Patent Application
20060207590
Not Applicable.
This invention relates to the field of solar radiation collectors intended to convert energy of solar radiation into thermal energy, especially, to the solar collectors, which incorporate single-curvature or compound-curvature concentrators.
In the case of application of single-curvature parabolic mirrors as the concentrators, the modular solar radiation collector is constructed as combination of an elongated receiver, the single-curvature concentrator and a tracking mechanism, which ensures steady positioning the elongated receiver in the focal zone of the single-curvature concentrator.
It is known, that such solar collectors allow to achieve temperatures of a working fluid significantly higher than 100° C.; this in turn gives possibility to apply obtained thermal energy in different processes of industry or to convert this thermal energy into electricity with sufficiently high coefficient of performance.
In the most cases, the single-curvature concentrator is constructed as a trough-wise parabolic mirror or a single-curvature Fresnel lens.
The elongated receiver is constructed usually as a pipe with an outer coating intended to absorb concentrated and direct solar radiation, and a transparent (glass) elongated envelope positioned around the pipe. The transparent envelope is sealed with the pipe at its ends and the gap between the pipe and the elongated envelope is vacuum-insulated in order to suppress convective losses of thermal energy from the outer surface of the pipe.
There are some drawbacks, which characterize this construction.
1. Concentrated solar radiation illuminates only a part of the whole surface of the radiation receiving pipe; at the same time, heat loss by radiation occurs from the entire outer surface of this pipe.
2. Sealing the metal pipe of the receiver with the glass envelope is very expensive and sophisticated from the technological point of view.
3. It is impossible to insulate thermally the radiation receiving pipe in a modular manner.
4. Low strength of the glass envelope does not give possibility to apply this glass envelope as a carrying element of the construction of a solar collector.
Same drawbacks are true for the common solar collectors with application of compound-curvature dish-type concentrators.
A first version of this invention proposes a solar radiation modular collector with a concentrating unit of the single-curvature type (one-axis sun tracking concentrator) and with a receiver of concentrated solar radiation in the form of a radiation receiving pipe.
The radiation receiving pipe is provided with a thermal insulation layer in the form of a metal envelope, which can be vacuum-insulated or filled with material with low thermal conductivity. In addition, the internal cavity of this metal envelope can comprise some radiant shields from metal foil with high reflection coefficient in the infrared range. The single-curvature concentrator can be constructed as a parabolic trough-wise reflector, or as a single-curvature Fresnel lens or mirror.
The metal envelope insulates most of the outer surface of the radiation receiving pipe with significant diminishment of heat losses caused by convection and radiation from this part of the outer surface.
The metal envelope of the radiation receiving pipe is constructed from two elongated internal and external sections, which are joined by two elongated connection straps and sealed at their ends by face planes.
The internal elongated section comprises a cylindrical sub-section, which encloses a significant part of the radiation receiving pipe; this cylindrical sub-section is transformed at its longitudinal margins to flat or single-curved strips with a certain angle of convergence with respect to the cylindrical sub-section. In such a way, the cross-section of the internal section is somewhat similar to the vertical cross-section of a jug. The external section encloses the internal one.
The internal cavity between the internal and external sections of the metal envelope is evacuated in order to suppress convective loss of heat. In addition, this space can be filled with a porous material and/or layers of metal foil in order to diminish heat loss by radiation.
It is possible to apply filling the internal cavity of the metal envelope with a gas with low thermal conductivity, for example, krypton.
The gap between the elongated connection straps is glazed in order to diminish heat losses, which occur from the part of the radiation receiving pipe that is not enclosed by the cylindrical sub-section of the internal elongated section.
It should be noted, that some metal envelopes, which are constructed as it has been described about, could be situated sequentially around one radiation receiving pipe.
Thermal losses in the proposed construction of the thermal insulation occur mainly by three ways:
It is clear, that limited thermal conductivity of the walls of the metal envelope causes temperature gradient in it and in turn this can cause deformation of the metal envelope.
In order to prevent this, the internal and external sections of the metal envelope can be provided with corrugations, which decrease to zero in the vicinity of the connection straps. These corrugations can be directed inwards or outwards with respect to the internal cavity of the metal envelope.
The outer surface of the external section of the metal envelope can be painted with black or selective paint with very low emittance coefficient in the infrared range; it allows to elevate temperature of the external section of the metal envelope at the expense of the direct solar radiation falling on its surface. It in turn diminishes heat losses caused by thermal conductivity of the metal envelope and by radiation and thermal conductivity via the internal cavity of the metal envelope.
