DE102008005334A1 - Thermoelectric generator for exhaust gas stream, is attached at waste gas flue, and thermoelectric transducer element is arranged, which converts thermal energy into electricity - Google Patents

Abstract

The thermoelectric generator is attached at a waste gas flue, and a thermoelectric transducer element (1) is arranged, which converts thermal energy into electricity. A heat pipe (2) is arranged in the waste gas flue, which leads the thermal energy of the exhaust gas stream to the surface of the thermoelectric transducer element.

Description

The The invention relates to a thermoelectric generator for an exhaust gas stream connected to an exhaust passage, wherein at least one thermoelectric transducer element is arranged, which converts thermal energy into electrical energy and a heat exchanger element, which at least partially on a surface of the thermoelectric Transducer element and at least partially disposed in the exhaust passage is.

From the DE 10 2005 005 077 A1 For example, such a thermoelectric generator for the exhaust gas flow of a motor vehicle is disclosed. The generation of electrical energy using a thermoelectric generator element which converts thermal energy into electrical energy is known in the art. The thermoelectric generator element makes use of the Seebeck effect in which the temperature difference between two ends, a high temperature portion and a low temperature portion, a metal or a semiconductor part causes a potential difference between the high temperature portion and the low temperature portion of the metal or the semiconductor part. A larger temperature difference increases the electrical energy generated by the thermoelectric generator element.

such Thermoelectric generators are in terms of their efficiency not yet optimally trained. A weak point in the known thermoelectric generators is not yet optimal utilization the heat of the exhaust stream. In addition, influence Elements of the heat exchanger in the exhaust stream this negative.

Of the The inventor has therefore set itself the task of a thermoelectric Generator for an exhaust flow available too provide better efficiency and the exhaust gas flow less affected.

These Task is by a thermoelectric generator for an exhaust gas stream according to claim 1 solved.

Of the Inventor has recognized that it is possible to use the thermal To improve the efficiency of a thermoelectric generator, when the heat transfer from the exhaust gas to the thermoelectric conversion element done with the help of heatpipes. A heatpipe allows a higher heat transfer, the Heat transfer not only by heat conduction but also by heat convection (Evaporation and condensation) comes about.

Out the discoveries won out beats the inventor before, a thermoelectric generator for an exhaust gas flow, which is connected to an exhaust passage, wherein at least one thermoelectric Transducer element is arranged, which thermal energy into electrical Energy converts and a heat exchanger element, which at least partially on a surface of the thermoelectric conversion element and at least partially disposed in the exhaust passage, to that effect to improve that at least one heat pipe arranged in the exhaust duct is which the thermal energy of the exhaust stream to the surface of the thermoelectric conversion element passes.

Of the new thermoelectric generator is suitable for power generation from the waste heat of an internal combustion engine, in particular a gas engine for burning biogas. This results Applications at exhaust gas temperatures of about 150 ° C to 600 ° C. The new thermoelectric generator can, for example, after a Exhaust gas turbocharger to be switched into the exhaust stream. The usage a heatpipe allows a high heat transfer from the exhaust, where the heat transfer is not only by heat conduction, but in addition also by heat convection. this makes possible a compact design, which is the weight for the heat exchanger unit can reduce up to 80%. As a heat-releasing medium Both liquid and gaseous are suitable Substances such as water, glycol, thermal oil or hot or exhaust gas. As a heat absorbing medium on the side the thermoelectric conversion element are also suitable both liquid as well as gaseous substances. The thermoelectric Generator can be composed of several modules, which consists of a Variety of thermoelectric elements exist. The modules can electrically connected either in series or in parallel. in the Exhaust duct allows multiple modules both in parallel as well be arranged in series one behind the other.

With a heat pipe heat can be transported very efficiently from one place to another. It can transport around 100 to 1000 times more heat than a solid copper component of the same size. The heat pipe utilizes the physical effect that when vaporizing and condensing a liquid enormous amounts of energy with minimal temperature gradients are implemented. In the heat pipe there is a negative pressure of about 10 ^-5 bar, so that the working fluid evaporates already at low temperatures. The heatpipes can be designed as rods with a round cross section or even flattened.

