ES2341836B1 - SOLAR CYLINDER-PARABOLIC COLLECTOR WITH DOUBLE UNIFORM REFLECTION. - Google Patents

Abstract

Solar collector parabolic trough with uniform double reflection, constituted by two parabolic branches, on each side, in the mirror primary, with greater focal length in the outer branch, being the rays concentrated by each branch of the primary reflected again by two cofocal mirrors with each branch; lightning strikes doubly reflected by the inner branches, on the tube absorber located in the vicinity of the virtual apex of the parable inside primate; and moving the reflected rays successively by the outer branches in paths parallel to the axis of symmetry, not incidents on the tube, from which they pass from long, to be reflected by a pair of symmetric mirrors, at each side, which project them on the underside of the tube, which its entire surface is illuminated.

Description

Solar collector parabolic trough with double reflection standardized

Technical sector

The invention falls within the field of solar thermal energy, particularly the one that uses concentration of the original radiation to reach high temperature in the good useful, which usually materializes in a heating fluid that transports absorbed solar heat to a thermodynamic cycle. Within this field it fits in the collectors parabolic trough, which concentrates the radiation solar in a longitudinal focal axis in which a tube is located absorber, inside which the heating fluid circulates.

The absorber tube is surrounded by a cover, also cylindrical, glass or resistant material and transparent, which serves to keep empty between both tubes, with in order to reduce convection losses, and avoid aggression of the air on the paint or adhesive of high absorptivity and low emissivity that covers the absorber tube.

Background of the invention

There are currently several commercialized Cylinder-Parabolic Collectors (CCP), (www.fplenergy.com/
portfolio / contents / segs_viii.shtml) and ( www.flaqsol.com/andasol ) which are used in the plants and platforms that are being built, and have in common that they have to rotate on their axis of support, which usually coincides, or almost, with the apex of the parabola (in each straight section) so it is a line parallel to the focal axis, located at a distance of about 2 meters depending on the size of the collectors, which come to have an optical aperture of about 6 meters

The aforementioned tube translation turn (associated with the cylinder in a whole) involves a problem: it must have a rotating coupling from the ends of the tube absorber to the fixed connecting pipes with the installation of energy conversion, fixed on land. This is currently done. by means of a radial tube, which goes from the line of the clamping shaft to the focal axis, or vice versa (depending on whether or not the fluid in the collector enters), said radial tube having to be connected to the focal axis tube by an elbow-shaped tubular piece, which at one end has a rotating joint to connect to the tube of the parabolic shaft. TO in turn, a piece in similar elbow, with rotary joint, is necessary to connect the radial tube with the fixed tube that connects with the fixed installation This means that in a solar thermal power plant of parabolic trough collectors there are tens of rotary joints, which are a weak element of the system, being able to leaking heat fluid, which is not just bad economically for the installation itself, but it can also have environmental and safety repercussions.

To overcome this problem posed by rotary joints, a type of collector has recently been proposed parabolic trough with fixed tube with respect to earth, without rotating joints at the junctions of its ends, with double co-focal reflection, which has been materialized in the Spanish patent application P200800440, "Solar-parabolic trough collectors thermal with fixed absorber tube ".

However, both in cases of collectors conventional mobile tube with rotary joints, as in the fixed tube collectors, the characteristic of the concentrated solar radiation strikes the absorber tube for only a part of its surface, which generally does not cover 180º (sexagesimal degrees) of the 360º occupied by the perimeter circumferential of the tube. This causes the energy deposited by the radiation, per unit area of the tube, present large variations, being very high in slightly less than half of the surface, and being null on the face not illuminated by radiation (which we could call shadow face).

This huge azimuthal asymmetry in the distribution of heat deposition on the tube surface it causes very high temperature circumferential gradients, even if the tube material has good conductivity of heat, with the consequent problem of mechanical stresses induced by thermal differences, which can produce important plastic deformations in the tube, arriving eventually to the creep of the latter, contacting the envelope glass exterior, in which there would be a heating and local overpressure in the contact zone, which would carry its break.

To eliminate this danger of tube breakage absorber or its glass cover, has been proposed recently, for simple reflection collectors, the request for patent of this same applicant, P200900854 proposing a configuration that standardizes, at least in average values, the incident radiation on both sides of the tube, the illuminated and the that was originally in shadow. But such optical geometry only It is applicable to simple reflection CCP devices, and not to those of double co-focal reflection, of great interest to build CCP with fixed absorber tube, without rotating joints, and mass balanced.

This application presents a new double reflection CCP configuration, in which it is achieved combine all these technical objectives.

Description of the invention

The invention consists in configuring the mirror primary collector, where direct solar radiation affects, with two parabolic branches on each side, one after the other, having the second branch, more external, a focal length greater than the first or inner, although that second focus remains on it axis of symmetry than the focus of the first parable, although more away from the apex (extreme point) of it, because its focal distance. This arrangement of the spotlights prevents interference, optical lens type, which produces the outer shell glass cylindrical, or glass tube, concentric to the tube absorber, when reflected, in the secondary mirror, the radiation to the tube.

This double parabolic branch on each side of the shaft of symmetry, it causes two families of solar rays to form, the first being the one that affects and is reflected on the inner branch, and the second one that affects and is reflected in the outer branch.

