CN219868554U

CN219868554U - Novel cylindrical surface reflector spliced groove type solar heat collection system

Info

Publication number: CN219868554U
Application number: CN202320187846.5U
Authority: CN
Inventors: 黄卫东
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2023-01-18
Filing date: 2023-01-18
Publication date: 2023-10-20
Anticipated expiration: 2033-01-18

Abstract

The utility model discloses a novel cylindrical reflector spliced groove type solar heat collection system, which uses cylindrical reflectors to splice to form a parabolic groove type reflector, so that spherical aberration and meridian aberration caused by the use of spherical reflectors are eliminated, and the performance of the system is very small compared with that of a parabolic groove type system under the same optical error; under the current mainstream technology, the gradient error of the cylindrical reflector is 1mrad, and the parabolic surface is 2-3mrad, so that the performance of the cylindrical splicing groove type system is obviously better than that of the parabolic groove type system. The utility model provides a cavity receiver with larger light collection ratio, and a cylindrical transparent glass cover plate is added at the opening, so that heat loss and incident light reflection loss are reduced; the utility model provides a condensing lens with a V-shaped groove, which increases the dimming ratio and reduces the heat loss.

Description

Novel cylindrical surface reflector spliced groove type solar heat collection system

Technical Field

The utility model relates to the technical field of groove type solar heat collectors, in particular to a novel cylindrical reflector spliced groove type solar heat collecting system.

Background

The concentrating solar heat collector uses a concentrating technology to focus a large amount of low-density solar energy onto a small area to form high-density solar energy, so that high-temperature heat energy can be generated, the concentrating solar heat collector is used for solar thermal power generation, heat can be stored, continuous power generation can be realized, and the concentrating solar heat collector is a thermal power generation technology which is hopeful to replace a coal-fired power plant. The main concentrating solar heat collection technologies at present are tower type, groove type, linear Fresnel and dish type concentrating solar technologies. The trough type solar heat collector uses a line focusing paraboloid as a condenser, is the most mature technology, realizes commercialization as early as 30 years ago, has stable performance, but has the advantages of less than 30 times of condensation, low working temperature and difficult improvement of performance, wherein one of the main reasons is that the line focusing paraboloid is used, the processing cost is high, the optical error is large, and the condensation multiple is low.

Patent cn 20052017069. X proposes that the use of a groove-type circular arc surface mirror instead of a parabolic mirror can simplify the production process, greatly reduce the manufacturing cost of the mirror, but the performance is greatly reduced, and the main reason is that the cylindrical mirror has larger aberration, the ratio of the width to the focal length of the cylindrical mirror is far smaller than that of the parabolic mirror under the same groove width, the aberration can be eliminated, and the focal length of the cylindrical mirror is far larger than that of the parabolic groove system under the same groove system width, and the receiver radius is in direct proportion to the focal length and is far larger than that of the parabolic groove system, so that the light collecting ratio and the working temperature are reduced, and the performance is far lower than that of the ordinary parabolic groove system.

The proposal proposed in the patent CN200920231849.4 includes using a multi-segment circular arc mirror instead of a trough-type parabolic mirror, but does not give a method of how to splice the multi-segment circular arc mirror and simulate the parabolic mirror, for example, embodiments 1 and 2 use a 2-segment circular arc mirror instead of the parabolic mirror, and still have large aberration; the improved form comprises an embodiment 3, and although a plurality of arc surfaces are spliced, how to determine the positions and the mirror surface directions of all the arc reflectors and the arc radiuses of the arc reflectors is not described, and in the given implementation diagram, all the arc reflectors are arranged in a staggered manner, obviously deviate from a paraboloid, and the performance is difficult to ensure.

CN201110462998.3 proposes that the flat mirrors are spliced to form a trough-type parabolic mirror, and since the flat mirrors necessarily generate parallel light image spots on the focal plane, the light concentration ratio of the system is greatly reduced, so that the performance is far lower than that of a parabolic trough-type system.

In the solution proposed in CN200920231849.4, it is proposed to use a compound parabolic surface for secondary focusing, so as to improve the performance and the light-condensing ratio, but the compound parabolic surface used in this system can reflect light many times, requiring very high processing precision, otherwise, the reflected light error can increase linearly with the number of reflections, so as to reduce the system performance, making the solution very poor in economical efficiency.

