WO2022053467A1

WO2022053467A1 - Generator generating energy from at least one radiation emitting source,the generator being in the form of blades which have vertical faces and rotate horizontally in a substantially toroidal containment casing

Info

Publication number: WO2022053467A1
Application number: PCT/EP2021/074611
Authority: WO
Inventors: Méryl BROTHIER; Thibaud Delahaye
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2020-09-14
Filing date: 2021-09-07
Publication date: 2022-03-17
Also published as: FR3114201A1; FR3114201B1

Abstract

The invention essentially relates to an energy converter (10) that converts radiant energy into electrical energy and has vertical blades which generate rotational forces from a radiant energy source and which are confined in a pressure-controlled casing, the peripheral part of the casing being in the form of a torus having a cross-section that is homothetic to that of the blades with a very small and constant clearance between the inner wall of the torus and the blades.

Description

Title: Energy generator from at least one radiative emission source, of the blade type with vertical faces, rotating horizontally in a containment envelope of essentially toric shape.

Technical area

The present invention relates to the field of energy converters from any type of radiative emission source which may be solar or of the waste heat type.

The present invention aims mainly to improve the energy efficiency provided by the converters according to the state of the art.

The invention makes it possible to generate electrical energy even in the occasional absence of an external radiative source.

Prior technique

Radiant energy, or radiative energy, is the only energy that can propagate in a vacuum, in the absence of matter. It is based on the principle of electromagnetic radiation, itself based on the movement of photons. Light (visible wavelength range) and thermal (infrared) energy is radiative energy.

To date, photovoltaic (PV) panels are the most widespread technology that converts radiative energy into electricity. Regardless of their intrinsic efficiency, which has been steadily increasing for many years, PV panels have several major drawbacks that can be summarized as follows:

- they are effective and efficient only for particular wavelengths,

- their energy payback time (production time required for the energy produced to exceed that necessarily spent to develop the constituent materials of the panels) is long, typically around 3 to 5 years,

- they show a loss of yield over time,

- their availability rate is relatively low (about 15%).

Other systems have been imagined but little used industrially or only for very specific niche applications with very low energy efficiency.

These systems are based on the exploitation of radiative energy which can cause a thermal slip likely to generate a force in line with the surface on which the thermal gradient is applied. Patent US182172 discloses one of these oldest systems, which has been popularized under the term Crookes radiometer, without at the time of its design, all the forces actually brought into play to induce the rotation of the blades making up the system has not been specified.

Figures 1 and 2 schematically show such a Crookes radiometer, generally designated by the reference 1. The radiometer 1 comprises a confinement envelope 2 maintained under a rarefied atmosphere, a vertical axis 3 which forms a point pivot supporting a hub 4 that which is fixed a number of four blades 5 with a diamond section, which extend at 90 ° from each other and each vertically in the casing 2. Each of the blades 5 comprises a main face 50 which is reflective (emissivity close to 0) and on the opposite side a main face 51 which is dark (emissivity close to 1). When they are subjected to a heat flux, for example solar radiation, they begin to rotate around the pivot 3 according to the arrow symbolized in FIG. 2, so that the dark faces 51 are subjected to a resultant force normal to their area.

As originally designed, Crookes Radiometer 1 cannot generate a large enough mechanical torque to be considered a viable power generator for industrial or even practical applications. Indeed, it is possible to demonstrate that the radiometric force generated in line with the blades 5 is of the order of 10 ^-6 N.

This force results from a so-called radiometric pressure which is a function of the radiation pressure (pressure exerted by the photons at the surface of the blade) to within one parameter, which is the ratio of the speed of light in the medium considered on the velocity of the gas molecules within the confinement envelope, as given by equation 1.

[Eq 1]

Pradiometric ~Pradiation.c/u in which

Pradiometric: radiometric pressure exerted on a given surface,

Pradiation: radiation pressure exerted on a given surface by a given radiation intensity, c: speed of light in vacuum, u: speed of molecules in the close vicinity of the surface subjected to radiation. To increase the recoverable energy, patent US4410805 proposed to multiply the number of blades and thereby the sum of the forces generated. However, this increase in blades does not allow a sufficient increase in the recoverable energy.

Prior concentration of the radiative flux has also been proposed, for example in patent application US2015/0013337. Here again, the energy efficiency remains limited.

In general, the theoretical performances targeted by the radiative energy conversion systems which have already been proposed have been very far from being achieved, mainly due to an insufficient understanding of the various mechanisms involved, in particular before publication [1] which for the first time analytically explained the influence of resistance forces on radiometric thrust.

In fact, only the radiometric surface force was really taken into account.

And, it has been demonstrated that it is not so much the surface as the perimeter developed by the surface subjected to radiation that is taken into account: [2].

Thus, more than the increase in the surface developed by the blades via their number as proposed by patent US4410805, another way of increasing the recoverable energy is to increase the perimeter of the surfaces at the right of which a temperature gradient is imposed.

This results in equation 2 which connects the force exerted on the surface subjected to thermal gradient to the perimeter which it develops.

[Eq 2]

P: mean pressure at the surface of a blade, p: perimeter developed by the surface of a blade, λ: mean free path of the gas,

Th: Temperature of the hot face (dark), Tc: temperature of the cold face (reflecting),

T: average temperature of the blade, l: thickness of the blade.

Thus, the perimeter developed is a first-order parameter for increasing the intensity of the forces making it possible to set the blades in rotation in a radiative energy conversion system. Several patents, in particular US Pat. No. 4,397,150, have proposed increasing the developed perimeter of the blades by perforating them, and whether they are in an open environment or in a containment envelope.

