ES2931217B2 - THERMOELECTRIC DEVICE AND GENERATOR - Google Patents

Description

DESCRIPTION

THERMOELECTRIC DEVICE AND GENERATOR

OBJECT OF THE INVENTION

The present invention belongs to the technical field of the conversion of heat energy into electricity, and vice versa, due to the Seebeck and Peltier effects. In particular, the present invention is included within the sector of electricity generation through devices for taking advantage of the thermoelectric effect. More particularly, the present invention is directed to a thermoelectric device and to different embodiments of thermoelectric generators that include the thermoelectric device.

BACKGROUND OF THE INVENTION

Since the discovery, at the beginning of the 19th century, of the first thermoelectric effect (Seebeck), the science of thermoelectricity has evolved considerably to give rise to the development of numerous devices that take advantage of thermoelectric effects for various applications in different fields. Thus, there are applications for temperature measurement (thermocouples), power generation (thermopile, thermoelectric generators), waste heat recovery (for example in vehicle exhaust pipes or in pipes and cooling circuits of thermal power plants), temperature control ( refrigerator/Peltier cell), to modern thermocyclers that use Peltier technology to benefit from the properties of semiconductor materials, or even space applications for power supply of probes and equipment of artificial satellites.

As a general denominator, from this conception of thermoelectricity, the different developments have sought to increase the conversion performance carried out by a thermoelectric system, that is, the relationship between the heat flow and potential difference through the material.

In particular, to increase the efficiency and performance of the different thermoelectric devices, various developments are aimed at attempting to optimize the Figure of Merit (ZT) by reducing the thermal conductivity of the thermoelectric material without reducing the electrical performance. For this purpose, complex technologies for deposition of omasking nanoparticles on thin sheets of thermoelectric material have recently been developed to give rise to nanostructured devices, or nanometric lattices, that allow modifying the transport of phonons in the material, and thereby reducing its thermal conductivity.

DESCRIPTION OF THE INVENTION

The present invention proposes a solution to increase the efficiency of a thermoelectric device by means of a thermoelectric device according to claim 1, and a thermoelectric generator according to claim 25. Preferred embodiments of the invention are defined in the dependent claims.

In a first inventive aspect, a thermoelectric device is defined that comprises:

- a first sheet arranged on a first portion of substrate;

- a second sheet arranged on a second portion of substrate;

- two electrically insulating layers, each layer being configured to exchange heat with a thermal focus, respectively; and

- four electrical contacts;

wherein the first portion of substrate is thermally and electrically insulating and comprises a first and a second end, wherein the first end is in contact with an electrically insulating layer and the second end is in contact with the other electrically insulating layer;

wherein the second portion of substrate is thermally and electrically insulating and comprises a first and a second end, wherein the first end is in contact with an electrically insulating layer and the second end is in contact with the other electrically insulating layer;

wherein the first sheet is a sheet of thermoelectric material, of type n or type p electrical conductivity, and comprises a first and a second end, where the first end is in contact with an electrically insulating layer, and where the second end is in contact with the other electrically insulating layer;

wherein the second sheet is a sheet of thermoelectric material, of a type opposite to that of the first sheet, and comprises a first and a second end, wherein the first end is in contact with an electrically insulating layer, and the second end is in contact with the other electrically insulating layer;

wherein two electrical contacts are arranged on the first sheet, each electrical contact being arranged close to one end of said first sheet, respectively;

wherein the other two electrical contacts are arranged on the second sheet, each electrical contact being arranged close to one end of said second sheet, respectively;

wherein the cross-sectional area of thermoelectric material is equal to or less than one tenth of the cross-sectional area of substrate.

Regarding the nomenclature used throughout the text, it will be understood that the term sheet refers to the component of the thermoelectric device composed of the thermoelectric material. In relation to the nature of said thermoelectric material of which the sheets of the thermoelectric device of the invention are composed, the person skilled in the art will understand that it may be thermoelectric material with electrical conductivity type "p" or type "n". That is, it will be understood that if the thermoelectric material is of type "p", it will be a material in which the majority charge carriers are positive or hollow. Therefore, it will be understood that if the thermoelectric material is of type "n" , it will be a material in which the majority charge carriers are electrons.

That is, for the operation of the device and/or successive generators that implement a plurality of devices according to the invention, it will be understood that connections are established between successive first and second sheets, alternatively, of thermoelectric materials of opposite types, respectively.

Regarding these connections, it will be understood that there are no direct physical contacts between the different sheets. Said electrical connection between sheets is made through different electrical contacts (through connectors, wiring and/or through the electrical contacts themselves configured and/or sized for this purpose).

In the device according to the invention, the cross-sectional area of the sheets is much smaller than that of the substrate (i.e., equal to or less than one tenth of the cross-sectional area of the substrate) and, therefore, their relative cross-sectional area will be small regardless of the absolute cross-sectional area of the thermoelectric device.

In a particular embodiment, said sheets have a thickness of the order of micrometers (> 1^m), which allows there to be no inhomogeneities throughout the thickness of the sheet that could cause electrical leaks, at the same time that it allows reducing costs of manufacturing.

According to the arrangement and geometry of the elements that make up the thermoelectric device, the heat flow travels parallel to the surface of the sheet of thermoelectric material. Although other configurations in the state of the art where the heat flow runs perpendicular to the plane of the sheet allow high values of the figure of merit (ZT) to be obtained, a serious disadvantage appears in these configurations because both sides of the device tend to reach very similar temperatures due to the small distance between the sources of higher and lower temperatures. This fact forces additional energy to be provided to maintain the temperature on the lower temperature side of the bulb, which drastically decreases the efficiency values.

Advantageously, the heat flow parallel to the surface of the thermoelectric sheet of the thermoelectric device of the invention makes it possible to avoid this drawback, avoiding the use of extra energy, and thus increasing the efficiency of the device.

Additionally, the arrangement of elements of the thermoelectric device of the invention allows increasing efficiency through an effective “decoupling” of the thermal and electrical parameters. In particular, in steady state and according to Fourier's law, the heat flow established between a hot focus and a cold focus generates a temperature gradient in a homogeneous material that is inversely proportional to the thermal conductivity of the material. In the particular case of the thermoelectric device of the invention, where each of the first and second sheets are arranged on a portion of thermal insulating substrate (with a thermal conductivity, therefore, much lower than that of the sheets of thermoelectric material) and electrical, and where the heat flow through the sheets of thermoelectric material is parallel to their surface, the average thermal conductivity of the system depends on the cross-sectional area of the sheet and the substrate. Since the cross-sectional area of the sheets is much smaller than the cross-sectional area of the substrate (at most one-tenth of the cross-sectional area of the substrate), the steady-state temperature gradient will be governed by the thermal conductivity of the substrate.

The "cross-sectional area" shall be understood as the area of a cross-section perpendicular to the heat flow established when the device is in use, that is, a cross-section perpendicular to the surface of the sheet. Thus, the cross-sectional area of thermoelectric material and of substrate will be understood as the area provided, respectively, by the sheet(s) of thermoelectric material and the portions of substrate in said cross section.

According to the present invention, the first and second substrate portions can be implemented as portions of the same substrate, or as two independent substrates.

In the case of two independent substrates, each with a single sheet of thermoelectric material disposed thereon, in each substrate and sheet assembly the cross-sectional area of the sheet is equal to or less than one-tenth of the cross-sectional area of the substrate. The "cross-sectional area" of the sheet and substrate is, respectively, the area of the sheet and substrate taken from a cross section perpendicular to the heat flux established when the device is in use, that is, a cross section perpendicular to the sheet surface.

In the case of a substrate with more than one sheet of thermoelectric material disposed on it, the cross-sectional area corresponding to the sheets is equal to or less than one-tenth of the cross-sectional area of the substrate.

On the other hand, and given that the substrate is also electrically insulating, said substrate does not affect the electronic transport properties of the sheets, thus obtaining said effective decoupling of thermal and electrical transport throughout the thermoelectric device.

In one embodiment, the first substrate portion is implemented as a first substrate and the second substrate portion is implemented as a second substrate independent of the first substrate. Advantageously, in this embodiment the heat flow is distributed (under ideal conditions) along each substrate, thus increasing the temperature difference between its ends.