Disclosure of Invention

The utility model aims to make up the defects of the prior art and provides a novel cylindrical reflector splicing groove type solar heat collection system which has the advantages of high light concentration ratio, higher optical efficiency, reduced processing difficulty and reduced cost. The utility model has the advantages that firstly, a plurality of cylindrical reflectors are spliced to form an approximate line focusing paraboloid, so that the optical error of the system can be reduced, the performance of the system is almost the same as that of the groove type heat collector with the same optical error, and under the same processing technology, the optical error of the cylindrical reflectors is lower, and the optical performance and the light condensation multiple of the system can be improved; the second point of the utility model is that a cavity receiver is used for replacing a tubular receiver, and we prove that the light ratio is increased and the heat loss is reduced; the third point of the utility model is to add a V-shaped groove type reflection condensing lens in front of the receiver, so as to greatly increase the condensing multiple, thereby improving the working temperature of the system and increasing the efficiency of the groove type solar thermal power generation system.

The utility model is realized by the following technical scheme:

the novel cylindrical surface reflector spliced groove type solar heat collection system comprises a reflector group and a receiver, wherein the reflector group is formed by splicing a plurality of strip-shaped cylindrical surface reflectors, the centers of the strip-shaped cylindrical surface reflectors form parabolas, and the normal vector of the center of each strip-shaped cylindrical surface reflector is consistent with the normal vector of the parabola of the installation position of each strip-shaped cylindrical surface reflector, so that the installation direction of each strip-shaped reflector is determined; the receiver is arranged on a parabolic focus formed by the centers of the plurality of strip-shaped cylindrical reflectors; the reflecting mirror group and the receiver are both arranged on the sunlight tracking equipment, the sunlight tracking equipment is used for tracking the position change of the sun, and the reflecting mirror group is used for focusing the sun rays to the receiver.

The circular radius r of the strip cylindrical surface reflector and the edge angle of the center of the circular radius r on the paraboloidAnd the parabolic trough focal length f, as determined by:

the receiver is a tubular receiver or a strip-shaped cavity receiver or a flat plate receiver; the tube receiver is a vacuum heat collecting tube;

when the receiver is a tubular receiver, the radius R is determined by:

when the receiver is a bar-shaped cavity receiver or a flat-plate receiver, the half-width R of the receiver is determined by the following formula:

wherein W is half groove width of the groove type solar heat collection system,is the edge angle of the trough type solar heat collection system, sigma is the Gaussian distribution variance of the reflected light intensity, and lambda is the incident angle of sunlight on the trough type solar heat collection system.

When the receiver is a tubular receiver, the ratio of the width w of the strip-shaped cylindrical surface reflector to the radius r meets the following condition:

when the receiver is a strip-shaped cavity receiver or a flat plate receiver, the ratio of the width w of the strip-shaped cylindrical surface reflector to the radius r meets the following condition:

wherein, sigma is the Gaussian distribution variance of the reflected light intensity, lambda is the incident angle of sunlight on the trough type solar heat collection system,is the edge angle of the trough type solar heat collection system.

The solar energy collecting system further comprises a V-shaped groove type reflection collecting lens, wherein the inlet of the V-shaped groove type reflection collecting lens is arranged on the focal plane of the groove type solar energy collecting system, and the receiver is arranged on the outlet of the V-shaped groove type reflection collecting lens; the V-shaped groove type reflection condensing lens consists of 2 inclined plane reflecting mirrors, the included angle theta between the reflecting surface and the vertical direction is 2-10 degrees, the entrance half width of the V-shaped groove type reflection condensing lens is equal to the radius or half width R of a receiver tube of the groove type solar heat collection system, the exit width R' of the V-shaped groove type reflection condensing lens is equal to the radius or half width R of the receiver tube after the V-shaped groove type reflection condensing lens is added, and the V-shaped groove type reflection condensing lens is calculated according to the following formula:

when the receiver uses the bar-shaped cavity receiver, the cylindrical surface transparent glass cover plate is arranged at the opening of the bar-shaped cavity receiver, and the concave surface is arranged in the cavity receiver.