The proposed receiver of the solar radiation can be rigidly joined by a set of truss struts with the single-curvature concentrator, which should be turned by a tracking mechanism in accordance with the sun motion. In this case, the receiver is turned and moved through turning the single-curvature concentrator.
However, the mechanical strength of the metal envelope allows to construct the modular solar collector in such a way, that its metal radiation receiving pipe is stationary, and the metal envelope with the single-curvature concentrator, which is rigidly joined with the metal envelope by the set of the truss struts, is turning around the metal radiation receiving pipe by the tracking mechanism. In such a way, the radiation receiving pipe plays the role of a bearing element and an axle.
The radiation receiving pipe can be provided in this case with a set of ribs in order to prevent contact of the internal surface of the metal envelope with the black or selective coating of the radiation receiving pipe. In addition, the cylindrical surface of these ribs can be provided with an antifriction coating.
The proposed construction of the thermal insulation of the radiation receiving pipe allows to assemble the solar radiation collector in modular manner without expensive sealing between a glass cylindrical envelope and the radiation receiving pipe.
Some solar radiation modular collectors can be situated in some rows and the solar radiation modular collectors, which are positioned in the parallel rows, can be provided with common tracking mechanisms.
The second version of the proposed solar collector is based on application of same technical solutions in the case, when compound-curvature concentrators and, particularly, dish-type parabolic mirrors are used as the concentrators of solar radiation.
In the case of application of the compound-curvature concentrators in the form of the dish-type mirrors, a module of the proposed system comprises a bearing pipe that is mounted on the vertical posts. A heat transfer medium (working fluid) flows in the bearing pipe.
The bearing pipe is provided with a layer of thermal insulation.
Some T-pieces are built into the bearing pipe. The lower branch of each T-piece is sealed by a metal convex spherical cap and a part of the outer surface of the T-piece is covered with a layer of thermal insulation.
In addition, there is a solar radiation receiving member, which is constructed from a dish-type plate and a double-wall funnel.
The upper side of the dish-type plate has the concave surface in the form of a spherical segment with the radius almost identical to that of the metal convex spherical cap. In such a way, this pair: the spherical cap of the T-piece and the concave surface of the dish-type plate present a spherical joint. The lower surface of the dish-type plate is covered with a layer of a solar radiation absorption coating.
The upper surface of the dish-type plate and the outer surface of the metal convex spherical cap can be provided with antifriction coatings.
The upper edge of the internal wall of the double-wall funnel is joined with the edge of the dish-type plate and the edge of its outer wall is provided with a flange.
The distal (lower) aperture of the double-wall funnel can be glazed in order to diminish heat losses via its internal cavity. In addition, this glazing can be provided with a transparent coating, which reflects back infrared radiation from the layer of the solar radiation absorption coating of the dish-type plate.
The internal surface of the internal wall of the double-wall funnel can be provided with the property of high reflectivity for solar radiation; in such a way, this internal wall plays a role of an additional non-imaging concentrator of the solar radiation.
There is a bearing housing with a split lower flange and two longitudinal slots; this housing is mounted on the thermal insulation of the T-piece.
The open sections of the longitudinal slots are closed by a clamp.
The flanges of the bearing housing and the outer wall of the double-wall funnel are joined by a flexible joint, which plays at the same time a role of a thermal insulator.
The outer wall of the double-wall funnel serves at the same time for mounting truss struts, which serve in turn for installation of a dish-type concentrating mirror with its frame.
The frame of the dish-type mirror is joined through cylindrical hinges with tracking rods.
The internal cavity between the walls of the double-wall funnel and between the flexible joint and the lower branch of the T-piece can be filled with thermo-insulating material with low thermal conductivity.
It should be noted that heat transfer from the internal surface of the spherical cap to the working medium is performed mainly by natural convection, conduction and boiling. In order to diminish temperature drop between this internal surface and the working medium, the internal surface of the spherical cap may be provided with fins and/or a porous coating from metal powder; this porous coating has open porosity.
It is possible to apply a funnel with a single wall instead of the aforementioned double-wall funnel; in this case the lower edge of the funnel is joined with a connecting branch with a flange; this connecting branch is joined in turn with the lower flange of the flexible joint. The truss struts are joined in this case with the connecting branch.
