WO1981002624A1

WO1981002624A1 - Catoptric concentrator collector of radiation beams of small divergence,particularly solar radiation or beams obtained by means of lasers

Info

Publication number: WO1981002624A1
Application number: PCT/FR1981/000028
Authority: WO
Inventors: P Malifaud
Original assignee: Opthra Soc Civ; P Malifaud
Priority date: 1980-03-05
Filing date: 1981-03-04
Publication date: 1981-09-17
Also published as: FR2477686A1; MX149472A; EP0047751A1

Abstract

Concentrator for example for solar radiation. The concentrator is determined by an assembly of lineic reflecting elements (8), each of them acting in a single plane and independently of each other. The curvature of the element (8) is determined so that the beam (1) received at the end (2) is reflected directly towards the end (6) of section (4) of the pupil, that the beam (10) received at the end (9) is reflected towards the end (7) and that the points of the element (8) intermediate between (2) and (9) reflect the radiation towards the points of section (4) which are between (6) and (7).

Description

Catoptric concentrator sensor of beams of radiations of low divergence, in particular of solar radiation or of beams obtained by means of lasers.

The beams of electromagnetic radiation are said to be "parallel" when the rays which compose them have a slight divergence, of the order of a few sexagesimal degrees and, in the strict sense, less than 1 °. Solar radiation, for example, has a divergence on the order of 30 '; the beams obtained from lasers or masers can exhibit a much less divergence. A beam or a combination of such beams can be picked up in a collecting pupil having a certain cross section, then concentrated in a receiving pupil having a smaller cross section. The concentrating sensors may be dioptric, constituted for example by converging lenses, or else be catoptric, constituted by mirrors. A classic concentrating mirror for these so-called "parallel" radiations is the parabolic mirror which provides its focal point with a very punctual concentrated spot whose distribution is very inconsistent around the brightest central point. When, as is the general case, the pupil of the receiver is not punctual and one wishes to provide it with a density of radiation as homogeneous as possible, the parabolic mirror is not suitable. One can, of course, exfoca read the receiving pupil to deconcentrate the image spot, but one then obtains an even more inhomogeneous distribution in a brilliant ring with a clearly darker zone in the center. Another solution is the frusto-conical mirror whose inventor of the present invention has proposed optimizations in previous patents. The principle of a conical mirror acting as such is to subject the captured rays to several reflections whose average effects are integrated at the level of the receiving pupil. As these are radiations of low divergence, the solution of a simple frustoconical mirror is impracticable with the optimizations described in these prior patents. In the case for example, of the solar radiation whose divergence there is of the order of 30 ', that is to say a 1/100 radian, the angle at the top of the conical mirror must be chosen smaller, for example of value half as it has been recommended, that is 1/200 radian. If it is proposed to capture the solar radiation in a collecting section of 10 m2 (corresponding to a power of 10 Kw), that is to say a circle of approximately 3.50 m in diameter, for a pupil received with a diameter of around, for example, 0.50m (surface concentration around 50 times), the length of the frusto-conical mirror would be around (3.5-0.5) cotg 1/200 radian , or 700 meters. We are then forced in such cases to use an additional optical system, pre-concentrator, for example a parabolic mirror, which greatly reduces the length of the cone, which completes only the pre-concentration. This solution is valid for large concentrations (from several thousand suns up to the limit of 40,000 suns). But it has more disadvantages than advantages when looking for lower concentrations of the order of, for example, one or two thousand suns, or medium (hundreds of suns), or even low (tens of suns ). Not only is it then too complicated and too expensive, but the optimization relationships no longer apply because the number of reflections implemented becomes too small. It is appropriate in such cases to seek a solution of a different principle any excljant pre-concentrators and does not involve the combined effect of multiple flexions re ^¬ characterizing the conical mirrors Such a solution is provided by the present invention.

Furthermore, there is known U.S. Patent 2,791,214 which describes a reflector structure comprising a plurality of concentric annular elements, with rectilinear generator (column 4, lines 56 to 59).

They are arranged relatively to each other (column 4 lines 59-60) and have, in themselves, no defined characteristics. The relationship concerns at least three elements since the distances (column 4 line 6) which separate them must increase from the optical axis.

In addition, the generators of the reflecting elements are oriented so that they all converge towards a common point located on the optical axis. In other words, each reflecting element is formed by a frustoconical crown. The virtual cones are concentric and have a common vertex. They are even more spaced that their angle at the top is large.

The frustoconical crowns are provided at a constant distance from the top of the cones, that is to say according to a spherical cap.

None of these indications teaches the principle of the present invention which applies to the constitution of a possibly unique reflecting element. Even supposing that one confines oneself to the embodiment of the invention according to which there are several associated reflecting elements, their generatrices cannot be convergent since they are not frustoconical crowns belonging to virtual cones of common summit (cf. in particular page 18 lines 22 to 25 of the request).

In addition, the present invention describes reflective elements which can be curved, superimposed, juxtaposed, in the form of a gutter, etc.

Furthermore, it is clear in FIG. 1 and even more in FIG. 2 of US Pat. No. 2,791,214 that the ray reflected by one end of an element does not necessarily reach the end of the pupil, which is incompatible with the invention and provides a less con The document "APPLIED OPTICS" vol. 17 N ° 7 describes a concentrator constituted by the reflecting surface of a volume whose generator is a parabola. The foci of these parabolas (of infinite number) are located on the outer circumference of the pupil (of diameter P2 - P'2). The improvement described consists in adding a lens.

The arrangement of the focal points is completely different from that which is the subject of the present inventi on without lens since the latter provides that the focal point of the parabola, an arc of which forms part of the generator of a reflecting element, is situated in a position "quite distant" from the pupil.

U.S. Patent 4,162,824 shows that concentrators in the form of gutters or troughs are already known. However, this arrangement does not take up the fundamental characteristic of the invention.

U.S. Patent 2,415,211 describes an image projection system of which all the elements are immersed (column 6 lines 26 to 30). In any case, it is a system concerning divergent rays.