When the cavity receiver is used, the cylindrical surface transparent glass cover plate is arranged at the opening of the cavity receiver, and the concave surface faces the inside of the cavity receiver. The cylindrical surface transparent glass cover plate is added at the opening of the cavity receiver, firstly, heat loss is reduced, the transparent glass material is selected to have high visible light transmittance and low infrared radiation transmittance, and is similar to the glass material used for the outer tube of the vacuum heat collecting tube, so that the heat loss is low; and secondly, the semi-circular structure is adopted or is larger than the semi-circular structure, so that the sunlight of reflection loss can be reduced, and the absorptivity of the receiver to sunlight is increased.

The utility model has the advantages that:

the utility model uses the cylindrical surface reflector to splice and form the parabolic trough reflector, and the requirements are set, so that the spherical aberration and meridian aberration caused by the use of the spherical surface reflector can be eliminated, and the performance difference between the system performance and the parabolic trough system performance under the same optical error is very small; the parabolic processing difficulty is high, under the same process, the optical error is often 2 to 3 times that of the cylindrical reflector, and under the current main stream process, the gradient error of the cylindrical reflector is 1mrad, and the parabolic surface is 2-3mrad, so that the performance of the cylindrical splicing groove type system is obviously better than that of the parabolic groove type system.

The utility model uses the cavity or the flat plate receiver to replace the commonly used tubular receiver, such as a vacuum heat collecting tube, and the trough system using the cavity receiver or the flat plate receiver has larger light collection ratio and is obviously superior to the trough system using the tubular receiver. In addition, the use of a cavity receiver is advantageous over a tube receiver and a flat receiver because the cavity receiver absorbs light substantially all the way into the cavity, but the tube receiver and flat receiver reflect a portion of the intercepted solar light, typically about 5% -10%, resulting in a lower absorption.

The utility model provides a V-shaped groove type reflection condensing lens, which has a simple structure although the condensing multiple is lower than that of a compound paraboloid, and can focus incident light rays in a certain direction by using two inclined plane reflecting mirrors, and the plane reflecting mirrors used by the V-shaped groove are easy to process and have small optical errors, so that adverse effects caused by repeated reflection are eliminated; the condensing ratio is increased, so that heat loss can be reduced, and the working temperature of the system is increased, thereby increasing the efficiency of the subsequent power generation system and improving the total efficiency and performance of the groove type thermal power generation system.

According to the utility model, the cylindrical transparent glass cover plate is added at the opening of the cavity receiver, so that heat loss is reduced, the transparent glass material is selected to have high visible light transmittance and low infrared radiation transmittance, and is similar to the glass material used for the outer tube of the vacuum heat collecting tube, so that the heat loss is low; and secondly, the semi-circular structure is adopted or is larger than the semi-circular structure, so that the sunlight of reflection loss can be reduced, and the absorptivity of the receiver to sunlight is increased.

Drawings

FIG. 1 is a graph showing the surface energy density distribution of a evacuated collector tube according to example 1 of the present utility model.

FIG. 2 is a graph showing the fluence density distribution at the entrance focal plane of a receiver using cavities in accordance with example 2 of the utility model.

FIG. 3 shows the fluence distribution at the entrance focal plane of the cavity receiver after adding a V-groove concentrator to example 3.

Fig. 4 is a block diagram of a cylindrical mirror tiled parabolic trough system when the receiver is a tubular receiver.

Fig. 5 is a block diagram of a cylindrical mirror tiled parabolic trough system when the receiver is a cavity receiver.

FIG. 6 is a block diagram of a cylindrical mirror tiled parabolic trough system with a V-shaped trough reflective collection mirror.

Detailed Description

The novel cylindrical surface reflector spliced groove type solar heat collection system comprises a reflector group 1 and a receiver, wherein the reflector group 1 is formed by splicing a plurality of strip cylindrical surface reflectors, the centers of the strip cylindrical surface reflectors form parabolas, and the normal vector of the center of each strip cylindrical surface reflector is consistent with the normal vector of the parabolas of the installation position, so that the installation direction of each strip reflector is determined; the receiver is arranged on a parabolic focus formed by the centers of the plurality of strip-shaped cylindrical reflectors; the reflecting mirror group and the receiver are both arranged on sunlight tracking equipment, the sunlight tracking equipment is used for tracking the position change of the sun, and the reflecting mirror group 1 is used for focusing the sun rays on the receiver.

