FR3097304A1 - HYBRID RADIATION ABSORBER FOR SOLAR POWER PLANTS, AND PROCESS FOR PREPARING SUCH AN ABSORBER - Google Patents

Abstract

The present invention relates to a solar radiation absorber, for a concentrated solar thermal power plant, characterized in that it is formed from a monolithic piece of silicon carbide, the absorption surface of which is for example coated with tungsten dendrites, in particular for the production of a collector or a system for a solar power plant, as well as a process for preparing such an absorber

Description

HYBRID RADIATION ABSORBER FOR SOLAR POWER PLANTS, AND METHOD FOR PREPARING SUCH AN ABSORBER

Field of invention

The present invention relates to the field of energy absorbers, the characteristics of which approximate the behavior of a black body.

The black body is an ideal object that would perfectly absorb all the electromagnetic energy it receives, without reflecting or transmitting it. Under the effect of thermal agitation, the black body emits electromagnetic radiation. At thermal equilibrium, emission and absorption balance each other and the radiation actually emitted depends only on the temperature (thermal radiation).

Non-limiting typical applications: Gaseous fluid: Stirling/Ericsson type external combustion engine, hot air turbine (turbo alternators), industrial processes, cooking, etc. the liquid fluid can be water that one wishes to heat, a liquid to be sterilized, steam production to supply a standard turbo-alternator, DHW (domestic hot water/heating), various fluids, etc.

The invention relates more particularly to the field of absorbers intended for the production of energy from solar radiation by thermo-solar power plants supplemented by an ideally hho or renewable flame.

The thermo-solar processes have better yields than the photovoltaic processes, of the order of 30%, on the other hand they are more cumbersome and adapted for a significant production of electricity.

New devices coupling a Stirling engine with a concentrator are currently being developed to produce electric current. However, the thermodynamic efficiency is correlatively linked to the inlet temperature, which then needs to be high enough for the best efficiency. Existing devices are limited to 650/800°C and therefore cannot exceed 40% efficiency. The invention makes it possible to reach 1200°C and therefore to reach and exceed 60% net efficiency.

On the other hand, the absorber according to the invention allows the hybridization of different heat sources, for example solar and "solar fuel" = hho (or biogas, petroleum derivatives, etc.), thus allowing continuous and full operation. power of an installation despite variations or absences of the solar flux.

State of the art

There are different techniques for concentrating solar radiation, for transporting and possibly storing heat and for converting heat into electricity. In any case, one of the essential elements of a concentrated solar thermal power plant is the solar radiation absorber element which forms part of the receiver. In order to maximize the performance of the absorber, the latter generally comprises a coating, called selective coating or selective treatment. The selective coating is intended to allow maximum absorption of incident solar energy while re-emitting as little infrared radiation as possible (black body principle). In particular, such a selective coating is considered perfect if it absorbs all the wavelengths below a cut-off wavelength and reflects all the wavelengths above this same cut-off wavelength. The optimum cut-off wavelength depends on the operating temperature of the absorber element considered and it is generally between 1.5 μm and 2.5 μm. It is, for example, approximately 1.8 μm for a temperature of the order of 650 K.

There are different types of selective coatings, each generally comprising an anti-reflective layer intended to limit the reflection of incident solar rays. In particular, a type of selective coating consists in depositing, on the surface of the absorber, a material intrinsically possessing the desired properties. This type of material is rather rare and the most efficient of them is ZrB ₂ , in particular when it is associated with an antireflection layer of SÏ3N ₄ , of S1O2 or of Al2O3.

Another way consists in structuring the surface of the absorber, to create favorable conditions for absorption (principle of multiple reflection or refractive index gradient, depending on the scale of the surface structuring), while by limiting infrared emissions. The main obstacle to this type of selective treatment is of a technological nature: there is currently no means of large-scale industrial production of a suitable submicron structuring.

The selective coating can also consist of an interference filter, formed by a stack of several thin layers of carefully controlled thicknesses, typically of the order of a few nanometers. This type of selective processing makes it possible to obtain excellent performance, but its realization is relatively difficult to implement.