With the progress of micro or even nano-fabrication, it is now possible to produce perforations with a diameter close to the average free path of the gas. It is also necessary for the thickness of the blade to be very small, i.e. of the order of magnitude of the mean free path, while being insulating and rigid, as proposed in patent applications US2006/001569A1 and WO2007/002600A1.

For the case where a blade subjected to a gradient would have a perforation rate equal to 50% and whose diameter of the holes would be of the order of the mean free path of the gas molecules present in the close vicinity of the blade, the thrust developed per unit surface of such a blade is given by the following equation 3:

[Eq 3]

where: n: number of gas molecules per unit volume, k _B : Boltzmann constant,

R: radius of the blade perforations, λ: mean gas free path,

Th: Temperature of the hot face (dark), Tc: temperature of the cold face (reflecting).

Nevertheless, perforated blade systems have never really been operational, due to real performance that is much lower than theoretical performance.

On the one hand, certain systems with perforated blades described add heavy components which burden their performance. For example, in applications US2006/001569A1 and WO2007/002600A1, Peltier modules with a cooling/heating function are integrated in line with the surfaces subjected to the radiative flux, and the arrangement of the electrical connectors as such is prohibitive to increase performances.

On the other hand, as already mentioned, these systems do not take into account the reality of the forces opposing those generating the rotation of the blades.

The sum of the forces acting on a blade is in effect a balance between the radiometric surface force, the edge forces, which are in the same direction as the surface force radiometric, the friction forces induced by the pivot, and finally, the braking force, also called shear force, which is another force opposing the movement. The shearing force is induced by thermal transpiration and is applied on the side surface of the blade in the direction of the cold (reflecting) face towards the hot (dark) face, which actually slows down the rotational movement of the blade. blade.

It has been demonstrated that this shearing force becomes significant especially at low Knudsen number (Kn): see publication [3], in particular figure 4.

Patent US9705383B1 proposes a radiative energy converter with four blades which extend and whose rotation takes place in a horizontal plane, directly in contact with the external environment. Shear forces are only partially reduced in such a converter.

Furthermore, various means of converting the rotational energy of blades into electricity have already been envisaged.

Patent US4926037 thus proposes a mechanical coupler.

Patent application US2014/159377A1 describes an electromagnetic converter.

The aforementioned patent US9705383B1 discloses the arrangement of a permanent magnet below the horizontal plane of rotation of the blades which each incorporate within them a conductive wire connected to the support of the blades forming a first electrical contact, the blades being surrounded by a ring fixed electrically conductive connected to a second electrical contact. When the blades are rotating, their conductive wires are subjected to a magnetic field flux varying from the flux of the permanent magnet, and thus generate an electric current between the first and the second contact.

There is a need to further improve converters of radiative energy into electrical energy, in particular in order to further increase the forces generating the rotation of the blades relative to the opposing forces, with a view to increasing their conversion efficiency.

More generally, there is a need for a converter of radiative energy into electrical energy, which can both:

- optimize the level of recoverable energy for a given radiative source,

- be easily implemented on a larger scale than that planned so far, in order to generate significant levels of electrical energy,

- generate electricity continuously, even in the event of a variation in the intensity of the radiative source. The general object of the invention is then to respond at least in part to this (these) need(s).

Disclosure of Invention

To do this, the invention firstly relates to a converter of radiative energy into electrical energy, comprising:

- a confinement envelope with controlled internal pressure, the envelope being of axisymmetric shape around a vertical axis of symmetry, the envelope comprising a torus and of which at least a part is transparent with respect to the radiative source at value;

- A converter support extending along the axis of symmetry of the casing;

- a hub mounted at the free end of the support, defining a horizontal plane of rotation;

- a plurality of blades each fixed to the hub by a blade support, the blades being distributed angularly around the hub while being arranged inside the torus of the containment envelope, the main faces of the blades being orthogonal to the plane of rotation horizontal, one of the main faces of at least part of the blades comprising an emissivity surface distinct from the other of the main faces, the section of the blades being homothetic to that of the torus of the containment envelope with a clearance E between each blade and the inner wall of the substantially constant torus.

Preferably, the blades are evenly distributed angularly around the hub.

Preferably again, the emissivity surface of one of the main faces of the blades has an emissivity value close to 1 while that of the other of the main faces has a value close to 0.

Thus, the invention essentially relates to a converter with vertical blades generating the rotational forces from a source of radiative energy, which are confined in a pressure-regulated envelope whose peripheral part is in the form of a torus with section homothetic to that of the blades with a very low and constant clearance between the internal wall of the torus and the blades.

Advantageously, the clearance E and the characteristic length L of each blade are determined so that 10 ^-6 <ε/L <10 ^-2 .

Such a ratio is advantageous because the confinement volume to be established around the blades is thus minimized (material saving, size limitation) and the applied braking forces generated at the end of the blades are reduced to a minimum, i.e. i.e. in the close vicinity of the containment envelope. In other words, with an optimized volume of the right cylinder for the containment of the blades makes it possible to minimize the braking forces tangential. Indeed, with a ratio ε/L as above, the clearance between the blades and the walls delimiting the confinement volume of the latter is as low as possible. The impact of the size of a blade confinement envelope has been shown: [4]. More precisely still, the radiometric force is inversely proportional to the distance between the wall of the containment envelope and the blades.

Moreover, when the pressure increases, the effect of the distance from the wall tends to increase because the thermal gradient becomes more accentuated.

Also, advantageously, in order to reduce the braking force exerted at the blade tips, the confinement volume can have a regulated wall temperature close to the average temperature of the blades. This reduction in the braking force is made possible by an attenuation of the thermal gradient thus obtained at the blade tips.