The invention also consists in providing a second parabolic mirror, or secondary mirror, which is structured also in two branches, each with the same focus (co-focal) that the corresponding branch, interior and exterior, of the first mirror. Mirror width inner co-focal, on each side, is determined because its final outermost reflected beam is tangent to the tube absorber by its corresponding side. To be co-focal the inner branch with respect to the parabola of the inner primary mirror, its final reflected rays are parallel to the axis of symmetry. And the outer branch of the mirror co-focal, which reflects on each side the rays of the second family, has its inner endpoint at the point that is reflection in the lightning path that, after the second reflection, It is tangent to the transparent tube. The outer rays to that, make up the second family of rays, being the opening or width of that parabolic branch a free parameter, to be fixed according to the concrete application, with the prescriptions given in this invention. And for the last reflection of that second family of rays, it It has a third mirror, or tertiary mirror, on each side, which makes that radiation affect the surface of the tube where it has not The radiation of the first family was affected. The location of this mirror is also uniquely prescribed in the embodiments of the invention.

With this configuration, the entire perimeter circumferential of the absorber tube receives radiation; and although this one do not reach exactly uniform values everywhere, the distribution is very uniform, avoiding a face strongly illuminated, and the opposite with zero illumination.

To conveniently expose the prescriptions geometric above, you need to take into account properties basic geometric parables, plus a fundamental principle of reflection, and that is that the ray reflected by a surface, it forms a flat angle with the incident ray, being the bisector of said angle the normal line to the reflection surface. Like in our case the reflection surfaces will be surfaces longitudinal section of invariant straight section, the study of reflection becomes simply two-dimensional, and therefore expressible on a plane, even when the rays, incident and therefore reflected, may have a component of movement in the direction longitudinal, which does not disturb the conclusions obtained on the properties of the invention. The only caveat occurs at the longitudinal ends of the collectors, where it is lost a certain amount of radiation when reflected, because the reflected one does not find absorber tube, having finished this one. But this is not a peculiarity of the invention, but of every collector parabolic trough

As a consequence of this two-dimensional reality of the problem, the precise description of the invention is used flat trigonometry, and a coordinate system is used for the exact formulation of the invention. This system is based on the internal parabola of the primary mirror. The origin of coordinates at the apex (or extreme minimum, because the parable is consider open up) of the inner parable, even when this point is virtual, because the parable is cut in its zone central to accommodate the absorber tube and structural elements collector centrals. The ordinate axis coincides with the axis of symmetry that goes from the apex to the focus. The axis of abscissa is the line perpendicular to the axis of symmetry at the origin of coordinates

The properties of photon reflection Constituents of solar radiation, already mentioned, are used in embodiments of the invention to determine the position and sectional profile that secondary mirrors must have and tertiary with respect to the parabolic profiles of the two branches of the primary mirror All devices of the invention are symmetrical with respect to the longitudinal plane of symmetry of the first parabolic cylinder, in which is its focal axis, or straight line that it is the geometric place of the successive foci of the successive straight sections of the cylinder.

The invention thus establishes, for a given or chosen configuration of the primary mirror of the collector, the requirements to be met for the focal positions, tube position, branch widths and layout and profile of the additional mirrors, which is detailed in the preferred modes of realization.

The invention includes a mounting that allows the absorber tube is fixed with respect to ground, so as not to need rotary joints at the ends of the collector, always keeping on the axis of rotation of the collector, but making possible the dilations and contractions of the tube by having said assembly, that takes some longitudinal guide rails, in the grip the feet of the staff that supports the bearing of bearings that circumferentially hugs the thermal insulator that surrounds the tube absorber in the welded joint area between consecutive modules of tube, in whose area the transparent cylindrical cover is interrupted of the tube.

Explanation of the figures

Figure 1 shows the profile of two branches parabolic, on each side, that makes up the straight section of the mirror primary. The origin of coordinates for the prescriptions of embodiment of the invention is the minimum point, or apex, of the inner parable The axis of symmetry is that of ordinates, and its Perpendicular at the apex is that of abscissa.

Figure 2 shows the straight section of a double reflection manifold, with primary and secondary mirrors co-focal, with its structural elements, between which stands out its main longitudinal support beam in U, and the gearwheel geared screw that rotates the collector for its approach to the sun, being able to consider this collector as conventional, as proposed in the patent application Spanish P200800440.

Figure 3 shows the optical scheme and geometric of a double reflection manifold with fixed tube, in the that the invention has been incorporated, separating the two families of rays by two different parabolic branches in the mirrors primary and secondary, and incorporating additional mirrors inferior, or tertiary, of illumination of the opposite side to which He receives radiation from the first family. The figure is not at scale, for the very different size of its relevant elements (the width of the primary mirror can be greater than 5 meters, and the tube diameter is usually 7 centimeters).

Figure 4 shows the straight section of a double reflection manifold, with primary and secondary mirrors in two branches, respectively co-focal, with their structural elements, including the lift system by clamp-slide of the fixed absorber tube.

Figure 5 shows an enlargement of the area around the collector absorber tube, with the mirrors additional tertiary in the simplest or immediate position of the Prescribable

Figure 6 is similar to 5, but includes the fixing system of the tube to the main U beam of the structure, with a bearing clamp on a support sliding, or sliding, to absorb dilations and contractions of the tube.

Preferred embodiments of the invention

The various components of the invention are listed below, to facilitate the description of the drawings and of the embodiments, and therefore of the patent itself.

70.

Parable inside the primary mirror with two branches parabolic

71.

Outside parabolic branch.

72.

Apex or minimum point of the parabola inside.

73

System symmetry axis, which runs from the apex 72 to focus 74.

74.

Focus of the inner parable.

75.

Focus of the outer parabolic branch, which is also on the axis of symmetry 73, above the focus 74.

76

Abscissa axis, or X axis, perpendicular to the axis of symmetry 73 at apex 72, where it has its origin.

77.

Ordinate axis, or Y axis, which coincides with the axis of symmetry 73 and has its origin at apex 72.

78.

Original solar radiation.

79.

Primary parabolic profile mirror, in the double-reflection co-focal collectors, interrupted in the area of its apex.

80.

Longitudinal beam whose straight section is a U-clamp that supports the mirror 79 and its structure in the Co-focal double reflection collectors.