By way of example, patent application WO-A-2009/051595 proposes a selective solar coating of this family of coatings to cover the outer surface of a solar radiation absorber tube, typically made of stainless steel. The selective coating comprises a stack of several layers each having a function and a thickness determined by optical simulation. In a particular embodiment, the solar radiation absorber tube is successively covered by a succession of bilayers consisting of a layer of material that reflects IR radiation and by a layer of material that absorbs solar radiation, followed by the application of a anti-reflective layer. The solar radiation absorber tube is, for example, made of stainless steel of austenitic structure, for example of the AISI 316, 321, 347 or 304L type.

Patent US4316048 is also known describing a radiation energy conversion system, comprising a heat-insulated energy storage container, an energy storage material located inside the container, input means of energy and energy output means, characterized in that the energy storage material has a thermal conductivity greater than 41.81 watts per meter Kelvin (0.1 calorie/cm ² /cm/ ^O C/s), a latent heat of fusion greater than 4.184 kilojoules (1 kilocalorie) per mole, and a melting point not less than 960°C, and the energy output means includes a length band converter of thermal energy into a selected narrow band of radiant energy wavelengths, which is optically coupled to a photovoltaic converter efficiently responding to the selected band of energy wavelengths. This document mentions the fact that the emitter is dendritic tungsten.

This document does not concern solar thermal conversion, but photovoltaic, which is not the subject of the invention.

We know in particular in the state of the art the European patent EP 2462345 B1 a system for the production and storage of electrical and thermal energy from a cyclo turbine describing a process for the production and storage of electrical energy and heat of solar origin, characterized in that it comprises:

a) a light phase which includes the production of kinetic energy and thermal energy by accelerating and heating a gas through at least one cycloturbine under the action of solar radiation, l use of these energies to produce electricity while cooling, or even liquefying said gas, by accumulating part of the energies of the gas in at least one tank comprising at least one water compartment and at least one solution compartment saturated with sodium acetate, storage of energy from solar radiation, in potential energy by heating said gas under variable volume conditions in a variable volume solar thermal accumulator and,

b) a dark phase, where the energy stored in the solar thermal accumulator and the tank is used to produce electrical and thermal energy.

Also known is US patent US9551507 describing a process for producing a solar radiation absorber element, for a concentrated solar thermal power plant, comprising the formation of a selective coating on an outer surface of a stainless steel substrate. The formation of the selective coating comprises the following successive steps:

- surface treatment by polishing the substrate

- and the heat treatment, in an oxidizing atmosphere, of the substrate in a range of temperatures between 550° C. and 650° C., to form on the outer surface of the substrate, at least one surface layer having a thickness greater than 70 nm so as to be inherently selective,

and in that the stainless steel of the substrate has an aluminum content greater than 0.5% by weight.

International patent application WO 1983000169 describes another method for manufacturing a selective solar collector absorber making it possible to obtain a surface for collecting solar radiation with a high absorption factor and a low emission factor. The capture surface is made from a ferrous alloy containing chromium which is immersed in an acid bath containing oxygen atoms and at least one metalloid substance based on sulphur, selenium and/or tellurium; beforehand, the state of the capture surface is adjusted in order to activate it.

Disadvantages of the Prior Art

The performances of state-of-the-art solutions are limited by the energy conversion capacities of the absorber, which leads to limited yields. On the other hand, the known absorbers are exposed to the open air generating significant heat loss. Known absorbers have a smooth capture surface that is not very absorbent and highly emissive. The materials of known absorbers do not allow use at high temperatures and cannot withstand excessive pressures or stresses.

Solution provided by the invention

In order to remedy these drawbacks, the invention relates, in its most general sense, to a solar radiation absorber, for a concentrated solar thermal power station, characterized in that a monolithic piece of silicon carbide is formed, the absorption surface of which is for example coated with dendrites of tungsten (or other substrate)

The invention also relates to a thermal collector for a concentrated solar thermal power plant, characterized in that it is formed by a cavity, for example made of graphite, with a transparent inlet window in which the absorber according to the invention is placed, formed by a monolithic silicon carbide part whose absorption surface is ideally coated with tungsten (or other) dendrites.

