Imaging-non-imaging coupling condensation heat collector with photon capture cavity and design method

Abstract

The invention discloses an imaging-non-imaging coupling condensation heat collector with a photon capture cavity and a design method, and belongs to the technical field of solar photo-thermal utilization. The heat collector comprises a linear heat absorbing body, a primary reflecting mirror located below the linear heat absorbing body and an inverted secondary reflecting mirror located above the linear heat absorbing body. The central reflecting area of the primary reflecting mirror is configured to directly converge paraxial light to the light facing surface of the linear heat absorbing body; the edge reflective region is configured to direct the far-axis light to the secondary mirror. Wing plates on the two sides of the secondary reflecting mirror extend downwards to form a semi-closed photon capturing cavity together with the linear heat absorbing body, and the semi-closed photon capturing cavity is used for intercepting edge light rays and secondarily reflecting the edge light rays to the backlight surface of the linear heat absorbing body. Through a cooperative light path of bottom direct injection and top secondary reflection, uniform distribution of energy flow in the circumferential direction of the linear heat absorption body is achieved while the geometric condensation ratio of the system is increased, the risks of pipe wall thermal bending and local heat transfer deterioration are eliminated from the source, and the heat pipe is suitable for high-flux and high-temperature working conditions such as supercritical carbon dioxide circulation.

Description

Technical Field

[0001] This invention relates to an imaging-non-imaging coupled concentrator with a photon trapping cavity and its design method, belonging to the field of solar thermal utilization technology. Background Technology

[0002] Currently, solar thermal power generation (CSP) technology is developing towards higher parameters (operating temperature > 550℃) and higher photothermal conversion efficiency to adapt to new power cycles such as supercritical carbon dioxide (sCO2). However, parabolic trough collectors (PTC), which are most widely used in the field of medium- and high-temperature thermal utilization, face severe thermodynamic and mechanical challenges.

[0003] Pain Point 1: High-Temperature Heat Loss Bottleneck Caused by Low Concentration Ratio Traditional PTCs, limited by imaging optics and the apparent angle of the sun, have long maintained a geometric concentration ratio of 30-40. Due to this low concentration ratio, to ensure light interception, the heat absorber must have a large diameter (typically 70mm-90mm), resulting in a huge heat dissipation area. According to radiative heat transfer theory, radiative heat loss is proportional to the fourth power of temperature. Therefore, when the operating temperature exceeds 450℃, the radiative heat loss of traditional PTCs increases exponentially, leading to a sharp decline in photothermal conversion efficiency and making it difficult to economically generate high-temperature heat energy above 550℃.

[0004] Pain Point 2: Thermal Stress Failure Caused by Unidirectional Concentration Traditional PTCs rely solely on unidirectional light focusing at the bottom, resulting in extremely high energy flux density on the lower semicircular surface of the absorber tube (peak values ​​often exceeding 20 times the average), while the upper semicircular surface receives only weak direct sunlight. This extreme energy flux difference creates a huge circumferential temperature gradient on the absorber tube wall, leading to two serious consequences: first, it causes axial thermal bending deformation of the metal tube (the "banana effect"); second, the huge temperature difference generates severe shear thermal stress at the glass-metal seal, which can easily lead to glass seal failure or even tube rupture ("tube burst"), seriously affecting power plant safety.

[0005] Existing improvement plans and their shortcomings To address the above problems, some attempts have been made in the existing technology, but all of them have significant drawbacks: (1) Approximate fitting scheme: Existing secondary reflectors usually use circular arcs or standard geometric curves to approximate (such as Chinese Patent Authorization Announcement No.: CN201497202U and Application Publication No.: CN101660845A), which cannot perfectly match the complex aberrations generated at the edge of the primary mirror, resulting in severe light spot divergence and making it difficult to achieve theoretical full reception.

[0006] Defect Analysis: The main purpose of this scheme is to approximate high-precision optical surfaces by using low-precision curved surfaces such as planes and arcs. Although this reduces processing costs, it causes severe beam divergence, making it difficult to exceed 30 times the geometric focusing ratio. In addition, the optical path of this design is complex, and some light rays need to undergo three or more reflections, resulting in huge optical efficiency losses. It cannot meet the requirements of high-temperature power generation for high energy flux density and low reflection loss.

[0007] (2) Solid dielectric scheme: Another type of prior art (such as US Patent Application Publication No.: US 2011 / 0100419A1) uses an eccentric parabolic surface and a solid transparent optical structure to achieve uniform irradiation of the photovoltaic cell surface.

[0008] Defect Analysis: This scheme relies on massive solid glass or plastic prisms for light transmission. While feasible in the photovoltaic field (small-scale), in large-scale solar thermal power plants (collectors hundreds of meters long), the weight of the solid medium is staggering and the cost is extremely high, and the volumetric absorption loss of sunlight within the thick solid medium is significant. More importantly, its design primarily pursues low-concentration uniform light (approximately 20 times), lacking the ultra-high concentration (>70 times) and high-temperature tolerance required for high-temperature solar thermal power generation.

[0009] In summary, existing technologies either sacrifice focusing performance for cost reduction, resulting in high optical losses, or their solid optical structures prevent large-scale and high-temperature applications, while also presenting significant weight and cost issues. There is an urgent need for a novel solar collector based on a hollow mirror structure that can simultaneously achieve ultra-high focusing ratio (low heat loss) and circumferentially uniform heating (low stress) to overcome the bottleneck in the development of photothermal technology to the 600℃ temperature range. Summary of the Invention

[0010] The purpose of this invention is to propose an imaging-non-imaging coupled concentrator with a photon trapping cavity and a design method therefor, which solves the problems existing in the prior art.