On the contrary, the invention applies to parallel and or substantially similar rays and provides that immersion (well known in itself) is partial in order to use a refractive effect in order to obtain an increase in concentration and judiciously achieve an improved implementation of the basis of the invention.

Compared to the state of the art thus established, the invention is characterized in that: a - A concentrator sensor can comprise only one reflective element which is defined by its linear profile.

This reflecting element may not be continuous and, in particular, may not be a truncated cone. b - The entire pupil receives, after a single reflection, all of the reflected radiation.

c - The reflected radiation is distributed with homogeneity which means not exclusively that at any point of the pupil finds an illumination of same value, since a variable illumination value (or optical density) can also be provided, in particular a decrease from the center towards the periphery of the pupil. The homogeneous distribution means that in no area of the pupil are there very different lighting values. They can be equal (there are, al ers, perfect homogeneity) or similar, d - Other characteristics, not referred to by the cited prior art, allow concentrators of various configurations to be optimally produced, depending on the applications envisaged. The invention will be better understood from the detailed description below made with reference to the accompanying drawing. Of course, the description and the drawing are only given by way of example and are not limiting.

Figure 1 schematically illustrates the most general features of the invention.

FIG. 2 shows a reflective profile according to the invention in the form of an osculating curve of a family of parabolas.

Figure 3 shows an arc-shaped profile of para boledont the axis and the focus are offset from the receiving pupil. Figure 4 shows a profile in the form of straight lines arranged end to end.

FIG. 5 shows, on an example similar to that of FIG. 4, an improved profile where account is taken of the divergence, although small, of the received beam. FIGS. 6, 7 and 8 illustrate, in the case where all of the reflective elements of the sensor constitute a regular pyramid, the determination according to the invention of the number of faces.

Figures 9, 10 show the sections of a gutter-shaped sensor in the case of a longiform receiver. Figure 11 shows a plan view. Figure 12 i 11 ustre the determination according to the invention of the axial height of the concentrator sensor under given conditions.

FIG. 13 shows a reflective profile according to the invention making it possible to benefit from optical immersion.

According to the invention, the concentrating sensor is not determined as a reflecting surface (surrounding a volume) and acting optically as such, but as a set of linear reflecting elements each acting in a single plane independently of each other .

By "linear" is meant here (preferably "linear" which evokes, more restrictively, rather a straight line) which is relative to. a line, to any curve with one dimension, as one understands by surface what relates to a two-dimensional surface and by volume what which relates to a three-dimensional volume.

FIG. 1 most generally represents profiles of concentrator sensors according to the invention. This involves collecting parallel or weakly diverging radiation in a collecting pupil and concentrating it in a smaller receiving pupil.

The average direction 1 of an elementary beam of radiation picked up at a point 2 of the periphery of a collecting pupil has been shown. The receiving pupil 4 has a central point 5. If it is a circle, this point is the center of the circle; otherwise, it is an average central point: The plane of the figure, in which the profile of the sensor is determined is the plane containing the average direction 1 and passing through the central point 5; plane which cuts the receiving pupil along a straight line whose ends are points 6 and 7. In this plane, the profile of the sensor is formed, according to the in vention, of at least one linear re-f1 element such as 8 whose ends are points 2 and 9. The curvature of the reflecting element is determined in such a way that the radius 1 received at the end 2 is reflected directly towards one of the ends of the section of the receiving pupil, for example towards point 6, and that the ray 10 received at the end 9 is reflected directly towards the other end of the section of the receiving pupil, or, here, towards point 7. And also i, in such a way that the points of the reflecting element 8, intermediate between 2 and 9 reflect the radiation (picked up in parallel directions) towards the points of section 4 intermediate between 6 and 7, so that this section receives the reflected radiation over its entire length continuously. For this purpose, the normal 11 to the linear reflecting element, at point 2, is determined as being the bisector of the angle formed by the radius 1 and the straight line joining points 2 and 6, so that the angle of reflection r of the radius received in 6 is equal to the angle of incidence i of the radius picked up in 2. The tangent 12 at point 2 is, of course, the perpendicular to the normal 11. The normals and the tangents pertaining to each of the points of the linear reflecting element 8 are determined as a function of a continuous variation of the direction of the ray reflected towards points continuously traversing the section 4, according to any known analytical or graphic method; or digitally by programming from a computer. With this half method, the profile can be determined so as to obtain such a distribution as desired between the various points of the section of the receiving pupil. The position of the end 9 is thus itself determined when, according to the method used, the normal 13 is such that the reflected ray passes through the point 7. Specific examples will be described below.

The profile of the sensor, in this same plane, can consist of several linear reflecting elements thus defined. In Figure 1, we see, following the element 8, a second element 15 whose end 9 (normal 14) reflects the parallel radiation towards the point

6 (3 arrows) and the end 16 reflects it towards the point

7 (4 arrows). And so on, possibly.

In this first example (very schematic), the linear reflecting element, receiving the radiation 1 at its end 2 furthest from the receiving pupil 4, reflects it towards the end 6 of this section closest to it, and, receiving it at its other end 9 closest to said selection, reflects it towards the other end 7 of this section, the farthest from it. The distribution of the radiation reflected in the section of the receiving pupil can also be operated in the opposite direction, as can be seen on the right-hand side of FIG. 1. We now consider the mean direction 17 of an elementary beam of radiation captured at a point. 18 of the periphery of a collecting pupil 19. The figuration of the receiving pupil 4 is unchanged. The plane of the figure, now taken into consideration, contains the radius 17, passes through the central point 5 of the receiving pupil, and cuts it according to the line segment of ends 7 and 6. The curvature of the element linear reflecting 20 is now determined so that the radius 17 received at the end 18, of the collecting pupil, the most distant from the receiving pupil, reflects it towards the end 6, of this section, the most distant from this element reflective. The normal 21 is the bisector of the angle formed by the radius 17 and the straight line joining the points 18 and 6 - the line 22 at the point 18 being the perpendicular to this normal. The other end, 23, of the reflecting element 20 is determined (after implementing the same process for determining the intermediate points as described previously) the fact that the normal at this end is such that the ray 24 is picked up at this end (closest to the collecting pupil) is reflected towards point 7 (end of the section of the receiving pupil closest to the 'reflective element).

