DE102005051309A1 - Exhaust gas heat exchanger for a thermoelectric generator and thermoelectric generator - Google Patents

Abstract

The invention relates to an exhaust gas heat exchanger for a thermoelectric generator, with at least one running in a plane and exhaust gas flowed through the exhaust passage, wherein a portion of the exhaust passage forms a channel flow and, seen in Abgsströmung, subsequent section of the exhaust passage forms a channel caster.
According to the invention, the channel flow runs with a first direction of curvature from the edge region of the exhaust gas heat exchanger to the inner region of the exhaust gas heat exchanger, merges with the curvature direction into the duct lag and this channel lag runs with a second direction of curvature different from the first direction of curvature from the inner region to the edge region of the exhaust gas heat exchanger ,
Moreover, the invention relates to a thermoelectric generator, in particular for heaters of the combustion type with such an exhaust gas heat exchanger.

Description

The The invention relates to an exhaust gas heat exchanger for one thermoelectric generator, with at least one, in one plane extending and exhaust gas flowed through the exhaust passage, wherein a Section of the exhaust passage forms a channel flow and one in the exhaust gas flow direction seen subsequent section of the exhaust duct a channel caster forms.

Furthermore The invention relates to a thermoelectric generator, in particular for auxiliary vehicle heaters.

Vehicle auxiliary heaters that be used in particular as auxiliary heaters and / or auxiliary heaters, are subject to a certain power consumption during their operation, for example for the business a blower and the control and Regelbe operation of the heater. To get through this power consumption an unwanted To avoid load on the battery, thermoelectric generators come to Use, which thermal energy, during the combustion process of the heater arises, to convert into electrical energy, which in the electrical system the motor vehicle can be fed or which directly to Power supply of the heater can be used.

In principle, a distinction is made between two types of thermoelectric generators. In a first type, the thermal generators are integrated into the heater and thus require a corresponding structural design of the heater. Retrofitting a thermoelectric generator in such a heater can be realized only at great expense. In addition, such a thermoelectric generator is exposed to very high temperatures, resulting in technological problems, such as the controllability of the thermal expansion coefficients or the desoldering of the thermocouples of the thermoelectric elements. A second type of thermoelectric generators is provided in the exhaust line of the heater, whereby a simple retrofitting is possible. Such a thermoelectric generator and the corresponding exhaust gas heat exchanger are of the DE 197 15 989 C1 known. Thermoelectric generators of this type usually generate too little electrical energy, however.

It is therefore the object of the present invention, the generic exhaust gas heat exchanger and the generic thermoelectric generator continue to optimize.

These The object is solved by the features of the independent claims.

advantageous Refinements and developments of the invention will become apparent the dependent Claims.

Of the exhaust gas heat exchanger according to the invention for one thermoelectric generator is based on the generic state The technique in that the channel flow with a first direction of curvature from the edge area of the exhaust gas heat exchanger to the interior of the exhaust gas heat exchanger runs, changing the direction of curvature goes into the channel caster and this channel wake with a second, from the first direction of curvature different curvature direction, from the interior to the edge region of the exhaust gas heat exchanger extends. By Such a structure of the exhaust gas heat exchanger is achieved the incoming name is Exhaust first is guided along the edge region of the exhaust gas heat exchanger. With increasing cooling the exhaust gas, the exhaust gas flow is further to the interior of the exhaust gas heat exchanger guided. As a result, a largely homogeneous temperature field on the surface of the exhaust gas heat exchanger obtained. Furthermore put through such an exhaust duct guide the exhaust gases at a given Space for a comparatively long distance through the exhaust gas heat exchanger back, as possible a lot of thermal energy to the material of the exhaust gas heat exchanger transferred to. Due to the special exhaust channel guide can Furthermore, very strong channel bends are avoided, the high Pressure losses would result. Thus, an exhaust gas heat exchanger is achieved with comparatively small space, comparatively low pressure loss (Back pressure) in the exhaust line of the heater, a homogeneous temperature distribution on the surface the exhaust gas heat exchanger, an efficient heat transfer from the exhaust gas to the material of the exhaust gas heat exchanger and thus finally one improved efficiency of the exhaust gas heat exchanger.