In one embodiment, the first and/or the second substrate has a prism geometry, and the first sheet and/or the second sheet, respectively, is disposed on a face of said substrate with a prism geometry. Preferably, the sheet is arranged on a side face of the prism geometry substrate and the first and second ends of the substrate in contact with the electrically insulating layers are the bases of the prism geometry substrate.

In an embodiment where the first and/or the second substrate has a prism geometry and the first sheet and/or the second sheet, respectively, is arranged on one face of said substrate with prism geometry, the thicknesses of said substrate with prism geometry of prism and the sheet arranged on one face of said substrate meet the following relationship:

where Ksub is the thermal conductivity of said substrate with prism geometry, ael

thickness of said substrate, Kthe thermal conductivity of the sheet arranged on said

substrate and the thickness of said sheet.

According to this embodiment, the thermal and geometric characteristics of the thermoelectric device are optimized in such a way that the potential difference and output power obtained are increased, with a minimum reduction of the short circuit electric current flowing through the device. sheet of thermoelectric material caused by the increase in electrical resistance due to their reduced thickness.

Additionally, the optimization parameters of this particular embodiment provide greater convenience from a materials selection and manufacturing point of view, as it is an optimization based on material thicknesses, and not on the selection/modification of thermal properties of the materials. themselves.

In one embodiment, the prism geometry substrate has a right prism geometry, and the sheet disposed on one face of said substrate has a rectangular geometry.

In one embodiment the prism geometry substrate has rectangular prism geometry.

In one embodiment, the contour of the sheet coincides with the contour of the face of the substrate on which it is disposed.

In one embodiment, the substrate with prism geometry has a number of faces greater than or equal to 6, that is, the substrate has 2 bases and a number of side faces greater than or equal to 4.

In one embodiment, the first and/or second substrate has cylindrical geometry; the first sheet and/or the second sheet, respectively, has curved geometry; and said first and/or second sheet with curved geometry is arranged on said first and/or second substrate of cylindrical geometry along a certain arc of its outer surface.

In an embodiment wherein the first and/or second substrate has cylindrical geometry, the first and/or second sheet has curved geometry, and the curved geometry sheet is arranged on the substrate with cylindrical geometry along an arc. of substantially 360°, the following relationship holds:

where K is the thermal conductivity of said substrate with cylindrical geometry, K is

<the thermal conductivity of the sheet arranged on said substrate,>Rsub<is the radius>of said substrate, andRTis the total radius of the cylindrical assembly formed by said substrate and said sheet.

Advantageously, said relationship optimizes the power of the device, in such a way that the potential difference is increased with a limited reduction in the short-circuit electric current flowing through the sheets of thermoelectric material caused by the increase in electrical resistance due to their reduced cross section. Under optimal conditions, this allows an output power similar to the equivalent case of a device in volume with a substantial saving of thermoelectric material greater than 90% of the equivalent device in volume of equal dimensions to the substrate.

In embodiments in which the first sheet and the second sheet are arranged, respectively, on a first substrate and a second substrate, independent of each other, the geometries of the first and the second substrate may be the same or may be different from each other. For example, the two substrates may have a cylindrical geometry, both may have a prism geometry, or the first substrate may have a cylindrical geometry and the second substrate a prism geometry.

In one embodiment, the first substrate portion and the second substrate portion are implemented as portions of the same substrate. In this embodiment, the first and second sheets share the same substrate and the same temperature gradient, dominated by the substrate as it has a lower thermal conductivity and greater cross-sectional area than the thermoelectric materials that form the first and second sheets.

In one embodiment, the substrate has a prism geometry, and the first and second sheets are each disposed on a different face of said substrate with a prism geometry. Advantageously, this embodiment allows several sides of the substrate to be used for the arrangement of sheets of thermoelectric material. Preferably, the first and second sheets are arranged on side faces of the substrate with prism geometry and the first and second ends of the substrate in contact with the electrically insulating layers are the bases of the substrate with prism geometry.

In one embodiment, the substrate has a right prism geometry, and at least one of the first and second sheets has a rectangular geometry. Preferably, the first and second sheets have rectangular geometry.

In one embodiment the substrate has rectangular prism geometry.

In one embodiment, the device comprises a third sheet of n-type or p-type thermoelectric material, and a fourth sheet of thermoelectric material of the opposite type to that of the third sheet, wherein the first and second sheets are arranged on a pair of adjacent faces of the substrate, and where the third and fourth sheets are arranged on another pair of adjacent faces of the substrate. The sheets are arranged on the substrate without direct physical contact between them. Advantageously, this embodiment allows more sides of the substrate to be used for the arrangement of sheets of thermoelectric material. Preferably, the third and fourth sheets are arranged on side faces of the prism geometry substrate and the first and second ends of the substrate in contact with the electrically insulating layers are the bases of the prism geometry substrate.

In one embodiment the substrate has a number of faces greater than or equal to 6, that is, the substrate has 2 bases and a number of lateral faces greater than or equal to 4. The use of geometries with more faces for the substrate allows the deposition of a greater number of sheets on a single substrate. The series and parallel connection of the different thermoelectric pairs of the device allows the final voltage and/or the final current intensity to be varied.

In one embodiment, the contour of at least one sheet coincides with the contour of the face of the substrate on which it is arranged. Preferably, the contour of each sheet coincides with the contour of the face of the substrate on which it is arranged.

In one embodiment, the substrate has cylindrical geometry; the first and second sheets have curved geometry; and said first and second sheets are arranged on the substrate along a certain arc of its outer surface.

In one embodiment, each of the first and second sheets of thermoelectric material covers a proximal arc of less than 180°.

In one embodiment the device comprises a third sheet of n-type or p-type thermoelectric material, and a fourth sheet of thermoelectric material of the opposite type to that of the third sheet, the third sheet and the fourth sheet being arranged on the cylindrical substrate along along a certain arc of its outer surface. The sheets are arranged on the cylindrical substrate without direct physical contact between them.

In one embodiment, at least one substrate comprises glass, quartz or ceramic.

In an embodiment where there are at least a first and a second substrate, each substrate comprises a different material. Advantageously, this embodiment allows the substrate material to be chosen depending on the type of thermoelectric material of the sheet or sheets arranged on it, which allows the efficiency of the thermoelectric device to be optimized.

In one embodiment at least one substrate is configured as a hollow solid shell filled with a gas. In this embodiment, the cross-sectional area of the substrate is the sum of the cross-sectional areas occupied by each of the elements that make up the substrate. Advantageously, in this embodiment the thermal conductivity of the substrate is lower than in the case of a solid material substrate and allows the thermal gradient between the first and second ends of the substrate to be increased for the same constant heat flow. In one embodiment the gas that forms part of the substrate is air or an inert gas, such as N2.

In one embodiment, at least one sheet of thermoelectric material comprises at least one of the following materials: pyrite (FeS2), a trichalcogenide (such as TiS3 or ZrS3), a metal, a semimetal, a metal alloy such as Ni-Cr or Ni -Cu, black phosphorus, or SnSe.

Traditionally, the selection of the type of thermoelectric material, especially in the context of electricity generation, obeys an optimization criterion through a compromise between its properties related to thermal and electrical conduction.

More specifically, this fact is revealed through the expression of the

Figure of merit where S is the Seebeck coefficient, to the conductivity

electrical, and<k>thermal conductivity, and where the productS 2 is known as power factor. That is, in said context of electrical generation, the useful power will vary in the same direction as said power factor.

Due to the inverse relationship between the power factor (electrical conductivity) and the thermal conductivity of the thermoelectric material in the Figure of Merit (ZT), as previously explained in the Background of the invention, various developments are aimed at increasing the efficiency and performance of thermoelectric devices by seeking to reduce the thermal conductivity of the thermoelectric material, trying to harm its electrical performance as little as possible.

Therefore, said developments of the state of the art use a thermoelectric material selection criterion in which a material simultaneously has high electrical conductivity and low thermal conductivity, characteristic of insulating materials.

Due to this fact, materials with a high power factor have not traditionally been used because the high thermal conductivities prevented the establishment of an adequate temperature difference between both extremes.

Advantageously, thanks to the properties and arrangement of elements that allow the effective decoupling of the thermal and electrical phenomena in the device of the invention, that is, of the electrically insulating layers, as well as the thermally insulating substrate, the sheets of thermoelectric material of the invention can use said materials, taking advantage of the high power factor regardless of the value of the thermal conductivity of these materials.