The linear reflecting element can, in this case, be a straight segment such as 25. It is obtained by extending the tangent 22 at point 18 to point 26 where the radius 27, parallel to the radius 17, is reflected towards the end 7 of section 4, in direction 26-7, parallel to that of the reflected ray 13-6. This particularly simple example of embodiment will be repeated later.

To return to the first type of profile of the kind shown diagrammatically on the left-hand side of FIG. 1, a particular example of embodiment is shown in FIG. 2. The end 28 of the linear reflecting element 29, the most distant end of the receiving pupil 4, is a point on the periphery of the collecting pupil of the sensor. The ray 29 picked up at point 28 is reflected towards the end 6 of the section of the receiving pupil and the normal to the reflective element at point 28 is determined accordingly as already said. The elementary reflective linear portion at point 28 is here coπsi derëe as belonging to a parabola having for axis the average axis 30 normal to the e ecting pupil and having for point point 6. The points of the reflecting element

29 are determined step by step considering that they each belong to a parabola whose axis remains the axis

30 and whose focus occupies step by step the points of section 4 by continuously traversing this section from the end 6 to the end 7. In other words, the linear reflecting element here is an oscillating latent curve of a family of parabolas infinitely close to each other, the respective foci of which occupy the points of section 4 by covering it continuously. Some of these points have been shown in the drawing, thus having the corresponding captured and reflected rays. The result, in the example shown, is obtained with a single osculating curve. By running section 4 several times continuously through the focal points of the parables, we can obtain the desired result with several osculating curves arranged end to end. cn then passing to the second type of profile of the kind shown diagrammatically on the right-hand side of FIG. 1, a particular example of embodiment is represented in FIG. the axis is distant from the mean axis 30 normal to the receiving pupil and is situated with respect to the arc 31 on the other side of the mean axis and parallel to it. The parabolic arc at two ends, the first at point 32, located on the periphery of the collector pupil, and the second which coincides with the end 7 of section 4 of the receiving pupil or which is located in the vicinity from this end 7. The focal point of the parabola is at a point 33 located on the extension of the straight line joining point 32 and the other end 6 of section 4, in a position far enough from this point 5 so that the the illumination in the central part 5 of the section 4 is substantially equal to the half-sum of the illuminations in the parts surrounding the extreme points 6 and 7 of the section of the receiving pupil. The distribution of the illuminations in this section depends on the position of the focal point in relation to point 6. If the focal point was located in point 6, the illumination would be entirely concentrated at this point and the other points of the section would not receive any of the rays reflected by the points of the parabola arc. As the focal point is moved away from point 6, the lighting in. this point decreases in favor of the other points of the section, the illumination at point 6 is however always greater than the illumination at point 7. The position determined preferably for the focal point is that where the illumination in the central part 5 of section 4 is substantially equal to the half-sum of the illuminations at point 6 and at point 7. In this way, the linear reflecting element 34, parabolic arc symmetrical of the arc 31, having a focal point 35 symmetrical of the focal point 33 with respect to the axis 30 of the receiving pupil, produces at point 7 an illumination equal to that which the arc 31 produces at point 6, and at point 6 an illumination equal to that which the arc 31 produces at point 7 and, on the other hand in the central part 5 of section 4, an illumination substantially equal to the half-sum of the illuminations at point 7 and at point 6. Thus, the effects of the parabolic arcs 31 and 34 being combined, the illuminations at the ends 6 and 7 and in the central part 5 are all equal, achieving a very homogeneous distribution. It should be noted here that these parabolic arcs do not belong to the same parabola but to two distinct parabolas. Their conjugation according to the invention makes it possible to obtain homogeneity while in known systems where one exfocalizes a parabolic mirror, one results in a very great homogeneity.

Figure 4 shows the particular example of a linear reflecting element in the form of a line segment. The description has already been started with reference to FIG. 1 The reflecting straight line 25 has been defined by its ends 13 and 26. The radius 17 picked up at point 18 assumed to be parallel to the mean axis 30 of the receiving pupil, The end 6 of section 4 is directly reflected from the end, and the radius 27 picked up at point 26 is directly reflected towards the end 7 of section 4. The characterization of the reflecting segment 25 can be specified. The angles of incidence and reflection at point 18 being equal on either side of the normal 21 (see fig. 1), their supplements designated by a in FIG. 4 are also so. Another angle is also equal to α, that made by the reflecting segment 25 with the extension of the picked-up ray 17: this angle is opposed by the vertex with one of the angles designated by α The ray 36, reflected from point 18 towards the point 6, therefore made with the extension of the radius 17, parallel to the axis 30, an angle designated by β equal to 2α If we denote by R the distance between the mean axis 30 and the end 18 to the reflecting segment, c 'is to say the distance between this point 18 and its projection 37 on the mean axis; by r half the linear section 4 of the receiving pupil; by h the distance on the mean axis 30 between the mean center 5 - of the receiving pupil and the point 37; we can determine the value of the anglβ _/ δ in the triangle formed by the reflected ray 36, the parallel to the axis 30 passing because point 6 and the segment designated by R extended until it meets at point 38 with this parallel. By noting that the distance between points 37 and 38 is equal to r, we have:. And, like, we can characterize the year

gle α that the reflecting segment 25 does with the direction of the mean axis by the relation;

Point 26 is characterized geometrically. It is the point of the straight line 25 such that the ray 39 reflected at this point, that is to say the parallel led by 26 to the ray 36, passes through the point 7.

By considering point 26 as in turn playing the role previously assigned to point 18, we can similarly characterize another reflecting segment 40, reflecting at its end 26 the radius 27 towards point 6 (in the direction indicated by three arrows) and reflecting at its end 41 the radius 42 towards the point 7. And so on, if desired.

