herein.
With regard to its inner and outer shape, the TEM or the TEM tube may have different designs.
Accordingly,
In the exemplary embodiment illustrated in
Both the first medium and the second medium may be guided on both the inside and the outside of TEM tubes 14. The first and second media are not in direct contact with each other, and they do not mix with each other. As a result, TEM tubes 14 separate the two media streams of the first and second media along a heat transfer route, i.e., in radial direction 18. A length of TEM tubes 14 in axial direction 11 corresponds to the heat transfer route in TEG 1. A beginning and an end of TEM tubes 14 represent the inlet and outlet of the first or second medium on the heat transfer route within TEM tube 14.
TEG 1 according to the invention my have four diffusers 7, via which TEG 1 may communicate with connections on the gas and coolant sides. For example, a first radial diffuser 26 acts as an inlet for exhaust gas, another radial diffuser 26 opposite the first radial diffuser acts as an outlet for the exhaust gas, a first axial diffuser 27 acts as an inlet for a coolant, and another axial diffuser 27 opposite the first axial diffuser acts as an outlet for the coolant.
Knob-like, protruding structures, which ensure mutual support of TEM tubes 14 against each other, may be embossed into surfaces of TEM tubes 14 illustrated in
The individual TEM tubes of the TEG are connected to each other in their particular longitudinal axial end areas by means of bases 5.
Base 5 separates the media flows of the first medium and the second medium at the end faces of the heat transfer route, i.e., at its inlet and outlet, and thus in the axial direction. Base 5 is a deformed metal sheet which is manufactured, for example, from high grade steel. It is provided with a plurality of recesses, the number, configuration and shape of which correspond to the TEM tubes, which may be connected to the recesses in base 5. The connection may be carried out, for example, by laser welding. For this purpose, the tubes may be first inserted into the recesses in base 5. In general, one base 5 is joined to one inlet and outlet of the tube bundle. The recesses and the circumferential outer contour of base 5 may be provided with passages.
To assemble the TEG according to the invention in a media-tight manner, the circumferential contour of the base may be connected to a housing and/or a diffuser of the TEG. Laser welding, for example, may again be used as the connecting technique in this case.
With regard to its shape, housing 6 is a round or rectangular, rounded tube. Housing 6 may be offset multiple times in axial direction 11. The first or second medium may be guided between an outer side of the TEM tubes and an inner side of housing 6 crosswise, i.e., in directions 18, 19, 20, or longitudinally, i.e., in direction 11, in relation to the TEM tubes. Housing 6 thus separates the media flow of the first medium or the second medium from the surrounding atmosphere in radial direction 18 along the heat transfer route. A collection of this media flow upstream and downstream from housing 6 is therefore not necessary.
Housing 6 is provided with an opening 24 on each of two opposite sides in the radial direction (18). This opening 24 may be provided with a passage. In
Another small opening may be provided in the housing through which, for example, electric lines of the TEM tubes may be run. The opening would have to be sealed with an appropriate substance, e.g., adhesive. An opening of this type is not illustrated in
Diffuser 7 may be formed from a deformed and/or welded metal sheet. It has two openings. On the side of the first opening, diffuser 7 is connected to a power line; on the side of the second opening, it is connected to the base and/or to the housing of the TEG. The openings naturally and generally have different diameters. Diffuser 7 is provided with an advantageous flow design. The space between an inner wall of an axial diffuser and the base forms a chamber which collects the medium communicating with the TEM tubes prior to entering the tubes and after exiting the tubes. As a result, two diffusers are generally provided for each TEG in the axial direction.
In the embodiments of the TEG illustrated in
A ribbing 28 is provided on the outside of TEM tubes 14. Thin sheet strips 28, which are stacked one on top of the other in a parallel configuration or layered in axial direction 11 are provided as guide sheets, which are penetrated by the bundle of TEM tubes 14 orthogonally to sheets 28. For this purpose, each sheet strip 28 has recesses whose shape matches the outer contour of TEM tubes 14. In cross section, these sheet strips may have a round as well as rectangular shape or a shape which deviates therefrom. Sheet strips 28 may be provided with a profiling 4.