In addition, it is possible to obviate application of the dish-type plate. The outer surface of the metal convex spherical cap is provided in this case with a radiation absorption coating. This coating must be stable against friction with the upper edge of the aforementioned double- or single-wall funnel.
A solar radiation collector can be assembled from some solar radiation modular collectors, which are described above; these some solar radiation modular collectors are placed in the form of parallel rows and bearing pipes are interconnected in series in each row.
The solar radiation modular collectors, which are positioned in parallel and/or belong to one set of interconnected in series bearing pipes, have the common tracking units.
It comprises: a radiation receiving pipe 101 with a selective coating 102 of its outer surface and low circular ribs 103, and a metal envelope 104.
This metal envelope includes an internal elongated section 105 and an external elongated section 106, which are joined by two elongated connection straps 107 and sealed at their ends by face planes; the internal elongated section 105 comprises in turn a cylindrical sub-section 108, which encloses a significant part of the radiation receiving pipe 101; this cylindrical sub-section 108 is transformed at its longitudinal margins to flat strips 109 with a certain angle of convergence with respect to the cylindrical sub-section 108.
The external elongated section 106 comprises a cylindrical sub-section 110, which encloses the cylindrical sub-section 108; this cylindrical sub-section 110 is transformed at its longitudinal margins to flat strips 111 with the same angle of convergence as the flat strips 109.
Two elongated connection straps 112 join the flat strips 109 and 111.
The internal space between the internal and external sections is evacuated in order to suppress convective losses of heat. In addition, this space can be filled with a porous filler 113.
In addition, radiation shields in the form of metal foils 114 are situated in the internal cavity of the metal envelope 104.
The flat strips 109 are provided with longitudinal clamps 115, which serve for fastening glazing 116.
It comprises a cylindrical sub-section 201, which is transformed at its longitudinal margins to flat strips 202.
The cylindrical sub-section 201 and the flat strips 202 are provided with corrugations 203, which decrease to zero at their lower margins, these corrugations 203 are directed inwards with respect to the cylindrical sub-section 201.
It comprises a cylindrical sub-section 301, which is transformed at its longitudinal margins to flat strips 302.
The cylindrical sub-section 301 and the flat strips 302 are provided with corrugations 303, which decrease to zero at their lower margins, these corrugations 303 are directed outwards with respect to the cylindrical sub-section 301.
Flanges 406 are installed on the ends of the metal pipe 401.
It shows posts 501 with pipes 502 installed on their upper sections. A metal envelope 503, which is provided with glazing 504, is situated on pipe 502 and can rotate around this pipe. Truss struts 505 serve for fastening frames 506, which in turn serve for installation of parabolic trough-wise mirrors 507. A common tracking rod 508 is joined by hinged units 509 with frames 506. This allows to perform tracking after the sun motion by a common tracking unit.
It comprises bearing pipes 601 with expansion units 621, which are mounted on vertical posts 602. A working medium flows in the bearing pipes 601. The bearing pipes 601 are provided with layers 603 of a thermal insulation.
T-piece 604 is built into the bearing pipes 601. The lower branch of T-piece 604 is sealed by a metal convex spherical cap 605.
T-piece 604 is covered with layer 606 of a thermal insulation.
In addition, there is a solar radiation receiving member, which constructed from a dish-type plate 607 and a double-wall funnel 608.
The upper side of the dish-type plate 607 has the concave surface in the form of a spherical segment with the radius almost identical to that of the metal convex spherical cap 605. In such a way, this pair: the metal convex spherical cap 605 and the concave surface of the dish-type plate 607 present a spherical joint.
The lower surface of the dish-type plate 607 is covered with layer 608 of a solar radiation absorption coating.
The upper edge of the internal wall of the double-wall funnel 608 is joined with the edge of the dish-type plate 607 and the edge of its outer wall is provided with flange 609.
The distal (lower) aperture of the double-wall funnel 608 is glazed by glazing 610 in order to diminish heat losses via its internal cavity.
There is a bearing housing 611 with a split lower flange 612 and two longitudinal slots; this bearing housing 611 is mounted on the thermal insulation 606 of T-piece 604.
The open sections of the longitudinal slots of the bearing housing 611 are closed by a clamp. The flanges 612 and 609 of the bearing housing 611 and of the outer wall of the double-wall funnel 608 are joined by a flexible joint 613, which plays at the same time a role of a thermal insulator.
The outer wall of the double-wall funnel 608 serves at the same time for mounting truss struts 614, which in turn serve for installation of a dish-type concentrating mirror 615 with its frame 616.