These segments, arranged end to end, cannot join the end 7 of the section of the receiving pupil. A certain hiatus remains between this end and the last end of the reflecting segments. To avoid this hiatus, it is possible to have, following the last reflecting segment, a parabolic arc as defined opposite this in FIG. 3. For example, in FIG. 4, the parabolic arc 43.

In the plane of the figure, another profile, symmetrical to that which has just been described, is shown on the left.

Hitherto, the angle of divergence of the beam of radiation picked up at each point of the linear reflecting element has been neglected, a legitimate approximation in that it this is called "parallel" radiation. However, there may be cases where this angle of divergence, although small, is not negligible, as well as cases where it is desired to give an additional angular margin of capture around the axial direction of the radiation, this which is equivalent to taking into account a greater angle of divergence than the real angle.

In FIG. 5, we consider an elementary beam of axis 44 having a divergence 2γ of 6 ° in the example shown, beam delimited in the plane of the figure by extreme radii 45 and 46 at 3 ° on both sides. other of Tax 44. This beam is picked up at point 47, the most distant end of Tax of a, linear reflecting element 48 which is assumed in this example to be a straight line segment of ends 47 and 49. If we wants the radiation beam reflected at point 47 to fully penetrate the receiving pupil of section 4, ends 6 and 7, the reflected ray 50, corresponding to the extreme received ray 45, must be directed towards point 6. The axial reflected ray 51 must therefore no longer be directed towards the end 6 of the receiving section but towards a point 52. It is then necessary to replace, in the modes of determination of the linear reflecting element described above, the end 6 , from section re however by the point such as 52 located at a distance from the end such that the extreme radius of the reflected beam does not extend beyond the end 6. This amounts to saying that in the relation determined above, the angle α must be reduced of half the divergence angle γ of the received beam:

Similarly, at the end 49 of the linear reflecting element 48, the beam of radiation of axis 53 and of extreme rays 54 and 55 being picked up, it is the reflected ray 56 corresponding to the picked up ray 55 (in the opposite direction by relative to its axis of that of radius 45 close into account at the end 47) which must be directed towards the end 7 this the receiving section. So the point 57 towards which is reflected the axial radius 53 is located, here too, at a certain distance from the end 7. The case separating point 57 from the end 7, the closest to the linear reflecting element, is smaller than the distance separating the point 52 of the end 6, the furthest from this reflecting element.

The concentrator sensors according to the invention have been defined throughout the above description by their linear profile in a given plane. Of course, a concentrator sensor is made up of a set of these linear wires acting independently of each other. This set may be discontinuous. In order to implement the greatest possible number of linear profiles, the assembly can be continuous and compose the geometric shape of a surface which can close in on itself, possibly of revolution. However, each of the linear reflecting profiles acts independently of the others. For example, if the set of linear reflecting elements in the form of straight line segments constitutes the geometric shape of a conical surface, the optical properties of this set are in no way those of a conical mirror which requires the implementation of reflections multiple between opposing generators and comes out of es relationships integrating the effects of these multiple reflections. In the case of a concentrator sensor according to the invention, each of the generators has been defined for itself and acts alone.

A particular case is that where the linear reflecting elements together make up the geometric shape of a pyramid, possibly regular. In the latter case, the number of faces of the pyramid is optimally determined according to the invention.

In FIGS. 6, 7, 8, which are plan views, the collecting pupil of the sensor, supposed to be polygonal, has a circumscribed circle 58, and the receiving pupil, supposed to be delimited by a regular polygon homothetic to that of the collecting pupil, has a circumscribed circle 59 and an inscribed circle of diameter designated by d _3. For the concentration to take place without loss of radiant energy, the number of faces of the ..pyramid cannot be any number. In the example shown in Figure 6a if the homothetic polygons of the collecting pupil and the receiving pupil were squares of sides such as 60-61 and 62-63 respectively we see that the rays received extreme perpendicular to the plane of the figure between points 60 and 64 and between points 65 and 61 (the mediating segment 64-65 being equal to the side 62-63) would be reflected respectively in directions (plan views) indicated by arrows and would not enter the receiving pupil. The same would apply to all the peacocks captured in the hatched areas shown in the square pyramid. In order for all the rays received to reach the receiving pupil, the number of these faces of the pyramid must be fixed in such a way (not at all obvious) that the side of the collecting polygon is smaller or at most equal to the diameter of the inscribed circle. in the receiving polygon. This is not the case in the example this figure with a square pyramid whose collector side 60-61 is larger than the diameter of the circle 66 inscribed in the receiving square, diameter equal to the side 62-63 of this square.

We know that half of the side, of a regular polygon of n sides inscribed in a circle of radius R and exinscribed to a circle of radius r, is equal to

By designating by d, the diameter of the circle 58 circumscribed at the collecting polygon, by d ₂ the diameter of the circle 59 circumscribed at the receiving polygon, by d ₃ , the diameter of the circle inscribed in the receiving polygon (diameter whose value varies according to the number n sides of the polygon), the number n of the faces of the regular pyramid must be such that Ton has:

This condition can be expressed as a function of the concentration C characterizing the concentrator sensor, concentration equal to the ratio between the air of the collecting pupil and the air of the receiving pupil. The ratio of these areas is the square of the ratio of the diameters d ₁ and d ₂ , it comes:

The number n of the faces of the pyramid will be fixed in such a way that we have:

Since the number n must be an integer, the value determined by the above relationship will be rounded off, preferably by default, in order to be sure that the side of the collecting polygon is smaller than the diameter of the circle inscribed in the receiving polygon. Of course, when the whole number rounded by excess is close to the calculated value, we will round as well by excess because then the side of the collector polygon will be barely larger with the diameter d ₃ .