Advantageously, the sensor comprises a burner arranged inside said cavity, directing a flame in the direction of said absorber.

Alternatively, it includes an optical fiber carrying solar energy to said absorber.

Advantageously, at least part of the inner surface of the cavity has cavities that behave like a light trap (conical honeycomb).

The invention also relates to a system consisting of a thermal sensor for a concentrated solar thermal power plant thermally and mechanically coupled to the inlet of a thermal machine, characterized in that said sensor is formed by a graphite cavity with an inlet window transparent in which is arranged an absorber formed by a monolithic piece of silicon carbide whose absorption surface is coated with tungsten dendrites.

Advantageously, said expansion machine with an upper part made of silicon carbide.

The invention also relates to a process for the preparation of an absorber according to the invention, characterized in that it comprises a step of depositing a thin layer absorbing the radiation which can consist, for example, of a projection by a plasma torch or flux sunburst concentrate of tungsten dendrites on the surface of a monolithic piece of silicon carbide. Said layer can also advantageously be deposited immediately after molding, the paste obtained being relatively sticky and thus allowing easy attachment of the dendrites by simple mechanical spraying or dusting.

According to a variant, the method comprises a step of laser projection of tungsten dendrites on the surface of a monolithic piece of silicon carbide.

According to other variants, the invention relates to:

A thermal collector for a concentrated solar thermal power station characterized in that it is formed by a cavity insulated under vacuum, for example made of graphite, with a transparent inlet window in which is placed an absorber formed from a monolithic piece of silicon carbide of high purity whose absorption surface is coated with tungsten dendrites.

Advantageously, this solar radiation absorber, for a concentrated solar thermal power plant, has:

a honeycomb configuration whose cells are conical / flared with a greater height in the center and presenting microcavities.

- a sealed spherical interface supporting upper/lower acting as an assembly/sealing flange with a support having a nest and fins and an assembly by threads of a pipe on a thermodynamic device.

- fins for heat exchange with the fluid in the shape of rosettes and having microcavities with a higher height in the center.

- a shut-off disc and fluid passage ports.

- a central helical tapered section with a 90° offset and a flared/conical shape.

- a burner arranged inside said cavity, directing a flame in the direction of said absorber.

- exchange surfaces with microcavities.

The invention also relates to a system consisting of a thermal collector for the aforementioned concentrated solar thermal power plant, thermally and mechanically coupled to a pipe (hot fluid outlet) or to the inlet of a thermal machine, characterized in that said sensor is formed by a graphite cavity with a transparent inlet window in which is placed an absorber formed of a monolithic piece of silicon carbide whose absorption surface is coated with tungsten dendrites.

Preferably, said expansion machine with upper part in silicon carbide.

Advantageously, it comprises a step of spraying tungsten dendrites by plasma onto the surface of a monolithic part made of silicon carbide and/or a step of deposition by powdering during the production in the pasty phase of tungsten dendrites on the surface of a monolithic part in silicon carbide.

Detailed description of a non-limiting example of the invention

The present invention will be better understood on reading the detailed description of a non-limiting example of the invention which follows, with reference to the appended drawings where:

Figure 1 shows an absorber seen in section, upper part upwards (sun/flame) comprising the honeycomb, the sealed interface in the middle (3) and the fins of the fluid exchanger below

Figure 2 shows a bottom view of the exchanger with its helical cone in the center.

FIG. 3 represents a section of the interface and of the lower part alone.

Figure 4 shows a view of the honeycombs

Figure 4A shows a view of the dendrites

Figure 5 is a simplified representation of the honeycomb array

Figure 6 is a representation of a first enlarged tungsten dendrite shape

Figure 6A is a representation of another magnified form of tungsten dendrite

Figure 7 shows a close-up of fused dendrites on the CSi support

Figure 8 shows an external containment enclosure (unit for solar concentrator).

Figure 9 shows a detailed section of the helical cone

Figure 10 shows a 3D representation of the helical cone for understanding the device.