Wherein the circle radius r of the strip cylindrical surface reflector and the edge angle corresponding to the center of the strip cylindrical surface reflector on a paraboloidAnd the parabolic trough focal length f, as determined by:

wherein when using the tube receiver 2, the ratio of the strip cylindrical mirror width w to the radius r should satisfy the following condition:

sigma is the variance of Gaussian distribution of reflected light intensity, lambda is the incident angle of sunlight in a trough system, typical design values can respectively take 10mrad and pi/6 radians,the edge angle of the groove type system can be pi/2 radian, and w/r is less than or equal to 0.21 by substituting calculation; where r is equal to 2 times the parabolic trough focal length f. This illustrates that when using a tube receiver, such as a evacuated collector tube, the upper limit of the cylindrical mirror width w of a parabolic trough collector system employing multiple cylindrical mirrors to splice together is 0.42 times the parabolic trough focal length f.

When the cavity receiver 3 is used, the ratio of the width w of the strip-shaped cylindrical mirror to the radius r should satisfy the following condition:

using similar design values, wherePi/4 radian is substituted into the raw material to obtain w/r which is less than or equal to 0.1993 and equal to 1/5; where r is equal to 2 times the parabolic trough focal length f. This means that when using a cavity or flat plate receiver, the upper limit of the cylindrical mirror width w of a parabolic trough collector system employing multiple cylindrical mirrors for tiled parabolic trough is 0.40 times the parabolic widthSlot focal length f.

The receiver is a tube receiver 2, or a cavity receiver 3 or a flat receiver; when a tube receiver is used as the receiver, the receiver tube radius is determined by:

where W is the half slot width of the slot system,is the edge angle of the trough system, sigma is the Gaussian distribution variance of the reflected light intensity, and lambda is the incident angle of sunlight on the trough system;

if a cavity or flat plate receiver is used, the receiver half-width R is determined by:

the system can also comprise a V-shaped groove type reflection condensing lens 5, an entrance is arranged on the focal plane of the groove type system, a receiver is arranged on the exit of the V-shaped groove type reflection condensing lens 5, the V-shaped groove type reflection condensing lens consists of 2 inclined plane reflecting mirrors, the included angle theta between the reflecting surface and the vertical direction is 2-10 degrees, the half width of the entrance of the V-shaped groove is equal to the radius or half width R of the receiver calculated by a parabolic groove type condensing lens without the V-shaped groove, and the width R' of the exit of the V-shaped groove is equal to the radius or half width of the receiver after the V-shaped groove type reflection condensing lens is added, and the radius or half width of the receiver can be calculated according to the following formula:

the cavity receiver opening can be also provided with a cylindrical transparent glass cover plate 4, and the concave surface faces the inside of the cavity receiver.

A method of designing a trough solar collector system using a tubular receiver as a receiver, comprising the steps of:

firstly, determining the width of a trough type heat collection system;

second, determining the edge angle of the trough systemThe value range is 80-100 degrees, and the optimized value is 90 degrees;

third step, according to half groove width W and edge angleCalculating the focal length f of the system, wherein the calculation formula is as follows:

fourth, if the system uses cylindrical surface splicing to construct parabolic trough system reflectors, firstly determining the radius r of each cylindrical surface reflector circle, if the edge angle of the installation center position of one cylindrical surface reflector on the parabolic surface isThe r is calculated as:

secondly, determining the width of the cylindrical reflector, wherein the width can be determined according to the following formula;

at this time, r should use the minimum value, that is, r=2f, and calculate the maximum width w of the cylindrical reflector for stitching with the above method;

fifth step, determining the receiver size, if a tube receiver is used, the tube receiver radius R, calculated as:

where σ is the reflected solar ray gaussian distribution variance, which can be approximated as:

here σ _sun The Gaussian distribution variance of the solar light intensity is measured by adopting the installation site; sigma (sigma) _slopex Sum sigma _slopey The slope error Gaussian distribution variance of the groove type reflecting mirror in the x direction and the y direction are respectively; sigma (sigma) _tracking Is the tracking error gaussian distribution variance; sigma (sigma) _disp The system installation error Gaussian distribution variance; sigma (sigma) _specular Is the gaussian distribution variance of the reflector material error; the actual measurement should be taken.