In particular, examples of materials with high power factor that can be used for the sheets of thermoelectric material of the device of the invention include semimetals, such as the element antimony or compounds such as CoS2, or metal alloys such as Ni-Cr or Ni-Cu. .

Advantageously, greater versatility of configurations and manufacturing possibilities is provided by being able to combine these materials with the classic materials known in the state of the art in the same device. Examples of these classic materials include, among others: Bi2Te3, Sb2Te3, PbTe or SiGe.

In particular, the use of metals allows for greater thinning of the sheet, which in turn allows the miniaturization of devices and the use of sheet deposition techniques. On the other hand, semimetals and alloys such as Ni-Cr and Ni-Cu allow for greater sheet thicknesses (i.e., larger cross sections compared to the substrate cross section) and, therefore, different manufacturing methods through the adhesion of said sheet on the substrate. Other semimetals such as C0S2 or CoFe alloys offer good power factor values.

In one embodiment, each sheet of a thermoelectric device comprises a different material.

In one embodiment, the device comprises at least one support in contact with one of the electrically insulating layers. Preferably the device comprises two supports, each support being in contact with one of the insulating layers.

In one embodiment, at least one support comprises an essentially flat surface.

In a second inventive aspect a thermoelectric generator is defined comprising a plurality of thermoelectric devices according to any embodiment of the first inventive aspect.

In one embodiment, at least a subset of the plurality of thermoelectric devices is distributed forming a row of devices connected in series.

In one embodiment, the thermoelectric generator comprises several rows of thermoelectric devices electrically connected in series, wherein said rows are electrically connected to each other in parallel.

In one embodiment, the rows of devices are substantially parallel.

In one embodiment, at least a subset of the plurality of thermoelectric devices are arranged according to an annular geometry.

All features and/or method steps described herein (including the claims, description and drawings) may be combined in any combination, except for mutually exclusive combinations of such features.

DESCRIPTION OF THE DRAWINGS

These and other characteristics and advantages of the invention will become more clearly evident from the following detailed description of a preferred embodiment, given solely by way of illustrative and non-limiting example, with reference to the accompanying figures. .

Figures 1a-1c These figures show an elevation view, a profile view and a cross section of an embodiment of a part of a thermoelectric device according to the invention, in particular a sheet of thermoelectric material arranged on a portion of an insulating substrate thermal and electrical.

Figure 2 This figure shows an example of an embodiment of a thermoelectric device that comprises two sheets of thermoelectric material arranged on separate thermal and electrical insulating substrates, according to the invention.

Figures 3a-3b These figures show an example of an embodiment of a thermoelectric device that comprises two sheets of thermoelectric material with curved geometry arranged on separate thermal and electrical insulating substrates with cylindrical geometry, according to the invention, and a schematic cross section.

Figures 4a-4b These figures show an example of an embodiment of a thermoelectric device that comprises two sheets of thermoelectric material with curved geometry arranged on a thermal and electrical insulating substrate with cylindrical geometry, according to the invention, and a schematic cross section.

Figures 5a-5e These figures show perspective views, profile views, and section views of the device at different heights of an embodiment of the thermoelectric device that comprises two sheets of thermoelectric material with rectangular geometry arranged on opposite faces of an insulating substrate. thermal and electrical with prismatic geometry, according to the invention, as well as a schematic cross section.

Figure 6a-6e These figures show perspective views, profile views, and respective section views of the device at different heights of an embodiment of a thermoelectric device that comprises two pairs of sheets of thermoelectric material with rectangular geometry arranged two by two on adjacent faces of a thermal and electrical insulating substrate with prismatic geometry, according to the invention, as well as a schematic cross section.

Figure 7 This figure shows a thermoelectric generator according to an embodiment of the invention, comprising a plurality of thermoelectric devices distributed in a row.

Figure 8 This figure shows a thermoelectric generator according to an embodiment of the invention, comprising a plurality of thermoelectric devices distributed according to an annular configuration.

Figure 9 This figure shows a thermoelectric generator according to an embodiment of the invention, which comprises a plurality of thermoelectric devices distributed forming several rows electrically connected in parallel.

Figure 10 This figure shows a thermoelectric generator according to an embodiment of the invention, which comprises a plurality of thermoelectric devices distributed in rows and columns.

Figure 11 This figure shows a thermoelectric generator according to an embodiment of the invention, which comprises a plurality of thermoelectric devices distributed in rows and columns.

DETAILED STATEMENT OF THE INVENTION

Figures 1a and 1b show an elevation and a profile view of a part of a thermoelectric device (10) according to an embodiment of the invention. In particular, for illustrative purposes, a basic element is shown that comprises a sheet (16) of thermoelectric material arranged on a portion of a thermal and electrical insulating substrate. More particularly, in this embodiment said portion of substrate is implemented as a substrate (15) with rectangular prism geometry, and Figures 1a and 1b serve to describe how, according to the invention, each sheet (16) of thermoelectric material with the portion of substrate on which it is arranged. In the same way, and by virtue of said relationship and integration between elements, it is described what beneficial effects are obtained, and that they can be transferred to a complete configuration of thermoelectric device (10), where different sheets (16) of different types of thermoelectric material to generate electricity.

In particular, it is noted that, in this embodiment, the thermoelectric device (10) shown comprises, in its most extreme positions, two supports (11, 12), separated by a certain distance, configured to conduct heat and in contact, each one, with an electrically insulating layer (13, 14).

Said electrically insulating layers (13, 14) are configured to exchange heat with a thermal focus, and as can be seen in the figures, they are respectively arranged on the internal surfaces, that is, facing each other, of the supports (11 , 12). Said layers (13, 14) of the embodiment shown in Figures 1a and 1b are composed of an electrically insulating material and in one embodiment they have a thickness of the order of micrometers (> 1^m), that is, their thickness is much smaller. than a characteristic length of the rest of the elements that make up the thermoelectric device (10) shown.

Although in other embodiments the presence of said supports (11, 12) is not necessary to communicate heat energy to the thermoelectric material of the device (10), in the example shown said supports (11, 12) act as thermal sources, introducing and evacuating heat from the most extreme points of the device (10) in contact with the electrically insulating layers (13, 14). More particularly, in the embodiment shown, the support (11) shown in the upper area acts as a heat source, or hot focus, and the support (12) shown in the lower area acts as a heat sink, sink, or cold focus. .

Arranged between both supports (11, 12) and in thermal communication with them through the electrically insulating layers (13, 14), the element of thermoelectric material is arranged, in particular a sheet (16) of a type-n thermoelectric material or typop. In particular, said sheet (16) comprises a first end (16.1) connected to the upper layer (13), and a second end (16.2) connected to the lower layer (14).

The sheet (16) is arranged, in turn, on the thermal and electrical insulating substrate (15), which is also located between the two supports (11, 12), in thermal communication with them through the layers (13, 14). ) electrically insulating. In particular, said substrate (15) comprises a first end (15.1) connected to the upper layer (13), and a second end (15.2) connected to the lower layer (14).

Regarding the geometric configuration and dimensional relationships between the sheet (16) of thermoelectric material and the substrate (15), it is observed in Figures 1a and 1b that in this embodiment said substrate (15) has a rectangular prism geometry, while that the sheet (16) has a rectangular geometry and is arranged on the substrate (15) completely covering one face thereof, that is, the contours of said sheet (16) and the face of the substrate (15) on which it is arranged. they match.

By virtue of the configuration shown, two synergistic advantageous effects are achieved. On the one hand, the heat flow is transmitted between both supports (11, 12) parallel to a plane of the coupling interface between the sheet (16) and the substrate (15). On the other hand, the decoupling of electrical and thermal effects is achieved.

For the decoupling of electrical phenomena, the joint action of the electrically insulating substrate (15), along the face of the sheet (16) with which it is in contact, and of both layers (13, 14), which allow the thermal conduction of the sheet (16) with the supports (11, 12) but prevent electrical conduction through their respective ends (16.1, 16.2), allows the sheet (16) to be electrically confined, in such a way that it is guaranteed that The thermoelectric power generated comes exclusively from the sheet (16) of thermoelectric material.

Regarding the decoupling of thermal phenomena between the sheet (16) and the substrate (15), it is achieved thanks to the relationship between the cross-sectional areas of both elements. In particular, in stationary thermal conditions between the hot focus, that is, the upper support (11) and the cold focus or heatsink, that is, the lower support (12), the temperature difference that is established between the two extremes is determined by the total thermal resistance of the sheet assembly (16) plus substrate (15).