Description of the context of use of an absorber according to the invention

The thermal sensor absorbs solar radiation to transform it into heat. This heat is then transmitted to a heat transfer fluid. A collector is made up of an absorber, a heat transfer fluid, insulation, sometimes glazing and reflectors.

The absorber is one of the most important elements of a thermal sensor; it converts solar radiation into heat.

The absorber is characterized by two parameters:

- the solar absorption factor α* (or absorptivity): the ratio of the light radiation absorbed by the incident light radiation;

- the infrared emission factor ε (or emissivity): the ratio between the energy radiated in the infrared when the absorber is hot and that which a black body would radiate at the same temperature.

In solar heating applications, the aim is to obtain the best solar absorption factor/infrared emission factor ratio. This ratio is called selectivity.

The material constituting the absorber is generally copper or aluminum but also sometimes plastic. The properties of some materials used as absorbers.

The structure of the absorber is illustrated in figures 1, 2, 3 and 8.

It comprises a honeycomb structure (1) exposed to solar radiation through a porthole (10). It is fixed to the enclosure by a flange (2). A membrane (3) forms a sealed interface. A seal (4) ensures the seal between the flange (2) and an internal shoulder of the enclosure. A structure (6, 12) has a central truncated helical section with lower fins (5). It is fixed by screws (7).

A shutter disc (11) extends under the structure (12).

In the area between the porthole (10) and the honeycomb structure (1), a burner injects hot gases. This zone also has evacuation orifices (14).

The honeycomb structure receives the heat flow, and has a sealed interface in the center, with a flange on the sides with the fins over the entire height (allows to withstand high pressures), below in the center the helical cone ( allows the fluid to be returned at 90°), at the bottom the closing disc = allows the fluid circuit to be sealed and allows circulation from the periphery to the center and vice versa (reversible/alternating)

Materials absorptivity emissivity selectivity Max. temperature α* ε α* / ε Blackened nickel (Black nickel) 0.88 - 0.98 0.03 - 0.25 3.7 - 32 300°C Graphite films 0.876 - 0.92 0.025 - 0.061 14.4 - 36.8 250°C Black copper 0.97 - 0.98 0.02 48.5 - 49 250°C Black chrome (Black chrome) 0.95 - 0.97 0.09 - 0.30 3.2 - 10.8 350 - 425°C

In order to obtain better performance, certain systems therefore consist of a particular coating.

The heat transfer fluid (or heat transfer fluid) makes it possible to evacuate the heat stored by the absorber and to transmit it to where it must be consumed. A good heat transfer fluid must take into account the following conditions:

- be chemically stable when it reaches a high temperature, in particular during sensor stagnation;

- possess antifreeze properties in correlation with local weather conditions;

- have anticorrosive properties depending on the nature of the materials present in the sensor circuit;

- possess a high specific heat and thermal conductivity in order to transport heat efficiently;

- be non-toxic and have a low impact on the environment;

- have a low viscosity in order to facilitate the task of the circulation pump;

- be readily available and inexpensive

The good compromise in relation to these criteria is a mixture of water and glycol (used in automobile coolant), even if it is not uncommon to find systems operating on pure water or simply to air depending on use.

The glazing makes it possible to protect the interior of the collector against the effects of the environment and to improve the yield of the system by greenhouse effect.

If effective glazing is desired, it must have the following properties:

- reflect light radiation to a minimum regardless of its inclination;

- absorb light radiation to a minimum;

- have good thermal insulation by keeping infrared radiation to a maximum;

- withstand the effects of the environment over time (rain, hail, solar radiation, etc.) and large temperature variations.

The main glazings used for thermal sensors are based on non-ferruginous glass or acrylic glass, and often have an anti-reflective coating.

The thermal insulation makes it possible to limit the thermal losses, its characteristic is the coefficient of conductivity; the lower the better the insulation. The main materials used for thermal sensors are rock and glass wool, polyurethane foams or even melamine resin.

