EP3983730A1

EP3983730A1 - Hybrid radiation absorber for solar power plant, and method for preparing such an absorber

Info

Publication number: EP3983730A1
Application number: EP20743185.9A
Authority: EP
Inventors: Sylvain Pare
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-06-13
Filing date: 2020-05-26
Publication date: 2022-04-20
Also published as: AU2020290036A1; JP2022536366A; KR20220024542A; CA3142844A1; CN114127484A; FR3097304A1; WO2020249885A1; IL288880A; FR3097304B1

Abstract

The present invention relates to a solar radiation absorber for a concentrated solar thermal power plant, the absorber being characterised 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. The invention also relates to a method for preparing such an absorber.

Description

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

Field of the invention

The present invention relates to the field of energy absorbers, the characteristics of which are similar to 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. In thermal equilibrium, emission and absorption are balanced and the radiation actually emitted depends only on the temperature (thermal radiation).

Typical non-limiting 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 you want to heat , a liquid to be sterilized, a production of steam to supply a standard turbo alternator, a DHW (domestic hot water / heating), various fluids, ...

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. Thermo-solar processes have better yields than photovoltaic processes, of the order of 30%, on the other hand, they are more bulky and suitable for a large 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 requires 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% of 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 operation and at full power of an installation despite variations or absence of 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 efficiency of the absorber, the latter generally has a coating, called a selective coating or a 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 wavelengths less than a cutoff wavelength and reflects all wavelengths greater than this same cutoff wavelength. The optimum cutoff wavelength depends on the operating temperature of the absorber element considered and is generally between 1.5 pm and 2.5 pm. It is, for example, about 1.8 μm for a temperature of the order of 650 K.

The patent application US2015033740 describes a solar receiver comprising: • a low pressure fluid chamber configured to operate at pressures of up to 2 atmospheres, and including a fluid inlet, a fluid outlet and an opening to receive concentrated solar radiation;

• a solar absorber housed in the low pressure fluid chamber; and

• a plurality of transparent objects which define a segmented wall of the low pressure fluid chamber;

• wherein the concentrated solar radiation received through the opening passes through the segmented wall and between transparent objects to pass into the low pressure fluid chamber and strikes the solar absorber.

Patent application US4047517 describes a radiant energy receiver comprising a plurality of elongated vane structures arranged in a converging configuration from an exterior portion thereof to an interior throat portion thereof, the exterior surfaces to the surfaces. intermediate vanes being at least in part a reflective surface and the surfaces intermediate the inner surfaces of the vanes being at least in part of a selective surface which absorbs radiant energy hitting the selective surface at a small angle of incidence, but reflects such energy striking at a larger angle of incidence, the radiant energy striking the outer parts of the vane being reflected back to the converging groove of the vanes and the radiant energy in the inner part hitting the selective surface at an angle d 'relatively low incidence, as would indicate an incipient or actual reversal of the direction of movement of the radiant energy e relative to the vanes is absorbed while that striking the selective surface at a relatively large angle of incidence is reflected in the groove of the vanes to generate a high temperature adjacent to the groove of the vanes. Disadvantages of the prior art

The performances of the solutions of the state of the art 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 a significant heat loss. Known absorbers have a smooth, poorly absorbent and highly emissive collection surface. The known absorber materials do not allow use in high temperatures and cannot withstand too high 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 plant, characterized in that a monolithic piece of silicon carbide is formed, the absorption surface of which is formed. is for example coated with tungsten dendrites (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 arranged, formed by a monolithic silicon carbide part, the absorption surface of which 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.

According to one variant, it comprises an optical fiber transporting solar energy to said absorber.

Advantageously, at least part of the interior surface of the cavity has cavities behaving like a light trap (conical honeycomb). The invention also relates to a system consisting of a thermal sensor for a concentration solar thermal power station 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 preparing an absorber according to the invention, characterized in that it comprises a step of depositing a thin layer absorbing the radiation, which may consist for example of a projection by plasma torch or flux. solar concentrate of tungsten dendrites on the surface of a monolithic silicon carbide part. Said layer can also advantageously be deposited right out of the molding, the paste obtained being relatively tacky and thus allowing easy fixing of the dendrites by simple mechanical spraying or powdering.