[0011] The imaging-non-imaging coupled concentrator solar collector with a photon trapping cavity according to the present invention includes: A linear heat absorber extending along the focal line; A primary reflector disposed below the linear heat absorber; and, A secondary reflector is disposed above the linear heat absorber with its reflective surface facing downwards; The primary reflector and the secondary reflector form an open light transmission space; The reflecting surface of the primary mirror is divided into the following sections in cross-section: The central reflective area is configured to directly reflect and converge the received paraxial incident light rays onto the lower half surface of the linear heat absorber; Edge reflective areas, located on both sides of the central reflective area, are configured to reflect and guide the received off-axis incident light rays to the linear heat absorber and the secondary reflector; The secondary reflector is configured to intercept light from the edge reflection zone and reflect the light to the upper half surface of the linear heat absorber; The two sides of the secondary reflector extend downward to form wing plates, and the ends of the wing plates are not lower than the highest point of the linear heat absorber, so that the secondary reflector and the upper surface of the linear heat absorber together define a semi-enclosed photon trapping cavity.

[0012] Preferably, the cross-sectional profile of the central reflective zone is parabolic, quasi-parabolic, circular, or a curve fitted by multiple straight lines; Preferably, the cross-sectional profile of the edge reflection zone is a composite parabolic surface, a high-order polynomial surface, or a freeform surface curve; Preferably, the central reflective area and the edge reflective area are connected in space by a C0 continuity or a C1 continuity, or there is a gap between them.

[0013] Preferably, the reflective surface profile of the secondary reflector is formed by connecting multiple continuous curve segments; Preferably, any point Q on the curve i The optical path coupling condition is satisfied: such that the optical path coupling from the corresponding point P on the edge reflection region is satisfied. i The reflected light rays pass through point Q. i After reflection, it is tangential to the surface of the linear heat absorber.

[0014] Preferably, the secondary reflector has a hollow structure or a thin shell structure, and a heat dissipation structure is provided on its back surface; Preferably, the heat dissipation structure includes heat dissipation fins, which are arranged along the extension direction of the secondary reflector.

[0015] Preferably, the linear heat absorber includes an internal heat absorber tube and an external light-transmitting vacuum cover; Preferably, the radius r of the heat absorber tube is equal to the projection opening width A of the primary reflector. ap The ratio is based on the preset light source segmentation factor K and the system receiving half-angle θ. a It's confirmed.

[0016] The core design parameter "light source segmentation factor K" is defined as follows: At the outermost endpoint of the edge reflection zone (i.e., the end point of the non-imaging segment), its reflected light cone (total angular span of 2θ) a It is decoupled into two parts in terms of angle: Recapture component ΔS2: An angular component with a proportion of K, which is configured to point towards the secondary reflector; Direct component ΔS1: The proportion is (1 The angular component of K) is configured to point directly at the linear absorber.

[0017] The mathematical relationship is expressed as:

[0018] Based on the above definition and the Edge Ray Principle, to ensure that the innermost critical ray (i.e., the boundary ray of the direct component) at the endpoint of the edge reflection zone is tangent to the surface of the heat absorber, the theoretical minimum radius r of the heat absorber can be determined by the following geometric relationship:

[0019] in, e The edge angle is the endpoint of the primary mirror's edge reflection zone relative to the focal point. This formula establishes the intrinsic geometric relationship between the absorber tube size and optical design parameters.

[0020] Preferably, the light reflected by the edge reflection area forms a focal spot at the secondary reflector, and the lateral width of the secondary reflector is greater than or equal to the theoretical width of the focal spot, so as to block the escaping light.

[0021] Preferably, the photon trapping cavity is configured to receive light from the edge reflection region, the light being guided to the backlight region of the linear absorber in at least one of the following ways: (a) Directly projected onto the surface of the linear heat absorber; (b) After being reflected once by the secondary reflector, it is projected onto the surface of the linear heat absorber; (c) After multiple reflections between the secondary reflector and the linear absorber, the image is projected onto the surface of the linear absorber.

[0022] The design method of the imaging-non-imaging coupled concentrator solar collector with a photon trapping cavity according to the present invention includes the following steps: S1: Define design parameters, introduce the light source segmentation factor K, and mathematically decouple the reflected light cone at the endpoint of the edge reflection area into: the direct component ΔS1 directly projected onto the linear heat absorber, and the recapture component ΔS2 projected onto the secondary reflector. S2: Based on the principle of edge rays, the contour of the edge reflection area is constructed using the recapture component ΔS2 as a boundary condition; S3: Determine the minimum theoretical radius and center position of the linear heat absorber based on the edge light trajectory of the edge reflection zone to meet the light interception threshold; S4: Construct the outline of the central reflective zone with the position of the linear heat absorber as the focal point; S5: Construct the contour of the secondary reflector using the reverse iteration method: For points on the contour, establish equations based on the principle of optical path conservation, so that they simultaneously receive light from the edge reflection area and reflect light tangent to the surface of the linear heat absorber.

[0023] Preferably, in step S5: By solving the optical path identity equation, which includes the angular step size v and the linear absorber radius r, a series of discrete points are generated point by point and then spliced ​​together to form the quasi-elliptical curve profile of the secondary reflector.