Some insulators used for thermal sensors:

Materials Thermal conductivity Rockwool 0.032 - 0.040 W/m.K Glass wool 0.030 - 0.040 W/m.K Polyurethane foams (sealing) 0.022 - 0.030 W/m.K

In the case of glazed thermal collectors, it is also interesting to replace the insulation between the glass and the absorber with air. Indeed, the air has a great power of insulation, it is thus used in the double glazing. Always with the aim of obtaining better yields, some manufacturers use other gases such as argon or xenon, and when possible, it is even preferable to use a vacuum. Here are the insulation coefficients of gases used as insulators:

Gas Thermal conductivity at 283 K, 1 bar. Air 0.0253 W/m.K Argon 0.01684 W/m.K Xenon 0.00540 W/m.K

Description of the absorber according to the invention

The absorber according to the invention consists of a monolithic CSi part on which are deposited during production in the pasty phase, or even projected by laser or plasma, tungsten dendrites, a crystalline form absorbing 98% of the infrared radiation. red and has a melting point above 3,400°C.

By dendrite is meant within the meaning of the present patent a crystalline form obtained by solidification, and having a tree-like shape. A snowflake, for example, has a dendritic structure. Said dendrites are preferentially industrial residues or dust or be produced by solar means at high temperature.

The agglomeration of tungsten dendrites on the CSi can be carried out in a thin layer and under high temperature or by any other process.

The absorber thus forms a light trap, in particular using micro cavities made during molding, to present characteristics close to a black body.

Detailed description of the invention

The main qualities of an absorber are:

1. Ability to receive and transfer the maximum amount of energy
2. Be a very good thermal conductor
3. Do not reflect or radiate IR (infra red)
4. Support a very high energy density
5. Withstand thermal shocks and remain chemically inert
6. Do not deteriorate over time
7. Have the lowest possible manufacturing cost
8. Be easily industrialized
9. Have significant mechanical properties

The first quality of an absorber is its ability to receive radiation (sun/flame) and transfer it to a fluid with the best possible efficiency.

The absorber is located in a vacuum enclosure allowing perfect thermal insulation, which is ideally made of graphite and covered with a window transparent to solar radiation and covered with an anti-reflection coating limiting optical losses. The vacuum cavity is equipped with a burner to provide the necessary energy in the absence of solar flux and an outlet is provided to evacuate combustion residues.

The majority of known absorbers use materials such as stainless steel, with or without an absorbent/selective coating. This material has a very limited absorption rate and redistributes a good part of the infrared radiation. On the other hand its conductivity is very limited since of the order of 20 W/m.K, which is very little compared to other recognized materials such as copper = 386 W/m.k which turns out to be 20 times better conductor thermal, an important property for the quality of an absorber. Then, stainless steel can only be used up to 800°C, which limits the advantageous thermodynamic yields in the high temperature ranges. One of the suitable materials proposed in the invention and which will be cited by way of example is CSi (silicon carbide) in a relatively pure form.

Pure CSi is an excellent thermal conductor up to 1,200°C with a maximum conductivity of approximately 350 W/m.k close to that of copper, which gives it exceptional properties, moreover it perfectly conducts IR (infrared) . It withstands significant thermal shocks and its very high hardness and mechanical resistance makes it possible to design parts that can withstand very high stresses, thus allowing the production of thin parts with excellent thermal conductivity. Chemically inert, it withstands very high temperatures and does not degrade over time.

On the other hand, pure CSi is marred by several problems because it is almost transparent to solar radiation, resembling glass, and therefore does not absorb the concentrated solar flux. On the other hand, it is very difficult to produce parts of complex geometry necessary to produce almost perfect absorbers. Finally, its implementation requires a very large amount of energy and very high temperatures.

To remedy this, the absorber according to the invention is covered with a thin layer of tungsten dendrites on the side exposed to the heat source. Tungsten dendrites have the property of perfectly capturing solar radiation or radiation from a flame and transmitting it to a support substrate with an efficiency of 98%. For this, the dendrites are deposited by means, for example, of a plasma torch or any other suitable process, in particular when the CSi comes out of the molding phase, its adherent pasty consistency allowing perfect cohesion.