According to a variant, the method comprises a step of laser projection of tungsten dendrites onto the surface of a monolithic part made of silicon carbide.

According to other variants, the invention relates to;

A thermal collector for a concentrated solar thermal power plant, characterized in that it is formed by a vacuum insulated cavity, for example in graphite, with a transparent inlet window in which an absorber is placed, formed from a monolithic piece of silicon carbide big 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 of which the cells are conical / flared with a greater height in the center and having microcavities.

a sealed spherical upper / lower supporting interface serving as an assembly / sealing flange with a support having a nest and fins and a threaded connection of a pipe on a thermodynamic device.

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

- a sealing disc and fluid passage ports.

- a central helical frustoconical section with a 90 ° return 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 constituted by a thermal sensor for a solar thermal power plant with aforementioned concentration, 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 disposed an absorber formed of a monolithic piece of silicon carbide, the absorption surface of which is coated with tungsten dendrites.

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

Advantageously, it comprises a step of plasma projection of tungsten dendrites on the surface of a monolithic part. in silicon carbide and / or a powder deposition step during the production in a 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.

- Figure 3 shows a section of the interface and 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 matrix

- Figure 6 is a representation of a first form of tungsten dendrite enlarged

- Figure 6A is a representation of another form of enlarged tungsten dendrite

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

- Figure 8 shows an external confinement enclosure (unit for a 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, an insulation, sometimes a glazing and reflectors.

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

The absorber is characterized by two parameters:

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

- the infrared emission factor e (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 window (10). It is fixed to the enclosure by a flange (2). A membrane (3) forms a sealed interface. A seal (4) seals between the flange (2) and an internal shoulder of the enclosure. A structure (6, 12) has a central helical frustoconical 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 window (10) and the honeycomb structure (1), a burner injects hot gases. This zone also has evacuation openings (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 shutter disc = allows the fluid circuit to be sealed and allows circulation from the periphery to the center and vice versa (reversible / alternative)

Table 1

In order to obtain a 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 towards there where it should 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 when the sensor is stagnant;

- possess antifreeze properties in correlation with local meteorological conditions;

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

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

- 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 with respect to these criteria is a mixture of water and glycol (used in the coolant of automobiles), although it is not uncommon to find systems operating on pure water or simply in air according to use.

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

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

reflect the light radiation at least whatever its inclination;

- absorb light radiation to a minimum;

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

resist over time the effects of the environment (rain, hail, solar radiation, etc.) and large temperature variations. The main glazings used for thermal collectors 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 weaker 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:

Table 2

In the case of glazed thermal collectors, it is also advantageous to replace the insulation between the pane and 1 absorber with air. Indeed, the air has a great power of insulation, it is thus used in the double glazing. Still with the aim of obtaining better yields, some manufacturers use other gases such as argon or xenon, and when possible, we will even prefer to use a vacuum. Here are the insulation coefficients of gases used as insulators: Table 3

Description of the absorber according to the invention

The absorber according to the invention consists of a monolithic piece in CSi on which are deposited during the preparation in the pasty phase, or 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.

For the purposes of the present patent, the term “dendrite” is understood to mean a crystalline form obtained by solidification, and having a tree shape. A snowflake, for example, has a dendritic structure. Said dendrites are preferably industrial residues or dust or be produced by the solar route at high temperature.

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

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

Detailed description of the invention

The main qualities of an absorber are: a) Ability to receive and transfer the maximum amount of energy b) To be a very good thermal conductor

c) Do not reflect or radiate IR (infra red)

d) Support a very high energy density

e) Withstand thermal shocks and remain chemically inert

f) Do not deteriorate over time

g) Have the lowest possible manufacturing cost h) Be easily industrializable

i) Have important mechanical properties

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

The absorber is in a vacuum chamber allowing perfect thermal insulation, which is ideally in 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 making it possible to provide the necessary energy when there is no solar flow and an outlet is fitted to evacuate the 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 re-diffuses a good part of the infrared radiation. On the other hand, its conductivity is very limited since around 20 W / mK, which is very little compared to other recognized materials such as copper = 386 W / mk 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 efficiencies in high temperature ranges. One of the suitable materials provided in the invention and which will be cited by way of example is CSi (silicon carbide) in relatively pure form.