A method of designing a trough solar collector system using a cavity or flat panel receiver, comprising the steps of:

firstly, determining the width of a trough type heat collection system;

second, determining the edge angle of the trough systemThe value range is 40-50 degrees, and the optimized value is 45 degrees;

fourth, if the system uses cylindrical surface splicing to construct parabolic trough system reflectors, firstly determining the radius r of each cylindrical surface reflector circle, if one cylindrical surface reflector is arranged on the side of the parabolic surface at the installation center positionEdge angleThe r is calculated as:

at this time, r should use the minimum value, that is, r=2f, to calculate the maximum width w of the cylindrical reflector for stitching;

and fifthly, determining the half width R of the receiver, wherein the calculation formula is as follows:

When the novel groove type system comprises a V-shaped groove, the design method further comprises the design of the V-shaped groove, wherein the inlet width of the V-shaped groove is equal to the width R of a receiver in the design method, and if the inclination angle of two reflectors of the V-shaped groove is theta, the outlet width is R', and the method can be calculated according to the following formula:

θ can be 2-10 degrees, and after the V-shaped groove type reflection condensing lens is added, the edge angle of the groove type systemThe value range is 20-60 degrees, the optimized value is 45, a strip-shaped cavity receiver is used, and the half width of the cavity is R'; the tube type receiver is used as the receiver, and the radius of the heat collecting tube is R'.

Embodiment one: as shown in fig. 4, the groove width is 8 meters, a vacuum heat collecting tube is used as a receiver, the edge angle of the groove system is 90 degrees, the focal length is 2 meters, a parabolic groove type reflector is formed by splicing strip-shaped cylindrical reflectors with the width of 0.5 meter, the circular radius of each cylindrical reflector is calculated according to the formula, the centers of all strip-shaped reflectors form parabolas, and the normal vector of the center of each strip-shaped reflector is consistent with the normal vector of the parabolas of the installation position, so that the installation direction of each strip-shaped reflector is determined; the vacuum heat collecting tube receiver is arranged on the parabolic focus; the reflector and the receiver are both arranged on the tracking device, and the sun rays are focused on the receiver by tracking the sun position change through the tracking device; at an incidence angle of 30 degrees, assuming a reflected optical gaussian distribution variance of σ=4.27 mrad, the receiver radius r= 39.45 mm is calculated by a formula, with a 40 mm extinction ratio of 32.3. The system is mounted to a single axis tracking device such that sunlight is focused onto the receiver. It is pointed out that in the previously filed patent 202221295614.3, the stress points should be arranged around the mirror when supporting the condensing mirror, and that in all three technical embodiments, considering the thin glass used for the mirror, the cylindrical mirror width is chosen to be 0.5 meters instead of the calculated maximum value of 0.8 meters.

We have established ray tracing program simulations to calculate the system performance, as shown in fig. 1 for the fluence density distribution under design conditions with an interception rate of 99.2%.

In the second embodiment, as shown in fig. 5, the slot width is 8 meters, a strip-shaped cavity is used as a receiver, the edge angle of the slot system is 45 degrees, the focal length is 4.8284 meters, a parabolic slot-shaped reflector is formed by splicing strip-shaped cylindrical reflectors with the width of 0.5 meter, the radius of each cylindrical reflector is calculated according to a formula, the centers of all strip-shaped reflectors form parabolas, and the normal vector of each strip-shaped reflector is consistent with the normal vector of the parabola of the installation position, so that the installation direction of each strip-shaped reflector is determined; the vacuum heat collecting tube receiver is arranged on the parabolic focus; the reflector and the receiver are both arranged on the tracking device, and the sun rays are focused on the receiver by tracking the sun position change through the tracking device; assuming that the variance of the Gaussian distribution of the reflected light is sigma=4.21 mrad, the radius R of the receiver is calculated according to a formula to obtain the half-width R= 77.85 mm of the cavity receiver, and the light concentration ratio is 50.0 times by adopting 80 mm. The system is mounted to a single axis tracking device such that sunlight is focused onto the receiver.

