THERMOELECTRIC COATING AND THE METHOD OF ITS APPLICATION, ESPECIALLY ON THE ELEMENTS OF THE HEAT EXCHANGER

Abstract

A thermoelectric coating containing “p” and “n” semiconductor elements in the form of non-contacting layers, which are arranged alternately with each other, so that between the “p” layers there is a “n” layer, with the “p” and “n” layers “n” are connected to each other in series with conductive elements with connection terminals for the output of the generated electrical energy, and containing an electrical insulator layer, is characterized in that a layer (2a) of an electrical insulator with a thickness of at least 200 nm is applied to the substrate (1), with layers of conductive elements (3a) with a thickness of 200 nm to 5 .Math.m, on which semiconductor layers “p” and “n” with a thickness of 50 nm to 5 .Math.m and a width of 0.1 mm to 5 mm are applied.

Claims

1. A thermoelectric coating comprising “p” and “n” semiconductor elements in the form of non-contacting layers, which are arranged alternately with each other, so that between “p” layers there is an “n” layer, with the “p” layers and “n” are connected to each other in series with low-resistivity conductive elements provided with connection terminals for outputting generated electrical energy, and containing an electrical insulator layer, wherein a layer (2a) of an electrical insulator with a thickness of at least 200 nm is applied to a substrate (1), on which there are layers of the low-resistivity conductive elements (3a) with a thickness of 200 nm to 5 .Math.m, on which are applied semiconductor layers “p” and “n” in the form of rings with a thickness of 50 nm to 5 .Math.m and a width of 0.1 mm to 5 mm, on which layers are applied of the conductive elements (3b) with a thickness of 200 nm to 5 .Math.m, the total thickness of the coating not exceeding 20 .Math.m, and the electrical insulator layer (2a) comprises Al.sub.2O.sub.3 or SiO.sub.2 or MgO, wherein the layers of the conductive elements (3b) is wider than the previously applied layers of comductive elements (3a) to provide a good connection point for transmitting the generated electricity, wherein the thermoelctric coating generates electricity directly from a temperature difference without converting thermal energy into kinetic energy, and wherein insulation material of the electrical insulator is homogeneous and continuous in its structure.

2. The thermoelectric coating according to claim 1, wherein the layer (2b) of the electrical insulator with a thickness of at least 200 nm, containing Al.sub.2O.sub.3 or SiO.sub.2 or MgO, is provided on the layers of the conductive elements (3b).

3. The thermoelectric coating according to claim 1, wherein a chromium or nickel intermediate layer (4a, 4b) is provided in the form of rings between the “p” and “n” semiconductor layers and the layer of conductive elements (3a, 3b), the semiconductor layer being made of bismuth telluride, and the layer of the conductive elements (3a, 3b) provided in the form of rings is made of copper.

4. The thermoelectric coating according to claim 3, wherein the intermediate layer (4a, 4b) has a thickness of 50 nm to 200 nm.

5. The thermoelectric coating according to claim 1, wherein the coating is applied to a wall of the combustion chamber of cylindrical shape or on a conical heat exchanger and/ or on a cylinder-shaped or conical-shaped housing of a burner, so that coating layers are annular in shape.

6. A method of applying layers of a thermoelectric coating, especially “p” and “n” semiconductor layers and layers of conductive elements, using PVD technology, on a surface of cylindrical or conical shape, wherein the element on the cylindrical or conical surface of which layers are the thermoelectric coating, in particular the “p” and “n” semiconductor layers and layers of conductive elements, are rotated at a predetermined speed, and said layers are applied through a system of slotted screens located as close as possible to the rotating element.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0015] The invention is illustrated in the drawing in which:

[0016] FIG. 1 shows the thermoelectric coating in cross-section,

[0017] FIG. 2 shows the exposed “p” and “n” semiconductor layers of a thermocouple in the form of rings applied to the cylindrical wall of the heat exchanger combustion chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An exemplary thermoelectric coating includes “p” and “n” semiconductor elements in the form of non-contacting layers, which are alternately arranged in such a way that there is an “n” layer between the “p” layers, with the “p” layers “And” “n” are connected in series with the conducting elements 3a, 3b. The conductive elements 3a, 3b are provided with connection terminals for the discharge of the generated electricity.

[0019] Moreover, the conductive elements are insulated with an electric insulator layer 2a, 2b. Additionally, an intermediate layer may be applied between the “p” and “n” semiconductor layers and the layer of conductive elements 3a, 3b, 4a, 4b, for example from chromium or nickel.