To absorb an incident flux as efficiently as possible, it is necessary to produce a particular geometry which can capture and trap the incident radiation. Known absorbers generally have a smooth surface, which reflects a large part of the radiation. The invention has a geometry acting as a light trap and is comparable to a black body. For this, the surface consists of a honeycomb structure whose section is conical, thin in the upper part, and wide in the lower part. Thus it is possible to capture with the greatest efficiency that is the incoming radiation because it cannot thus escape and is perfectly captured by the dendrites which then transfer the flux into the CSi substrate. On the other hand, the conical conformation of the honeycomb allows easy demolding

Regarding the production, the state of the art does not currently allow the manufacture of parts with complex geometries, especially since for a good absorber it is necessary to limit the thickness as much as possible, to the detriment of its solidity, which does not is currently not possible in the state of the art because it requires machining with tools whose diameter and length are limited for mechanical reasons.

The invention makes it possible to remedy these problems thanks to two innovative processes, one being high pressure isostatic pressing, the second in additive manufacturing by 3D printer.

The high pressure isostatic pressing developed by the inventor makes it possible to send a CSi paste into a mold formed of two or more parts, almost similar to plastic or metal injection, one for the upper part, and the second for the lower part, and possibly a third for the central helical cone which may require a screwing/unscrewing function or even two independent molding half-shells. It is thus possible to obtain parts of complex geometry with a very small thickness, which can be of the order of a millimeter, the geometric architecture of the part allowing this kind of realization. The blanking disc can be added immediately to obtain a monolithic part.

The second process successfully tested by the inventor is additive printing or 3D printing. A nozzle or a set of nozzles gradually deposits the CSi paste on a plate gradually forming a part with a geometry whose complexity is almost infinite or the obtaining of shapes impossible to achieve otherwise.

The honeycomb surface is ideally made up of a rough surface with microcavities that advantageously absorb light and allow easier attachment of the dendrites. Similarly, the fins of the lower part may have microcavities generating micro turbulence, which contribute on the one hand to increasing the heat exchange coefficients, on the other hand to reducing friction on the surfaces increasing the overall efficiency.

The parts, after various appropriate treatments, are then sintered in a high-temperature furnace, traditionally powered by gas or electricity, but can also ideally be sintered by concentrated solar power to drastically reduce production costs. The absence of the solar source being ideally compensated by the combustion of an hho mixture which produces a flame of very high quality at 2800°C whose residue is only water vapor which can be recycled indefinitely. The hho mixture, also called "solar fuel", can ideally be produced by solar energy and reduce the energy cost accordingly. The other advantage of this solar process is that you can then consider controlled annealing to release the tensions, which is very inexpensive.

It is thus possible to envisage the industrial production at a very high rate of parts of complex geometry and at very low manufacturing cost while having a carbon index close to or equal to zero and therefore no environmental impact.

The absorber, although monolithic, is divided here into three sections for the sake of understanding the description. The first section is the upper part receiving the heat flow, the second is the interface allowing to support the two main sections and to carry out the assembly in a pressurized structure while guaranteeing sealing. The third section is the lower part, which is responsible for transmitting thermal energy within a fluid. The assembly is concave in shape so as to optimize the capture and transfer of energy, but also to ensure the best possible mechanical resistance by making the energy flows and the mechanical forces applied to the surfaces homogeneous.

The upper part, described previously, is a honeycomb structure of conical shape flared towards the opposite part (Fig 4) so as to even out the temperature gradients, and its surface is covered with a thin layer of tungsten dendrites. . These cones are higher and wider in the center because a solar flux or a flame is always more important in its center, thus requiring a greater density of matter which then transmits by conduction to the surrounding elements.

Due to the excellent properties of CSi and the implementation method according to the invention, it is possible to produce convection fins (honeycomb) with a thickness of the order of a millimeter at its upper part. The "leading edge" (terminology?), which receives direct solar radiation or the flame (therefore the top), is rounded to avoid sharp angles that are too fragile and allow demolding

The other advantage of the honeycomb structure is that it perfectly distributes both thermal and mechanical stresses. The height of the honeycomb being greater in the center than at the periphery, both thermal and mechanical stresses are thus uniformly distributed over the entire surface and the structure can therefore undergo a much greater pressure in its center. which makes it possible to withstand the most extreme energy and mechanical densities, unlike known absorbers, for example made of stainless steel, the surface of which is smooth, spherical and of constant thickness.