[0024] Compared with existing technologies, the imaging-non-imaging coupled concentrator solar collector and its design method with a photon trapping cavity of the present invention exhibit the following beneficial effects in terms of technical performance and practical application: 1. Extremely high optical interception rate and fault tolerance: This invention employs a reverse differential construction method based on the "edge ray principle" to design a secondary reflector. Unlike traditional designs that use a single circular arc or standard ellipse for fitting, the "quasi-elliptical" profile of this invention can accurately match the non-ideal aberration light cone generated by the edge reflection area of ​​the primary reflector.

[0025] The specific advantages lie in the fact that, through the synergistic constraint of "instantaneous fixed focus" and "sliding dynamic focus," it mathematically guarantees that all light rays reflected from the edge reflection zone (including the most unfavorable edge rays) can be intercepted and tangentially reflected to the linear absorber by the secondary mirror without spillage. Even considering a solar angular size of 0.5° and certain installation errors, this design can still maintain an extremely high geometric interception factor, thereby supporting the system to achieve a geometric concentration ratio (>70 times) that significantly surpasses that of traditional PTC systems.

[0026] 2. By employing a hybrid optical path of "bottom imaging direct beam + top non-imaging recapture," the central parabolic segment precisely converges the near-axis light rays onto the sun-facing surface of the linear absorber; the edge non-imaging curved segment (truncated CPC) guides large-angle light rays to the secondary reflector; the secondary reflector, through an "energy flow spatiotemporal reconstruction" mechanism, compresses the edge light rays a second time and reflects them onto the back surface of the linear absorber, achieving secondary focusing and circumferential uniform distribution of the light spot, maximizing the utilization of light energy and minimizing the heat dissipation area. Breaking the thermodynamic efficiency limit: For a design receiving half-angle of 0.5° (covering the solar angular displacement and optical error), compared to the theoretical concentration ratio limit of traditional parabolic trough collectors (PTC) under this condition (approximately 36.5), this invention significantly improves the geometric concentration ratio of the linear focusing system, with a relative increase of over 105%. The minimized surface area of ​​the linear absorber significantly reduces high-temperature radiation heat loss, making the net photothermal conversion efficiency of the system at 600°C significantly better than traditional technologies, thus adapting to efficient sCO2 cycling.

[0027] 3. Engineering feasibility and low cost: Compared with the existing technology that uses solid medium lenses, the present invention adopts a fully hollow structure, which avoids the weight problem, high cost and optical attenuation risk caused by material aging and yellowing when the solid medium is large in size, and has the potential for large-scale commercial promotion.

[0028] 4. Completely eliminate the risk of thermal stress: The "circumferential heating" achieved through secondary reflection effectively fills the energy gap on the back surface of the linear heat absorber, significantly reducing the peak-to-average power ratio (PAR) and coefficient of variation of the circumferential energy flux density distribution of the heat absorber tube, thereby reducing the circumferential temperature gradient of the tube wall by more than 50%, eliminating the risk of tube wall thermal bending deformation (banana effect) and glass-metal seal failure from the source.

[0029] 5. High optical tolerance and net benefit: Thanks to the photon trapping cavity's tolerance for light, the system maintains an overall energy interception rate of 82.11% even with the secondary mirror's central obstruction and the primary mirror's segmented gaps. Despite optical obstruction losses, the reduction in radiative heat loss at high temperatures (due to the doubling of the focusing ratio) far outweighs the optical losses, resulting in a significant improvement in the system's overall energy efficiency. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the cross-sectional structure of the composite curved surface two-stage concentrating solar collector according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the optical path propagation principle according to an embodiment of the present invention; Figure 3 yes Figure 1 A magnified schematic diagram of the region containing the linear heat absorber and the secondary reflector; Figure 4 This is a schematic diagram illustrating the geometric construction principle of the secondary reflector's cross-sectional profile. The figure shows the point Q i Iterate to Q i+1 The process; in which P i The instantaneous fixed focal point (i.e., the most unfavorable light source point) on the edge reflection zone is the point in the calculation of the infinitesimal element Q. i Q i+1 Keep still; C i and C i+1 These are the dynamic focal points (tangent points) on the surface of the linear absorber. The dashed lines in the figure represent the light propagation path, and their geometric relationship follows |P|. i Q i |+|C i Q i |+Larc(C i C i+1 )=∣P iQ i+1 |+|C i+1 Q i+1 | equal optical path constraint (Larc(C) i C i+1 ) is C i and C i+1 (Arc length between points).

[0031] Figure 5 This is a schematic diagram of the geometric decomposition of the incident and reflected light cones at the endpoints of the edge reflection zone (showing the decoupling definition of the light cone by the light source segmentation factor K). Figure 6 This is a schematic diagram of the overall three-dimensional structure of the solar collector of the present invention; Figure 7 This is a comparison curve of the circumferential energy flux density distribution of the heat absorber tube between the present invention and the traditional PTC. Figure 8 This is a flowchart illustrating the design method of a composite curved surface two-stage concentrating solar collector provided in an embodiment of the present invention.