Pure CSi is an excellent thermal conductor up to 1,200 ° C with a maximum conductivity of around 350 W / mk close to that of copper, which gives it exceptional properties, in addition it conducts IR (infra red) perfectly. . 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 in with excellent thermal conductivity. Chemically inert, it supports very high temperatures and does not deteriorate 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 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 face exposed to the heat source. Tungsten dendrites have the property of perfectly capturing solar radiation or from a flame and transmitting it into a support substrate with an efficiency of 98%. For this, the dendrites are deposited by means of, for example, 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 with the greatest possible efficiency an incident flux, 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 that acts as a light trap and is compared to a black body. For this, the surface consists of a honeycomb structure whose section is conical, thin at the top, and wide at the bottom. Thus it is possible to capture with the greatest efficiency that is the incoming radiation because it cannot escape and is perfectly captured by the dendrites which therefore transfer the flux into the substrate in CSi. On the other hand, the conical shape of the honeycomb allows easy demoulding Concerning the production, the state of the art does not currently allow the manufacture of parts with complex geometries, especially as for a good absorber it is necessary to limit maximum thickness, to the detriment of its strength, which is not currently possible in the state of the art because it requires machining with tools whose diameter and length are limited for mechanical reasons.

The invention enables these problems to be remedied by means of two innovative methods, 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 two independent half-shells of moldings. It is thus possible to obtain parts of complex geometry with a very small thickness, which may be of the order of a millimeter, the geometric architecture of the part allowing this type of realization. The shutter disc can be added at once 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 deposits the CSi paste as it goes on a plate progressively forming a part of geometry whose complexity is almost infinite or the obtaining of shapes impossible to achieve otherwise. The honeycomb surface ideally consists of a rough surface having microcavities which advantageously absorb light and allow easier attachment of the dendrites. Likewise, 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 the friction on the surfaces increasing the overall efficiency.

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

It is thus possible to envisage the industrial production at very high speed 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 it is 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 making it possible to support the two main sections and to carry out the assembly in a structure under pressure while guaranteeing tightness. 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 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 taller and wider in the center due to the fact that a solar flux or a flame is always greater in its center, thus requiring a higher density of material which then transmits by conduction to the surrounding elements.

Owing to the excellent properties of CSi and of 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 too fragile sharp angles and to allow demoulding

The other advantage of the honeycomb structure is that it perfectly distributes both thermal and mechanical stresses. The height of the honeycomb being greater at 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 much greater pressure at its center. which allows 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 exchange parts, upper and lower. This interface ensures the continuity of the seal between the two opposite parts and good energy transmission uniformly 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 smallest thickness possible, thus contributing to thermal efficiency. This small thickness also makes it possible to limit the mechanical stress or the molecular defects known in a large thickness as well as the quality of the sintering, which is essential to ensure the durability and reliability of the absorber.

To ensure the watertight mounting of the absorber between the various components of a thermal device, the outer periphery consists of a peripheral bearing surface similar to a flange, which is assembled with the external devices. This is of a thickness adapted to the stresses which will be subjected to it and is designed to fit into a cylinder of slightly larger section on which the absorber is positioned and ensure a tight assembly.

For this it is possible to envisage a ring identical to a seal, which is made on the central periphery so as to apply pressure on a limited surface defined as within a flange, ideal in the context of very high pressures. applied. This raised ring can also be replaced by a groove receiving a standard seal or be a flat surface for certain flat seals, in particular of the type metallic. An insulating gasket, for example made of graphite, can also be ideally considered to withstand high temperatures; the other advantage of this type of gasket 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 external receiving cylinder as in Fig 8, and sufficient gas pressure is applied allowing rapid and easy mounting, like tubeless tires, considering all the more more than the window of the cavity receiving the absorber is ideally under vacuum. This avoids creating a mechanical stress during expansion differences of the various components of the device by allowing self-adjustment and displacement of the absorber on the sealed surface.