Recesses 29 in sheet strips 28 may have passages or indentations and/or introduction angles which facilitate the joining of sheet strips 28 with the TEM tubes or which may ensure a connection between sheet strips 28 and the TEM tubes over a wider area. The heat transfer resistance may be reduced in this manner. The passages or indentations or insertion angles are not illustrated in
For example, the connection between a recess 29 and a TEM tube or a passage of a recess and a TEM tube is a press fit, it being possible to deform recess 29 or the recess having passage 30 during the joining of sheet 28 to the TEM tube. The connection may therefore be a force-fit or form-locked connection and thus represent a mechanical connection. Alternatively or additionally, the connection may also be an integral connection, which may be produced, for example by soldering. The passages enlarge the contact surfaces on the TEM tube and may be used as spacers for sheet strips 28. Adjacent sheet strips 28 then touch each other at these points.
In the TEG, the sheet strips are generally spaced a distance apart. The hot medium, for example, flows between the sheet strips. The axial distance between the sheet strips may be 1-6 mm according to the invention and preferably 2-4.5 mm. A shorter distance could cause the pressure drop to increase disproportionately due to fouling, e.g., due to soot and particle deposits. A greater distance, in turn, could have the disadvantage that the heat transfer and the transfer surfaces are reduced, which could result in a lower capacity.
To permit or improve a spacing between the sheet strips, these sheet strips may have indentations, bent notches and/or latching tabs which are used to space the sheet strips a distance apart. Adjacent sheet strips then touch each other at these points.
Sheet strips 28 may have surface-increasing and heat transfer-increasing profilings 4 or embossed areas 4 and/or stamped areas 4 and/or notches 4 such as winglets 4 and/or knobs 4 and/or ribs 4 and/or gills 4, which may be used as spacers 31 for sheet strips 28.
According to one exemplary embodiment of the invention, profilings 4 of sheet strips 28 are not only used to enlarge the heat transfer surface and to interrupt the laminar limiting layer in the flow and/or to produce swirls in the flow, which may be used to increase the capacity of the TEG. Profilings are also used to advantageously guide and/or deflect the flow, for example of the second medium. This may be necessary, in particular, when the bundle of TEM tubes 14 have a relatively high packing density for reasons of installation space. In this case, TEM tubes 14 follow each other very closely in dimensions 18, 19, 20, whereby the unwanted production of still water zones between two adjacent or two consecutive TEM tubes 14 may be avoided. This is the case, in particular, when the hot media flow is able to flow unhindered in radial direction 18 if TEM tubes 14 are disposed in aligned configuration 21. To prevent this, profilings 4 are disposed according to the invention as shown in
It is apparent from
As explained in connection with
For example, housing geometry 6 may be adapted to the bundle of TEM tubes 14, viewed over the cross section, so that similar flow gaps advantageously prevail in the entire external area of TEM tubes 14, in particular in width direction 19, so that a favorable, uniform distribution of the mass flow density may be achieved.
An adaptation of housing geometry 6, or a special type of adaptation of housing geometry 6, to the configuration of TEM tubes 14 is provided in the exemplary embodiments of the TEG in
In contrast thereto, an exemplary embodiment of housing geometry 6, which is not specially adapted to TEM tube bundle (14), is shown in
According to the exemplary embodiment of the invention illustrated in
However, this height may exceed the distance if profilings 4 of sheet strips 28 are partially inserted into the negative structures of profilings 4 of adjacent sheet strips 28, as is apparent on the basis of the exemplary embodiment illustrated in
Sheet strips 28 may be stacked in stacks of the same type and of the same orientation.
According to the schematic diagram illustrated in
According to the invention, adjacent sheet strips 28 may likewise be situated such that they are alternately rotated 180 degrees in relation to each other or rotated tangentially, as shown on the basis of the exemplary embodiment of a guide sheet configuration 28 illustrated in
The embodiments according to
Alternatively, the heat exchanger described in connection with
Accordingly,
According to the exemplary embodiment illustrated in
If the air is guided on the outside of TEM tubes 14, TE-HC 32 may be designed without a housing and without radial diffusers. If the coolant or refrigerant is guided on the outside of TEM tubes 14, TE-HC 32 may be designed without axial diffusers 27.
The TEG described in connection with
In this connection,
The exemplary embodiments described have been selected only by way of example and may be combined with each other.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 058 676.8 | Dec 2009 | DE | national |
This nonprovisional application is a continuation of International Application No. PCT/EP2010/069107, which was filed on Dec. 7, 2010, and which claims priority to German Patent Application No. DE 10 2009 058 676.8, which was filed in Germany on Dec. 16, 2009, and which are both herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2010/069107 | Dec 2010 | US |
| Child | 13525698 | US |