81.

Center of the fixed tube in the double manifolds co-focal reflection, which coincides with the center of rotation of the mirror 79 and its structure supported on the U-beam 80. This coincidence is what marks the position of the tube. At the same time, coincides with the center of gravity of the rotating assembly, so which beam 80 may be poised below, but this does not It is part of the invention.

82.

Fixed absorber tube, in double manifolds co-focal reflection

83.

Earth or foundation where the pillars or feet rest rights 84 and the porch 87.

84.

Pillars supporting the fixed tube 82 on the ground or foundation.

85.

Worm screw that engages the toothed belt existing in part of the outer surface of the clamp 80, and used to rotate this and the mirror 79 and its structure.

86.

Screw actuator 85.

87.

Gantry to support the auger 85.

88.

Mirror Focus 79.

89.

Radiation reflected by 79, which goes to the focus 88.

90.

Secondary mirror with parabolic profile, in Co-focal double reflection collectors. His focus is also point 88.

91.

Radiation reflected by 90, which runs parallel to the axis of symmetry (or axis of ordinates).

92.

Part of radiation 91 that directly affects the tube, and is contained between rays 93 and 94.

93.

Lightning reflected from the mirror 90, which is tangent to tube 82 on the right.

94.

Lightning reflected from the mirror 90, which is tangent to tube 82 on the left.

95.

Ray reflected from the mirror 90, by its point far right, 96.

96.

Right end point of the mirror 90.

97.

Lightning reflected from the mirror 79, from its point right end, 98, and that affects the right end 96 of the mirror 90.

98.

Right extreme point of the mirror 79.

99.

Point of the mirror 90 from which the beam 93 comes out, which is the reflection of lightning 100.

100

Lightning strikes 99, and comes from reflection in mirror 79, at point 101.

101.

Mirror point 79 from which the beam is reflected 100, which is the one that separates the first from the second family of rays in these collectors.

102

Additional mirror on the right of tube 82, where the right branch of the second family of Ray.

103.

Additional mirror on the left of tube 82, where the left branch of the second family of Ray.

104.

Short straps that fix the additional mirrors 102 and 103 to clamp 80.

105.

Braces that fix the mirror 90 to the mirror 79. Those braces only exist at the ends of the tube modules, each module being about 4 meters long.

106.

Apex or minimum orderly point of the mirror 90.

107.

Inner parabolic primary mirror in the double reflection collectors.

108.

External parabolic branch in the primary mirror in The double reflection collectors.

109.

Inner end point of the mirror 107.

110.

External end point of the mirror 107.

111.

Inner end point of the mirror 108.

112

External end point of the mirror 108.

113.

Focus of the inner parabolic primary mirror 107.

114

Exterior parabolic primary mirror focus 108.

115

Interior parabolic mirror of second reflection, co-focal with the 107.

116.

External parabolic mirror of second reflection, co-focal with 108, which has two branches, left and right.

117.

Lightning reflected from point 109, towards the focus 113.

118.

Lightning reflected from point 110, towards the focus 113

119.

Inner end point of the mirror 115.

120.

Lightning reflected from point 119, which goes parallel to axis 73.

121.

Maximum order point of tube 82.

122.

Transparent tube covering tube 82, with vacuum among them.

123

External end point of the mirror 115.

124.

Lightning reflected from point 123, which goes parallel to axis 73.

125

Highest abscissa point of tube 82 (point further to the right).

126.

Lightning reflected from point 111, towards the focus 114

127.

Inner end point of the mirror 116.

128.

Lightning reflected from point 127, which goes parallel to axis 73, and is tangent on the right with the transparent tube 122.

129.

Inner end point of mirror 102, where it strikes lightning 128.

130.

Minimum order point in tube 82, which is in the axis 73.

131.

Lightning reflected from point 112, towards the focus 114

132.

Exterior endpoint of the mirror 116.

133

Lightning reflected from point 132, which goes parallel to axis 73.

134

External end point of the mirror 102, where it strikes lightning 133.

135

Lightning reflected from point 134, which affects the point 125.

136.

Lightning reflected from point 129, which affects the point 130.

137.

Cooling fins of mirrors 102 and 103.

138.

Longitudinal and transverse fins of cooling mirrors 115 and 116, which in turn confer them mechanical stiffness

139.

Thermal insulation in the welded joint between modules consecutive absorber tube 82.

140.

Bearing bearing that hugs insulator 139, on which it rotates when the clamp 80 rotates to focus the collector in the sun, keeping the absorber tube fixed 82.

141.

Cylindrical bearing cover 140.

142.

Cover holding rod 141 to the clamp 80.

143.

Legs of Staff 142, sympathize with him.

144.

Feet of legs 143, cylindrical geometry longitudinal.

145.

Longitudinal guide rails of the feet 144, which allow free longitudinal movement of the staff 142 and the bearing 140, when dilations or contractions occur length of the tube, due to temperature variations.

146.

Channels that cross the U-clamp beam, 80, for cooling the mirrors 102 and 103.

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A) Performance mode with concentration reflection double, in fixed tube collector with respect to ground, with only one parable in the primary mirror

Figure 2 shows the manifold assembly parabolic-cylinder proposed in the application for Spanish patent P200800440, in which solar radiation original, 78, affects a mirror 79 of parabolic profile, supported by a thick U-beam clamp, 80, which is supported by fastening means that are located in the longitudinal ends of the collector, and which are not presented here by Do not affect the invention. The U-clamp, 80, rotates around a center of rotation that coincides with the center 81 of the absorber tube 82, which is fixed to ground, 83 by means of pillars, 84.