By "characteristic length" of a blade, we mean here and in the context of the invention, the usual meaning mentioned for example in the publication [5], ie "the characteristic length L of a solid (a shape) F arbitrary (bounded) can be defined as the ratio of its volume to its area or better as this ratio multiplied by twice the dimension of the surrounding space. »

Another representative characteristic length can be given by the following equation: L = 1/3(L + l + h): with:

L, 1 and h the length, width and height of the solid that can be defined by these dimensions. Advantageously, the Knudsen number, characterizing the flow regime of the fluid inside the casing on the blades, is between 0.1 and 0.5

According to an advantageous characteristic, the blades have a tapered profile at their periphery. This makes it possible to minimize both the temperature gradient and the surface on which this braking force is applied.

According to a first advantageous embodiment for the electromagnetic conversion, the converter further comprises:

- a plurality of permanent magnets individually attached to one of the blades;

- at least one induction coil fixed and centered on the axis of symmetry of the casing, the coil(s) being arranged facing the permanent magnets so that the rotation of the blades generated by a radiative energy source generates an electromotive force in the coil(s). Thus the magnetic field generated by the rotating permanent magnets just above the turns of the induction coil generates an electric current induced therein.

The converter support may be a fixed support. The connection between the fixed support and the hub is designed in such a way that it limits friction to facilitate the rotation of the blades.

Several advantageous variants can be provided:

- the fixed support can be in a point connection with the hub. Preferably, materials are then chosen which induce very low coefficients of static and dynamic friction, typically of the order of 0.1 or even a few hundredths. These may be materials such as glass, polished steel, even Teflon or other anti-friction polymers;

- the fixed support and the hub can each comprise a magnetic sphere, the two magnetic spheres being in mutual contact. This variant can be chosen in particular when the blades with their support are of low mass;

- the hub and the blades can be supported by at least one magnetic bearing, one part of which is fixed to the fixed support and the other to at least one part of the blades.

According to a second embodiment, the converter support is a rotatably mounted shaft around which the hub is fixed; the converter further includes:

- a plurality of permanent magnets fixed and angularly distributed all around the rotating shaft;

- at least one induction coil and centered on the axis of symmetry of the casing, the coil(s) being arranged opposite the permanent magnets being arranged so that the rotation of the blades generated by a radiative energy source generates an electromotive force in the coil.

Preferably, the space between the permanent magnets and an induction coil is less than 1mm. Such a small space between the magnets and the coil turns makes it possible to optimize the conversion of the kinetic energy of the rotating blades into electrical energy.

According to an advantageous embodiment, at least a part of the blades is each extended radially by an extension arm which extends radially outside the blades. The permanent magnets are advantageously fixed individually on one of the extension arms. Thanks to this, the relative speed of the magnets with respect to the coil(s) for generating the electromotive force sought is further increased. According to a variant embodiment, each extension arm consists of two arm portions at 90° to each other, one portion of which is integral with a blade which extends vertically and the other portion which extends horizontally. at the end of which is fixed a permanent magnet.

According to an advantageous embodiment, the converter comprises a plurality of pairs of fixed induction coils centered on the axis of symmetry of the envelope, the coils of each pair being arranged two-by-two parallel, so that the rotation of the blades moves the permanent magnets between the coils of each pair.

Advantageously, the converter comprises a radiative flux concentration system. For example, the radiative flux concentration system can consist of:

- either a system of mirrors focusing the radiative source in the direction of a focal point,

- either a reflective surface of generally parabolic shape causing the radiative source to converge towards its focus at the level of which can be placed convergent lenses making it possible to direct all or part of the radiative flux collected towards a system aiming to distribute this radiative flux to the right faces of the blades with the lowest surface emissivity.

These two configurations are advantageously exploited in the case where the radiative source is the sun or a source emitting in the visible spectrum and at least part in a spectrum belonging to the infrared.

As a distribution system, it is possible advantageously to provide a Fresnel lens arranged at the level of the hub of the blades, so as to receive all or part of the radiation collected by the concentration system, and at least one mirror arranged at the level of a blade, so as to receive all or part of the radiation from the lens to direct it onto the faces of the blades with less emissivity.

To facilitate the stability of the rotation of the platter, the hub and the blades are advantageously arranged so that their center of gravity is at a vertical height below the point or plane of connection with the converter support or the rotary shaft.

Preferably, the thickness of the blades being between 100 nm to 100 μm.

According to another advantageous embodiment, at least part of the blades comprises several through holes, arranged approximately parallel to each other in the direction of the thickness of the blade. According to this mode and a first variant embodiment, the part of the blades is a porous material comprising at least certain emerging porosities.

The porous material can be a ceramic, preferably chosen from alumina, mullite, tungsten carbide or a combination thereof.

According to a second variant, the part of the blades being a polymeric film with open perforations.

The polymer of the film can be chosen from polyethylene (PE), polystyrene (PS), polymethyl methacrylate (PMMA) or a combination thereof.

According to a third variant, the part of the blades is a very ductile sheet of metal comprising at least some emerging perforations.

The highly ductile sheet metal can be chosen from gold or silver.

According to an advantageous embodiment, at least part of the blades is (are) coated with at least one catalytic coating suitable for implementing an endo or exothermic reaction.

Preferably, the surfaces of lower emissivity are coated with at least one catalytic coating suitable for implementing an endothermic reaction while the surfaces of higher emissivity being coated with at least one catalytic coating suitable for implementing an exothermic reaction .