The energy flow density distribution on the receiving surface is calculated as shown in fig. 2, and the obtained interception rate is 97.3% and is lower than 97.7% estimated by the theoretical formula, because the ray tracing program established by us simulates three reflection lines formed when solar rays are reflected by a glass back reflector, wherein the first reflection line is a direct reflection part on the upper surface of the glass and accounts for about 5%, and the second reflection line is reflected by a silver-plated reflection layer on the back surface of the glass and accounts for about 90%; the third strand is the triple reflection part passing through the upper and lower glass surfaces and occupies about 4 percent. The third ray is reflected for 3 times, so that the optical error is larger, and the actual interception rate is lower.

In the third embodiment, as shown in fig. 6, a V-shaped groove type reflection condensing lens is added on the basis of the second embodiment, the half width of an opening of the V-shaped groove is 80 mm, the half width of an outlet is 40 mm, the half width of a cavity receiver is also 40 mm, the light condensing ratio is 100, the widths of 2V-shaped groove reflecting mirrors are 140.2 mm, and the inclination angle is 5 degrees. The system is mounted to a single axis tracking device such that sunlight is focused onto the receiver. The performance of the system is simulated by establishing a ray tracing program, the incident angle is 30 degrees, the edge angle is 46 degrees, the performance is slightly better than 45 degrees, and the energy flow density distribution on the receiving surface is shown in figure 3.

The calculated interception rate is 96.3%, which is lower than 97.7% of the interception rate estimated by the theoretical formula, because the calculation model further considers the loss part of the V-shaped groove type reflection condenser, so that the actual interception rate is lower.

The parabolic trough type reflecting mirror is formed by splicing the cylindrical reflecting mirror, and each design parameter is determined according to the above content, so that spherical aberration and meridian aberration caused by splicing the spherical reflecting mirror can be eliminated, and the performance difference between the system performance and the parabolic trough type system performance under the same optical error is very small; the parabolic processing difficulty is high, under the same process, the optical error is often 2 to 3 times that of the cylindrical reflector, and under the current main stream process, the gradient error of the cylindrical reflector is 1mrad, and the parabolic surface is 2-3mrad, so that the performance of the cylindrical splicing groove type system is obviously better than that of the parabolic groove type system.

The utility model provides a method for eliminating meridian coma of a spliced cylindrical surface reflector, which comprises the following steps: the circular radius expression of the spliced cylindrical surface reflector is calculated, so that the correct circular radius of the cylindrical surface is selected, meridian coma is eliminated, and how to do so is described below.

First, we describe how to eliminate meridional coma of the cylindrical surface. Referring to the focal length theory of the meridian plane of the spherical heliostat established in chapter seven of Rabl Active solar collectors and their applications, analogized to the cylindrical mirror, we derive the focal length of the cylindrical mirror when the calculated incident angle is greater than 0 through geometrical optics: when the cylindrical reflector is used for splicing, the edge angle of the parabolic trough type system corresponding to the installation center position isAt this time, the incident angle λ of the solar ray on the groove system is +.>If the focal length of the cylindrical mirror is f', then +.>Therefore, we need to properly enlarge the focal length of the cylindrical surface to focus it on the original focal point. If the corresponding edge angle of the cylindrical mirror center for splicing is +.>It is +.>Focal length of the cylindrical surface

Radius of circle in cylindrical mirror

When it is installed at the edge angleWhen in position, the meridian plane coma can be completely eliminated. Otherwise, meridian coma is generated, for example, without meridian coma correction, the conventional design is to make the radius of the cylindrical mirror equal to 2 times of the focal distance from the center of the mirror to the parabolic trough, that is:

at this time, since the actual focal position is not in the groove paraboloid focus, meridional coma is generated, that is, the image spot width is increased, which is equal toFor a trough system with half width of 4m and edge angle of 90 degrees, the width of the image spot is increased to be +.>Much larger than the receiver diameter.

Secondly, the utility model provides a spherical aberration eliminating method of the spliced cylindrical surface reflector, which is to limit the width of the spliced reflector and provide an upper limit calculation formula of the ratio of the width of the spliced cylindrical surface reflector to the radius of the spliced cylindrical surface reflector.