We see that the number n cannot, in any event, be less than 5. Indeed, the expression

has an upper limit, for C = 1. We then have:

This borderline case does not operate with effective concentration (d ₂ becomes equal to d ₁ ). For it to be larger than l, the number n of the faces of the pyramid must be at least equal to 5 (pentagonal pyramid).

To fix the value of n, we will calculate and

we will round, preferably by default, the number n, by r

In the example shown in Figures 7 and 8, Concentration 4,7). We find :

Arc tg 0.46 = 24 ° 44 '

By rounding by default, finds n = 8. The polygon is an octagon shown in Figure 7. aside 67-68. The reflected rays chis in 67 and 68, in directions represented by arrows, penetrate into the receiving pupil, inside the circle inscribed 69. But the value 24 ° 44 'is not very far from 25 ° 43' to what corresponds a heptagon (n = 7, by excess), the side of which is represented in FIG. 6 c in 70-71 and which may be appreciably suitable for the concentration characterizing this example.

The rays captured in 70-71, reflected in directions represented by arrows, slightly extend beyond the inscribed circle 72 of the receiving pupil.

The number n thus fixed is optimal in the sense that it makes it possible to obtain the desired concentration, without losing flux with the minimum of planar faces.

Sectional view in a median axial plane, each of the faces of these regular pyramids according to the invention has a reflecting profile of the type described with reference to FIG. 4.

A particular case is that in which the number of faces tends towards infinity, in which case the lateral surface of the sensor is in the form of a cone of revolution, moreover in no way acting like a conical mirror, each of its generatrices acting independently of the other. Rather than in the form of a simple truncated cone, the concentrator sensor consists of truncated cones arranged end to end, according to the profile shown in FIG. 4.

The conical shape in itself constitutes another kind of optimization. If it is preferable, in fact, in the case of regular pyramids, to limit the number of faces as much as possible in order to simplify the manufacture, we go all at once with the truncated cones to a die shape veloppable easy to make.

Figures S and 10 show two sections, one transverse 9, the other longitudinal 10, and a plan view 11, of a concentrator sensor according to the invention in the case where the receiving pupil 73 is elongated, by example a pipe traversed by a heat transfer fluid. The whole of the greater part (the elongated pupil being most often much longer, rel ati vexent, than it is represented in the drawing) of the linear reflecting elements compos.e then the shape of a gutter, each of these linear elements, such as 74 or 75 reflecting the collected radiation according to the invention, in a plane perpendicular to the mean longitudinal axis 76 of the elongated pupil (plane of FIG. 9.), the mean central point then considered in each section being a point on the axis such as point 76 in FIG. 9, or a point close to this axis. These central points continuously and entirely cover the longitudinal axis of the receiving pupil; in other words, the reflective profiles such as 74 make up a surface of cylindrical shape in the particular case shown in FIG. 9, or prismatic.

The ends of the gutter, such as 77 and 78 (FIG. 10) may consist of different sets of linear reflecting elements, each of these reflecting the captured radiation, in a plane cutting said at least approximately longitudinal pin receiving at a point that its axis constituting the mean center of at least one of its parts, and continuously covering at least this part of the section.

For example, in FIG. 10, assumed in the median plane of the gutter, perpendicular to the plane of FIG. 9, and passing through the axis 75 of the receiving pupil, the linear reflecting element 77 reflects the radiation picked up as it is indicated in solid lines with single and double arrows, covering the entire center section 79. But if the pupil is very long, the linear reflecting element can be designed so as to reflect the radiation (dotted line with triple arrows) in covering only part of the pupil, part having its mean central point for example at 80. The symmetrical (independent) reflecting element 78 then covers the symmetrical part of the pupil around a center 81.

The plane of FIG. 10 cuts the receiving pupil in a strictly longitudinal fashion passing through its axis 76. It can be a little differently in other section planes. For example, we see in FIG. 11 represented in top view, a linear reflecting element 82 which operates in a plane cutting diagonally the receiving receptor 11 at its center 79, and containing another linear (independent) reflecting element 83, symmetrical of 82 with respect to the center 79 The reflections by the element 82 can thus cover only a part of the pupil, of center 84 for example. The reflective element can also be linear tr ^o uver more obliquely such that the element 85 and not having a corresponding symmetric on the other end that the gutter. In this case, it returns the radiation captured in a plane cutting very approximately longitudinally, the receiving pupil at a point such as 86 of its axis and the reflections continuously cover the part 87 shown in solid lines. This type of concentrator sensor relates to all the applications where a liquid passing through a pipe is heated such as cal oducs, dowtherms, boilers, distillation installations, etc. A particular application, according to the invention, consists in constituting, with such a concentrator sensor, a trough or drinker intended for breeding, in particular calves. It has been established that a temperature of the order of 25 to 30 ° C is favorable to the development of calves and a concentrator sensor of the type described above can easily raise water from 10 or 15 ° to 25 or 30 °. The concentrator sensor proper, forming the side walls, can, for example, be covered with aluminum or mylar sheets, and the receiving pupil can be constituted by the bottom of the drinker and possibly the bottom part of the side walls, this background and these parts being made black to absorb the radiation and transform it into heat.

FIG. 12 represents three examples of linear reflecting profiles made up of straight line segments arranged end to end as described above considering, for the same dimension of collecting section of diameter d ₁ and the same receiving section, three different axial lengths h ₁ , h ₂ , h ₃ . With this type of concentrating sensor according to the invention, there is always a part of the captured flux which is lost, owing to the fact that the end of the last reflecting segment, closest to the receiving pupil, always presents a hiatus with the end of the section of this pupil closest to it. The section of the pupil being designated by 6-7 in the figure, the ends of the three sensors represented in example closest to the pupil are designated by 88, 89, 90. The hiatuses are respectively 88-6, 89-6, 90-7.