[0032] In the diagram: 1. Linear absorber; 11. Absorber tube; 12. Transparent vacuum cover; 2. Primary reflector; 21. Central reflection area; 22. Edge reflection area; 3. Secondary reflector; 31. Secondary reflection surface; 32. Heat dissipation structure; 41. Central ray; 42. Edge ray; 5. Photon trapping cavity; 71. Lowest extreme ray of sub-source ΔS1 at the edge end of the primary reflector; 72. Boundary ray between the two sub-sources; 73. Uppermost extreme ray of sub-source ΔS2 at the edge end of the primary reflector; 74. Angle of incidence is π / 2 - θ a The extreme ray reflected after reflection by the starting point PS of the edge segment of the primary reflector; 81, the left extreme ray of the reflected light cone; 82, the right extreme ray of the reflected light cone. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] Example 1: like Figures 1-6 As shown, the imaging-non-imaging coupled concentrator solar collector with a photon trapping cavity based on imaging and non-imaging coupling according to the present invention includes: Linear heat absorber 1 extending along the focal line; A primary reflector 2 is positioned below the linear heat absorber 1; and a secondary reflector 3 is positioned above the linear heat absorber 1 with its reflective surface facing downwards; the primary reflector 2 and the secondary reflector 3 form an open light transmission space; the reflective surface of the primary reflector 2 is divided in cross-section as follows: The central reflective region 21 is configured to directly reflect and converge the received paraxial incident light rays onto the lower half surface of the linear heat absorber 1; Edge reflective areas 22, located on both sides of the central reflective area 21, are configured to reflect and guide the received off-axis incident light rays to the linear heat absorber 1 and the secondary reflector 3. The secondary reflector 3 is configured to intercept light from the edge reflector 22 and reflect the light to the upper half surface of the linear heat absorber 1; The two sides of the secondary reflector 3 extend downward to form wing plates. The ends of the wing plates are not lower than the highest point of the linear heat absorber 1, so that the secondary reflector 3 and the upper surface of the linear heat absorber 1 together define a semi-closed photon trapping cavity 5.

[0035] The cross-sectional profile of the central reflective zone 21 is parabolic, quasi-parabolic, or circular arc curve; The cross-sectional profile of the edge reflection zone 22 is a composite parabolic CPC type, a high-order polynomial surface type, or a freeform surface type curve; The central reflective area 21 and the edge reflective area 22 are connected in space by a C0 continuous or C1 continuous manner, or there is a gap between them.

[0036] The reflective surface profile of secondary mirror 3 is composed of multiple continuous curve segments; any point Q on the curve i The optical path coupling condition is satisfied: the optical path coupling from the corresponding point P on the edge reflection region 22 is satisfied. i The reflected light rays pass through point Q. i After reflection, it is tangent to the surface of the linear heat absorber 1.

[0037] The secondary reflector 3 has a hollow structure or a thin shell structure, and a heat dissipation structure 32 is provided on its back surface. The heat dissipation structure 32 includes heat dissipation fins, which are arranged along the extension direction of the secondary reflector.

[0038] The linear heat absorber 1 includes an internal heat absorber tube 11 and an external light-transmitting vacuum cover 12; Linear absorber 1 structure: It consists of a heat absorber tube 11 (made of stainless steel, emissivity 0.8) nested inside a light-transmitting vacuum cover 12, with a vacuum degree ≤10. - 4 Pa effectively isolates convective heat loss.

[0039] Size optimization and definition: The radius r of the heat absorber 11 (optimized to 3.766 mm in this embodiment) and the projection opening width A of the primary reflector 2 are... ap The ratio is based on the preset light source segmentation factor K and the system receiving half-angle θ.a It's confirmed.

[0040] The light source segmentation factor K (0.77 in this embodiment) is defined as: the proportion of the component that points to the secondary reflector 3 in the angular span of the reflected light cone at the outermost end of the edge reflection zone 22, and the remaining component that points directly to the linear heat absorber 1.

[0041] Based on the minimum theoretical radius calculated by this logic, the heat dissipation area is reduced by more than 50% compared to traditional PTCs (typically 70-90mm in diameter).

[0042] The light reflected by the edge reflection area 22 forms a focal spot at the secondary reflector 3. The lateral width of the secondary reflector 3 is greater than or equal to the theoretical width of the focal spot to block the escaping light.

[0043] The photon trapping cavity 5 is configured to receive light from the edge reflection region 22, the light being guided to the backlight region of the linear heat absorber 1 by at least one of the following methods: (a) Directly projected onto the surface of the linear heat absorber 1; (b) After being reflected once by the secondary reflector 3, it is projected onto the surface of the linear heat absorber 1; (c) After multiple reflections between the secondary reflector 3 and the linear heat absorber 1, the image is projected onto the surface of the linear heat absorber 1.

[0044] The back surface of the secondary reflector 3 is provided with a heat dissipation structure 32; the heat transfer medium flowing inside the linear heat absorber 1 is supercritical carbon dioxide, molten salt or high temperature and high pressure steam, and the operating temperature range is 400℃ to 750℃.

[0045] In this embodiment, the solar collector is a line-focusing type, extending along the focal line, and its main components include: Linear absorber 1: It consists of absorber tube 11 (with internal flow of sCO2 working fluid, operating temperature 600℃) and light-transmitting vacuum cover 12 (thermal insulation), with a radius of only 3.766mm (the minimum theoretical value dynamically calculated by light source segmentation factor K=0.77). Primary reflector 2: Segmented hollow surface reflective structure, including central reflective area 21 (parabolic cylinder, imaging optical area) and edge reflective area 22 (truncated compound parabolic surface CPC, non-imaging optical area); Secondary reflector 3: Inverted hollow surface reflective structure, including secondary reflective surface 31 (quasi-elliptical trajectory) and heat dissipation structure 32 (aluminum fins to reduce reflector temperature rise). Photon trapping cavity 5: a semi-enclosed space formed by the two wings of the secondary reflector 3 and the upper surface of the linear heat absorber 1, used to intercept the escaping light and refocus it.