Said total thermal resistance is established by the relationship between the cross-sectional areas of both elements, that is, of the sheet (16) and the substrate (15). In Figure 1c, a cross section of the sheet (16) and substrate (15) assembly is schematically represented, where the cross-sectional area (A) of the sheet (16) and the cross-sectional area (Asub) of the substrate (15) have been identified. ). In Figure 1c, the cross-sectional area (Asub) of the substrate has been represented with a checkered pattern and the cross-sectional area (A) of the sheet has been represented without a frame. Due precisely to the difference in cross-sectional areas between the sheet (16) and the substrate (15), the temperature difference that is established is governed by the substrate (15), and not by the sheet (16) of thermoelectric material, which, due to the nature of the thermoelectric materials, has a higher thermal conductivity than that of the substrate (15) and which alone would reduce, therefore, the temperature difference at the cold and hot ends, to the detriment of the thermoelectric performance. of the device (10). That is, as the cross-sectional area of the sheet (16) is much smaller, in particular, less than or equal to one tenth of the cross-sectional area of the substrate (15), the steady temperature gradient is governed by the thermal conductivity of the substrate ( fifteen).

More particularly, in this embodiment of planar geometry, with prismatic substrate, this decoupling of the thermal gradient is maximized when the thicknesses of the sheet (16) and the substrate (15) meet the following relationship:

K being the thermal conductivity of the sheet (16) of thermoelectric material, Ksubla

thermal conductivity of the substrate (15), the thickness of the substrate (15) and the thickness of the sheet (16) of thermoelectric material.

Therefore, the embodiment example shown in Figures 1a and 1b of an element that is part of a thermoelectric device (10) according to the invention manages to effectively and efficiently decouple the thermal transport phenomena, leaving the thermal gradient in charge of the substrate (15) and the electronic transport is in charge of the sheet (16) of thermoelectric material. Thus, the thermoelectric device (10) shown achieves greater performance while reducing the amount of thermoelectric material used.

The exemplary embodiment shown in Figures 1a and 1b comprises two electrical contacts (17, 18) arranged on the sheet (16) of thermoelectric material, each electrical contact (17, 18) arranged close to one end (16.1, 16.2) of said sheet (16), respectively. Said contacts (17, 18) will allow the connection, one by one, between a plurality of devices (10) in which the nature of the thermoelectric material (type-n or type-p) used for the sheet (16) alternates, allowing the development of scalable thermoelectric generators depending on the number of devices (10) connected.

Figure 2 shows an example of an embodiment of a thermoelectric device (10) according to the invention where two elements like the one in Figures 1a and 1b are shown connected, thus giving shape to a complete example of a device (10) that comprises a first sheet (16) arranged on a first portion of substrate and a second sheet (160) arranged on a second portion of substrate. In particular, the first substrate portion is implemented as a first substrate and the second substrate portion is implemented as a second substrate independent and separate from the first substrate.

The first (16) and the second (160) sheet are sheets of thermoelectric material of opposite type, that is, the material of the first sheet (16) is of type n, and that of the second sheet of type p, or vice versa. .

In this embodiment, the second substrate is identical to the first substrate, being arranged in the same way as the first one, between the hot and cold foci, that is, between the upper support (11) and the lower support (12), and being in thermal communication with them, through the electrically insulating layers (13, 14) through a first end and a second end of the second substrate, respectively.

Also in the same way as the substrate and the sheet (16), shown in Figures 1a and 1b, the second sheet (160) shown in Figure 2 is arranged on the second substrate, being located between the two supports (11, 12) and in thermal communication with them through the electrically insulating layers (13, 14) through a first end (160.1) and a second end (160.2) of the second sheet (160), respectively.

Regarding the geometric configuration and dimensional relationships between the second sheet (160) of thermoelectric material and the second substrate, it is observed that they are also as shown in Figures 1a and 1b. In particular, the second substrate has a rectangular prism geometry, while the second sheet (160) has a rectangular geometry and is arranged on the second substrate completely covering one face thereof, that is, the contours of the face of the second substrate on the that the second sheet (160) is arranged and said second sheet (160) coincide.

The cross-sectional area of the first sheet (16) is equal to or less than one-tenth of the cross-sectional area of the first substrate and the cross-sectional area of the second sheet (160) is equal to or less than one-tenth of the cross-sectional area of the second substrate. The cross section of each sheet (16, 160) and substrate assembly is as shown schematically in Figure 1c.

In this embodiment of planar geometry, with one sheet per substrate and the width of the sheet being equal to the width of the substrate on which it is arranged, the relationship between cross-sectional areas of sheet and substrate depends exclusively on the relationship between sheet thicknesses. and substrate. The length of the sheet (16, 160) is equal to the length of the substrate on which it is arranged.

Likewise, to optimize the decoupling between the thermal gradient set primarily across each substrate from the electronic transport through each sheet (16, 160), in one embodiment the relationship between their thicknesses meets the following relationship. On the one hand, the thicknesses of the first sheet (16) and the first substrate meet the following relationship:

where K± the thermal conductivity of the first sheet (16), Ksub lla conductivity

thermal of the first substrate, a ±the thickness of the first substrate and d ±the thickness of the first sheet (16).

On the other hand, the thicknesses of the second sheet (160) and the second substrate meet the following relationship:

where k 2 is the thermal conductivity of the second sheet (160), Ksub, 2 is the conductivity

thermal of the second substrate, a 2the thickness of the second substrate and d 2the thickness of the second sheet (160).

As indicated, the thermoelectric material of the first (16) and the second (160) sheet are different. In particular, in this embodiment the first sheet (16) is of n-type material, and the second sheet (160) is of p-type material. With a view to taking advantage of the thermoelectric phenomenon to generate electricity, it is observed that the second sheet (160) comprises two electrical contacts (170, 180) arranged, in the same way as occurs with the electrical contacts (17, 18) of the first sheet (16), close to each end (160.1, 160.2) of said second sheet (160), respectively. It is also observed that an electrical contact (17) of the first sheet (16) is connected to an electrical contact (170) of the second sheet (160), leaving the respective opposite electrical contacts (18, 180) free in the embodiment shown. of each sheet (16, 160).

For illustrative purposes, said free electrical contacts (18, 180) are shown projecting a certain length from the geometric limit of the support (12) to indicate that through said contacts (18, 180) electrical connections can be established, as with elements external to the device or with adjacent thermoelectric devices (10).

Just as the thermoelectric materials of the first (16) and the second (160) sheet are different, the materials of the first and second substrate can also be different in order to optimize the relationship between thicknesses and conductivities described above.

Although in the embodiments shown in Figures 1a, 1b and 2 the substrates are configured with a rectangular prism geometry, the substrate of the device (10) according to the invention can be configured with other geometries. Figure 3a shows an example of an embodiment of a thermoelectric device (10) according to the invention that comprises two independent substrates (15, 150) that have cylindrical geometry.

In this embodiment, the device (10) comprises two sheets (16, 160) of thermoelectric material with curved geometry, each sheet (16, 160) being arranged on a corresponding first and second portion of substrate, which, as can be seen, They are implemented as a first substrate (15) with cylindrical geometry, and as a second substrate (150) with cylindrical geometry, respectively. The figure shows the two substrates (15, 150) of cylindrical geometry, with a sheet (16, 160) of thermoelectric material arranged on the outer surface of each substrate (15, 150), along a certain arc. The arc covered by each sheet (16, 160) may correspond to a portion of the outer surface or the entire outer surface of the cylindrical substrate (15, 150) on which it is arranged. The arrangement of a sheet (16, 160) of thermoelectric material along the entire external surface of a substrate (15, 150) allows optimizing the total use of the effective area of said thermal and electrical insulating substrate (15, 150).

The cross-sectional area of thermoelectric material is equal to or less than one-tenth of the cross-sectional area of substrate. Figure 3b schematically represents a cross section of the two sets of sheet and substrate of the device of Figure 3a, where the cross-sectional area (A1, A2) of the sheets (16, 160) and the cross-sectional area (A1, A2) have been identified. Asub,1, Asub,2) of the substrates (15, 150). In Figure 3b, the cross-sectional area (Asub,1, Asub,2) of the substrates has been represented with a checkered pattern and the cross-sectional area (A) of the sheets has been represented without a frame. In this embodiment, the cross-sectional area of thermoelectric material is the area (A) contributed by the two sheets of thermoelectric material (A=A1+A2) and the cross-sectional area of substrate is the area (Asub) contributed by the two substrates (Asub =Asub,1+Asub,2) in said cross section. It is also true for each substrate and sheet assembly that the cross-sectional area of the sheet is equal to or less than one-tenth of the cross-sectional area of the substrate.