Of the exhaust gas heat exchanger according to the invention can be further developed in an advantageous manner that two exhaust ducts are arranged symmetrically, with a common exhaust inlet and a common exhaust outlet of the exhaust ducts are located on the axis of symmetry. By This development becomes the effect of homogeneous temperature distribution even further reinforced, there Now almost the entire edge area first of the hot, incoming exhaust flows through becomes.

In a preferred embodiment of the exhaust gas heat exchanger according to the invention is white Terhin provided that the at least one exhaust duct is divided by at least one extending in the exhaust gas flow direction web into subchannels. By providing the web (s), the contact area between the hot exhaust gases and the exhaust gas heat exchanger is increased, thus enabling an improved transition of the thermal energy of the exhaust gases into the material of the exhaust gas heat exchanger.

Furthermore can the exhaust gas heat exchanger according to the invention be developed such that seen in the flow direction of the exhaust gas, a End region of the channel lead neighbors and separated by a bridge from an initial region of the channel wake-up. This will be a countercurrent realized in the course of the exhaust duct. This has the consequence that already cooling Exhaust gases through the fresh incoming name is Exhaust gas reheated become. This effect amplifies the homogeneous temperature distribution on the surface of the exhaust gas heat exchanger.

Of Further, the exhaust gas heat exchanger according to the invention be developed so that the exhaust gas heat exchanger is made of aluminum. Due to the choice of aluminum can be a comparatively high thermal power can be decoupled from the exhaust gas because aluminum a very good thermal conductivity has.

Furthermore can the exhaust gas heat exchanger according to the invention be formed so that the exhaust gas heat exchanger two identical, mirrored together Exhaust gas heat exchanger parts comprises, where at the joint surfaces of the Exhaust gas heat exchanger parts one half of the cross section each the at least one exhaust duct is formed and at the joining surfaces of the Exhaust gas heat exchanger parts each asymmetry is provided as an assembly aid. Through this mirror image arrangement of two identical parts, the exhaust gas heat exchanger economical getting produced. Thus, only an always identical part has to be produced be, that per exhaust heat exchanger is used twice. Furthermore This structure also provides a uniform temperature distribution in reaches the normal direction to the joining surface. As the exhaust gas heat exchanger when used in an electrothermal generator on both Pages with thermoelectric elements is planked, is thus Ensures that all thermoelectric elements are equally thermal Energy supplied becomes. If you put one at the joining surfaces Asymmetry available, so a correct installation of the two heat exchanger parts is ensured.

Of the exhaust gas heat exchanger according to the invention can also be formed by the exhaust gas heat exchanger parts solid aluminum castings are in which by means of appropriately trained molds the corresponding cross-sectional halves the at least one exhaust duct are formed. Through this training can the exhaust gas heat exchanger Despite its complex geometry in large numbers produced very inexpensively become.

Farther can the exhaust gas heat exchanger be designed so that the flow of a diesel exhaust is not more than 3 mbar of pressure loss, with an exhaust gas flow rate of about 350 l / min, in the exhaust gas flow caused. Thereby, the advantage can be obtained that the pressure loss in the exhaust line of the heater smaller than conventional exhaust mufflers is. Thus, the exhaust gas heat exchanger a previous exhaust muffler substitute.

Of the inventive thermoelectric generator builds on the generic state The technique in that the thermoelectric generator a Exhaust gas heat exchanger comprises, which is constructed as described above. This results the advantages explained in connection with the exhaust gas heat exchanger according to the invention and properties in the same or similar ways.

Of the thermoelectric generator can be developed by that between the exhaust gas heat exchanger and the thermoelectric elements, a thermal grease as a Wärmeleitmedium is provided. Through this thermal compound will improve heat transfer from the exhaust gas heat exchanger realized to thermoelectric elements.

alternative may be provided in the thermoelectric generator that between the exhaust gas heat exchanger and the thermoelectric elements, a heat conduction foil as a heat conduction medium is provided. The advantage of the heat-conducting foil is in one better processability and better durability against high temperatures (> 200 ° C) over one longer Period.