These endo and exothermic reactions make it possible to maintain or even amplify the temperature difference between the dark and light faces of the blades due to the reaction heat released or absorbed.

The catalytic coating can be selected from chloride salts, hydrides or a combination thereof. at least part of the blades having a free end, the profile of which is tapered in the direction of the containment envelope.

According to another advantageous embodiment, the converter comprises a system for regulating the temperature of the containment envelope.

An alternative embodiment of the regulation system may consist of a means for measuring the temperature of the blades without contact, preferably a laser pyrometer and a means for heating at least the internal wall of the containment envelope, the operation of which is controlled to the measurements of the non-contact measuring means of the temperature of the blades. The management of games in motion, in particular the E game can be difficult to achieve easily. In this case, the temperature regulation system will make it possible to ensure a wall temperature close to the value of the average temperature of the blades in order to make it possible to minimize the shearing force induced by the thermal gradient at the tip of the blade.

To do this, the rotational torque generated can be monitored by a sensor and can communicate with the temperature regulation system of the wall of the confinement toroid to adapt the temperature of the latter as needed.

Another subject of the invention is the use of a converter as described previously for converting the energy coming from a light source and/or from a thermal source into electricity.

The thermal source can be a fatal heat source such as an incinerator hearth, a cement plant, a foundry bath, etc.

Other advantages and characteristics will emerge better on reading the detailed description, given by way of illustration and not limitation, with reference to the following figures.

Brief description of the drawings

[Fig 1] Figure 1 is a schematic side view of a Crookes radiometer.

[Fig 2] Figure 2 is a top view of Figure 1.

[Fig 3] Figure 3 is a schematic perspective view of an example of a converter of radiative energy into electrical energy according to the invention.

[Fig 4] Figure 4 is a detail view of Figure 3 showing the very small and constant space between a blade and the torus of the containment envelope of the converter according to the invention. [Fig 5] Figure 5 is a view of a square blade section according to the invention.

[Fig 6] Figure 6 is a view of a blade diamond section according to the invention.

[Fig 7] Figure 7 is a side view of a blade variant with a tapered profile at its end

[Fig 8] Figure 8 is a schematic view from above showing the increase in the linear velocity in the middle of the blade for the same radiometric force applied to blades at different distances from the point of rotation.

[Fig 9] Figure 9 is. a schematic view from above illustrating the influence of an extra length obtained by an extension arm on the linear speed of rotation of a permanent magnet fixed thereto [Fig 10] Figure 10 is a schematic perspective view of an embodiment of the converter according to the invention showing the electromagnetic conversion part with permanent magnets and induction coils.

[Fig 11] figure 11 illustrates in the form of a curve the evolution of the value of the magnetic field according to the air gap, that is to say the distance between the face of a permanent magnet and a coil turn.

[Fig 12] Figure 12 is a detail view showing an alternative embodiment of a point connection between a fixed converter support and the hub to which part of the plate blades is fixed.

[Fig 13] Figure 13 is a detail view showing another alternative embodiment of a point connection between a fixed converter support and the hub to which part of the plate blades is fixed.

[Fig 14] Figure 14 is a side view showing a variant of connection by magnetic bearing between a fixed converter support and the hub to which part of the blades of the platter is fixed.

[Fig 15] Figure 15 illustrates a perforated blade variant according to the invention.

[Fig 16A] Figure 16A illustrates a first step in making another variant of perforated blade according to the invention.

[FIG 16B] FIG. 16B illustrates a second stage of production of this other variant of perforated blade according to the invention.

[FIG 16C] FIG. 16C illustrates a first stage of production of this other variant of perforated blade according to the invention.

[Fig 17] Figure 17 illustrates a variant with catalytic coating for endothermic and exothermic reactions within a blade according to the invention.

[FIG 18] FIG. 18 illustrates in the form of a curve the evolution of the speed of rotation as a function of the pressure prevailing within a containment envelope in accordance with the invention.

[Fig 19] figure 19 illustrates in the form of a curve the evolution of the mean free path as a function of the pressure, the temperature and the nature of the gas considered within a containment envelope in accordance with the invention . [FIG 20] FIG. 20 illustrates in the form of a curve the temperature of the faces of a blade according to the invention exposed (dark face) and not exposed (dark face) to a constant heat flux, the faces being thermally insulated.

[FIG 21] FIG. 21 illustrates in the form of a curve the temperature of the exposed face of a blade according to the invention and the evolution of the incident heat flow.

[FIG 22] FIG. 22 illustrates in the form of a curve the evolution of the resultant force per unit of perimeter developed and per degree of temperature gradient applied to the right of the blades according to the invention.

[Fig 23] Figure 23 illustrates an integrated containment vessel wall temperature control system according to the invention.

[Fig 24] Figure 24 is a schematic top view of a converter according to the invention provided with a radiative flux concentration system.

[Fig 25] Figure 25 is a side view of Figure 24.

detailed description

Throughout this application, the terms "below", "above", "lower" and "upper" are to be understood by reference to the horizontal arrangement of the blade supports of the converter according to the invention and the vertical blades.

The same element according to the state of the art and according to the invention is designated by the same numerical reference.

Figures 1 and 2 relating to a Crookes radiometer have already been described in the preamble. They are therefore not commented on below.

An example of radiative energy converter 10 according to the invention is illustrated in FIG.

It comprises a containment envelope 2 with controlled internal pressure, in the form of a torus 20 in its peripheral part and two parallel discs 21, 22 in its central part. The two discs 21, 22 define with the inside of the torus the closed volume of the containment envelope.