[0046] Linear absorber 1 structure: Absorber tube 11 (stainless steel, emissivity 0.8) is nested inside a light-transmitting vacuum cover 12, with a vacuum degree ≤10. -4 Pa effectively isolates convective heat loss; Function: Absorbs solar radiation energy and converts it into heat energy to heat the internal SCO2 working fluid to 600℃; Primary reflector 2-segment design logic: Central reflective area 21: parabolic cylinder, focal length 266.911mm, longitudinal offset 173.763mm, responsible for directing the central ray 41 (paraxial incident light) onto the light-facing surface of the linear heat absorber 1; Edge reflection zone 22: cuts off CPC, with an edge angle φs=165° at the starting point PS (intersection with the center segment) and an end point φe=210°, responsible for guiding the edge light 42 (large angle incident light) to the secondary reflector 3; Structural characteristics: Hollow aluminum-based reflector (reflectivity 0.94), the light transmission path is in the air medium, and there are no solid refractive elements.

[0047] The secondary reflector 3 has an inverted design with the secondary reflective surface 31 facing downwards and the two wings extending downwards to 10mm above the linear heat absorber 1. The heat dissipation structure 32 consists of aluminum fins (2mm thick, 5mm spaced). Function: Intercepts large-angle light reflected from the edge reflection zone 22 of the primary reflector and refocuses the light onto the back surface of the linear heat absorber 1 through the quasi-elliptical trajectory reflection surface; Photon trapping cavity 5: It consists of two wings of secondary reflector 3 and the upper surface of linear heat absorber 1 forming a semi-enclosed space, with a light capture rate of ≥82%, forming a "circumferential heating" effect.

[0048] Central imaging area (21 segments): Following the principles of imaging optics, the central light ray 41 is precisely focused onto the light-facing surface of the linear heat absorber 1, achieving a paraxial light interception rate of 100%. Edge non-imaging region (segment 22): Following the principle of edge rays in non-imaging optics, edge rays 42 are guided to photon trapping cavity 5. Specifically: The lowest extreme ray 71 (lowest side of ΔS1) of the sub-light source ΔS1 at the edge end of the primary reflector: after being reflected by the non-imaging area of ​​the edge, it directly hits the light-facing surface of the linear heat absorber 1; The boundary ray 72 between the two sub-light sources (the boundary between ΔS1 and ΔS2): after being reflected by the edge non-imaging area, it enters the photon trapping cavity 5; The extreme ray 73 (uppermost side of ΔS2) of the sub-light source at the edge end of the primary reflector: after being reflected by the non-imaging area at the edge, it is intercepted by the secondary reflector 3; The angle of incidence is π / 2 - θ aThe reflected light ray 74 (the incident angle is π / 2 - θ) after the extreme light ray is reflected by the starting point PS of the edge segment of the primary reflector a ): After being reflected by the starting point PS of the edge non-imaging area, it enters the photon capture cavity 5.

[0049] The quasi-elliptical trajectory of the secondary reflector 3 is constructed by the point-by-point iteration method: Initialization: The starting point Q1 is located above the vertex of the linear heat absorber 1, and its coordinates satisfy the optical path conservation constraint; Iterative calculation: At each step, the fixed focus P on the primary reflector 2 i and the dynamic tangent point C on the linear heat absorber 1 i are determined, and the adjacent trajectory points are solved through the equation ; Surface construction: By solving the optical path constraint equation, a continuous quasi-elliptical segment is directly constructed. Through the tangency constraint on the most unfavorable critical light ray (such as the left extreme light ray 81 of the reflected light cone), it is ensured that the entire reflected light cone, including the right extreme light ray 82 of the reflected light cone, is guided to the backlight surface of the linear heat absorber 1 without overflow and is completely intercepted.

[0050] Embodiment 2: As Figure 8 shown, the imaging-non-imaging coupled concentrator collector design method based on imaging and non-imaging coupling described in the present invention adopts a "from the outside to the inside" reverse construction logic, including the following steps: S1: Input design parameters: Set the projection opening width of the primary reflector, the design acceptance half-angle of the system, and the starting point parameters and ending point parameters of the edge non-imaging curved surface segment; Establish a two-dimensional Cartesian coordinate system. Set the projection opening width of the primary reflector 2 as A ap , the design acceptance half-angle as θ a (for example, 0.5°), and the angle between the line connecting the edge point of the primary reflector and the focus and the optical axis (Y-axis) (i.e., the edge angle) is e .

[0051] S2: Construct the edge reflection area model: Introduce the light source splitting factor K, and split the reflected light cone at the edge of the primary reflector into a direct light sub-source and a re-captured light sub-source ; Based on the edge ray principle, construct the contour of the edge non-imaging curved surface segment; When constructing the edge reflection area 22 (i.e., the second curve segment), the present invention introduces the core design parameter - the light source splitting factor K (0 < K < 1). This factor decouples the angular span (2θ a ) of the reflected light cone at the edge of the primary reflector into two independent functional sub-sources ΔS1 and ΔS2 in mathematics:

[0052] In this configuration, the light beam corresponding to ΔS1 is configured to directly strike the linear absorber 1; the light beam corresponding to ΔS2 is configured to point towards a virtual focal point above the linear absorber, requiring secondary capture via a secondary reflector 3. By adjusting the K value, the ratio of direct light to secondary reflected light can be dynamically allocated, thereby controlling the energy flow distribution on the surface of the linear absorber.

[0053] S3: Dynamically determine the size and position of the linear heat absorber: Based on the endpoint parameters of the edge non-imaging curved surface segment, the receiving half angle and the light source segmentation factor K, the minimum theoretical radius and center coordinates of the linear heat absorber are determined through theoretical initialization and simulation correction strategies; Based on the determined edge angle e Receive half angle θ a In addition to the light source segmentation factor K, this invention adopts a dual strategy of "theoretical initialization + simulation correction" to determine the final size and position of the linear heat absorber 1, so as to pursue the minimum heat dissipation area while ensuring a high interception rate.