Put simply, heatpipes are sealed tubes with a working fluid and the steam. The inside of the heat pipe is provided with a capillary structure, wherein the structure of the inside can be either sintered or formed with multi-layered metal fabric. If heat is supplied to the heat pipe from outside, the liquid evaporates inside the heat pipe. The steam flows in the direction of the temperature gradient and condenses at the cooler parts of the heat pipe (contact body) with the release of energy. The condensate is transported back to the point of evaporation by the capillary forces of the internal structure.

ever the finer the structure, the greater the capillary forces. It is advantageous to use capillary structures with small radii, So small mesh size or small grain size in sintered metal. The heatpipes can be a pure copper surface alloyed with tin, nickel, brass, silver, chrome or Gold. Alternatively, the heatpipes can also be made of stainless steel Be steel.

The Working medium in the heat pipe is selected depending on the operating temperature, preferably water, because of the highest heat transfer performance at temperatures of about 2 to 300 ° C. At higher Temperatures of about 120 to 550 ° C mercury, while still higher temperatures cesium, potassium, sodium, Lithium and silver. At lower temperatures may arrive Mixture with water, alcohol, ammonia and acetyl used.

The Working medium should have the following properties: high surface tension, low Viscosity, good thermal conductivity, high evaporation enthalpy, neither extremely low nor extreme high vapor pressures, good wetting ability.

by virtue of the additional gravitational influence on the working medium In the heat pipe, the installation is preferably carried out vertically with the condensation side (Heat sink) upwards. Alternatively, the Heatpipes also horizontal or combined, for example oblique or bent, to be installed. Unfavorable affects the installation with the condensation side (heat sink) after down there because here the capillary force against gravity work got to.

It is advantageous if a thermoelectric transducer element Seebeck element is used. The Seebeck effect becomes thermoelectricity used. Some of the free moving electrons can leave the surface of a metal if its kinetic Energy at least equal to the exit or detachment work is. Since this is material-dependent, occur in a intimate Touching two metal surfaces some electrons from the lower work function metal to the other. It creates a touch voltage whose size tem peraturabhängig is. A thermocouple consists of two of these contact points. If there is no difference in temperature between them, they are equal two touch voltages. Do the two connection points different temperature, so flows as a result of a Thermoelectric voltage a thermo-current. Its size depends except from the circuit resistance of the materials and the temperature difference. The metals can be considered in terms of their Classify thermoelectric voltage into a thermoelectric voltage series.

alternative this can be done as a thermoelectric transducer element, a Peltier element used, which converts electrical energy into thermal energy transforms. The reversal of the thermoelectric effect is called called the Peltier effect. A current flows through one Metal combination analogous to the thermocouple, so arises between the two points of contact a temperature difference. And Although the place cools, the same direction a thermo-current would have to be heated.

The absorbed by the thermoelectric conversion element amount of heat is caused by coolant on the surface of the thermoelectric conversion element dissipated. The coolant can, for example, a Be heat sink, that of a cooling medium is flowed through.

Between thermoelectric transducer element and exhaust duct should at least an insulating element may be arranged, which the transducer element and thermally separates the exhaust duct. This is the thermoelectric Transducer element decoupled from the exhaust duct, thus, above all thermal losses but also thermomechanical tensions very kept low. With a powerful cooling unit, which on the other surface of the thermoelectric Transducer unit is arranged to the thermoelectric conversion unit to cool and separated by an isolation from the exhaust duct is, the efficiency of the thermoelectric generator can continue be optimized.

It is favorable if at least one contact body in thermoelectric generator is arranged, wherein the thermoelectric Transducer element between contact body and cooling attached, preferably clamped, is arranged. At the contact body and / or on the heat sink are means, preferably Elevations or depressions that move or slip the contact body and heat sink in contact prevent. The contact body can be used as a heat storage act, in which the heat pipes open and on the surface the thermoelectric conversion unit is arranged.

Around should improve the heat absorption from the exhaust stream on the surface of the heatpipes several heat exchanger surfaces be arranged. The heat exchanger surfaces can while being formed as fins and equal or unequal distances have each other. The slats themselves can be as level Be formed surface. Alternatively, a wavy one and / or a zigzag-shaped profile of the slats favorably. As material for the heat exchanger surfaces are good heat conducting metals, such as copper or Aluminum.