Frame 616 of the dish-type concentrating mirror 615 is joined through cylindrical hinges 619 and 620 with tracking rods 617 and 618.
It comprises: bearing pipes 701 and 702 with insulting layers 703 and 704; T-piece 705 with an insulating layer 706, the lower branch of this T-piece 705 is sealed by a metal convex spherical cap 707. In addition, there is a solar radiation receiving member, which is constructed from a dish-type plate 708 and a double-wall funnel 709.
The upper side of the dish-type plate 708 has the concave surface in the form of a spherical segment with the radius almost identical to that of the metal convex spherical cap 707. In such a way, this pair: the metal convex spherical cap 707 of T-piece 705 and the concave surface of the dish-type plate 708 present a spherical joint.
The lower surface of the dish-type plate 708 is covered with layer 710 of solar radiation absorption coating.
The upper edge of the internal wall of the double-wall funnel 709 is joined with the edge of the dish-type plate 708 and the edge of its outer wall is provided with flange 711.
The distal (lower) aperture of the double-wall funnel 709 is glazed with glazing 712.
There is a bearing housing 713 with a split lower flange 714 and two longitudinal slots; this bearing housing 713 is mounted on the thermal insulation 706 of T-piece 705.
Flanges 714 and 711 of the bearing housing 713 and of the outer wall of the double-wall funnel 709 are joined by a flexible joint 715, which plays at the same time a role of a thermal insulator.
The outer wall of the double-wall funnel 709 serves at the same time for mounting truss struts 716, which in turn serve for installation of a dish-type concentrating mirror with its frame.
It comprises: bearing pipes 801 and 802 with insulting layers 803 and 804; T-piece 805 with an insulating layer 806, the lower branch of T-piece 805 is sealed by a metal convex spherical cap 807. In addition, there is a solar radiation receiving member, which constructed from a dish-type plate 808 and a single-wall funnel 809.
The upper side of the dish-type plate 808 has the concave surface in the form of a spherical segment with the radius almost identical to that of the metal convex spherical cap 807. In such a way, this pair: the metal convex spherical cap 807 of the T-piece and the concave surface of the dish-type plate 808 present a spherical joint.
The lower surface of the dish-type plate 808 is covered with layer 810 of a solar radiation absorption coating.
The lower edge of the single-wall funnel 809 is joined with a connecting branch 811 with flange 812, which is joined in turn with the lower flange of a flexible joint 813. Truss struts 814 are joined in this case with the connecting branch 811, these truss struts serve in turn for installation of a dish-type concentrating mirror with its frame.
The distal (lower) aperture of the single-wall funnel 809 is glazed with glazing 815.
There is a bearing housing 816 with a split lower flange 817 and two longitudinal slots; this bearing housing 816 is mounted on the thermal insulation 806. The split lower flange 817 of the bearing housing 816 is joined with the flexible joint 813, which plays at the same time a role of a thermal insulator serving in turn for installation of a dish-type concentrating mirror with its frame.
It comprises: bearing pipes 901 and 902 with insulting layers 903 and 904; T-piece 905 with an insulating layer 906, the lower branch of T-piece 905 is sealed by a metal convex spherical cap 907.
The outer surface of the metal convex spherical cap 907 is provided with a radiation absorption coating 908.
There is a double-wall funnel 909; the upper edge of this double-wall funnel is in immediate contact with the radiation absorption coating 908 of the metal convex spherical cap 907, and the double wall funnel 909 can be turned in two directions around this metal convex spherical cap 907.
In such a way, this pair: the metal convex spherical cap 907 of T-piece 905 and the double-wall funnel 909 present a spherical joint.
The outer edge of the outer wall of the double-wall funnel 909 is provided with flange 910.
The distal (lower) aperture of the double-wall funnel 909 is glazed with glazing 911.
There is a bearing housing 912 with a split lower flange 913 and two longitudinal slots; this bearing housing 912 is mounted on the thermal insulation 906 of T-piece 905.
Flanges 913 and 910 of the bearing housing 912 and of the outer wall of the double-wall funnel 909 are joined by a flexible joint 914, which plays at the same time a role of a thermal insulator. The outer wall of the double-wall funnel 909 serves at the same time for mounting truss struts 915, which serve in turn for installation of a dish-type concentrating mirror with its frame.
Other embodiments and configurations may be devised without departing from the spirit of the invention and the scope of appended claims.