At one longitudinal end of the collector is an auger 85, which rotates using a motor actuator electric 86, all of which rests on a small porch 87. The screw is geared to a small band of the U-clamp, 80, which functions as a toothed semicircular crown, which performs the gear with the endless thyme, and rotate the entire mirror assembly 79 and other optical system, around the center 81 of the fixed tube 82, as needed collimation in the sun. The toothed band in a external part of the clamp 80 is not shown in the figure, for not be relevant to the invention proposed here.

It is relevant that the original radiation 78 is reflected towards the focus 88 of the parabolic mirror 79, giving rise to radiation 89. Before reaching focus 88, this radiation 89 find another parabolic mirror, 90, with the convexity down, and that has the same focus, 88, as the first mirror, 79. The result of this second reflection, co-focal with the First, it is a new radiation current, 91, which is parallel, within the tolerances of solar radiation, to radiation original, 78, although much more intense, because it is concentrated in a much smaller space. In the aforementioned patent application Spanish P200800440, the width of the second parabolic mirror, 90, matches the diameter of the absorber tube, 82, and that produces the lighting of a very concentrated radiation on the fixed tube, but it only affects the face of the tube 82 that is looking at the mirror 90. The other side receives no radiation, with the consequent thermomechanical problem.

In the invention proposed here, and that in its simplest version is shown in figure 2, the width of the mirror 90 becomes larger than the diameter of the tube 82, so that the doubly reflected radiation, 91, does not affect all of it on the tube. In this figure 2, and in this first version of the invention For this type of collector, it is considered that the tube does not have transparent cover, or that this is perfectly transparent and not It affects radiation. This simplification may be applicable to some cases, and in turn involves the simplification that the primary mirror is made of a single parable, which can also be considered as, in this simplification, the two branches parabolic proposed by the general invention, coincide, and there is no more than a focus, which is 88.

The radiation 91 reflected by the second mirror Parabolic is composed of two families of rays: the internal or first, 92, which directly affects the tube, and is contained between two extreme rays, 93 and 94, these two rays being the tangents to the surface of the tube 82, and the second family or external, which are the rays, on each side, external to the rays Tangents mentioned. On the right side (the left is symmetric) the outermost ray of that second family of rays is 95, which corresponds to the one reflected from the point, 96, end right of the mirror 90, which in turn corresponds to the reflection of the ray 97, reflected from the end 98 of the first mirror, 79.

In turn, lightning 93, tangent to the surface from tube 82 on the right, comes from the reflection in point 99, of mirror 90, of ray 100, reflected from point 101 of the first mirror, 79.

The second family of rays, on the side right, it is constituted by all the rays that affect the mirror 79, between points 101 and 98 identified above. Rays that internally affect the 101, form the first family of Ray.

The invention thus consists in putting a second parabolic mirror co-focal 90 wider than the tube diameter 82, and numerical location specifications of that mirror are given below. That provision generates two lightning families: a first family of lightning strikes directly on the tube after the second reflection, and a second family that passes by with respect to the tube, after the second reflection. The invention is complemented by the addition, for each side, of two longitudinal mirrors, 102 and 103, integral to the U-clamp 80 through short straps, 104. For each side, these mirrors 102 and 103 reflect the rays of the second family on the tube 82, on the underside of it, with respect to the mirror 90, thus achieving a much more uniform illumination on The tube. For completing the explanation, although not part of the invention, it is indicated that the mirror 90 also rotates integral with the U-clamp, 80, and mirror 79 for being attached to the structure of the latter through the braces 105, which are arranged in the joints between consecutive modules of tubes, of the fixed tube 82.

To prescribe the position of the mirror 90 and of its significant points, the coordinate system of Figure 1, in this case the parabola corresponding to the profile of the mirror, 79, with one exception. For the constructive disposition of this type of collectors, there is no physical apex of the parable 79, which does not prevent it from being considered existing as an entity of reason to fix in it the origin of coordinates. If that there is the apex of parable 90, which we call 106, and it is a essential point to locate the mirror 90 precisely.

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At any point identified in this system, they have an abscissa and an ordinate, which we denote by X and Y followed by the identification number of the point. For example, the apex of parabola 90, point 106, will have coordinates X106 e Y106.

Similarly it will be denoted with M, followed by number of the line or ray in question, on the slope of said line or lightning

Since the parable of the profile of this mirror 90, must have the same focus as that of mirror 79, must be used that condition as fundamental for its positioning. Remembering that the apex of parabola 90 is point 106, the equation of this parable is written as

one

b being the fundamental parameter of the parabola, which is the coefficient of proportionality between the square of the abscissa and the value of its ordinate, both counted values from its own apex (not from the general system of reference, in which the equation is expressed as such). Between the ordinate Y108 and the one of focus 88, is fulfilled, as property essential of the parable

2

Well, that is the focal length. So well, parable 90 can be written how

3

The value of Y88 is known, for being the orderly of the focus of the parable of the first mirror, but another one is necessary equation to determine b. That equation is given by the points counterparts of mirrors 79 and 90 in the successive reflection of rays. Specifically, it is enough to specify what the reflected ray should be of the extreme beam on the right, because the left part will be symmetric More exactly, you must specify which is the half-width (width of the right side) of radiation 91 reflected from 90. If that half-width value is called W, that it will be the abscissa of the right end point 96, of the mirror 90. But the point 96 must also be on the straight line of ray 97, which goes from the right end, 98, of the mirror 79, towards the focus 88, to which would arrive if the mirror 90 did not intercept it. The straight line of lightning 97 is can write as

4

where M97 is the slope of the straight, what okay

5

Combining the above equations you have

6

And since it has been specified that parable 90 and line 97 must be cut at an abscissa point W, it have

7

Which leads to the next value of b

8

So, the value of b, which determines uniquely parabola 90, according to equation (3), is fixed to the specify M97, which depends on the focal length and aperture from the first parable, 79, plus the semi-width specification W that is set for the radiation reflected by the mirror itself 90.