The traditional optical theory aims at imaging quality, light source images are required to be perfectly reproduced on a focal plane, the requirement for eliminating spherical aberration is very high, see (Su) Octalop et al, research and inspection of optical systems, page 175, a spherical reflector is used as a main mirror, the relative aperture is not more than 1:10.8, namely the ratio of the caliber of the reflector to the focal length is less than or equal to 1/10.8, and the ratio of the caliber of the reflector to the spherical radius is converted to less than or equal to 1/21.6. In the solar field, the main purpose of the optical system is to collect light, which is much lower than the optical imaging requirement, and the requirement of eliminating spherical aberration in the solar field is proposed.

Referring to the above, according to the geometrical optics principle, in general, the lateral spherical aberration δx of the spherical mirror is calculated as:

δ _x ＝r*tan(ψ)*sin ² (ψ/4)/cσs(ψ/2)＝w sin ² (ψ/4)/cos(ψ)

where w is the diameter of the circular spherical mirror used for stitching, r is the radius of the spherical mirror sphere, and ψ is the central angle corresponding to the largest arc of the spherical mirror.

For a line focusing trough condenser, when using a cylindrical mirror, we derive the cylindrical lateral aberration using the principle of geometrical optics as well:

where w is the cylindrical mirror width and r is the cylindrical radius, then we derive the receiver radius

Where σ is the variance of the Gaussian distribution of the reflected light intensity, a tableThe rear part of the expression is the receiver radius required to completely intercept the Gaussian distribution + -2σ part of the reflected light, where W is the half-groove width of the parabolic trough system, λ is the incident angle of the sunlight at the trough system, and the expression is based on the furthest out of focus point, the edge angle isIs derived from the reflected light of (a) the reflected light of (b). Concentration ratio of

When the incident angle is 30 degrees and sigma is 5mrad, if 2 cylindrical reflectors are used instead of the parabolic reflectors, i.e. W/w=1, the maximum condensing ratio can be numerically solved to be only 6.84, corresponding toAbout the degree. Comparing the edge angle of the parabolic trough system to 90 degrees, we deduce the maximum condensing ratio:

this illustrates that the use of 2 cylindrical surfaces instead of a line focus parabolic surface is far less efficient than a parabolic trough system. This is because using cylindrical mirrors, when the edge angle is large, the spherical aberration is large, and when the edge angle is small, the focal length of the same width mirror is large, so that the required receiver radius is large at the same interception rate, and the light collection ratio is lowered.

Our studies have shown that with a tubular receiver, the requirement to eliminate spherical aberration is that the lateral spherical aberration does not exceed 5% of the parabolic trough system radius, which results in:

where ψ is the central angle corresponding to the arc length of the cylindrical reflector and σ isThe reflected light intensity Gaussian distribution variance, lambda is the incident angle of sunlight in a trough system, and the influence caused by spherical aberration is small. Since the requirement ψ is small, it can be approximately considered that sin (ψ/4) ≡ψ/4; cos (ψ) =1-sin ² (ψ/2)≈1-ψ ² 4; the following is obtained:

on the other hand, in the other hand,

sin(ψ/2)＝w/(2r)，

here, 2f=r is applied because the focal length and radius of the cylindrical mirror near the vertex of the parabolic trough are the smallest, the opening angle is the largest and the spherical aberration is the largest for the same width, so we only need to discuss this mirror. Then

Typical values of sigma and lambda may take 5mrad and pi/6 radians respectively,the edge angle of the groove system can be pi/2 radian, and w/r is less than or equal to 0.21 and equal to 1/5; we can also choose w/r to exceed 1/5, where performance is further degraded. The above formula is thus that the parabolic trough system of the tubular receiver uses cylindrical reflectors to splice to form parabolic reflectors, and the conditions required to eliminate spherical aberration are required. Since r=2f is selected, the above equation can be converted into: w/f is less than or equal to 0.42, which indicates that when a tube receiver such as a vacuum heat collecting tube is used, the upper limit of the width w of the cylindrical reflector of the parabolic trough heat collecting system spliced by a plurality of cylindrical reflectors is 0.42 times of the focal length f of the parabolic trough.