The exemplary embodiment of the device (10) shown in Figure 3a comprises two electrical contacts (17, 18) arranged on the first sheet (16) of thermoelectric material, where each electrical contact (17, 18) is arranged close to one end. (16.1, 16.2) of said first sheet (16), respectively. Furthermore, the device (10) comprises two additional electrical contacts (170, 180) arranged on the second sheet (160) of thermoelectric material, where each electrical contact (170, 180) is arranged close to one end (160.1, 160.2) of said second sheet (160), respectively. As occurred in the example embodiment shown in Figure 2, the thermoelectric material of the first (16) and the second (160) sheet are different. In particular, in this embodiment the first sheet (16) is of n-type material, and the second sheet (160) is of p-type material. In order to take advantage of the thermoelectric phenomenon to generate electricity, an electrical contact (17) of the first sheet (16) is connected to an electrical contact (170) of the second sheet (160).

Just as the thermoelectric materials of the first (16) and the second (160) sheet are different, the materials of the first and second substrate can also be different in order to optimize the efficiency of the thermoelectric device.

In an embodiment in which the first (16) and/or the second (160) sheet is arranged covering a 360° arc on the surface of the corresponding substrate (15, 150), the following is true:

whereKis the thermal conductivity of the thermoelectric sheet (16, 160),Ksubla

thermal conductivity of the substrate (15, 150), Rsubel radius of the substrate (15, 150), and RTthe total radius of the cylindrical assembly formed by the substrate (15, 150) and at least one sheet (16, 160) arranged on its surface.

Figure 4a shows another embodiment of a thermoelectric device (10) according to the invention. As in the embodiment of Figure 3a, in this embodiment a thermal and electrical insulating substrate (15) configured with a cylindrical geometry is shown, and the device (10) comprises a first sheet (16) and a second sheet (160) of thermoelectric material, both sheets (16, 160) with curved geometry. However, unlike the embodiment of Figure 3a, in the embodiment of Figure 4a the first sheet (16) and the second sheet (160) are both arranged on separate portions of the same substrate (15), each one along a certain arc of the outer surface of said substrate (15). The first sheet (16) and the second sheet (160) are one of type n and the other of type p and are arranged on the substrate (15) without physical contact between them to avoid uncontrolled electrical connections between both sheets (16, 160). . To establish an electrical communication and take advantage of the thermoelectric phenomenon to generate electricity, as occurred with the examples of embodiments of thermoelectric devices (10) shown in Figures 2 and 3a, the device (10) shown in Figure 4a comprises two contacts electrical contacts (17, 18) arranged on the first sheet (16), where each electrical contact (17, 18) is arranged close to one end (16.1, 16.2) of said first sheet (16), respectively. On the other hand, the device (10) comprises two additional electrical contacts (170, 180) arranged on the second sheet (160), where each electrical contact (170, 180) is arranged close to one end (160.1, 160.2) of said second sheet (160), respectively.

The cross-sectional area of thermoelectric material is equal to or less than one-tenth of the cross-sectional area of substrate. Figure 4b schematically represents a cross section of the set of sheets and substrate of the device of Figure 4a, where the cross-sectional area (A1, A2) of the sheets (16, 160) and the cross-sectional area (Asub) have been identified. of the substrate (15). In Figure 4b, the cross-sectional area (Asub) of the substrate has been represented with a checkered pattern and the cross-sectional area (A) of the sheets has been represented without a checkered pattern. In this embodiment, the cross-sectional area of thermoelectric material is the area (A) contributed by the two sheets of thermoelectric material (A=A1+A2) and the substrate area is the area (Asub) contributed by the only substrate in said section cross.

In one embodiment each of the first (16) and second (160) sheet covers a proximal arc of less than 180°. In other embodiments, the device (10) may include more than two thermoelectric sheets arranged along the outer surface of the substrate (15) and without establishing physical contact with each other.

Figures 5a and 5b show a perspective view and another profile view of an exemplary embodiment of a thermoelectric device (10) comprising a first (16) and a second (160) sheet, both sheets (16, 160) arranged on respective portions of substrate implemented as the same substrate (15). In particular, each sheet (16, 160) is composed of a thermoelectric material of opposite type. That is, the material of the first sheet (16) is an n-type material, and that of the second sheet (160) is a p-type material. As in Figures 1a and 1b, it is observed that in this embodiment the thermoelectric device (10) shown comprises, in its most extreme positions, two supports (11, 12), separated by a certain distance, configured to conduct heat and in contact, each, with an electrically insulating layer (13, 14).

As in Figure 4a, and as indicated above, the first sheet (16) and the second sheet (160) are both arranged on the same substrate (15). However, in this case, the substrate ( 15) has rectangular prism geometry, and the first (16) and the second (160) sheet have rectangular geometry. The sheets (16, 160) are arranged on opposite faces of the substrate (15), each sheet (16, 160) completely covering the face on which it is arranged.

In the same way as in Figure 4a, to establish an electrical communication and take advantage of the thermoelectric phenomenon to generate electricity, the device (10) shown in Figures 5a and 5b comprises two electrical contacts (17, 18) arranged on the first sheet (16) of thermoelectric material, where each electrical contact (17, 18) is arranged close to one end (16.1, 16.2) of said first sheet (16), respectively. On the other hand, the device (10) comprises two additional electrical contacts (170, 180) arranged on the second sheet (160) of thermoelectric material, where each electrical contact (170, 180) is arranged close to one end (160.1, 160.2). ) of said second sheet (160), respectively. Figure 5c shows a plan view in which, for illustrative purposes, both the upper support (11) and the upper electrically insulating layer (13) have been omitted from showing. Thus, visualization of the connections established between the first (16) and the second (160) sheet is allowed. In particular, electrical connections (19) are observed connected to the corresponding electrical contacts (17, 170) closest to the top of the device. In the same way, Figure 5d provides a plan view in which the body of the device has been truncated in a plane perpendicular to the sheets by a section at an intermediate height between the electrically insulating layers (13, 14). Thus, a view of the electrical connections (19') provided for connection with additional thermoelectric devices or with devices of another type is provided. Thus, by means of electrical connections (19, 19') such as those shown schematically in Figures 5a-5d, the first (16) and the second (160) sheets can be electrically connected to each other, as well as electrically connected with additional thermoelectric devices or with devices of another type.

In the device of Figures 5a-5d the cross-sectional area of thermoelectric material is equal to or less than one tenth of the cross-sectional area of substrate. Figure 5e schematically represents a cross section of the set of sheets and substrate of the device of Figures 5a-5d, where the cross-sectional area (A1, A2) of the sheets (16, 160) and the cross-sectional area (A1, A2) have been identified. Asub) of the substrate (15). In Figure 5e, the cross-sectional area (Asub) of the substrate has been represented with a checkered pattern and the cross-sectional area (A) of the sheets has been represented without a checkered pattern. In this embodiment, the cross-sectional area of thermoelectric material is the area (A) contributed by the two sheets (16, 160) of thermoelectric material (A=A1+A2) and the substrate area is the area (Asub) contributed by the only substrate (15) in said cross section.

Figures 6a - 6d respectively show perspective views, profile views, and respective section views of the device (10) at different heights of an example of embodiment of a thermoelectric device (10) similar to that of Figures 5a - 5d, but in where, in this case, the device (10) comprises four sheets (16, 160, 16', 160') of thermoelectric material. As in the examples of Figures 4a and 4b, there is a single thermal and electrical insulating substrate (15). Said substrate (15) has a rectangular prism geometry, and the four sheets (16, 160, 16', 160') have a rectangular geometry, each one being arranged on one face of the substrate (15). However, on this occasion, as can be seen, each sheet (16, 160, 16', 160') only partially covers the face of the substrate (15) on which it is arranged. In addition, the pairs of sheets (16, 160, 16', 160') of materials of opposite types are arranged on adjacent faces to facilitate their connection. In particular, as can be seen, the first sheet (16) arranged on the front face of the substrate (15) is made of an n-type material, while its p-type pair is the second sheet (160) arranged on the right lateral face as seen in figure 6a. The third sheet (16'), composed of a p-type material, is connected to its n-type pair, that is, the fourth sheet (160'). In the cross sections shown as figures 6c and 6d, the arrangement of the four sheets (16, 16', 160, 160') can be seen. The four sheets (16, 16', 160, 160') are arranged on the substrate (15) without direct physical contact between the different sheets.