A converter support 3 extends along the axis of symmetry of the envelope. The support 3 is fixed in the example shown in Figure 3, a hub 4 rotatably mounted around the support. At least one of the two discs 21, 22 can be crossed with sealing by the support 3. The converter 10 comprises a plurality of blades 5 each fixed to the hub 4 by a blade support 6.

The blades 5 are distributed angularly around the hub 4 while being arranged inside the torus 20 of the confinement envelope, the main faces of the blades being orthogonal to the horizontal plane of rotation.

The blade supports 6 are arranged between the two discs 21, 22 of the containment envelope.

For each blade 5, one of the main faces 50 comprises an emissivity surface higher than the other of the main faces 51.

According to the invention, as illustrated in FIGS. 1 and 2, the section of the blades 5 is similar to that of the torus 20 with a play ε between each blade and the internal wall of the torus which is substantially constant and very small.

In the example illustrated in FIGS. 1 and 2, the blades 5 and torus 20 have a circular section but any section can be considered. For example, it can be a square section (Figure 5) or a diamond section (Figure 6).

The clearance E and the characteristic length L of each blade are determined so that the ratio E/L is between 10 ^-6 and 10 ^-2 .

Specific tapered profiles on the periphery of the blades 5 can be made to minimize both the temperature gradient and the surface on which the braking force is applied. An example of tapered profiles is shown in figure 7.

The support 6 of the blades is of reduced length because for a given force applied to the blades, the speed of rotation (in rad/s) will be all the greater as the distance from the axis of rotation will be small.

Nevertheless, a blade 5 further from the center of rotation induces a greater linear speed in the end in the middle or at the tip of the blade, this latter speed changing in order of magnitude like the square root of the ratio of length of the blade to large radius d shaft (R2) and that of the small radius blade (R1), as shown in figure 8.

This can be translated into the following equation:

[Eq 4]

where V2 is the linear speed of the blade with large radius R2, and V1 that with small radius R1. To ensure the conversion of the kinetic energy of rotation of the blades 5 into electrical energy, it is desired to generate an electric current by rapid displacement of permanent magnets 7 secured to the blades 5 in the close vicinity of induction coils 8 (turns) .

It is not relevant to have supports 6 that are too long because this would also impact the ratio of the volume of the torus 20 of confinement to the surface of the blades 5.

Consequently, in order to remain within limited values of the lengths of blade supports 6 while increasing the drive speed of the permanent magnets 7, a variant consists in providing extension arms outside the blades. Such extension arms make it possible, for a given linear speed of rotation of the blades (V1), to have an increased linear speed of rotation of the permanent magnets 7 (Vx), according to the following equation: [Equ 5]

with :

R: length equivalent to the sum of the radius of the arm of the blade and its own length Δx: excess length induced by the extension arm 60.

Such a configuration with an extension arm 60 is shown schematically in Figure 9.

Figure 10 illustrates a configuration of the electromagnetic force generation system from the kinetic force of rotation of the blades 5.

The system comprises a plurality of permanent magnets 7 individually fixed at the end of one of the extension arms 60 of the blades 5.

In the example illustrated, each extension arm 60 consists of two arm portions 600, 601 at 90° to each other, one portion 600 of which is integral with a blade which extends vertically and the other portion 601 which extends horizontally at the end of which is fixed a permanent magnet 7.

During the rotation of the blades 5, each permanent magnet 7 comes sequentially into a space between two fixed induction coils 8.

Thus, during the rotation of the blades, each of the permanent magnets 7 which moves, generates an electromotive force in the turns 80 of the coils 8 and therefore induces an electric current therein.

The optimum air gap Δ, that is to say the spacing between the permanent magnets 7 and the turns 80 of the coils 8 is less than 1 mm. The conversion of the momentum of the blades 5 into electromotive force (em) induced due to the variation of the magnetic field through the n turns 80 is according to the following formula:

[Eq 6]

with

Φ: magnetic field generated by magnets 7, n: total number of turns 80.

The expected electromotive force expressed as a function of the rotation speed and the distance from the axis of rotation of the magnets can be expressed in view of the following elements:

Φ = BS, i.e.:

[Eq 7]

However, the magnetic field B is independent of time, hence dB/dt = 0 Knowing also that the surface seen by the magnetic field is: S = Vx.Δt.l with:

Vx: linear velocity of the permanent magnet,

Δt: the time taken by the permanent magnet between two coils 8, l: width of the permanent magnet.

This gives the following equation.

[Eq 8]

Furthermore, the magnetic field B is a function of the air gap distance z between the surface of the permanent magnet 7 and the surface of the turns 80 according to the following equation: [Equ 9]

with

Br: remanent field, independent of the geometry of the magnet, z: distance to the surface of the pole on the axis of symmetry,

L: length of the magnet,

W: magnet width

D: thickness of the magnet.

The evolution of the magnetic field B as a function of the height/distance of the air gap between a permanent magnet and a turn 80 is shown in figure 11, it being specified that the remanent field Br is equal to 1.5 T.

As an indication, considering:

- an air gap dimension between permanent magnet 7 and turns 80 equal to 0.5 mm,

- a field B of the order of 0.4 T

- a width of the turn 1, equal to 20mm

- a speed at the end of the extension arm Vx =θ.R with θ = 40 rad/s and R = 0.5 m then, dΦ > /dt = B.1.Vx is equal to 0.25.

This corresponds for a number of 100 turns, to an electromotive force eM of the order of 25 Volts.

In the example illustrated, there are two stages of turns 80 between which each permanent magnet can move.

It is therefore possible to obtain an electromotive force eM of the order of 50 V.