[0020] The parameters of semiconductor materials are selected optimally for the intended operating temperature of the coating, which in turn allows to maximize the efficiency of the thermoelectric coating. When used, for example, in a heat exchanger, the temperature range is 100 to 150° C. The individual layers of the thermoelectric coating are produced by PVD technology, for example by evaporation, laser ablation, magnetron sputtering, filtered electric arc sputtering or electron beam excitation. The “p” and “n” semiconductor layers are obtained from the following groups of materials: bismuth tellurides, tellurium compounds, germanium compounds, silicon compounds, scutterides, inorganic clathrate compounds, chalcogenides and half-Heusler compounds. The production process of the thermoelectric coating must be carried out in a well-maintained vacuum system equipped with the necessary equipment for sputtering thin films. For good performance, it is recommended to use materials with a purity of at least 99.99% for each component applied.

[0021] The element on which the thermoelectric coating is to be applied must be properly cleaned and placed in a vacuum workstation. Further surface cleaning can be achieved by initiating a glow discharge and ion bombardment with high energy working gas atoms. On the cleaned substrate, for example the cylindrical wall of the combustion chamber of a heat exchanger, an electrical insulator layer 2a with a thickness of at least 200 nm is applied. This will allow the thermoelectric layer to be electrically independent of the substrate material. Layer

[0022] The insulation material must be homogeneous and continuous in its structure. This will ensure a high level of resistance to electrical breakdown. On the electrical insulator layer 2a, layers of low-resistivity conductive elements 3a are applied to allow the free flow of current in the form of rings with a thickness of 200 nm to 5 .Math.m, which will form the basis for the next semiconductor layers “p” and “n”.

[0023] On the layers of conductive elements 3a, additional intermediate layers 4a, with a thickness of 50 nm to 200 nm, can be applied in the form of rings, the purpose of which is to lower the electrical resistance between the two layers where the intermediate layer is situated, by creating good electrical contact and preventing undesirable physical and chemical reactions.

[0024] Correctly located semiconductor layers made of “p” and “n” pairs, in the form of rings, with a thickness of 50 nm to 5 .Math.m and a width of 0.1 mm to 5 mm, are applied to the intermediate layers 4a. There are many thermoelectric materials for this application which can be selected depending on the operating temperature and the desired thermoelectric performance (ZT).

[0025] Then, on the already formed semiconductor layers of the p and n pairs, additional intermediate layers 4b, with a thickness of 50 nm to 200 nm, can be applied in the form of rings, on which layers of conductive elements 3b, also in the form of rings, with a thickness of 200 nm, are applied. up to 5 .Math.m, which should be wider than the previously applied layers of conductive elements 3a to provide a good connection point for transmitting the generated electricity.

[0026] On the layers of conductive elements 3b, if there is a need to isolate them from the environment, an electrical insulator layer 2b with a thickness of at least 200 nm is applied. Total coating thickness does not exceed 20 .Math.m. The layers 2a, 2b of the electrical insulator are based on Al.sub.2O.sub.3 or SiO.sub.2 or MgO.

[0027] With some groups of materials, there is a risk of a chemical reaction between the layers, which in turn can lead to problems such as increased electrical resistivity, impaired carrier transportation, and a reduction in the overall efficiency of the thermoelectric coating. This problem has been solved by the use of the above-mentioned intermediate layers 4a, 4b. For the bismuth telluride semiconductor layer and the copper conductive layer, it has been found that the interlayer should be chromium or nickel. The thickness of each intermediate layer must be between 50 nm and 200 nm.

[0028] Semiconductor layers “p” and “n” and layers of conductive elements 3a, 3b, on the heat exchanger elements like the cylindrical wall of the combustion chamber and the cylindrical housing of the burner, are applied using a specially designed system of slotted screens. This modification allows for the deposition of conducting and semiconductor layers in the form of rings on a cylindrical surface. The slotted screen must be placed as close as possible to the surface of the cylindrical wall, but allow free, contactless rotation. The screens must be constructed in such a way as to allow the sprayed material to pass through in an orderly manner while filtering the excessively diffused material that would lead to the application of rings with very blurred edges.

[0029] When designing and making sieves for a given substrate, the geometry and curvature of the slots as well as its total thickness should be taken into account, affecting the efficiency of filtering the beam. An element on whose cylindrical or conical surface layers of a thermoelectric coating are applied, is set in rotation with a set by speed, and said layers are applied through a system of slotted screens located as close as possible to the rotating element. The thus produced thermoelectric coating meets the expected parameters. According to Seebeck’s theory, the temperature difference on both sides of the shell causes an orderly movement of charges in the semiconductor layers contained in the thermoelectric shell. The potential difference occurs between the outer terminals due to the series connection between the elements of the semiconductor layer.