The aim is to reduce the optical hiatus as much as possible and to determine an optimal compromise between the various parameters involved, having regard to other disadvantages which also arise. The hiatus turns out to vary in opposite direction to the axial length h of the sensor. It is therefore advantageous, to decrease the hiatus, to increase this length h, otherwise di.t. To move the collecting pupil away from the receiving Dupille. On the other hand, the longer the concentrator sensor is extended, the more it creates drawbacks of size, weight, wind resistance, price increase. An optimal compromise is proposed here, according to the invention. Taking as a unit of length the average diameter 6-7 of Your receiving pupil cμj'on denote by d ₂ , we will preferably set for the axial value h a value of the order of 3 to 5, the average diameter d ₁ of the collecting pupil being of the order of 6 to 7, the mean terminal diameter d of the concentrator sensor then being of the order of 1.5 to 2.

A concentrator sensor corresponding to this optimization is represented in the figure by three reflective segments end to end 91-92, 92-93, 93-90.

The loss of flux from the hiatus is proportional to; . The yield loss compared

is the quotient of this expression by:

, is :

We compared in the figure three concentrator sensors. The longest, 94-89, for which h ₂ is equal to 6 (d ₂ being chosen as a unit) and di equal to 1.23. The concentrator sensor 91-90 corresponding to the proposed optimization; h ₃ = 4 d ^" ₃ = 1.75. The concentrator sensor 95-88, the shortest; h ₁ = 2; d ₃ = 2.5. The diameter d ₁ of the collecting pupil is here equal to 5 for the tro.

The energy efficiency is, respectively

ment, in these three cases: 2%, 8%, 21%.

The 8% loss agreed with the optimization according to the invention represents the most acceptable compromise in view of the drawbacks inherent in the other two concentrator sensors. Another alternative embodiment of a concentrator sensor according to the invention, not shown in the drawing but here described, is characterized in that the concentrator sensor constitutes a solar barbecue.

The concentrator sensor is of one of the types according to the invention described above. Particularly suitable: surfaces with an osculating curve profile of parabolic families as described with regard to FIG. 2, with an arc-shaped profile of a dish with a focal point (FIG. 3), regular pyramids (FIGS. 5 and 4) ), the butt joints of trunks of cone of revolution. One can possibly take into account the divergence of the order of 30 'of the solar radiation and also give oneself a margin by conforming to the characteristics described with regard to FIG. 5. The receiving pupil is here provided with a grill and / or constitutes the entrance to an oven.

The sun dispenses, when the sky is clear, an energy of the order of 1 KW per m2. Taking into account the fact that food has a radiation absorption coefficient ranging from 0.5 to 0.2 approximately, that there are these losses by convection, possibly by the effect of air currents etc. . obtaining a temperature of the order of 150º to 200º C, suitable for cooking or grilling food, requires a concentration of the order of 6 to 9 times. A concentration of the order of 16 suns would allow safer and faster cooking. Referring to the table determined above, we see that in the case of a pyramid barbecue the simplest basic polygon is the octagon (6 suns).

The decagon allows a concentration of just over 9 suns. A concentration of 16 suns requires a decatriagon (13 sides). The assembly of the concentrator sensor and its pupil provided with a grill and possibly attached to an oven is oriented towards the sun and is provided with a tilting device in an approximately east-west direction, possibly operated by hand. Two wires are arranged in the flow input section of the sensor and their intersection is in the center of this section, so that when the shadow cast by this intersection is in the center of the receiving pupil, we see that the sensor is correctly oriented towards the sun. This allows you to control the pointing towards the sun. Optionally one or more glass panes with greenhouse effect are arranged in the vicinity of the exit pupil, either in sections of the concentrator sensor, or outside (when the pupil is at a distance). This, in order to return to the actopm of the concentration of solar energy especially in the case where the exit pupil leads to an oven. The vitrange (or them) can then close the oven by making it waterproof if necessary.

The receiving pupil, in which the cooking or grilling lines are arranged, especially when it is located at a certain distance from the concentrator sensor (in the case of a pyramid barbecue in particular), is protected from wind or drafts. air by a device such as screens and possibly constituting the walls, preferably black, of an oven surrounding the hob. The oven may contain stones or materials that store heat. It is the same when the receiving pupil leads directly to an oven, as has been said.

Finally, an important point is to obtain the greatest possible absorption of the radiation by the food placed in the receiving pupil. In the case in particular of "white" meat, the absorption is low and most of the radiation is returned by diffusion upwards and is lost. This is why greenhouse glass has been provided. It is also possible, according to a secondary characteristic of the invention, to use a special dark-colored sauce based for example on mashed black olives (of the "tapenade" kind), juice and colored aromatics. FIG. 13 represents a reflective profile of a concentrator sensor performing an optical immersion. It is recalled that an optical device, operating in air, is said to be "immersed" when its terminal part, where its optical action finishes, is made up of a medium with a higher refractive index n to 1. For a converging optical system, immersion has the effect, all other things being equal, of multiplying the concentration of the radiation by an additional factor n ² .