Become the lamellae on the surface with a catalytic Coating provided so can with the thermoelectric generator a purification of the exhaust gas flow are operated, for example can be carbon monoxide (CO) or hydrocarbons (HC) are oxidized from the exhaust stream. As possible coatings are metals, metal oxides, rare earths or Compounds suitable. For example, metals such as lanthanum, Cobalt, vanadium, cerium or precious metals such as platinum, silver, palladium, Rhodium, suitable. As a suitable metal oxide is, for example To call alumina.

Around to further increase the heat absorption from the exhaust gas flow the lamellas can surface-enlarging on their surfaces Elements in the form of ribs and / or studs and / or tips and / or Have pockets. The bags can also be used for recording of soot and / or particulate matter from the exhaust stream and serve thus form a filter for the exhaust stream. A regeneration or cleaning the filter can be done by lowering the heat dissipation be reached on the coolant side, reducing the temperature is increased in the exhaust passage and the soot and / or Fine dust particles are burned off.

In Another embodiment is at least one retaining element arranged in the exhaust duct, which secures the heat pipe in the exhaust duct. The attached in the exhaust duct retaining element serves as a holder for the heatpipes, so this in the flow direction are fixed. The material of the holding devices can with regard to Thermal thermal expansion be designed so that the heatpipes are not due to the thermo-mechanical expansions be braced in the exhaust passage.

In a particular embodiment is the thermoelectric generator and the exhaust duct as a muffler or rear silencer an internal combustion engine formed. The slats can then as absorber plates for the exhaust gas flow of the internal combustion engine act.

preferred Further developments of the invention will become apparent from the following Description. Various embodiments of the invention are without being limited thereto, with reference to the drawings explained in more detail. Showing:

1 : Side view of a thermoelectric generator,

2 : Further side view of a thermoelectric generator,

3 : Thermoelectric generator with exhaust duct; Hereinafter, the present invention will be described with reference to FIGS 1 to 3 described.

The 1 shows a side view of a thermoelectric generator. This consists in the upper part of a thermoelectric transducer element 1 which converts thermal energy into electrical energy. As a rule, the thermoelectric conversion element 1 a Seebeck element. The thermoelectric conversion element 1 is located on a contact body 4 , which serves as a heat storage. In order to obtain a large amount of electric power, a large temperature difference needs to be made between the high-temperature portion and the low-temperature portion of the thermoelectric conversion element 1 to be available. For this reason, the low-temperature portion of the thermoelectric conversion element becomes 1 from a cooling 5 traversed. The thermoelectric conversion element 1 is between the contact body 4 and the cooling unit 5 attached, preferably clamped. About holes 9 the individual elements can be connected further.

In the lower part of the 1 the heat exchanger element is shown, which has an insulation 6 from the thermoelectric conversion element 1 and the contact body 4 is thermally separated. As a result, especially thermal losses, but also thermo-mechanical stresses are kept very low. It can also be an elastic pad between thermoelectric transducer element 1 and cooling 5 to be available. Or a mechanical tension with springs guarantees an elastic tension, which pressure from outside on the cooling 5 , Contact body 4 and thermoelectric conversion unit 1 applies. The heat exchanger element is located in an in 1 not shown exhaust duct and consists in this embodiment of three heat pipes 2 , The heatpipes 2 allow a fast and high heat transfer from the exhaust gas through the insulation 6 to the contact body 4 and thus to the thermoelectric conversion element 1 , In order to improve the heat absorption from the exhaust gas flow, are on the surface of the heat pipes 2 slats 3 educated.

The topmost slat 8th forms a holding element and is based on their thickness stronger and provided with holes, so that by this holding element 8th the thermoelectric generator can be mounted in an exhaust duct. Similarly, the lowest lamella can be formed. And the uppermost and / or the lowest slat may at least partially form the exhaust duct.