In the continuity of the honeycomb structure comes an "interface" (sealed concave disc separating the lower and upper part), which receives the two exchanger parts, upper and lower. This interface ensures the continuity of the seal between the two opposing parts and the good transmission of energy evenly distributed over its entire surface. Its shape is preferably spherical and its concavity oriented towards the upper part (receiving the flow), which allows the absorber to withstand very high pressures with the lowest possible thickness, thus contributing to thermal efficiency. This low thickness also makes it possible to limit the mechanical stress or the molecular defects known in a high thickness as well as the quality of the sintering, which is essential to ensure the durability and reliability of the absorber.

To ensure the leaktight assembly of the absorber between the various components of a thermal device, the outer perimeter consists of a peripheral bearing similar to a flange, which is assembled with the external devices. This is of a thickness adapted to the constraints that will be subjected to it and is designed to fit into a cylinder of slightly larger section on which the absorber is positioned and ensures a sealed assembly.

For this, a ring identical to a seal can be envisaged, which is made on the central perimeter so as to apply pressure to a limited surface defined as within a flange, ideal in the context of very high pressures. applied. This ring in relief can also be replaced by a groove receiving a standard seal or be a flat surface for certain flat seals, in particular of the metallic type. An insulating seal, for example in graphite, can also be ideally considered to withstand high temperatures, the other advantage of this type of seal is that it constitutes a thermal bridge thereby avoiding the transmission of heat to the external support.

In this case, the absorber is mounted directly on the outer receiving cylinder such as Fig 8, and sufficient gas pressure is applied allowing quick and easy mounting, like tubeless tires, considering all the more than the porthole of the cavity receiving the absorber is ideally under vacuum. This avoids creating mechanical stress during expansion differences of the various components of the device by allowing self-adjustment and movement of the absorber on the sealed surface.

The lower part of the "flange" allows the assembly of additional components and devices and has in this sense elements allowing their mechanical connection such as threads or any appropriate assembly system, in particular a quarter-turn type assembly to allow a fast and economical assembly. Said threads or assembly devices may be on both sides to allow a durable and risk-free mechanical assembly while allowing perfect maintenance of the pressure to be exerted on the sealing device/seal.

The lower part Figures 2 and 3 is made up of thin fins forming a rosette (terminology to be checked) allowing the thermal energy to be transmitted to the heat transfer fluid or working fluid/fluid to be heated. The fins are nested in the "flange" part over their entire height so as to obtain a monolithic part particularly resistant to high pressures and to distribute the forces evenly.

The concentrated solar flux is similar to a Gaussian curve, i.e. with a maximum intensity in its center. As a result, the fluid ideally comes from the periphery towards the center to avoid heat losses at the level of the sealing flange. For this, a "light" (passage) is made all around the inlet of the fins to allow the passage of the fluid. This light is imposed by a shutter disc affixed to the fins and locked by a process such as mounting lugs to prevent its displacement or any vibrations. It can also advantageously be mounted in monolithic form according to the manufacturing method, the latter avoiding the addition of mechanical fixing/holding devices.

This arrangement in portions of circles (rosettes?) nested in each other makes it possible to create a certain amount of turbulence and to guide the fluid in a very precise direction. Moreover, the centripetal force makes it possible to increase the interaction of the fluid on the surface of the fins, thus improving the exchange coefficient. This singular arrangement also makes it possible to increase the exchange surfaces and increase the thermal efficiency of the absorber. The space between the fins is greater at the periphery than at the center for a perfect correlation with the energy density implemented on the surfaces.

On the other hand the fins are higher in their center than towards the periphery which allows on the one hand to optimize the thermal exchanges, the greatest density of energy being in the center, and on the other hand to contribute to the mechanical resistance of the assembly when it is subjected to very high pressures made necessary in particular in thermodynamic devices, for example of the Stirling type. It is thus possible to have a very thin interface while ensuring extreme mechanical resistance to very high pressures.