[0054] 1. Theoretical initialization of the radius of a linear heat absorber (r) initial ): First, based on the principle of edge rays, the theoretical minimum radius r of a linear absorber that satisfies the ideal high-concentration light condition is calculated. initial Its calculation model is as follows:

[0055] The formula gives the lower geometric limit of the edge beam that can be received under a given optical boundary. However, its position and size still need to be adjusted by ray tracing simulation combined with the left extreme rays of the reflected light cone at each point on the edge reflection area 22 (CPC).

[0056] 2. Linear absorber core coordinates (0, Y) ab Calculation of )

[0057] Where Y( e () represents the ordinate of the endpoint of the edge reflection zone.

[0058] 3. Parameter optimization of linear absorbers based on ray tracing To eliminate optical dead zones and ensure that all edge rays are effectively captured, it is necessary to use the theoretical initial value (radius r) initial , core (0, Y) abBased on this, ray tracing was used to verify and optimize the parameters of the linear absorber. The specific optimization process is as follows: Constructing the initial model: Constructing an initial model of the linear endothermic body based on the theoretical initial values.

[0059] Ray simulation and light leakage verification: Using a ray tracing algorithm, the light cone reflected by the edge reflection zone 22 is simulated, and the leftmost boundary light is verified to see if it escapes from the bottom of the linear heat absorber.

[0060] Iterative correction: If the above-mentioned light escape is detected, the radius r of the linear absorber and the tube center position (0, Y) are recalculated using the escaped light ray and the pre-determined extreme position light ray as joint constraints. ab This allows the new model to be tangent to both rays simultaneously, thus geometrically ensuring that the critical ray is completely intercepted.

[0061] Cyclic verification: Based on the corrected model, repeat steps 2-3 until no light leakage occurs, and obtain the final optimized parameters of the linear absorber.

[0062] This iterative process ensures the design robustness of the linear absorber size and location.

[0063] S4: Constructing the central reflection area: Based on the position of the linear heat absorber determined in step S3, a parabolic trajectory with the linear heat absorber as the focus is generated, and the geometric continuity and optical path alignment of the parabolic trajectory with the edge non-imaging surface segment are matched. After determining the starting point Ps of the edge reflection zone (i.e. the intersection of the second curve segment and the first curve segment) and the position of the linear heat absorber, the central reflection zone (first curve segment) of the primary reflector is constructed.

[0064] To ensure a perfect connection between the central segment (parabolic surface) and the edge segment (non-imaging surface) on the optical path, this invention employs an adaptive construction strategy based on half-angle judgment, specifically handling two cases: 1. Calculate the critical criterion: First, calculate the half-angle θ between the linear absorber 1 and the starting point Ps of the edge reflection zone. ab :

[0065] Where Ls is the distance from point Ps to the center (0, Yab) of the linear absorber tube:

[0066] 2. Branch creation logic: Scenario 1: θ ab >θ a (The angle of the opening is greater than the half-angle of the receiving angle); At this point, the starting point Ps of the edge reflection zone can be directly used as the endpoint of the central reflection zone, meaning the two are connected end to end.

[0067] The edge angle of the center segment rim This is the angle between point Ps and the line connecting the linear absorber core and the optical axis.

[0068] The focal length F and longitudinal offset y0 of the parabola are determined by the following formulas:

[0069] In this case, the equation of the central parabola is:

[0070] Scenario 2: θ ab ≤θ a (The angle of the opening is less than or equal to the receiving half angle); At this point, directly connecting point Ps would result in some light rays not being received by the linear absorber. Therefore, Ps cannot be used directly as the endpoint; instead, a new optimal endpoint P needs to be found along the left extreme of the reflected light cone from point Ps towards the linear absorber. PTC This makes the angle subtended by the linear absorber about this point exactly equal to the receiving half-angle θ. a .

[0071] Equations of rays at extreme positions:

[0072] New endpoint P PTC x0:

[0073] in 0 is the new endpoint P PTC The angle between the line connecting the core of the linear absorber and the optical axis needs to be solved iteratively using geometric relationships.

[0074] Corrected parabola parameters:

[0075] In this case, there is a slight geometric discontinuity between the central reflection area and the edge reflection area, but this is a necessary correction to ensure maximum optical efficiency.

[0076] S5: Based on the principle of optical path conservation and the point-by-point iteration method, the microscopic surface profile of the secondary reflector 3 is constructed in reverse; the construction process includes: for the current point (Q) on the profile... i Based on geometric constraints, a fixed focal point (P) is dynamically determined on the edge reflection region 22. i), and a dynamic focal point (C) on the surface of the linear heat absorber 1. i ); By solving the optical path constraint equation, the next contour point (Q) is calculated. i+1 ) and the corresponding new focus (C) i+1 ), where the fixed focus (P) i The remainder remains unchanged; in this way, a surface composed of multiple quasi-elliptical line segments is generated point by point.

[0077] After determining the parameters of the linear absorber, an inverted secondary mirror 3 is constructed. Due to aberrations at the edge of the primary mirror, the contour of the secondary mirror cannot be simply an arc; instead, a quasi-ellipse trajectory must be generated using an iterative, point-by-point method from the inside out.