The figures show two electrical contacts (17, 18) arranged on the first sheet (16), two electrical contacts (170, 180) arranged on the second sheet (160), two electrical contacts (17', 18') arranged on the third sheet (16') and two electrical contacts (170', 180') arranged on the fourth sheet (160'), each electrical contact being close to one end of the corresponding sheet. Figure 6c provides a plan view in which, for illustrative purposes, both the upper support (11) and the upper electrically insulating layer (13) have been omitted from showing. Thus, it allows the visualization of the connections established between the different sheets, two by two, in particular between the first (16) and the second (160) sheet and between the third (16') and the fourth (160') sheet. , respectively. In particular, it is observed that electrical connections (19) are connected to the corresponding electrical contacts closest to the upper part of the device. In the same way, Figure 6d provides a plan view in which the body of the device has been truncated in a plane perpendicular to the sheets by a section at an intermediate height between the electrically insulating layers (13, 14). Thus, a view is provided of the connections established between the different sheets, two by two, in particular between the first (16) and the fourth (160') sheet and between the second (160) and the third (16') sheet. , respectively. In particular, it is observed that electrical connections (19') are connected to the corresponding electrical contacts closest to the bottom of the device.

In these figures, electrical connections (19, 19') can be seen for the electrical connection of the corresponding sheets and/or for the connection with elements external to the device itself. In the perspective view of Figure 6a and Figures 6c and 6d, it is observed that the electrical connections (19') close to the support (12) and the electrically insulating layer (14) project a certain length from the geometric limit. of said support (12). This representation serves the illustrative purpose of indicating that through said electrical connections (19') they can be electrically connected to adjacent thermoelectric devices (10) or other devices. Although the figures have represented the electrical contacts and the electrical connections as different elements, the electrical contacts (18) and (180) themselves may have projections for the connection between the sheets of the device and/or for the connection with other devices.

In the device of Figures 6a-6d the cross-sectional area of thermoelectric material is equal to or less than one tenth of the cross-sectional area of substrate. Figure 6e schematically represents a cross section of the set of sheets and substrate of the device of Figures 6a-6d, where the cross-sectional area (A1, A2, A3, A4) of the sheets (16, 160, 16) has been identified. ', 160') and the cross-sectional area (Asub) of the substrate (15). In Figure 6e, the cross-sectional area (Asub) of the substrate has been represented with a checkered pattern and the cross-sectional area (A) of the sheets has been represented without a checkered pattern. In this embodiment, the cross-sectional area of thermoelectric material is the area (A) provided by the four sheets (16, 160, 16', 160') of thermoelectric material (A=A1+A2+A3+A4) and the area of substrate is the area (Asub) contributed by the only substrate (15) in said cross section.

Although in exemplified embodiments of thermoelectric devices with prismatic substrates the prismatic substrates have two bases and four side faces, the substrates may have a different number of side faces, for example six or eight side faces.

Two embodiments of the thermoelectric generator (20) of the invention are shown in Figures 7 and 8, which comprise a plurality of thermoelectric devices (10) connected in series. In the embodiments of Figures 7 and 8 each thermoelectric device (10) is of the type shown in Figure 2, with the difference that, while the thermoelectric device (10) of Figure 2 included an upper support (11) and a lower support (12), the thermoelectric devices (10) of the embodiments of Figures 7 and 8 do not each include individual supports, but rather all the thermoelectric devices (10) are coupled to two single global supports (110, 120 ). These global supports (110, 120) act as structural support for the plurality of thermoelectric devices (10) and as an interface to establish contact with two thermal focuses.

In the thermoelectric generator (20) of Figure 7, the thermoelectric devices (10) are distributed in a linear configuration, forming a row connected in series. In this figure each thermoelectric device (10) is represented schematically framed in a dashed line.

In an alternative embodiment to that shown in Figure 7 in which the thermoelectric devices (10) are distributed in a linear configuration forming a row, said thermoelectric devices (10) are connected in parallel.

In the thermoelectric generator (20) of Figure 8, the thermoelectric devices (10) are distributed according to an annular configuration. In this figure one of the thermoelectric devices (10) is represented schematically framed in a dashed line.

As described in relation to Figure 2, the thermoelectric devices (10) of the embodiments of Figures 7 and 8 comprise a first sheet (16) of thermoelectric material arranged on a first portion of substrate and a second sheet (160) of thermoelectric material arranged on a second substrate portion, the first sheet (16) and the second sheet (160) being of opposite types, and wherein the first substrate portion is implemented as a first substrate and the second substrate portion is implemented as a second substrate independent of the first substrate. In the embodiment of Figure 7, the first sheet (16) is of type n and the second sheet (160) is of type p.

In the embodiments of Figures 7 and 8, the substrates have a rectangular prism geometry and the first (16) and the second (160) sheet have a rectangular geometry and are arranged on one of the faces of the substrate.

The two independent substrates of each thermoelectric device (10) are arranged between the global supports (110, 120), with each end of the substrates in thermal communication with one of the global supports through an electrically insulating layer (13, 14). . The first (16) and the second (160) sheet of each thermoelectric device (10) are also arranged between the overall supports (110, 120), with each end of the sheets (16, 160) in thermal communication with one of the global supports (110, 120) through an electrically insulating layer (13, 14).

In the embodiment of Figure 7, with a linear configuration, the global supports (110, 120) are substantially straight and at least one of them has a substantially flat surface. This configuration is advantageous for flat surfaces, since it allows the thermoelectric generator (20) to be supported on the flat surface of the global support (110, 120).

In the embodiment of Figure 8, with an annular configuration, the global supports (110, 120) are substantially circular. This configuration is advantageous for arranging the overall interior support (120) around a pipe containing a hot gas or liquid.

In the embodiments of Figures 7 and 8, each thermoelectric device (10) comprises four electrical contacts (17, 18, 170, 180), in particular two contacts (17, 18) arranged close to each end of the first sheet (16). ) and two contacts (170, 180) arranged close to each end of the second sheet (160). In each thermoelectric device (10) a first electrical contact (17) of the first sheet (16) is connected to a first electrical contact (170) of the second sheet (160). In these embodiments the thermoelectric devices (10) are connected to each other in series, with the second electrical contact (180) of the second sheet (180) connected to a second electrical contact (18) of the first sheet (16) of the thermoelectric device (10) adjacent. Figures 7 show the electrical connections (19) between electrical contacts of the same thermoelectric device (10) and the electrical connections (19') between electrical contacts of different thermoelectric devices (10). Furthermore, in Figure 8 two protruding contacts are shown schematically to exemplify that they are the connection to the outside of the generator.

The configuration of thermoelectric devices (10) in series allows great versatility and, therefore, various geometries of the thermoelectric generator (20), adaptable to the type of heat source intended to be used as a hot focus in an operational situation of the thermoelectric generator. (twenty).

Figure 9 shows a thermoelectric generator (20') with a parallel connection between several rows of thermoelectric devices (10) electrically connected to each other in series. In the embodiment of Figure 9, each row of thermoelectric devices (10) shown can be understood as a thermoelectric generator (20) of the type shown in Figure 7. The different rows are electrically connected to each other in parallel by electrical connections (21). between electrical connectors of the thermoelectric devices (10) located at the ends of the rows. In this figure, the two ends of the input and output connections to the central row of thermoelectric devices have been represented as black circles to illustrate that these are the electrical connections with the outside of the generator.