Due to the particular geometry of the fins, a fast vortex is formed in the center of the lower structure, which is redirected outside the absorber by a truncated helical section resuming the direction of the initial flow in a perpendicular direction either towards a piping, or to a piston for certain thermodynamic devices. Said frustoconical section comprises fins of helical shape, which make it possible to direct the flow in the new perpendicular axis on the one hand, and to avoid overheating on the central zone most exposed to incident thermal radiation on the other hand due to increased flow velocity by Venturi effect. The center of the cone is relatively thick while its end is thinner. The lower base of the frustoconical section is advantageously of curved shape to avoid excessive turbulence and pressure drops that are detrimental to overall efficiency. This helical shape approximates the obturator disc to avoid losses linked to leaks or guide faults preferentially in one direction of the fluid.

To ensure the tightness of the lower part, an obturation disc makes it possible to close and thus perfectly direct the fluid intended to be heated. This disc has an opening in its center allowing the possible connection by a cylinder section on a pipe or the sending on a piston, as well as an outer diameter slightly smaller than the diameter of the fins thus allowing the passage of the fluid from the periphery. .

A hooking device with the body of the absorber is made on the blanking disc, the latter being able to be in several ways such as lugs, notches or any other assembly method, or constituting a monolithic assembly in the case of additive printing. Another advantageous process is the assembly of the disc as soon as the body of the absorber comes out of the molding, the adhesion then being done easily, or even during the production by additive printing.

In general, all sharp angles interfering with the movement of the fluid are rounded to avoid generating turbulence and other harmful pressure drops.

The lower part is also designed to allow rapid alternating passage without loss of fluid pressure in the outward and return direction, as for example in the case of an FPSE process (free piston Stirling engine, with frequencies that can be the order of several tens of cycles per second.

Claims (12)

- Thermal sensor for concentrated solar thermal power plant characterized in that it is formed by a vacuum insulated cavity, for example made of graphite, with a transparent inlet window in which is placed an absorber formed from a monolithic piece of silicon carbide whose absorption surface is coated with tungsten dendrites. - Thermal sensor for concentrated solar thermal power plant according to claim 1 characterized in that it has a honeycomb configuration whose cells are conical and flared with a greater height in the center and having microcavities. - Thermal sensor for concentrated solar thermal power plant according to claim 1 characterized in that it has a sealed spherical interface supporting upper and lower acting as an assembly and sealing flange with a support having a nest and fins and a assembly by threads of a pipe on a thermodynamic device. – Thermal collector for concentrated solar thermal power plant according to claim 1 characterized in that it has fins for heat exchange with the fluid in the form of rosettes and having microcavities with a higher height in the center. – Thermal sensor for concentrated solar thermal power plant according to claim 1 characterized in that it has a shutter disc and fluid passage lights. – Thermal sensor for concentrated solar thermal power plant according to claim 1 characterized in that it has a central helical frustoconical section with a 90° return and a flared and conical shape. – Thermal sensor for concentrated solar thermal power plant according to claim 1 characterized in that it comprises a burner disposed inside said cavity, directing a flame in the direction of said absorber. - Thermal sensor for concentrated solar thermal power plant according to claim 1 characterized in that it has exchange surfaces with microcavities. – System consisting of a thermal collector for a concentrated solar thermal power plant according to claim 1, thermally and mechanically coupled to a pipe (hot fluid outlet) or to the inlet of a thermal machine characterized in that said sensor is formed by a graphite cavity with a transparent inlet window in which is placed an absorber formed of a monolithic piece of silicon carbide whose absorption surface is coated with tungsten dendrites. – System for concentrated solar thermal power plant according to the preceding claim characterized in that said expansion machine with upper part of silicon carbide. – Process for the preparation of a thermal collector for a concentrated solar thermal power plant according to claim 1 characterized in that it comprises a step of plasma spraying of tungsten dendrites on the surface of a monolithic piece of silicon carbide. – Process for the preparation of a thermal collector for a concentrated solar thermal power plant according to claim 1 characterized in that it comprises a step of deposition by powdering during the development in the pasty phase of tungsten dendrites on the surface of a monolithic part in silicon carbide.