We must remember the important caveat that in this case the absorber tube has been simplified, assuming that It has no transparent cover, or that it has effects negligible about radiation. This in general is not acceptable, although the previous specifications on parabolic mirrors Co-focal points are perfectly valid in general. To address the general case, with transparent cover included, it has to resort to the general case of the invention, which uses two branches consecutive parabolics on each side, which is represented in the Figure 3 for this type of collectors.

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B) Method of realization of the general case

Figure 3 shows that the mirror Primary parabolic is formed, as prescribed by the invention in its general form, by two successive branches with different focuses, the inner branch being less focal length than the outer one. The inner branch is denoted by 107 and does not close in the area central, where is the axis of symmetry 73, which is where the apex of parable 107, which is why it is taken as virtual origin of the set coordinate system, for which it serves all the effects. The mirror of the outer branch is denoted by 108, and begins in the immediate vicinity where the first mirror ends, although physically there is a discontinuity for being functions different, both parabolic, but with different focuses. The inner parable 107 extends between the inner points, 109, and external 110; and outer branch 108 extends between points 111 and 112. The focus of parable 107 is point 113, and that of the Parable 108 is 114, which is above the previous one.

Lightning 117 is reflected from point 109, which falls and is reflected in point 119 of mirror 115, located before Lightning 117 reaches its focus. For being the 115 cofocal mirror with 107, according to the prescriptions given above, lightning 120 reflected from 119, goes in a downward direction parallel to the axis of symmetry 73, which is the axis of ordinates. The figure is not to scale, in order to identify all the elements, since the mirror 107 will be in industrial assemblies much larger than the radius of tube 82 and that the semi-opening of the U-clamp beam 80. This is indicated because the lightning 120 will affect tube 82 very close to its maximum point dimension, 121. The transparent cover 122 is included in the assembly, which, like tube 82, is fixed with respect to ground, being its center 81 the center of rotation of the U-80 clamp and all the set of reflective elements.

The aforementioned ray 117, which generates 120, is the innermost of the first family of rays, and the outermost is the 118. The latter affects mirror 115 at point 123, from which reflects ray 124, parallel to the axis of symmetry, and tangent to tube 82 at point 125. The rays of the first family, after double reflection in mirrors 107 and 115, affect on the upper face of the tube 82.

The second family of rays is caused by those reflected in the mirror 108. From its inner end 111 it reflects the beam 126, which falls on the mirror 116 at point 127, from which it is reflected as ray 128, which is tangent by the right to the transparent cylindrical cover 122. The beam, in the limit of its tangency, continue until you find the mirror 102, and introduced in figure 2, although the cover was not included transparent. From the mirror 102, the ray 128 is reflected in the point 129, to influence point 130 of tube 82, which corresponds to its minimum orderly point. Similarly, from point 112 it reflects lightning 131, which is the outermost of the second family, and goes to focus 114, which does not reach by impacting on the mirror 116 at point 132, from which lightning 133 is reflected, parallel to the axis of symmetry 73, and that will affect the mirror 102 in the point 134, from which it is reflected on point 125 of tube 82. In that way, the second family of lightning strikes in the end on the lower face of tube 82, thereby unifying considerably the radiation received by the tube, that of not having this arrangement with two families of rays and mirrors additional, it would only be illuminated on its upper face. A representation of the straight section of the collector of the invention, with the two parabolic branches in the primary mirror and the consequent secondary mirrors respectively co-focal to a and another branch, is presented in figure 4.

For the location of the mirror 102 there is a degree of freedom, relative to choosing one of its dimensions (the left, 103, it would be symmetric). Still recognizing this degree of freedom in the invention, is proposed as an especially simple embodiment and recommended, the one shown in figure 5. In it the mirror 102, and symmetrically its counterpart on the left side, 103, stands with an inclination of 45º sexagesimal, that is, with a pending 1; and its lower ordinate, that of point 129, is equal to that of point 130 with the lowest abscissa on the surface of tube 82. The ordinate of its upper point, 134, is equal to the ordinate of the point 125 on the surface of the tube (the one with the highest positive abscissa) than in turn it coincides with the ordinate of the center 81 of the tube. In the figure 5 fins 137 are also appreciated, for cooling the mirrors 102 and 103. This embodiment of the invention is complete making the width, in abscissa, of the radiation of the second family of rays, contained between rays 128 and 133, be equal to the radius of the tube, R. Given the homology between cited rays and points 129 and 134, this can be written how

9

What is completed with the prescriptions

10

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eleven

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The invention is further completed with the requirements to locate and define the profile of mirrors 115 and 116 (Figures 3 and 4), as well as 102 in the general case, although already in Eqs. (9) to (11), a specification for the latter, for a specific case, which is recommended by the combination of simplicity and equitable distribution of radiation between upper and lower faces of tube 82, although within each face The radiation does not affect evenly.

For mirror 115, the prescriptions of equations (1) to (6), with the specification of that the parameter W, applied to point 123 of that mirror, is the radius of tube 82, R

12

And the equation of mirror 115 is

13

being c the fundamental parameter of this parable, which is the coefficient of proportionality between the square of the abscissa and the value of its ordinate, both counted values from its own apex (not from the general system of reference, in which the equation is expressed as such). Following the prescriptions of equations (1) to (6), you have that parameter c okay:

14

M118 being the slope of the beam 118, which is

fifteen

The inside point of the mirror 115 (see figure 3) is automatically determined by the intersection of equation (13) of the parabola with the line that joins point 109 inside the internal primary mirror, with its focus 113; and in fact it is not necessary that determination for the realization of the mirror, which can be done all followed to the axis of symmetry 73, plus its left branch symmetrical, which gives it more mechanical consistency.