In addition, the thermoelectric generator may be configured such that the exhaust gas heat exchanger is provided substantially centrally with a through hole whose longitudinal axis is perpendicular to the plane in which the at least one exhaust passage extends, from the through hole a tube of alumina is received. Due to this measure, the risk of a thermal shunt between the exhaust gas heat exchanger and the coolant heat exchangers is avoided. Due to the fact that the tube made of aluminum oxide has very good thermal insulation properties with very good temperature has raturbeständigkeit, it is prevented that via a screw located in the through hole thermal energy is transferred directly from the exhaust gas heat exchanger to the coolant heat exchangers.

A preferred embodiment The invention will be explained by way of example with reference to the figures.

It demonstrate:

1 a schematic spatial illustration of the thermoelectric generator according to the invention of the combustion type;

2 an exhaust heat exchange part for forming the exhaust gas heat exchanger according to the invention;

3 a coolant heat exchanger of the thermoelectric generator according to the invention.

1 shows a schematic spatial illustration of the inventive thermoelectric generator of the combustion type. An exhaust gas heat exchanger 10 includes two identical exhaust gas heat exchanger parts 12 , which are mirrored together. This exhaust gas heat exchanger 10 is made up of four thermoelectric elements 14 , such as Peltier or Seebeckelementen sandwiched. Two adjacent thermoelectric elements 14 are on the same side of the exhaust gas heat exchanger 10 arranged. It is at the contact surface between the exhaust gas heat exchanger 10 and the thermoelectric elements 14 a thermal paste or a heat conducting foil provided as Wärmeleitmedium. This construction group, which the two exhaust heat exchanger parts 12 and the four thermoelectric elements 14 is sandwiched between two substantially cuboid coolant heat exchangers 16 arranged. On a longitudinal edge (top in 1 ) of the exhaust gas heat exchanger 10 is centered an exhaust inlet pipe 18 provided over which hot exhaust gases from a heater, not shown, in the exhaust gas heat exchanger 10 be directed. On the opposite longitudinal edge of the exhaust gas heat exchanger 10 is an exhaust outlet pipe 20 for discharging the exhaust gas from the exhaust gas heat exchanger 10 intended. In the longitudinal end region of the thermoelectric generator are coolant inlet pipes 22 provided, via which coolant the two coolant heat exchangers 16 is supplied. The inflowing coolant flow is therefore before entry into the two coolant heat exchangers 16 by means of a Y-distributor 23 divided up. In the opposite end region of the thermoelectric generator are Kühlmittelauslassrohre 24 intended. The coolant flows from both coolant heat exchangers 16 be using Y-distributor 23 together and finally discharged. The coolant heat exchangers 16 are along their edges with six tongue-shaped attachment tabs 26 provided, in each of which a through hole 28 is provided. Instead of these fastening tabs and spring clips can be used. In the middle of the respective coolant heat exchanger 16 is a through hole 30 intended. This is not to be replaced by a spring clip. In order to achieve the most uniform possible surface pressure in terms of heat transfer and mechanical stress, the fastening straps 26 arranged symmetrically. Equally symmetrical, the spring clips should be mounted. For mounting the thermoelectric generator, both the thermoelectric elements 14 as well as the exhaust gas heat exchanger 10 sandwiched between the coolant heat exchangers 16 taken up and by surface pressure between the coolant heat exchangers 16 fixed. These screws (not shown) through the through holes 28 as well as the through holes 30 plugged and at the other end with a mother (not shown) countered.

In operation, exhaust gas is passed through the exhaust gas heat exchanger in this thermoelectric generator 10 passed. The thermal energy of the exhaust gas is partly in the material of the exhaust gas heat exchanger 10 above. The coolant heat exchangers 16 are flowed through by relatively cool coolant whereby a temperature difference between the relatively hot exhaust gas heat exchanger 10 and the comparatively cool coolant heat exchangers 16 results. From this temperature difference creates a heat flow, from which the thermoelectric elements 14 generate electrical energy in a known manner, which can be tapped by lines not shown.