[0078] 1. Initialize starting point Q1: The starting point Q1 of the secondary reflector is located above the vertex of the linear heat absorber 1, and its coordinates satisfy:

[0079] 2. Iteratively calculate trajectory point Q i : A numerical iterative method is used, based on the currently known contour points Q. i Solve for the next infinitesimal point Q. i+1 The solution process is achieved through the following three logical steps: (1) Determine the "instantaneous fixed focus" P i (Most unfavorable light source point constraint): To ensure that all light rays reflected from the edge reflection zone 22 are captured, it is necessary to determine the most difficult light source point to capture at the current moment. Specifically, the light cone scanning method is used. Traverse the test points P on the edge reflection zone 22 and calculate the boundary angle range [α] of the reflected light cone relative to the optical axis at each point. min ,α max ], where α max / min =2 ±θa π / 2.

[0080] Calculate vectors The direction angle is selected from all test points that can be covered (i.e., the direction angle is within the range of the light cone mentioned above), and the point whose geometric position is closest to the linear heat absorber 1 is selected as the current fixed focus P. i .

[0081] (2) Determine the "dynamic tangent point" C i (Tangent-incidence constraint): According to the principle of edge rays, via Q iThe reflected light rays should be tangent to the surface of the linear heat absorber 1; this point of tangency is the dynamic point of tangency C at the current moment. i .

[0082] (3) Establish and solve the optical path identity equation: From Q i Growing to Q i+1 During the infinitesimal process, maintain a fixed focus P. i The position remains unchanged, while the dynamic tangent point moves along the surface of the linear absorber from C. i Slide to C i+1 Based on Fermat's principle, the following equal optical path constraint equation is established: |P i Q i |+|C i Q i |+Larc(C i C i+1 )=∣P i Q i+1 |+|C i+1 Q i+1 |; Where Larc is the arc length between two tangent points on the surface of the linear endotherm (i.e., r). ν, where ν is the angular step size). Q is calculated by numerically solving this equation. i+1 The coordinates.

[0083] And so on, using Q i+1 Repeat the above steps for a new starting point until the generated discrete point sequence covers the entire design aperture. After fitting, a smooth and continuous quasi-elliptical secondary mirror surface is obtained.

[0084] S6: Symmetrical mirroring to generate a solid entity: Symmetrically mirror the above secondary reflector surface along the focal line direction to generate a complete composite surface secondary concentrator solid entity.

[0085] Through the above judgment logic, the present invention can automatically select the optimal parabola construction method according to different geometric parameters, ensuring that the paraxial light reflected by the central segment can be completely received by the linear heat absorber 1 under any working condition, without theoretical overflow.

[0086] Based on the above mathematical model, let θ a =0.5°, s =165° e =210°, select light source segmentation factor K=0.77.

[0087] Furthermore, such as Figure 2As shown, the optical path was verified through ray tracing simulation. Clearly, the paraxial rays reflected by the central reflection area 21 (light beam 41 in the central region of the figure), represented by solid lines, converge directly onto the light-facing surface of the linear absorber, forming a solid focal point. Meanwhile, the edge rays reflected by the edge reflection area 22 (light beams 42 in the two side regions of the figure), represented by dashed lines, have their main energy (or most of the light) directed towards the virtual focal point above the linear absorber, ultimately being intercepted by the inverted secondary reflector 3 and reflected a second time to the back surface of the linear absorber. Simultaneously, depending on the angle of incidence, a small portion of the edge rays may also be directly projected onto the surface of the linear absorber and absorbed. This composite optical path of "mostly recaptured + a small portion directly incident" intuitively confirms the effectiveness of the "two-source co-concentration" theory described in this invention.

[0088] Verification through calculation and simulation: Concentrating performance: The system’s geometric concentration ratio reaches 83.97, and the effective geometric concentration ratio after deducting the effect of the gap between the secondary and primary mirrors is 74.824, which is 105.132% higher than the theoretical limit of traditional PTC (36.476).

[0089] Energy Intercept Factor: After taking into account geometric losses such as the central obstruction of the secondary mirror and the gaps between the primary mirror segments, the overall energy intercept factor of the system is 82.05%.

[0090] Thermodynamic benefits: Despite the optical loss of approximately 10.89%, thanks to the significant reduction in the surface area of ​​the linear heat absorber, the reduction in radiative heat loss far exceeds that of optical loss at 600°C, resulting in a significant improvement in the net efficiency of the system.

[0091] Energy flow homogenization: such as Figure 7 As shown, the standard deviation of the circumferential local concentration ratio (LCR) of the absorber tube decreased from 27.42 in the traditional PTC to 11.98, a reduction of 56.3%, which effectively verifies the role of the energy flow reconstruction mechanism in eliminating thermal stress.

[0092] To more intuitively demonstrate the breakthrough of this invention in thermodynamic performance, a detailed comparison of the key performance indicators of the design scheme of this invention with those of a traditional single-stage PTC was conducted, and the specific data are shown in Table 1.

[0093] Table 1 Comparison of circumferential energy flux density distribution characteristics and key statistical indicators of heat absorber tubes

[0094] As shown in Table 1, the comparative data demonstrates that the concentrating solar collector described in this invention outperforms traditional single-stage PTCs in all key performance indicators. In particular, the coefficient of variation (CV) decreases significantly from 88.5% to 17.32%, and the minimum energy flux (LCR) on the back surface is also significantly lower. min The 41-fold increase in light concentration ratio quantitatively confirms that the secondary mirror and photon trapping cavity structure successfully achieved the 'spatiotemporal reconstruction' and 'circumferential homogenization' of light energy. This not only solves the 'banana effect' and stress damage problems caused by temperature differences in traditional solar collectors, but also significantly improves the photothermal conversion efficiency of the system under high-temperature conditions by doubling the average concentration ratio.