Although the embodiments of Figures 7 to 9 comprise thermoelectric devices (10) of the type shown in Figure 2, the thermoelectric generator may include thermoelectric devices according to any of the embodiments of the invention. For example, Figure 10 shows a thermoelectric generator (20) comprising a plurality of thermoelectric devices (10) such as those shown in Figures 5a and 5b. As described in relation to Figures 5a and 5b, in this embodiment each thermoelectric device (10) comprises a single substrate (15) of rectangular prism configuration and first (16) and second (160) thermoelectric sheets (one of type n and another of type p) arranged on different faces of the substrate (15). Figure 10 shows the plurality of thermoelectric devices (10) distributed in rows and columns and electrically connected to each other through series and parallel connections. In particular, in the embodiment shown in each thermoelectric device (10) the first (16) and the second (160) thermoelectric sheet are electrically connected to each other by means of the electrical connectors arranged at the first end of the sheets (16, 160), and are each electrically connected to a sheet of the opposite type of an adjacent thermoelectric device (10) by means of electrical connectors arranged at the second end of the sheets (16, 160). In this way, the thermoelectric devices (10) in a row are connected in series with each other. The electrical connection between different rows is carried out in parallel, connecting together the free electrical connectors of the thermoelectric devices (10) arranged at the ends of the rows. Although a serial connection within rows and a parallel connection between rows have been described, the connection could equally be made between columns.

Figure 11 shows a thermoelectric generator (20) that comprises a plurality of thermoelectric devices (10) like those shown in Figures 6a and 6b. As described in relation to Figures 6a and 6b, in this embodiment each thermoelectric device (10) comprises a single substrate (15) of rectangular prism configuration and first (16), second (160), third (16') and fourth (160') thermoelectric sheets (two n-type and two p-type) each arranged on a different face of the substrate (15). Figure 11 shows the plurality of thermoelectric devices (10) distributed in rows and columns and electrically connected to each other. In particular, in each thermoelectric device (10) there is a parallel connection that allows the loss of current intensity produced by the use of sheets to be recovered, at least partially or even exceeded.

For illustrative purposes, in both figures 10 and 11 we have omitted to represent an upper support arranged covering all the devices, more specifically in contact with all the electrically insulating layers arranged on the upper part of each device. Thus, said support has been omitted to provide a view of the details relating to the schematic arrangement of the thermoelectric devices giving rise to a thermoelectric generator configuration.

However, it will be understood that in a final assembly configuration there will be said upper support that covers the entire upper part of the thermoelectric generator being in contact with each upper electrically insulating layer of each device, said support acting as a heat source.

In the figures of the present application the elements are not represented to scale.

The use of a bilayer system (the system formed by the substrate and the thermoelectric sheet) with different thermal conductivities and cross-sectional areas causes more voltage to be generated for each thermoelectric pair (pair of n-type and p-type sheets connected in series). and less current intensity compared to a commercial volume generator, depending on the cross-sectional area of the sheet. Regardless of this reduction in intensity, it is possible to ensure power gain by optimizing the ratio between cross-sectional areas of sheet and substrate. In order to compensate for the lower current intensity compared to the higher generated voltage, thermoelectric devices can be connected in different series and parallel configurations. In this way, depending on the number of thermoelectric pairs connected in series (responsible for the total voltage) and the number of series elements connected in parallel (responsible for the total electric current intensity), the output signal can be controlled and optimized in depending on what is required. The set of series and parallel connections between thermoelectric devices constitutes the thermoelectric generator.

On the other hand, if the thermoelectric device itself contains four or more sheets, said series and parallel connections can be made within the thermoelectric device itself, thus resolving the lowest generation of current intensity and acting on each individual thermoelectric device of the invention. as a complete n-p pair in commercial thermoelectric generators, also showing a greater total power generation than these.

As an example, if the ratio between thermal conductivities and thicknesses between the substrate and the sheets is 10, a thermoelectric device such as the one in the embodiment of Figures 5a-b will generate approximately 10 times more voltage and the same current intensity. compared to a thermoelectric generator that uses the same material with dimensions equivalent to the substrate - that is, a volume 10 times greater than that used in the sheet. In this same example, this would cause a power gain of a factor of 10.

The cross-sectional area and thickness of the sheets will be determined by the application and dimensions required and by the ratio between thermal conductivities of the thermoelectric material and the substrate. In one embodiment the thickness of the sheet (whether ultra-thin, thin or thick) is in the range of 1 nanometer to several millimeters. Thicknesses of millimeters are suitable for macroscopic applications, while thicknesses of less than 100 nanometers are suitable in miniaturized applications in which 2D materials with good thermoelectric performance are used as thermoelectric materials.

The manufacturing processes of thermoelectric devices and therefore of the complete thermoelectric generator depend on the applications (in terms of temperature of the hot and cold sources and the total heat flow), size, geometry and other requirements.

- Thin and thick sheets: Techniques such as cathodic erosion (DC sputtering, magnetron) or chemical vapor deposition (CVD) can be used for sheets from 50 nm to tens or hundreds of microns thick, and layer deposition atomic layers (atomic layer deposition, ALD) for thin films with a thickness of less than 50 nm. These techniques allow the use of masks to mark the deposit area, so that both the deposit of the adhesive sheet and the electrical contacts can be done in consecutive processes.

- Thick sheets: In this case, sheets of a few microns of metal alloys can be used that can be glued to the substrate with a suitable glue to adequately withstand thermal fatigue. This manufacturing method is especially interesting for applications in which metal alloys are used as thermoelectric material.

In a thermoelectric device or in a thermoelectric generator according to the invention, substrates and/or thermoelectric sheets made of different materials can be combined.

In one embodiment the substrate comprises quartz, glass or ceramics.

In one embodiment the first, second, third and/or fourth sheet comprises at least one of the following materials: a semiconductor (such as pyrite (FeS2)), a trichalcogenide (such as TiS3 or ZrS3), a semimetal, an alloy metal with a high Seebeck coefficient (such as Ni-Cr or Ni-Cu), 2D material (such as black phosphorus) or SnSe. SnSe is a thermoelectric material with excellent performance.

As an example, two tables are presented with optimized cross-sectional area ratios for various combinations of metals, semi-metals and alloys such as thermoelectric materials and different substrates according to the particular case of a flat sheet arranged on a single face of a substrate with prism geometry. (Table 1), and according to the particular case of a curved sheet arranged on a substrate with cylindrical geometry (Table 2). In each table the first four thermoelectric materials are metals and the remaining four materials are semimetals and alloys.

In the case of the substrate with prism geometry and sheet with flat geometry (Table 1), if the width of the sheet is equal to the width of the substrate on which it is arranged, the relationship between cross-sectional areas of sheet and substrate depends exclusively of the relationship between sheet and substrate thicknesses. In the cases of Table 1, the cross-sectional area (or thickness) ratio has been determined based on the thermal conductivities as:

beingAsubel cross-sectional area of substrate,Athe cross-sectional area of the sheet,Kla

thermal conductivity of the sheet,Ksubla thermal conductivity of the substrate,ael

thickness of the substrate and thickness of the sheet.

In the case of the substrate with cylindrical geometry and sheet with curved geometry (Table 2), the sheet is arranged on the substrate along an arc of substantially 360°. In the cases of Table 2, the cross-sectional area ratio has been determined based on the thermal conductivities as:

beingAsubel cross-sectional area of substrate,Athe cross-sectional area of the sheet,Kla

thermal conductivity of the sheet,Ksubla thermal conductivity of the substrate,Rsubel

radius of, and RTThe total radius of the cylindrical assembly formed by the substrate and the sheet.

The quantitative changes in the ratios of the cross-sectional areas between both geometries are derived from the equations indicated for said geometries and provide a guide for the choice of materials and geometries according to the requirements of the specific application.

Tables 1 and 2 represent the thermal conductivity (K), electrical conductivity (a) and Seebeck coefficient (S) of the thermoelectric material, the thermal conductivity (KSUb) of the substrate and the optimized cross-sectional area ratio for the different combinations. of thermoelectric material and substrate material.

It can be seen that the use of metals allows a greater reduction in the cross-sectional area of the sheet, especially interesting for miniaturization of devices and use of the aforementioned sheet deposition techniques. On the other hand, semimetals and alloys such as Ni-Cr and Ni-Cu allow larger cross-sectional areas of the sheet compared to the cross-sectional area of the substrate and, therefore, manufacturing methods by gluing said sheet on the substrate. Other semimetals such as CoS2 or CoFe alloys also offer good power factor values.

The thickness ratios shown in Table 1 may vary depending on the type of thermoelectric device. The values in table 1 have been estimated with the basic unit configuration of figure 2, although for the basic units of figures 5 and 6 it would be enough to divide by 2 and by 4, respectively, the thicknesses of the sheets in a first approximation.