2 shows an exhaust gas heat exchanger part 12 for forming the exhaust gas heat exchanger according to the invention 10 , This illustrated exhaust gas heat exchanger part 12 is a solid aluminum casting into which exhaust channels are formed by means of appropriately designed molds. In an exhaust gas heat exchanger part 12 is strictly speaking only a cross-sectional half or another fraction of the cross section of a later exhaust duct formed. The exhaust heat exchanger shear 10 is formed in that two such identical aluminum castings are joined together in mirror image, so that the exhaust duct structure is formed at the joining surfaces. An exhaust inlet 32 is with the exhaust inlet pipe 18 connected. Alternatively, one half of the exhaust inlet pipe 18 with the down gas heat exchanger 10 form a unit. From the common exhaust inlet 32 branch off two channel strands running in a plane, wherein a right channel strand (as in 2 shown) a portion of the incoming hot exhaust gas in the right half of the exhaust gas heat exchanger 10 leads and a left channel strand the other part of the incoming exhaust gas in the left half of the exhaust gas heat exchanger 10 leads. In the present embodiment, a channel strand is in each case by webs 34 in several subchannels 36 divided. However, only one channel strand may be provided, and / or a channel strand may comprise only a single exhaust duct. The incoming exhaust gas is by means of the subchannels 36 , whose arrangement will be discussed later, through the exhaust gas heat exchanger 10 guided and at an exhaust outlet 38 that with the exhaust outlet pipe 20 is connected, from the exhaust gas heat exchanger 10 released. The right channel branch is symmetrical to the left channel branch, with the common exhaust inlet 24 and the common exhaust outlet 38 located on the axis of symmetry. Because of this symmetry of the right and left channel strand, only the right channel strand will be explained in more detail below for reasons of clarity. This description also applies in a metaphorical manner to the left-hand channel strand. The subchannels 36 of the right channel strand are so through the exhaust gas heat exchanger 10 led them first from the middle of the top (as in 2 shown) in the inflow region, as seen in the exhaust gas flow direction, describe a left bend. Then describe the subchannels 36 the right channel strand a circular path along the edge region of the right half of the heat exchanger 10 , Here are the subchannels 36 the right channel strand, as seen in the exhaust gas flow direction, curved to the right. This direction of curvature is referred to as the first direction of curvature. The degree of curvature may vary, so that the subchannels first as close as possible to the edge of the exhaust gas heat exchanger 10 run. After the subchannels 36 described in about a three-quarter circle, the degree of curvature is increased so that the subchannels 36 to the interior, ie away from the edge area, are guided. In the present embodiment, the sub-channels become 36 of the right channel strand is led to an interior area which is approximately in the center of the right half (as in 2 shown) of the exhaust gas heat exchanger 10 lies. In this area, the direction of curvature of the subchannels 36 changed, ie in the course of the subchannels 36 these are, as viewed in the exhaust gas flow direction, curved to the left, which denotes a second direction of curvature. The course of the canal from the exhaust inlet 32 until the first change of curvature (change from left to right curvature in the right channel branch near the exhaust inlet 32 ) is called inflow area. The subsequent channel course up to the change of the direction of curvature in the center region of a channel strand (change from right to left curvature in the inflow region of the right channel strand) is referred to as a channel advance and the channel course thereafter as a channel delay. The subchannels run along the canal's wake 36 approximately in the form of a quarter circle to the exhaust outlet 38 , In other words, during the entire course of the flow through the exhaust gas heat exchanger, the exhaust gas flow direction in the right-hand channel strand initially rotates at least 90 ° counterclockwise in the inflow region. When flowing through the channel flow, the exhaust gas flow direction rotates in the present embodiment by at least 360 ° clockwise. More specifically, after flowing through the inflow region, the exhaust gas flow is directed to the right with a slight upward tendency. In the further course of the channel flow, the outflow direction then turns clockwise until the flow direction at the end of the channel forward to the right with a slight downward tendency is aligned. Finally, the exhaust gas flow direction in the wake of the wake turns at least 90 ° counterclockwise. The subchannels 36 of the left channel strand are, as seen in the exhaust gas flow direction, first to the right, then to the left, ie in a first direction of curvature, and then again to the right, that is curved in a second direction of curvature. In the area of the exhaust inlet 24 and the exhaust outlet 38 In the present embodiment, two subchannels are per channel strand 36 provided, whereas on a section 40 of the channel advance in the present embodiment, three subchannels 36 are provided.