For mirror 116, the prescriptions of equations (1) to (6), with the specification of that the abscissa width of this mirror depends on the amount of radiation that you want to send to the underside of tube 82, regarding the one sent to the upper face. If both radiations totals of the first and second family must be practically equal, the parameter W, applied to point 132 of that mirror, which we call X132 to match the abscissa of point 132 is

16

The equation of the parable of the mirror 116 is

17

where its parameter d, analogous to b and c previously presented, okay:

18

with

19

The interior point of the mirror 116 is determined for being that of the parable (equation 17) in the abscissa of point 129, What is it

twenty

In this case the mirror can also be extended to the axis of symmetry, to give greater mechanical consistency to the set, but that has to be made compatible with fins 138 (see Figure 4) to be placed on the top of both mirrors, to facilitate cooling. In that sense, these mirrors 115 and 116 are equipped with those upper fins, 138, which in turn do of elements of structural rigidity, and are arranged longitudinally on both mirrors, as well as transversely, with topology of honeycomb, which provides structural resistance and cooling to These mirrors

The additional mirror 102, and its symmetric, can be located as discussed with the immediate solution of figure 5, but in general terms it can be located differently, for which is to follow a set of design steps that are detailed then. As a starting point, a form is chosen parabolic for the profile of the mirror 102, which we define as

twenty-one

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And its slope

22

As part of the invention the following are given guidelines for determining the coefficients of the mirror equation, although other algebraic routes are possible, but they are less rooted in the geometric optics of the matter.

The process steps are

one.

Pin up Y134 on line 133, because X134 is fixed or chosen based on whatever has been decided when choosing the width of the mirror 116, so that

2. 3

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2.

The slope of the mirror 102 at point 134 causes the reflected beam, 135, go from point 134 to 125. To do this the slope (straight tangent) at point 134, that is Y'134, is in the bisector of perpendicular to ray 135 and perpendicular to ray 133, being the latter perpendicular a horizontal line in the system of coordinates used, so its slope is 0. The slope of the lightning 135 is

24

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So the slope Y'134 is

25

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3.

Known X134, Y134 and Y'134, it have the equations

26

27

Which allows express two of the coefficients according to the third, for example F0 and F1 depending on F2.

28

29

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Equations that are completed with the prescription additional, of a self-consistent nature, whereby lightning 136 that is reflected in point 129 of mirror 102, affects point 130 of tube 82, which is the lowest ordinate point on the surface of the tube. This prescription must be consistent with the function of the parable 102 and its first derivative, because the perpendicular to its Tangent is the angle bisector formed between ray 128, incident at point 129, which is the innermost of the mirror 102, and the beam reflected from 129, which is 136, which impacts the tube at point 130, the slope at 129 being the following

30

or equivalently, for the application of the prescription

31

and the prescription is resolved algebraically through an iteration that starts from a value Y'129 attempt, which is

32

which corresponds to flat mirror, this is F2 = 0, which is what equation (31) gives for that value, and for what is determined that

33

using these values of Y129 e Y'129 in the calculation of the ordinate where the straight line of lightning 136 cuts to the ordinate axis, giving the iteration concluded if that ordered matches, within the tolerances of solar radiation, with the ordinate of point 130; which is calculated from the slope of lightning 136, which is M136,

3. 4

having lightning 136 the equation

35

that cuts to the ordinate axis in the ordered Y0136, which corresponds to

36

and if Y0136 matches Y130 inside of the tolerances, said point 129 is valid, and valid is the equation (21) of mirror 102 with the coefficients F2, F1 and F0 that are is it so using;

and, in the general case of not matching, it is defined a figure of merit or approximation, which is

37

proceeding to a new calculation of the iteration according to the following instruction, which depends on whether the FA_ {1} value is positive or negative, so if it is positive, a new value of the slope Y'129 is taken that is a 10% higher than the previous one, and with this new value Y'129_ {1} recalculate F2 by equation (31) which is identified as F2_ {1} in the nomenclature followed, and that corresponds to

38

39

40

which in turn gives a new point 129, whose ordinate is, depending on the abscissa X129, always fixed for being lightning 128,

41

what allows, by using Equations (34) to (36), calculate the new ordinate at the origin of line 136, which we identify as Y0136_ {1}, and with which the new value of the figure of merit is calculated or approach

42

and if it is still FA_ {2} positive, the value of Y'129 is increased again, in such a way that in the n-th iteration okay

43

and the result of the iteration n-sima be

44

continuing the sweep of the iteration until the result FA_ {n + 1} is negative, in which case is linearly interpolated between the value of Y'129_ {n} e Y'129_ {n-1}, to give a null result of FA, the interpolated value of Y'129 being the one that meets the prescription of the mirror, and from which the values of F2, F1 and F0 expressing their position and profile;

and sweeping in the opposite direction, that is, progressively decreasing Y'129, if the value of FA_ {1} is negative, applying to the iteration n-th the value of

Four. Five

continuing the sweep of the iteration until the result FA_ {n + 1} is positive, in which case is linearly interpolated between the value of Y'129_ {n} e Y'129_ {n-1}, to give a null result of FA, the interpolated value of Y'129 being the one that meets the prescription of the mirror, and from which the values of F2, F1 and F0 expressing their position and profile;

mirror 103 is placed symmetrically to 102, each of the mirrors being in solidarity with the inner face of the clamp 80, by means of a clamping foot 104 for each mirror, and the mirrors having fins of cooling 137 on its opposite side to the reflective one.