As, as here, "parallel" radiation picked up in the direction of the axis of a concentrator sensor, the problem of immersion presented itself in a very special way. It would in fact be pointless to fill this concentrator sensor with a medium of index n. These rays captured parallel to the axis of the sensor would not undergo any refraction crossing the plane diopter of the collecting pupil which is perpendicular to this axis, and the concentration would operate as if there were no immersion. A slight divergence does not significantly change the situation. To obtain an additional concentration under these conditions using immersion, the concentrator sensor is composed, according to the invention, of at least minus two parts. One, terminal, whose linear reflecting profile (in one or more elements) is characterized as it was said previously, and contains an optical body of index n (larger than that of air) solid or liquid la filling up to the level of its own collecting pupil and. in optical contact with the receiving pupil. This end part, acts by its reflecting profile as if there were no immersion medium (refractive body), but it is the presence of this which makes it possible to determine according to the invention the reflecting profile of another part of the concentrator sensor, preceding the terminal part. It is this other part, operating in the air, (or whose volume is occupied by an optical body with a refractive index less than n) which obtains an additional concentration implementing the immersion. To this end, the characteristics of the reflecting profile of this other part (or of these others if it itself consists of several linear reflecting elements arranged end to end), are determined by taking into account the refraction undergone at the entry of the optical medium. filling the terminal part. According to all that has been described above, when there is no immersion medium, the rays picked up by a linear reflecting element are re-bent towards points of the receiving pupil which have been well specified. If there is an immersion medium of index n delimited by the plane diopter of the collecting pupil of the terminal part, that is to say the largest section, perpendicular to the axis of this terminal part, these reflected rays are deflected by refraction crossing the plane diopter. So that they are nevertheless sent to the points which have been specified, the reflective profile is modified, according to the invention, taking account of said refraction. This modification is made in the following manner, described with reference to FIG. 9 on an example of linear reflecting elements in the form of straight line segments. The terminal part 96 of the concentrator sensor is delimited laterally by linear reflecting elements such as 97 whose ends are 98 and 99, the end 98 being closest to the receiving pupil 100 whose ends are 101 and 102. An optical medium refractive index n, solid or liquid, fills this terminal part until it forms a plane diopter 103 at the level of the collecting pupil of this terminal part, in the plane perpendicular to the mean axis passing through the end 99 of the reflecting segment furthest from the axis, this optical miMeu is in optical contact with the receiving pupil 100. If it is a liquid medium, a waterproof wall is provided between the points 102 and 98, this wall can advantageously be constituted by a reflective profile in the form, for example of a parabolic arc with a focal point, as it was previously described and as shown in the drawing (98-102). The characteristics of the reflecting segment 97 are those which have already been described. By designating by R the distance to the middle axis 104 of the end 99, by r the half of the linear section 101-102 of the receiving pupil 100, by h the distance on the middle axis between the center 105 of the receiving pupil and the projection 106 on this axis of the end 99, the reflecting segment 97 makes with the direction 107 of the middle axis an angle a as as has been said

It is a question of determining, according to the invention, the reflecting segment 108 which precedes the submerged terminal segment 97. This reflecting segment makes with the direction 107 of the mean axis an angle α 'which it is a question of determining. It has two ends 99 and 109. The ray 110 picked up at point 109 must reach point 101, which is the end of the section of the receiving pupil furthest from the reflecting segment, after having undergone a reflection at point 109 and a refraction at point 110. The ray 111 picked up at point 99 must reach point 102, the other end of the section of the receiving pupil after having undergone a reflection at point 99 and a refraction. For clarity, figure 9 shows what must happen, by shifting point 99 a little, so that reflection and refraction occur at non-confused points as is the case for the borderline. very end of the reflecting segment. The refraction point is shown here at 112. The ray 111 undergoes a reflection at 99 and reaches the plane diopter 103 at point 112. Let i be the angle of incidence with the normal 107 to the plane diopter. The ray refracts at an angle of refraction r 'with the normal.

Sin i '= n Sin r'

The point 110 from which the ray coming from 109 is refracted, coincides with the parallel to the axis 104 led by the end 102 that the receiving pupil. Indeed, the radii 99-102 and 110-101 are parallel, each making an equal angle (denoted r ') with 102-110.

In the right triangle 99-110-102, the side 110-99 is equal to

R - r and we have: tg r 'or r' Arc tg

⁼

On the other hand, the radius 111 while reflecting at 99 on the reflecting segment 108 inclined by α 'relative to the direction 107, rotates by

2 α '(as we know) with respect to this direction. The angle of incidence i 'is 2 α' We have: sin 2α '= n sin r' = n sin Arc tg

To obtain the sought result, we will therefore determine α 'such that: α' = Arc sin n sin Arc tg

The end 109 of the segmen

reflecting 108, the furthest from the mean axis 104, is at a distance R 'from this mean axis, which must also be determined. The ray 115 picked up at point 109, after reflection reaches the plane diopter 103 at point 110 at an angle of incidence which is also equal to 2 α '. In the right triangle 109-116-110, we have: tg 2 α '=

by designating by h 'the distance 110-115, that is to say the distance between the plane diopter and the collecting pupil corresponding to the end 109.

From where :

R '= h' tg 2 α '+ r

And so on, one or more reflecting segments thus defined possibly possibly preceding this one.

We can clearly see that, thanks to the immersion from which we can benefit by the characteristics given to the reflected segment enissant 108, the angle α 'is more grana than in the case where there would be no immersion (that is to say as determined previously) and the collecting pupil of medium radius R ′ is also larger, which provides additional concentration. In cases where the reflective profile (such as 108 here) preceding the immersion is not rectilinear, an angle such that α 'is determined for the tangent at each of the points of the profile, in a manner analogous to that which comes to be said, R then being the distance from the point considered to the mean axis 104 and r being the distance separating the center 105 of the receiving cell from the point of section 100 which must be reached after refraction, the point which was targeted according to the foregoing description when there was no immersion, so that the section 100 is continuously covered at least once by the rays reflected by the reflecting profile. This characteristic of the invention which makes it possible to benefit from an additional concentration thanks to optical immersion, is particularly interesting in the case where it is precisely desired to carry out the terminal concentration in a medium of index greater than unity. For example, in the case where it is proposed to dissociate the water molecule using a concentration of solar energy in the presence of suitable catalysts, it would be particularly advisable to enclose this water in the terminal part of a concentrator sensor as just described according to the invention. One can also combine this characteristic with all those which have been described, in particular in the case of the trough or tank (drinking trough for cattle) which has been described.