In the design of the passageway through the exhaust gas heat exchanger particular care was taken to provide the channels with the largest possible arcs, so as to keep the exhaust gas flow as laminar as possible. In addition, sharp edges were avoided and realized a crossing and kink-free channel course. Due to this characteristic channel course, the pressure loss of the exhaust gas heat exchanger could 10 be minimized so far that it is smaller than the conventional exhaust muffler, ie less than 3 mbar. The course of the channel is thus optimized so that, on the one hand, the longest possible passage through the exhaust gas heat exchanger 10 is achieved in order to decouple as much thermal energy from the exhaust gas and on the other hand to keep the pressure loss as low as possible. Based on the realization that the temperature at the edge of the exhaust gas heat exchanger 10 is lower than in the middle, the exhaust gas flow is first led along the edge in the channel profile described above. This results in a more homogeneous temperature distribution on the surface of the exhaust gas heat exchanger 10 achieved, where as upper In particular, the contact surface of the exhaust gas heat exchanger surface 10 with the thermoelectric elements 14 referred to as. This more homogeneous temperature distribution is further supported by a countercurrent flow in the channel. The counterflow is achieved by the already slightly cooled exhaust gases from position 42 in 2 adjacent, separated by a web, to move to the incoming hotter exhaust gas. It is true, the farther from the position 42 the exhaust gas moves and thus cools, the hotter is the fresh incoming, adjacent thereto, exhaust gas. Thus, along this countercurrent, the cooling exhaust gas is heated by the newly flowing exhaust gas. Accordingly, this countercurrent supports the effect of the homogeneous temperature distribution on the surface of the exhaust gas heat exchanger. In the construction of the exhaust gas heat exchanger parts 12 Care was taken to avoid undercuts and sharp edges, leaving the exhaust heat exchanger parts 12 can be made by means of a die-cast aluminum. The surface finish achievable with aluminum casting was taken into account in the design so as not to exceed the desired pressure drop of 3 mbar. To the screw, passing through the through holes 30 the coolant heat exchanger 16 is guided, also through the exhaust gas heat exchanger, is in the middle of the exhaust gas heat exchanger 10 a through hole 44 intended. To a thermal shunt between the exhaust gas heat exchanger 10 and the coolant heat exchangers 16 avoid as possible, no mechanical connection directly between the exhaust gas heat exchanger 10 and the coolant heat exchangers 16 produced. Rather, the through hole was 44 made so large that between through the through hole 44 passed through screw and the exhaust gas heat exchanger 10 a tube of alumina can be inserted. Aluminum oxide has very good thermal insulation properties with very good temperature resistance. reference numeral 45 indicates an asymmetry, which in the present embodiment comprises a blind hole and a pin.

3 shows an opened coolant heat exchanger of the thermoelectric generator according to the invention. The installation of the coolant heat exchanger 16 in the thermoelectric generator has already been explained above. 3 shows beyond the design of the interior of the coolant heat exchanger 16 , wherein along the longitudinal direction extending webs 46 are provided for guiding the inflowing coolant. The in 3 not shown coolant inlet 22 and outlet 24 is arranged in the present embodiment, each in a corner region, as shown 1 is apparent. The coolant inlet 22 However, it can just as well on a front side of the coolant heat exchanger 16 and the coolant outlet 24 can be arranged on the opposite end side.

Furthermore, care was taken during construction not to exceed the space of an exhaust silencer of Webasto AG of 0.5 dm ³ . Thus, the thermoelectric generator with respect to the pressure loss and the installation space can substitute a conventional exhaust silencer. The thermoelectric generator is designed so that it gives a nominal voltage in the range of the electrical system voltage of a motor vehicle of about 12V at full load. As a result, the thermoelectric generator does not require a DC / DC converter for adaptation to the electrical system. The decoupling from the electrical system is preferably carried out by a freewheeling diode.

alternative for the production of the exhaust gas heat exchanger made of aluminum, this can also be made of copper or a copper alloy getting produced. These materials offer as well as aluminum the advantage of a high thermal conductivity.

The in the above description, in the drawings and in the claims disclosed features of the invention can both individually and also in any combination for the realization of the invention be essential.