An essential feature in the invention is that the entire optical structure of the collector, which includes its mirrors primary, secondary and tertiary, rotates in solidarity with each other and in solidarity with the beam-clamp 80, around of the absorber tube, 82, fixed with respect to ground. This condition of fixed tube is achieved by seating it on firm feet to the ground, which does not are subject of the invention, but the invention does contemplate how allow the entire optical system to rotate and the beam-clamp 80, around the fixed tube. For this takes into account that the active absorber tube modules, that carry the transparent cylindrical cover, have a length finite, about four meters, finishing the modules with about circular crown strips that are welded to the tube and cover, protruding a piece of tube to be welded to the next module. That welding zone is covered with a thermal insulator, 139, around which, in the invention, a bearing is arranged cylindrical bearings, 140, whose outer face, 141, is fixed to a Staff 142 with two transverse legs 143 that seat, through its longitudinally cylindrical feet, 144, on two rails longitudinal, 145, fixed on the beam-clamp 80, so in addition to allowing the entire optical assembly to rotate around the center, 81, of tube 82, allows the tube to change from length with respect to the optical assembly, depending on the temperature, as the bearing will move longitudinally as produce such length variations.

The described modes do not exhaustively cover the invention, and it is noted that the particular embodiments described above are subject to modifications of detail as long as they do not alter the fundamental principle and the essence of the invention.

Claims (4)

1. Calculation procedure for a parabolic trough solar collector with standardized double reflection, in which the direct solar radiation is reflected by a cylindrical mirror with a parabolic profile, and in which the radiation concentrated towards its focus is reflected again in a secondary co-focal mirror, in the opposite direction to the one that led after the first reflection, and in a direction parallel to the axis of symmetry, because the second mirror has the same focus as the first, so that the doubly reflected radiation hits the tube absorber, which in this case is fixed to the ground, and does not rotate as the optical set of the co-focal mirrors, which, for collimation in the sun, revolve around an axis of rotation that coincides with the central axis of the absorber tube, being the optical assembly and its structure supported by a thick U-clamp, which is integral with a hollow cylinder that rests on a bearing embedded in a pillar, having at each longitudinal end of the manifold one of these pillars, and having at the ends of the tube modules, and of its transparent cylindrical cover, braces that support the secondary co-focal mirror on the first distance, characterized by the fact that The primary mirror is divided into two branches consecutive parabolics on each side, being the first or more internal, 107, the one with the smallest focal length of the two, and whose virtual apex is used as the origin of coordinates, as the real apex does not exist physically, because the area around the virtual apex is occupied by the absorber tube 82 and its cylindrical cover transparent, 122, which are fixed and do not interfere with the rotating movement of the optical system, which in the primary mirror it has the aforementioned inner branch 107, and the outer branch 108, whose focus 114, with ordinate Y114, is on the axis of symmetry of the inner parable, but above focus 113, with ordinate Y113, of this, forming the rays reflected by the inner branch 107 the first family of rays, which before reaching its focus 113 are reflected by a downward convex mirror 115, whose focus is thus same focus 113, so the rays are directed towards the upper face of the fixed tube 82, where they are absorbed; having one second family of rays, which is initially reflected by the branch 108, which focuses on its focus 114, although before arriving he finds mirror 116, co-focal with 108, convex down, which reflects the rays in a direction parallel to the axis of symmetry, in trajectories that do not directly affect the tube 82, but they pass by, just beyond the deck transparent, until you find an additional mirror, 102 on the side right, there is reciprocal correspondence on the left side, where is the mirror 103, reflecting in both the branches corresponding to the second family of rays, which after that additional reflection impact tube 82 on its underside, understanding the top-down orientation and upper-lower than the system coordinates of the collector that has its origin at the apex of the parable 107 of the inner primary mirror, not with respect to the Earth's gravity, thus illuminating the entire surface of the tube, and not only the upper face, for which the invention includes a series of geometric prescriptions that are detailed to then using the Cartesian reference system that has been explained, which is integral to the optical assembly and its entire structure, so that in the turn to point the axis of symmetry to the sun, no there are variations of their relative positions, and there are materially with respect to the fixed tube 82 and its cover, but they are not geometrically significant for the tube, as the center of rotation coincides with the center 81 of the tube, placing the mirrors co-focal according to the following prescriptions, which for mirror 115 they start from their outermost point, 123, whose abscissa is X123, and is located in the cut of the rays of the rays 118 and 124, defining X123 as being equal to the radius of tube 82, R 46 being the mirror equation 115: 47 where its parameter c okay: 48 with 49 where X110 and Y110 are the coordinates from point 110, which is the outer end of the parabolic branch interior 107 of the primary mirror, and determining the interior point of mirror 115 automatically by the intersection of the equation (13) of the parabola with the line that joins the innermost point 109 of the internal primary mirror, with its focus 113; although the prescription it is completed constructively because the body of that mirror is you can do everything often to the axis of symmetry, plus its branch symmetric left, for reasons of mechanical consistency; Y using to define the mirror 116 prescriptions based on the specification that the abscissa width of this mirror is determined by the abscissa of point 132, which is the outer end of that mirror, and what we call X132, being its value fifty where the parable equation from mirror 116 is 51 and its parameter d okay: 52 with 53 where X112 and Y112 are the coordinates from point 112, which is the outer end of the parabolic branch exterior 108 of the primary mirror; and in turn the interior point of mirror 116 is determined to be that of the parable given by the equation (17) for the abscissa of point 129, which is 54 but the mirror extends until the axis of symmetry, by mechanical consistency of the set, including in this set the longitudinal cooling fins 138 and in the upper part of the assembly of both mirrors 115 and 116; completing the invention with the mirror arrangement additional 102, and its symmetric 103, whose location requirements and profile start from defining the parabolic shape of the mirror 102 how 55 and his pending 56 whose coefficients are determined with the prescriptions that follow, starting by setting the ordered, Y134, of point 134, which is the outermost of the mirror 102, on line 133, because abscissa X134 is fixed by 57 M135 being the slope of the beam 135 that goes from 134 to point 125, which is the most abscissa of the absorber tube surface, 82, the given value by 58 and the slope of the mirror 102 in the point 134, Y'134, is 59 disposing of the equations 60 61 with the values X134, Y134 and Y'134 said above, so it have 62 63 that are completed with the additional prescription, of a self-consistent nature, for which the ray 136 which is reflected in point 129 of mirror 102, affects the point 130 of tube 82, which is the lowest ordinate point in the tube surface, which must be consistent with the function of the parable 102 and with its first derivative, which is such that its perpendicular is the angle bisector formed between ray 128, incident at point 129, which is the innermost of the mirror 102, and the beam reflected from 129, which is 136, which impacts the tube at point 130, the slope being 129 at next 64 or equivalently, for the application of the prescription 65 and the prescription is resolved algebraically through an iteration that starts from a value Y'129 attempt, which is 66 which corresponds to flat mirror, this is F2 = 0, which is what equation (31) gives for that value, and for what is determined that 67 using these values of Y129 e Y'129 in the calculation of the ordinate where the straight line of lightning 136 cuts to the ordinate axis, giving the iteration concluded if that ordered matches, within the tolerances of solar radiation, with the ordinate of point 130; which is calculated from the slope of lightning 136, which is M136, 68 having lightning 136 the equation 69 that cuts to the ordinate axis in the ordered Y0136, which corresponds to 70 and if Y0136 matches Y130 inside of the tolerances, said point 129 is valid, and valid is the equation (21) of mirror 102 with the coefficients F2, F1 and F0 that are they are using; and, in the general case of not matching, it is defined a figure of merit or approximation, which is 71