To be compatible with an electrical network of frequency (f) 50 Hz, the blades 6 can rotate at a frequency fa of 15 Hz, because a=F/np with np, number of pairs equal to 4 in the example, i.e. eight magnets permanent 7.

To have the greatest possible electromotive force for given magnet characteristics, it is important to be able to minimize the distance between the magnets 7 and the turns 8, in order to optimize the magnetic field B. The turns 80 are therefore preferably incorporated/ integrated in a base/support (So) of the converter 10 as shown in FIG. 10. An adjustment system with several degrees of freedom can be provided to control the gap distance between permanent magnets 7 and turns 80.

The mechanical power developed is a function of the force developed for a given speed of rotation according to the following equation:

[Eq 10]

PM=F.Vx in which: F is the net driving force developed by the converter 10 whose blades 5 rotate at the speed Vx.

With the numerical values of the aforementioned example, Vx=10 m/s.

By considering that F can be approximated to a value of the order of 10 ⁻⁸ N/mm/°C, one obtains for the values of the components of the converter 10, characteristics quantified according to table 1 below.

[Table 1]

Figures 12 to 14 show different embodiments to minimize friction between fixed support 3 and hub 4/supports 6 of the blades, in order to further optimize the kinetic energy of rotation of the blades.

In FIG. 12, the hub 4 can be in the form of a magnetizable sphere which comes into contact with a sphere 31 at the end of the support 3, itself magnetized by a permanent magnet 32 within the support 3. In the figure 13, a pivot needle 33 at the end of support 3 is in point contact with hub 4. In FIG. 14, a system 11 of magnetic bearings, one part of which is fixed to the blade plate and the other is integral with the support 3, makes it possible to guarantee the rotation of the plate horizontally without mechanical contact.

To facilitate the stability of the rotation of the blades 5 with their support 5, provision is advantageously made for the connection between the pivot support 3 and the blades 6 to guarantee the latter a center of gravity at a level lower than that of the end of the pivot bracket 3.

The blades 5 are advantageously both very long, poorly thermally conductive, perforated with perforations of very small diameters while being rigid.

The porosity and at the same time the low transverse thermal conductivity can be ensured by a porous ceramic. The porosity of the ceramic can advantageously be chosen so that the plate cut or produced according to a given thickness, of the order of a micron to a few microns, can develop without particular machining a through porosity with an average diameter of the order of the free path. gas medium. To do this, it is possible to add ceramic powders with a porogen, then after uniaxial compaction, debinding/sintering the raw material obtained in order to achieve adequate through-porosity and a micrometric diameter.

An example of a blade 5 produced by this process is shown in FIG. 15: the thickness E of the blade can be very small, typically a few microns with through perforations 500 typically with a diameter of the order of a micron.

Another method for producing perforated blades may consist in using a perforating laser, for example a Femto-second laser, which potentially periodically impacts a blade surface.

Another process that can be envisaged is a nanofabrication process, that known by the acronym LF-PAM (“Laser-Fabricated Porous Alumina Membranes”), as explained in the publication [6]. The main steps of this process are shown in FIGS. 16A to 16C: a substrate 5, typically made of alumina, initially coated with a monolayer of spherical nanoparticles Bi is placed on a support S. A laser impacts the monolayer to create nano perforations / micrometric 500 in the substrate 5, which once detached from the support S, reveals emerging perforations 500.

The rigidity of the blades 5 can be ensured by the very structure of the constituent material, which is non-ductile. It is also possible to start from flexible materials, such as a polymer film, for example made of PTFE, which is stiffened by a support and/or a given radial tension and/or by crosslinking. Of course, the intensity of this tension should not cause it to break

It is also possible to consider adding a rigid frame which also makes it possible to better control the clearance between the wall of the closed volume of the containment envelope 2 and the blades 5. The control of this clearance makes it possible to limit the braking forces induced by the temperature gradient, i.e. the tangential force.

The constituent material of the blades 5 can be a catalyst for exothermic reaction(s) at the level of the dark faces 51 and endothermic(s) at the level of the light faces 50, in order to maintain or even amplify the temperature difference between these faces due to the heat of reactions released or absorbed.

Figure 17 illustrates these reactions and the thermal and thermodynamic cycling exploited at the level of the faces 50, 51 of the blades respectively in constituent material, reactive A, C. By applying a quantity of heat to A, it is converted into B which is still solid which generates also a gas. The face 50 where the endothermic reaction occurs being colder than the face 51 where the exothermic reaction occurs and knowing that the regime is that of thermal sliding, a flow of gaseous material will be established from the cold face 50 towards the face hot 51 and the gas produced at the cold face will be available to react with the constituent material C of the face 51 where the exothermic reaction occurs. The gas will then be absorbed therein to give the reagent D and generate a quantity of heat which will reinforce the temperature gradient between the two faces 50, 51.

The finished volume of the containment envelope 2 has, during the operation of the converter, a pressure regulated at a target setpoint value. It is possible to use for this a pumping system capable of reaching secondary or primary vacuums or working at atmospheric pressure or even a few bars if necessary. The system can comprise two distinct types of pump, for example a turbo-molecular pump and a vane pump, depending on the level of pressure to be reached. It is also possible to provide a gas supply system connected to the interior of the containment envelope. The gas and the pressure are advantageously chosen so as to adjust the value of the mean free path of this gas.

Moreover, there is an optimum of the overall resultant force as a function of the pressure, as shown in figure 18, taken from the publication [7]. Indeed, in the absence of molecules of gas, the blades are not subjected to molecular impacts allowing the rotation of the blades and vice versa, in the event of too much pressure, thermal transpiration is reduced and the friction forces (drag) greater.