Claims

Catoptric concentrator sensor of parallel or low divergence radiation, of the type comprising at least one reflecting element (8) associated with a non-point pupil receiving (4) the reflected radiation, characterized in that each reflecting element (8) has, in a section plane containing the mean direction (1) of an elementary beam of captured rays and intersecting the receiving pupil (4), a linear profile whose curvature at each of its points is determined by a tangent (12) and a normal ( II) such that on the one hand, receiving a ray (1) at one of its ends (2), this Linear profile reflects it directly towards one of the ends (6) or towards a point considered as such in the section of the receiving pupil (4) and, receiving a ray (10) at the other of its ends (9), it reflects it directly towards the other ends (7) or towards a point considered as such in said section (4 ) and that, further On the other hand, each of the intermediate points of this linear profile reflects a ray directly towards an intermediate point of said section (4) so that the entire pupil (4) receives after a single reflection and according to a homogeneous ^or substantially such distribution, all of the radiation reflected by each reflected element. Concentrator sensor according to claim 1. characterized in that it comprises at least two superposed reflective elements (8-15), preferably contiguous. Concentrating sensor according to claim 1, characterized in that the linear profile receiving a ray (1) at its end farthest (2) from the section of the receiving pupil (3) reflects it towards the end (6) of the section (4) closest to it and, receiving a ray (10) at its other end closest (9) to said section (4) reflects it towards the other end (7) of this section (4), the farthest from him, these extreme rays as well, that all the intermediate rays reaching said section (4) directly by covering it continuously. Concentrating sensor according to claim 3, characterized in that the linear reflecting profile is the osculating curve of a family of parabolas infinitely close to each other whose respective foci occupy the points of the section of the receiving pupil (4) covering continuously at least once throughout this section. Concentrating sensor according to claim 1, characterized in that the linear reflecting profile (25), receiving a ray (17) at its end furthest away (18) from the receiving pupil (4), reflects it towards the end (6 ) of this section (4) furthest from it and, receiving a spoke (27) at its other end closest (26) to said section (4) reflects it towards the other end (7) of this section ( 4) closest to it, these extreme rays as well as all the intermediate rays reaching said section directly by continuously covering it. Concentrating sensor according to claim 5, characterized in that the linear reflecting profile (31) has the shape of a parabolic arc the axis (32) of which is distant from the mean axis (30) normal to the receiving pupil ( 4) and is located, with respect to this arc (31), on the other side of this mean axis (30) and parallel to it, the end (7) of the parabola arc closest to these axes (30) coinciding with the end (7) of the section of said pupil (4) furthest from these axes (30) or being in the vicinity of this end (7), the focus (33) of the parabola is locating, on the extension of the straight line joining the end of the arc farthest (32) from its axis to the end (6) of the section of the pupil (4) closest to this axis (30) , in a position far enough from this last end (6) so that the illumination in the central part of the receiving pupil (4) is substantially equal to half the sum of the illuminations in the parts near the ends (6 and 7) of this pupil (4).

Concentrating sensor according to claim 5, characterized in that the linear reflecting profile in the form of a straight line (25) inclined relative to the mean axis (30) normal to the receiving pupil (4). its points approaching jointly this axis (30) and this pupil (4), this line segment (25) forming with the direction of the mean axis (30) an angle a defined by:

Arc tg

R, designating the distance to the mean axis (30) from the end of the most distant reflecting profile (18) from this axis (30), r, half of the linear section of the receiving pupil (4) by the meridian section plane containing this reflecting profile, h the distance on the mean axis (30) between the mean center (5) of the receiving pupil (4) and the projection on this axis (30) of the end of the reflecting profile the most distant (18) from the axis (30), this end (18) being the point such as a radius parallel to the mean axis (30), reflecting by making an angle of 2α with this axis (30 ), passes through the end (6) of the linear section of the receiving pupil (4) furthest from the reflecting profile (25), the other end of the profile, the closest (26) to the receiving pupil (4 ), being the point such as a radius parallel to the mean axis (30), reflecting by making an angle of 2α with this axis (30), passes through the end (7) of said section (4) closest to the reflecting profile (25).

Concentrating sensor according to Claim 6, characterized in that the said element (43) whose profile in the form of a parabolic arc is situated between another reflecting element (40) and the pupil (4) which it adjoins. Concentrator sensor according to claim 1. characterized in that. ends (6 and 7) of a section of the receiving pupil (4) are determined by two points of this section located at a distance from this s ends such as the extreme radii of the reflected beams, of non-negligible divergence, which extend beyond these two points do not extend beyond the ends of said section (4). Concentrating sensor according to claim 1, characterized in that the element, or at least one of the reflecting elements, is composed of an infinity of juxtaposed linear profiles thus constituting a continuous surface. Concentrator sensor according to claim 10, characterized in that the continuous surface is closed on itself, possibly along a surface of revolution. Concentrator sensor according to claim 10 characterized in that the juxtaposed profiles together make up the geometric shape of a possibly regular pyramid, in which case, for a concentration C of the flux, or ratio of the area of the collecting pupil to the 'area of the receiving pupil, the number of faces of the regular pyramid is fixed equal to the whole number n, preferably rounded by default, such that we have:

Concentrator sensor according to claim 10, characterized in that the continuous surface is generally in the form of a gutter, associated with a coaxial elongated pupil.

Concentrator sensor according to claim 13, charac terized in that it comprises axially ends made up of reflective elements.

Concentrator sensor according to claim 14, characterized in that it has a substantially trough shape and constitutes a reservoir such as a drinker, the bottom of which is black to absorb the radiation and heat the liquid contained in this trough.

Concentrating sensor according to claim 1 characterized in that it delimits a volume to be occupied by a refractive optical body whose refractive index is higher than that of air and in that it is associated with a concentrator of any known type which precedes it and which is surrounded by a body with a refractive index lower than the previous one and whose collecting pupil has a surface greater than that of the collecting pupil of said concentrator sensor. 17- Concentrator sensor according to claim 1, characterized in that it constitutes a solar barbecue and that for this purpose, its receiving pupil is provided with a grill and / or constitutes the entrance to an oven and in that '' it includes, in particular, a tilting device in an approximately east-west direction, possibly operated by hand, one or more greenhouse glazing in the vicinity of its receiving pupil, a device such as formed by screens protecting the plane of cooking air currents and possibly constituting the preferably black walls of an oven surrounding the hob, which may include stones or materials storing heat, further gratified by the use of a sauce intended to make spectral Meat and foodstuffs placed in the hob, absorbing a dark color based for example on black olive puree, juice and colored spices.