The 2 shows the thermoelectric generator 1 turned 90 degrees. In this view is particularly good to see that the heatpipes 2 in the contact body 4 lead to and form the high-temperature section. At this contact body 4 closes the high-temperature section of the two Seebeck elements 1 at. Also about insulation 6 disconnected, cooling is on the right and left 5 each on the low temperature side of the Seebeck elements to produce the highest possible temperature difference. About the holes 9 are the contact body 4 and the cooling 5 connected with each other.

In the lower part of the 2 is also analogous to the execution of 1 the heat exchanger element shown, which via an insulation from the thermoelectric conversion element 1 and the contact body 4 is thermally separated.

The 3 shows a thermoelectric generator via the retaining element 8th with the exhaust duct 7 can be connected. The exhaust duct 7 is preferably formed of stainless steel. To the lower ends of the three heatpipes 2 in the exhaust duct 7 to attach, in this further embodiment, further holding elements 10 arranged in the exhaust duct. The in the exhaust duct 7 attached holding elements 10 serve as a holder for the heatpipes, so that they are fixed in the direction of flow. The material of the holding devices 10 may be formed in terms of thermal expansion so that the heat pipes 2 due to the thermo-mechanical expansions not in the exhaust duct 7 be tense.

1

thermoelectric transducer element

2

Heatpipe

3

Heat exchange surface / plate

4

Contact body

5

cooling

6

insulation

7

exhaust duct

8th

Holding element / Supreme lamella

9

drilling

10

retaining element

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102005005077 A1 [0002]

Claims (13)

Thermoelectric generator for an exhaust gas flow, which is connected to an exhaust gas duct ( 7 ), wherein at least one thermoelectric conversion element ( 1 ), which converts thermal energy into electrical energy, and a heat exchanger element which is at least partially attached to a surface of the thermoelectric conversion element ( 1 ) and at least partially in the exhaust duct ( 7 ), characterized in that at least one heat pipe ( 2 ) in the exhaust duct ( 7 ), which determines the thermal energy of the exhaust gas flow to the surface of the thermoelectric conversion element ( 1 ). Thermoelectric generator according to claim 1, characterized in that the thermoelectric conversion element ( 1 ) is a Seebeck element. Thermoelectric generator according to claim 1 or 2, characterized in that the thermoelectric conversion element ( 1 ) is a Peltier element that converts electrical energy into thermal energy. Thermoelectric generator according to one of claims 1 to 3, characterized in that a coolant ( 5 ) on the surface of the thermoelectric conversion element ( 1 ) is arranged. Thermoelectric generator according to one of claims 1 to 4, characterized in that between thermoelectric transducer element ( 1 ) and exhaust duct ( 7 ) at least one insulating element ( 6 ) is arranged, which the transducer element ( 1 ) and the exhaust channel ( 7 ) thermally separates. Thermoelectric generator according to one of claims 1 to 5, characterized in that at least one contact body ( 4 ), wherein the thermoelectric conversion element ( 1 ) between contact bodies ( 4 ) and cooling ( 5 ), preferably clamped, is attached. Thermoelectric generator according to one of claims 1 to 6, characterized in that on the surface of the heatpipe ( 2 ) a plurality of heat exchanger surfaces ( 2 ) are arranged. Thermoelectric generator according to claim 7, characterized in that the heat exchanger surfaces ( 2 ) are formed as lamellae and have equal or unequal distances from each other. Thermoelectric generator according to one of claims 7 and 8, characterized in that the lamellae ( 2 ) are formed as a flat surface or have a corrugated and / or zigzag-shaped profile. Thermoelectric generator according to one of claims 7 to 9, characterized in that the lamellae ( 2 ) have a catalytic coating on the surface. Thermoelectric generator according to claim 10, characterized in that the lamellae ( 2 ) have on the surface surface enlarging elements in the form of ribs and / or knobs and / or tips and / or pockets. Thermoelectric generator according to one of claims 1 to 11, characterized in that at least one holding element ( 10 ) in the exhaust duct ( 7 ) is arranged, which the heat pipe ( 2 ) in the exhaust duct ( 7 ) attached. Thermoelectric generator according to one of claims 1 to 12, characterized in that the thermoelectric generator and the exhaust duct ( 7 ) are formed as a muffler of an internal combustion engine and the fins ( 3 ) Form absorber plates for the exhaust gas flow of the internal combustion engine.