[0095] In summary, this invention achieves multi-dimensional breakthroughs in the geometric optics, thermodynamics, and material mechanical properties of solar thermal collectors through rigorous mathematical derivation and reverse design. Detailed parameters are shown in Table 2 below.

[0096] Table 2 Summary of Geometric and Optical Performance Parameters of Concentrators

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An imaging-non-imaging coupled concentrator solar collector containing a photon trapping cavity, characterized in that, include: A linear heat absorber extending along the focal line (1); Primary reflector (2) disposed below the linear heat absorber (1); as well as, The secondary reflector (3) is disposed above the linear heat absorber (1) with its reflective surface facing downward. The primary reflector (2) and the secondary reflector (3) form an open light transmission space; The reflecting surface of the primary reflector (2) is divided in cross-section as follows: The central reflective region (21) is configured to directly reflect and converge the received paraxial incident light rays to the lower half surface of the linear heat absorber (1); The edge reflection zone (22), located on both sides of the central reflection zone (21), is configured to reflect and guide the received off-axis incident light rays to the linear heat absorber (1) and the secondary reflector (3). The secondary reflector (3) is configured to intercept light from the edge reflector area (22) and reflect the light to the upper half surface of the linear heat absorber (1); The two sides of the secondary reflector (3) extend downward to form wing plates, and the end of the wing plate is not lower than the highest point of the linear heat absorber (1), so that the secondary reflector (3) and the upper surface of the linear heat absorber (1) together define a semi-closed photon trapping cavity (5).

2. The imaging-non-imaging coupled concentrator with a photon trapping cavity according to claim 1, characterized in that: The cross-sectional profile of the central reflective area (21) is parabolic, quasi-parabolic, circular arc, or a curve fitted by multiple straight lines; The cross-sectional profile of the edge reflection zone (22) is a composite parabolic CPC type, a high-order polynomial surface type, or a freeform surface type curve; The central reflective area (21) and the edge reflective area (22) are connected in space by C0 continuity or C1 continuity, or there is a gap between them.

3. The imaging-non-imaging coupled concentrator with a photon trapping cavity according to claim 1, characterized in that: The reflective surface profile of the secondary reflector (3) is formed by connecting multiple continuous curves; Any point Q on the curve i The optical path coupling condition is satisfied: such that the optical path coupling from the corresponding point P on the edge reflection region (22) is satisfied. i The reflected light rays pass through point Q. i After reflection, it is tangential to the surface of the linear heat absorber (1).

4. The imaging-non-imaging coupled concentrator with a photon trapping cavity according to claim 1, characterized in that: The secondary reflector (3) is a hollow structure or a thin shell structure, and a heat dissipation structure (32) is provided on its back surface. The heat dissipation structure (32) includes heat dissipation fins arranged along the extension direction of the secondary reflector.

5. The imaging-non-imaging coupled concentrator with a photon trapping cavity according to claim 1, characterized in that: The linear heat absorber (1) includes an internal heat-absorbing tube (11) and an external light-transmitting vacuum cover (12). The projection opening width A of the primary reflector (2) ap The radius r of the heat absorber (11) has a geometric matching relationship, which makes: In a given system, half-angle θ is received. a Below, the light cone reflected from the outermost end of the edge reflection area (22) forms a light spot boundary after being reflected by the secondary reflector (3), which falls within the cross-sectional area of ​​the heat absorber (11) or is tangent to the heat absorber (11).

6. The imaging-non-imaging coupled concentrator with a photon trapping cavity according to claim 1, characterized in that: The light reflected by the edge reflection area (22) forms a focal spot at the secondary reflector (3), and the lateral width of the secondary reflector (3) is greater than or equal to the theoretical width of the focal spot to block the escaping light.

7. The imaging-non-imaging coupled concentrator with a photon trapping cavity according to claim 1, characterized in that: The photon trapping cavity (5) is configured to receive light from the edge reflection region (22), the light being guided to the backlight region of the linear heat absorber (1) by at least one of the following methods: (a) Directly projected onto the surface of the linear heat absorber (1); (b) After being reflected once by the secondary reflector (3), it is projected onto the surface of the linear heat absorber (1); (c) After multiple reflections between the secondary reflector (3) and the linear heat absorber (1), the light is projected onto the surface of the linear heat absorber (1).

8. A design method for an imaging-non-imaging coupled concentrator solar collector containing a photon trapping cavity as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Define design parameters, introduce light source segmentation factor K, and mathematically decouple the reflected light cone at the end of the edge reflection area (22) into: the direct component ΔS1 directly projected onto the linear heat absorber (1), and the recapture component ΔS2 projected onto the secondary reflector (3); S2: Based on the principle of edge rays, the contour of the edge reflection area (22) is constructed using the recapture component ΔS2 as the boundary condition; S3: Determine the minimum theoretical radius and center position of the linear heat absorber (1) based on the edge light trajectory of the edge reflection zone (22) to meet the light interception threshold; S4: Construct the outline of the central reflective zone (21) with the position of the linear heat absorber (1) as the focal point; S5: Construct the outline of the secondary reflector (3) using the reverse iteration method: For points on the outline, establish equations according to the principle of optical path conservation, so that they simultaneously receive light from the edge reflection area (22) and reflect it tangent to the surface of the linear heat absorber (1).

9. The design method of the imaging-non-imaging coupled concentrator solar collector with a photon trapping cavity according to claim 8, characterized in that, In step S5: By solving the optical path identity equation containing the angular step size v and the linear absorber radius r, a series of discrete points are generated point by point and spliced ​​together to form the quasi-elliptical curve profile of the secondary reflector (3).

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