Table 1

Table 2

The thermoelectric device and thermoelectric generator of the present invention can be implemented in a wide variety of applications, with highly variable dimensions. In all these applications, the thermoelectric generator is a passive system for recovery and use of thermal losses. Thus, the thermoelectric generator can be implemented, for example, in the following applications:

- Macro Applications: ovens, engines, industrial pipes, exhaust pipes or chimneys. In these applications, the use of semimetals and alloys such as Ni-Cu and Ni-Cr, cheap semiconductors and/or conventional thermoelectric materials in sheet format is advantageous. Likewise, the thermoelectric generator is also suitable for use in less common applications, such as superficial and thin applications (use of passive surfaces, such as walls).

- Micro Applications: electronic devices. In addition to the previous materials, the use of metals can be a good option as the ratio of cross-sectional areas between substrate and sheet of thermoelectric material is greater. Likewise, a possible application is the use of the thermoelectric generator in wearable technology, in which thermoelectric devices take advantage of the temperature difference between the skin and the environment to power low-power electronic devices.

- Nano applications: electronic devices. In these applications, the use of 2D materials such as thermoelectric materials is advantageous for the implementation of the thermoelectric generator in nanometric devices. An example would be the application for the use of waste heat in microprocessors.

Claims (1)

CLAIMS 1.- Thermoelectric device (10) that comprises: - a first sheet (16) arranged on a first portion of substrate; - a second sheet (160) arranged on a second portion of substrate; - two electrically insulating layers (13, 14), each layer (13, 14) being configured to exchange heat with a thermal focus, respectively; and - four electrical contacts (17, 18, 170, 180); wherein the first portion of the substrate is thermal and electrical insulating and comprises a first (15.1) and a second (15.2) end, where the first end is in contact with an electrically insulating layer (13) and the second end is in contact with the other electrically insulating layer (14); wherein the second portion of substrate is thermal and electrical insulating and comprises a first and a second end, wherein the first end is in contact with an electrically insulating layer (13) and the second end is in contact with the other layer (14). ) electrically insulating; wherein the first sheet (16) is a sheet of thermoelectric material, type n or type p, and comprises a first (16.1) and a second (16.2) end, where the first end (16.1) is in contact with a electrically insulating layer (13), and where the second end (16.2) is in contact with the other electrically insulating layer (14); wherein the second sheet (160) is a sheet of thermoelectric material, of the opposite type to that of the first sheet (16), and comprises a first (160.1) and a second (160.2) end, wherein the first end (160.1) is in contact with an electrically insulating layer (13), and the second end (160.2) is in contact with the other electrically insulating layer (14); wherein two electrical contacts (17, 18) are arranged on the first sheet (16), each electrical contact (17, 18) being arranged close to one end (16.1, 16.2) of said first sheet (16), respectively; wherein the other two electrical contacts (170, 180) are arranged on the second sheet (160), each electrical contact (170, 180) being arranged close to one end (160.1, 160.2) of said second sheet (160), respectively ; wherein the cross-sectional area of thermoelectric material is equal to or less than one tenth of the cross-sectional area of substrate; wherein the first substrate portion is implemented as a first substrate (15) and the second substrate portion is implemented as a second substrate (150) independent of the first substrate (15); wherein the first (15) and/or the second substrate (150) has a prism geometry; and wherein the first sheet (16) and/or the second sheet (160), respectively, is arranged on one face of said substrate (15, 150) with prism geometry; where the thicknesses of said substrate (15, 150) with prism geometry and of the sheet (16, 160) arranged on one face of said substrate (15, 150) meet the following relationship: where K is the thermal conductivity of said sheet (16, 160), Ksub is the conductivity thermal of said substrate (15, 150), the thickness of said substrate (15, 150) and the thickness of said sheet (16, 160). 2. - The device (10) according to claim 1, wherein said substrate (15, 150) with prism geometry has straight prism geometry; and where the sheet (16, 160) arranged on one face of said substrate (15, 150) has a rectangular geometry. 3. - The device (10) according to any of claims 1 to 2, wherein the contour of at least one sheet (16, 160) coincides with the contour of the face of the substrate (15) on which it is arranged. 4. - The device (10) according to any of claims 1 to 3, wherein the substrate has a number of faces greater than or equal to 6. 5. - Thermoelectric device (10) comprising: - a first sheet (16) arranged on a first portion of substrate; - a second sheet (160) arranged on a second portion of substrate; - two electrically insulating layers (13, 14), each layer (13, 14) being configured to exchange heat with a thermal focus, respectively; and - four electrical contacts (17, 18, 170, 180); wherein the first portion of the substrate is thermal and electrical insulating and comprises a first (15.1) and a second (15.2) end, where the first end is in contact with an electrically insulating layer (13) and the second end is in contact with the other electrically insulating layer (14); wherein the second portion of substrate is thermal and electrical insulating and comprises a first and a second end, wherein the first end is in contact with an electrically insulating layer (13) and the second end is in contact with the other layer (14). ) electrically insulating; wherein the first sheet (16) is a sheet of thermoelectric material, type n or type p, and comprises a first (16.1) and a second (16.2) end, where the first end (16.1) is in contact with a electrically insulating layer (13), and where the second end (16.2) is in contact with the other electrically insulating layer (14); wherein the second sheet (160) is a sheet of thermoelectric material, of the opposite type to that of the first sheet (16), and comprises a first (160.1) and a second (160.2) end, wherein the first end (160.1) is in contact with an electrically insulating layer (13), and the second end (160.2) is in contact with the other electrically insulating layer (14); wherein two electrical contacts (17, 18) are arranged on the first sheet (16), each electrical contact (17, 18) being arranged close to one end (16.1, 16.2) of said first sheet (16), respectively; wherein the other two electrical contacts (170, 180) are arranged on the second sheet (160), each electrical contact (170, 180) being arranged close to one end (160.1, 160.2) of said second sheet (160), respectively ; wherein the cross-sectional area of thermoelectric material is equal to or less than one tenth of the cross-sectional area of substrate; wherein the first substrate portion is implemented as a first substrate (15) and the second substrate portion is implemented as a second substrate (150) independent of the first substrate (15); wherein the first (15) and/or the second substrate (150) has cylindrical geometry; wherein the first sheet (16) and/or the second sheet (160), respectively, has curved geometry; and wherein said first (16) and/or second sheet (160) with curved geometry is arranged on said first (15) and/or second substrate (150) of cylindrical geometry along a certain arc of its outer surface; where the sheet (16, 160) is arranged on the substrate (15, 150) of cylindrical geometry along a 360° arc, and the following relationship is fulfilled: where K is the thermal conductivity of said sheet (16, 160), K is the conductivity thermal of said substrate (15, 150), Rsubel radius of said substrate (15, 150), and RTthe total radius of the cylindrical assembly formed by said substrate (15, 150) and said sheet (16, 160). 6. - The device (10) according to any of the preceding claims, wherein the first substrate portion and the second substrate portion are made of different materials. 7. - The device (10) according to any of the preceding claims, wherein the first substrate portion and/or the second substrate portion comprises glass, quartz or ceramic. 8. - The device (10) according to any of the preceding claims, wherein the first substrate portion and/or the second substrate portion is configured as a hollow solid casing filled with a gas. 9. - The device (10) according to any of the preceding claims, wherein at least one sheet (16, 160, 16', 160') of thermoelectric material comprises at least one of the following materials: pyrite (FeS2), a trichalcogenide, a metal, a semimetal, a metal alloy, black phosphorus, or SnSe. 10. - The device (10) according to any of the preceding claims, which comprises at least one support (11, 12) in contact with one of the electrically insulating layers (13, 14). 11. - The device (10) according to claim 10 wherein at least one support (11, 12) comprises a flat surface. 12. - Thermoelectric generator (20) comprising a plurality of thermoelectric devices (10) according to any of the preceding claims. 13.- The thermoelectric generator (20) according to claim 12, wherein at least a subset of the plurality of thermoelectric devices (10) is distributed forming a row of devices (10) connected in series. 14.- The thermoelectric generator (20) according to claim 13, comprising several rows of thermoelectric devices (10) electrically connected in series, wherein said rows are electrically connected to each other in parallel. 15. - The thermoelectric generator (20) according to claim 14, wherein said rows are parallel. 16. - The thermoelectric generator (20) according to any of claims 12 to 15, wherein at least a subset of the plurality of thermoelectric devices (10) are distributed according to an annular geometry.