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proceeding to a new calculation of the iteration according to the following instruction, which depends on whether the FA_ {1} value is positive or negative, so if it is positive, a new value of the slope Y'129 is taken that is a 10% higher than the previous one, and with this new value Y'129_ {1} recalculate F2 by equation (31) which is identified as F2_ {1} in the nomenclature followed, and that corresponds to 72 73 74 which in turn gives a new point 129, whose ordinate is, depending on the abscissa X129, always fixed for being lightning 128, 75 what allows, by using Equations (34) to (36), calculate the new ordinate at the origin of line 136, which we identify as Y0136_ {1}, and with which the new value of the figure of merit is calculated or approach 76 and if it is still FA_ {2} positive, the value of Y'129 is increased again, in such a way that in the n-th iteration okay 77 and the result of the iteration n-sima be 78 continuing the sweep of the iteration until the result FA_ {n + 1} is negative, in which case is linearly interpolated between the value of Y'129_ {n} e Y'129_ {n-1}, to give a null result of FA, the interpolated value of Y'129 being the one that meets the prescription of the mirror, and from which the values of F2, F1 and F0 expressing their position and profile; and sweeping in the opposite direction, that is, progressively decreasing Y'129, if the value of FA_ {1} is negative, applying to the iteration n-th the value of 79 continuing the sweep of the iteration until the result FA_ {n + 1} is positive, in which case is linearly interpolated between the value of Y'129_ {n} e Y'129_ {n-1}, to give a null result of FA, the interpolated value of Y'129 being the one that meets the prescription of the mirror, and from which the values of F2, F1 and F0 expressing their position and profile; mirror 103 being placed symmetrically to 102; each of the mirrors being in solidarity with the inner face of the clamp 80, by means of a clamping foot 104 for each mirror, and the mirrors having fins of cooling 137 on its opposite side to the reflective, the optical structure of the collector, which includes, on the right side, a the primary mirrors (107 and 108) secondary (115 and 116) and tertiary (102), and its symmetrical, solidarity with each other and solidarity to the beam-clamp 80, turning all around of the axis of the absorber tube 82, which is fixed with respect to land.

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2. Cylinder-parabolic solar collector with standardized double reflection, calculated according to the method of claim 1, characterized in that the additional mirror 102 is located as a flat mirror with an inclination of 45 ° sexagesimal, and therefore with a slope equal to 1, being its upper-outer end point 134 on the line of abscissa marked by ray 133 and on the ordinate of point 125, which is the largest abscissa on the surface of the tube 82; and the mirror 102 having its inner-lower end point 129 in the line of abscissa marked by ray 128, from which there is a distance in abscissa, to ray 133, equal to the radius R of tube 82, and being the ordinate of the point 129 equal to the ordinate of point 130, the lowest ordered on the surface of the tube 82; and mirror 103 being placed symmetrically to 102. 3. Cylinder-parabolic solar collector with standardized double reflection, calculated according to the method described in any one of claims 1 or 2, characterized in that the illumination on the tube is uniformized with a single parabola in the primary mirror, with the two branches attached one after the other with the same focal length, whereby the co-focal mirror 90 is likewise of a single parabola with the same focus 88, and with a semi-width of that mirror 90, on each side, in abscissa, greater than the radius of the tube 82, directly affecting the central part of the radiation reflected by the mirror 90, which is parallel to the axis of symmetry 4, comprised between rays 91 and 93, which are tangent to the surface of the tube 82 on the left and right, and the radiation outside the beam 93 affecting the mirror 102, which reflects said radiation outside the beam 93, on the underside of the tube 82; the symmetrical happening with the mirror 103 on the left side. 4. Cylinder-parabolic solar collector with standardized double reflection, calculated according to the method described in any of the preceding claims, characterized in that the welding zone between consecutive modules of absorber tube 82 is covered with a thermal insulator, 139, around which a cylindrical bearing of bearings 140 is disposed, whose outer face, 141, is fixed to a staff 142 with two transverse legs 143 which seat, through their feet in a longitudinal cylindrical shape, 144, in two longitudinal rails, 145, fixed in the beam-clamp 80.