This figure 18 shows a classic evolution of the speed of rotation of the blades of a radiometer according to the state of the art as a function of the pressure prevailing within the envelope surrounding it. In the same way as the converter according to the present invention, this figure 14 illustrates that there is a range of pressures for which the speed of rotation of the radiometer is optimal in full consistency with what can be shown theoretically.

A system for adjusting the pressure of the volume of the confinement envelope makes it possible to control the value of the mean free path of the molecules of gas contained within this volume. Figure 19 shows this evolution of the mean free path as a function of the pressure but also of the temperature and the nature of the gas.

It is thus possible to show that the diameter of the perforations of the blades 5 can vary from a hundred nanometers to a few microns for pressures varying respectively from bar to a few hundred Pa.

The increase in temperature is also favorable to the increase in the read mean path, which can also constitute an adjustment parameter beyond the pressure.

As an indication, perforations 500 of the order of 130 nm can be targeted for an operating pressure of the casing of 2 to 1 bar.

The temperature gradient on the two opposite faces 50, 51 of the blades, of distinct emissivity, induces the driving force.

In order to estimate the level of this thermal gradient, we consider here the blade of thickness e, of thermal conductivity λc, and subjected to a thermal flow denoted Φ th.

A heat balance at the level of the blade makes it possible to establish that the rise in temperature of an elementary volume of the blade subjected to a flow on one of these faces is due to the net heat contribution resulting from the incident heat flow. and losses induced by convection and radiation.

Assuming that the flux re-emitted by the blade is negligible compared to the convection and the incident heat flux (black body hypothesis) we can pose the following equation: [Equ 11]

with :

S: exchange surface developed by a perforated blade,

Tf: temperature of the cold face 50 of the blade.

A blade 5 can be considered as isothermal along the axis of its thickness.

On the other hand, the temperature of the plate is strongly dependent on time in the case where the incident heat flux Φ th begins to be applied and/or if this flux is variable as a function of time.

In the case where the flux Φ th is constant, the following expression of the temperature variation after a time t of exposure of the space to the flux Φ th can be drawn from the heat balance previously posed:

[Eq 12]

As an indication, the following values of the parameters can be considered, which corresponds to a face of the blade with PTFE as constituent material: e = 1 μm Φ th = 20 W/m ² h = 0.3 W/m ² /°C ρ = 2.16 g/cm ³

Cp = 0.25W/m/°C.

With these values, we obtain a profile shown for the establishment of the temperature of the hot face 51 of the hot blade as a function of time for a temperature of the cold blade of 50° C., illustrated in figure 20.

In the case where the heat flux imposed is unsteady and periodic because the dark faces 51 are illuminated intermittently, the heat balance in the same approach as that seen previously makes it possible to arrive at the following expression for the temperature Tc of the hot face 50 of the exposed blade:

[Eq 13]

with : Q = Φ th/(ρ.Cp.e) w: 2.π .ff: heat flux frequency (=1/Tth) φ: phase shift defined as follows: tanφ = (h/(ρCpe))/w sinφ = (h/(pCpe))/[(h/(ρCpe)) ² +w ² )] ^1/2 cosφ = w/[(h/(pCpe)) ² +w ² )] ^1/2

FIG. 21 shows the evolution of the temperature of the hot face 51 Tc of a blade according to the invention, as well as the evolution of the incident heat flux.

In order to estimate the force generated in the scenario presented above, it is necessary to recall the expression of the forces applied to the blades.

For the frictional force applied tangentially (FT) to the blade, the following expression, used in publication [1] can be used:

[Eq 14]

with: α _E : energy accommodation coefficient, p: perimeter developed by the blade, σ: diameter of the gas molecules present in the volume of the containment envelope

The radiometric force FN can be expressed as follows:

[Eq 15]

We then deduce the global component that can be expected on a blade 5: [Equ 16]

k: Boltzmann constant.

F is independent of the gas density and therefore of the pressure, as long as e is less than or equal to λ.

However, λ is a function of the pressure, the thickness of the blade should be reduced when the pressure increases.

In the case where the containment envelope 2 is filled with nitrogen, for a pressure of 100 Pa and at a temperature of 300 K, and for a blade thickness equivalent to the mean free path (i.e. here 93 μ), the force by perimeter unit of the blade is of the order of 2.10 ^-8 N/mm. Figure 22 gives the evolution of the net force per unit of perimeter developed and per degree of temperature gradient applied to the right of the blades.

The invention is not limited to the examples which have just been described; it is in particular possible to combine together characteristics of the examples illustrated within variants not illustrated.

Other variants and improvements can be envisaged without departing from the scope of the invention.

List of cited references

[1]: M. Scandurra et al., Physical Review E 75 026308 (2007).

[2]: A. Ketsdever et al., “Radiometric phenomena: from the 19th to the 21st Century”, vacuum 86 (2012) 1644-1662). [3]: S.F. Gimelsheim et al., “Analysis and Applications of Radiometric Forces in Rarefied

Gas Flows”, 27th International Symposium on Rarefied Gas Dynamics, Monterey, CA, 10-15 July 2010.

[4]: G. Hettner, “Zeitschrift fur Physik”, 30 258-267 (1924).

[5]: A.Curnier, “Mechanics of deformable solids” Polytechnic Press and Universitaires romands, ISBN 2-88074-544-6, 2005 (page 407).

[6]: A. Pereira et al., “Laser-Fabricated porous alumina membranes (LF-PAM) for the preparation of metal nanodot arrays,” Small (2008).