10

Exhaust gas heat exchanger

12

Exhaust gas heat exchanger part

14

thermoelectric element

16

Coolant heat exchanger

18

Exhaust gas inlet pipe

20

exhaust outlet pipe

22

Coolant inlet pipe

23

Y junction

24

coolant outlet

26

mounting tab

28

Through Hole

30

Through Hole

32

exhaust inlet

34

web

36

subchannel

38

exhaust outlet

40

channel section with three subchannels

42

starting position the countercurrent

44

Through Hole

45

asymmetry

46

web

Claims (12)

Exhaust gas heat exchanger ( 10 ) for a thermoelectric generator, having at least one, extending in a plane and exhaust gas flowed through exhaust passage, wherein a portion of the exhaust passage forms a channel flow and a downstream of the exhaust gas duct seen in the exhaust gas flow direction forms a channel caster, characterized in that the channel flow runs with a first direction of curvature from the edge region of the exhaust gas heat exchanger to the interior of the exhaust gas heat exchanger, merges with changing the direction of curvature in the channel caster and this channel caster with a second , the direction of curvature different from the first direction of curvature, from the inner area to the edge area of the exhaust gas heat exchanger ( 10 ) runs. Exhaust gas heat exchanger according to claim 1, characterized in that two exhaust gas ducts are arranged symmetrically, wherein a common exhaust gas inlet ( 32 ) and a common exhaust outlet ( 38 ) of the exhaust ducts are located on the axis of symmetry. Exhaust heat exchanger according to one of the preceding claims, characterized in that the at least one exhaust gas passage through at least one extending in the exhaust gas flow direction web ( 34 ) in subchannels ( 36 ) is divided. Exhaust heat exchanger according to one of the preceding claims, characterized in that, viewed in the flow direction of the exhaust gas, an end region ( 42 ) of the channel advance and separated by a land from an initial region of the channel wake. Exhaust gas heat exchanger according to one of the preceding claims, characterized in that the exhaust gas heat exchanger ( 10 ) is made of aluminum. Exhaust gas heat exchanger according to one of the preceding claims, characterized in that the exhaust gas heat exchanger ( 10 ) two identical, mirror-image juxtaposed exhaust gas heat exchanger parts ( 12 ), wherein at the joining surfaces of the exhaust gas heat exchanger parts ( 12 ) in each case a cross-sectional half of the at least one exhaust gas channel is formed and at the joining surfaces of the exhaust gas heat exchanger parts ( 12 ) each an asymmetry ( 45 ) is provided as an assembly aid. Exhaust gas heat exchanger according to claim 6, characterized in that the exhaust gas heat exchanger parts ( 12 ) are solid aluminum castings, in which by means of correspondingly formed molds, the corresponding cross-sectional halves of the at least one exhaust gas channel are formed. Exhaust gas heat exchanger according to one of the preceding claims characterized in that the flow of a diesel exhaust gas is not more than 3 mbar of pressure loss, with an exhaust gas flow rate of 350 l / min in the exhaust gas flow caused. Thermoelectric generator, in particular for an auxiliary heater, comprising: - an exhaust gas heat exchanger ( 10 ) according to one of claims 1 to 8, - at least two thermoelectric elements ( 14 ), wherein the exhaust gas heat exchanger ( 10 sandwiched between the two thermoelectric elements ( 14 ), - at least two coolant heat exchangers ( 16 ), wherein the assembly of exhaust gas heat exchanger ( 10 ) and thermoelectric elements ( 14 ) sandwiched between the coolant heat exchangers ( 16 ) is arranged. Thermoelectric generator according to claim 9, characterized in that between the exhaust gas heat exchanger ( 10 ) and the thermoelectric elements ( 14 ) a thermal grease is provided as a heat conduction medium. Thermoelectric generator according to claim 9, characterized in that between the exhaust gas heat exchanger ( 10 ) and the thermoelectric elements ( 14 ) a heat conducting foil is provided as a heat conducting medium. Thermoelectric generator according to one of claims 9 to 11, characterized in that the exhaust gas heat exchanger ( 10 ) substantially centrally with a through hole ( 44 ) whose longitudinal axis is perpendicular to the plane in which extends the at least one exhaust passage, wherein from the through hole ( 44 ) a tube of alumina is received.