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

The lower part in Figures 2 and 3 is made up of thin fins forming a rosette (terminology to be checked) allowing thermal energy to be transmitted to the heat transfer fluid or working fluid / to be heated. The fins are nested in the "flange" part over their entire height so as to obtain a monolithic part which is particularly resistant to high pressures and to distribute the forces uniformly. The concentrated solar flux is similar to a Gaussian curve, i.e. with a maximum intensity at its center. As a result, the fluid ideally comes from the periphery towards the center in order to avoid heat losses at the level of the sealing flange. For this a "light" (passage) is made around the entire periphery of 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. Its assembly can also advantageously be in monolithic form depending on the manufacturing method, the latter avoiding the addition of mechanical fixing / holding devices.

This arrangement in portions of circles (rosettes?) Nested one inside the other makes it possible to create a certain number of turbulences and to guide the fluid in a very precise direction. In addition, 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 unique 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 heat exchanges, the greatest energy density being in the center, and on the other hand to contribute to the mechanical strength 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 an interface of very low thickness 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 helical frustoconical section taking the direction of the initial flow in a perpendicular direction or towards a piping, or to a piston for certain thermodynamic devices. Said frustoconical section comprises helical shaped fins, 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 the incident thermal radiation on the other hand due to 'an increased flow speed by the Venturi effect. The center of the cone is relatively thick while its end is thinner. The lower base of the frustoconical section is advantageously curved in order to avoid excessive turbulence and pressure drops detrimental to the overall efficiency. This helical shape approaches the shutter disc to avoid losses linked to leaks or guiding faults preferably in one direction of the fluid.

To ensure the tightness of the lower part, a shutter 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 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 device for fastening with the body of the absorber is produced on the closure disc, the latter possibly being 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 method being the assembly of the disc as soon as the body of the absorber comes out of molding, the adhesion then being easily done, or again during production by additive printing.

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

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

Claims

1 - Thermal sensor for a concentration solar thermal power plant characterized in that it is formed by a vacuum insulated cavity, for example in graphite with a transparent inlet window in which is disposed an absorber formed of a monolithic piece of carbide silicon whose absorption surface is coated with tungsten dendrites.

2 - Solar radiation absorber for a concentrated solar thermal power plant according to claim 1 characterized in that it has a honeycomb configuration whose cells are conical / flared with a greater height in the center and having microcavities.

3 - Solar radiation absorber for a concentrated solar thermal power plant according to claim 1 characterized in that it has a sealed spherical interface supporting upper and lower serving as an assembly and sealing flange with a support having a nest and fins and a threaded assembly of a pipe on a thermodynamic device.

4 - Solar radiation absorber for a 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.

5 - Solar radiation absorber, for solar thermal power plant with concentration according to Claim 1, characterized in that it has a sealing disc and openings for the passage of the fluid.

6 - Thermal sensor for a concentration 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.

7 - Thermal sensor for a concentration solar thermal power plant according to claim 1, characterized in that it comprises a burner disposed inside said cavity, directing a flame towards said absorber.

8 - Thermal sensor for a concentration solar thermal power plant according to claim 1 characterized in that it has exchange surfaces with microcavities.

9 - System consisting of a thermal sensor for a concentration 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, the absorption surface of which is coated with tungsten dendrites.

10 - System for a concentrated solar thermal power plant according to the preceding claim characterized in that said expansion machine with upper part made of silicon carbide.

11 - Process for preparing an absorber according to claim 1 characterized in that it comprises a step plasma projection of tungsten dendrites onto the surface of a monolithic silicon carbide part.

12 - Process for preparing an absorber according to the preceding claim, characterized in that it comprises a step of depositing by powdering during the production in the pasty phase of tungsten dendrites on the surface of a monolithic part made of silicon carbide .