[7]: http://www.u3p.net/projets/contrib/TIPE_Vivien_Parmentier.pdf

Claims

26 Claims

1. Converter (10) of radiative energy into electrical energy, comprising:

- a containment envelope (2) with controlled internal pressure, the envelope being of axisymmetric shape around a vertical axis of symmetry, the envelope comprising a torus (20) and of which at least a part is transparent vis-à-vis view of the radiative source to be enhanced;

- a converter support (3) extending along the axis of symmetry of the casing;

- a hub (4) mounted at the free end of the support, defining a horizontal plane of rotation;

- a plurality of blades (5) each fixed to the hub by a blade support (6), the blades being distributed angularly around the hub while being arranged inside the torus of the confinement envelope, the main faces of the blades being orthogonal to the horizontal plane of rotation, one of the main faces of at least part of the blades comprising an emissivity surface distinct from the other of the main faces, the section of the blades being homothetic to that of the torus of the envelope of confinement with a clearance ε between each blade and the internal wall of the substantially constant torus.

2. Converter according to claim 1, the blades being equidistributed angularly around the hub.

3. Converter according to claim 1 or 2, the clearance ε and the characteristic length L of each blade being determined so that 10 ^-6 <ε /L <10 ^-2 .

4. Converter according to one of the preceding claims, comprising a system (200) for regulating the temperature of the containment envelope.

5. Converter according to claim 4, the control system comprising a non-contact measuring means (201) of the temperature of the blades, preferably a laser pyrometer and a heating means (204) at least of the internal wall of the containment envelope whose operation is controlled by the measurements of the means of non-contact measurement of the temperature of the blades.

6. Converter according to one of the preceding claims, the Knudsen number, characterizing the flow rate of the fluid inside the casing on the blades, being between 0.1 and 0.5.

7. Converter according to one of the preceding claims, the blades having a tapered profile at their periphery.

8. Converter according to one of the preceding claims, further comprising: - A plurality of permanent magnets individually secured to one of the blades;

- at least one induction coil fixed and centered on the axis of symmetry of the casing, the coil(s) being arranged facing the permanent magnets so that the rotation of the blades generated by a radiative energy source generates an electromotive force in the coil(s).

9. Converter according to one of the preceding claims, the converter fixed support being in point connection with the hub.

10. Converter according to one of claims 1 to 9, the fixed converter support and the hub each comprising a magnetic sphere, the two magnetic spheres being in mutual contact.

11. Converter according to one of claims 1 to 9, the hub and the blades being supported by at least one magnetic bearing, part of which is fixed to the fixed converter support and the other to the blade supports.

12. Converter according to one of claims 1 to 8, the converter support being a rotatably mounted shaft around which the hub is fixed; the converter further comprising:

13. Converter according to claim 8 to 12, the space (Δ) between the permanent magnets and an induction coil being less than 1 mm.

14. Converter according to one of the preceding claims, at least a portion of the blades each being extended radially by an extension arm which extends radially outside the blades.

15. Converter according to claim 14 in combination with claim 8 or 12, the permanent magnets being fixed individually on one of the extension arms.

16. Converter according to claim 15, each extension arm consisting of two arm portions at 90° to each other, one portion of which is integral with a blade which extends vertically and the other portion which is extends horizontally at the end of which is fixed a permanent magnet.

17. Converter according to claim 15 or 16, comprising a plurality of pairs of induction coils fixed and centered on the axis of symmetry of the envelope, the coils of each pair being arranged two-by-two parallel, so that the rotation of the blades moves the permanent magnets between the coils of each pair.

18. Converter according to one of the preceding claims, comprising a radiative flux concentration system.

19. Converter according to claim 18, comprising a Fresnel lens arranged at the level of the blade hub, so as to receive all or part of the radiation collected by the concentration system, and at least one mirror arranged at the level of a blade, so as to receive all or part of the radiation from the lens in order to direct it onto the faces of the blades with less emissivity.

20. Converter according to one of the preceding claims, the hub and the blades being arranged so that their center of gravity is at a vertical elevation below the point or plane of connection with the converter support.

21. Converter according to one of the preceding claims, the thickness of the blades being between lOOnm to 100 μm.

22. Converter according to one of the preceding claims, at least part of the blades comprising several through holes, arranged approximately parallel to each other in the direction of the thickness of the blade.

23. Converter according to claim 22, the part of the blades being a porous material comprising at least some emerging porosities.

24. Converter according to claim 23, the porous material being a ceramic, preferably chosen from alumina, mullite, tungsten carbide or a combination thereof.

25. Converter according to claim 24, the part of the blades being a polymeric film with open perforations.

26. Converter according to claim 25, the polymer of the film being chosen from polyethylene (PE), polystyrene (PS), polymethyl methacrylate (PMMA) or a combination thereof.

27. Converter according to claim 22, the portion of the blades being a sheet of highly ductile metal comprising at least some open perforations.

28. Converter according to claim 27, the highly ductile metal of the sheet being chosen from gold or silver.

29. Converter according to one of the preceding claims, at least a portion of the blades being coated with at least one catalytic coating suitable for implementing an endo or exothermic reaction.

30. Converter according to claim 29, the surfaces of lower emissivity being coated with at least one catalytic coating suitable for implementing an endothermic reaction while the surfaces of higher emissivity being coated with at least one catalytic coating suitable for carry out an exothermic reaction.

31. Converter according to claim 29 or 30, the catalytic coating being chosen from chloride salts, hydrides or a combination thereof.

32. Use of a converter according to one of the preceding claims for converting the energy originating from a light source and/or from a heat source into electricity.

33. Use according to claim 32, the heat source being a waste heat source such as an incinerator hearth, a foundry bath, etc.