By eliminating the spherical aberration by the above measures, we can ignore the influence of the spherical aberration, and the following analysis is performed as described aboveIt is required to eliminate the difference between the spherical aberration of the spliced cylindrical surface and the parabolic trough type system. The incident angle lambda is pi/6 radian, sigma is 5mrad, W is 4.0m, and the edge angleWhen the radian is reached, the minimum R is approximately equal to 4.0m, the width of the spliced cylindrical surface is less than or equal to 0.8 m according to the formula (9), the maximum value is 0.8 m, the spherical aberration of the cylindrical surface is calculated to be 0.50mm according to the formulas (2) and (3), the radius R of the cylindrical surface mirror spliced parabolic tube-added receiver is equal to 46.7mm, the radius of the receiver of a compared parabolic trough type system is 46.2mm, and the spherical aberration is increased by 0.5mm only, by about 1.1 percent, so that the performance is not affected basically. The spherical aberration can be further reduced by adopting smaller sub-mirror width, but the improvement on the performance is small, and on the contrary, the processing and installation workload and the cost are increased; increasing the width increases the spherical aberration, affecting the system performance. Therefore, the cylindrical surface reflector spliced parabolic trough system used by the system is that the width of the cylindrical surface can be selected to be 0.8 meter at maximum.

The condition for eliminating the influence of the spherical aberration is provided, wherein w/r is less than or equal to 1/5 and is equal to the required relative caliber w/f is less than or equal to 1/2.5, which is far lower than 1/10.8 required by the field of optical imaging, so that the actual implementation is easier to achieve.

If a cavity receiver is used, if the lateral spherical aberration does not exceed 5% of the parabolic trough system radius, then the result is:

the conditions required to be satisfied for eliminating spherical aberration of the cylindrical reflector are as follows:

due to the optimized edge angle when using the cavity receiverDegree of adoption of the same waySample parameters were obtained: w/r is less than or equal to 0.199 and equal to 1/5. The requirements are far lower than those of imaging in the optical field, similar to those of using a tube receiver.

We have also established a ray tracing program to verify the above two aberration elimination requirements, namely, constructing a parabolic trough system using cylindrical surface stitching, according to which, including 8 m wide by using cylindrical surface reflectors with a width of 0.8 m and 90 degrees at the edge angle, the radius of each cylindrical surface reflector when using a parabolic trough system of a tube receiverWhen the optical errors are equal, the interception rate and the optical efficiency are identical to those of the same groove system using parabolas, and the difference is not more than 0.1%. In contrast, when the selected cylindrical surface radius is not equal to the calculation result of the above formula, the performance is degraded; increasing the cylindrical surface width also reduces system performance. Considering that the cylindrical surface optical error is much smaller than that of a paraboloid, the system performance of the system is obviously superior to that of a traditional paraboloid groove system. Quantitative results, including theoretical estimates and ray-tracing simulation results, are also presented later.

The utility model also provides a calculation formula for estimating the radius and the width of the receiver of the slot system, so that the design parameters of the system can be conveniently determined. Generally, a groove type system uses a tubular receiver, a vacuum heat collecting tube is commonly used, and how to select the radius of the receiver is often a large number of simulation calculation of system performance under different conditions, and the radius of the receiver can be determined by comprehensively considering the influence of a plurality of factors, for example, groove type system research report Optical analysis and optimization of line focus solar collectors published by Bendt et al in the United states.

On the other hand, in theory, optical system errors are often ignored, reflected light is seen as coming from a solar sphere, and the minimum receiver radius that can be selected by the trough system is estimated, so that the maximum theoretical light concentration ratio of the trough system can be estimated, but the theoretical estimation is not helpful for people to design an actual trough system. The utility model is to say the theory, we put forward the theory and calculation formula of estimating the radius of the receiver of the slot system, thus get the design parameter of the maximum condensing ratio, briefly set forth as follows:

the intensity distribution of sunlight reflected by a parabolic trough mirror can be described by a gaussian distribution. The reflected light distribution angle intercepted by the receiver determines the interception rate, for example, when the half distribution angle of interception is equal to the gaussian distribution mean variance sigma, about 68% of light is intercepted, and when the interception rate is increased to 2sigma, the interception rate is increased to 95.4%, and when the interception rate is increased to 4sigma, the interception rate is increased to 100%. We choose the half-spread angle at which all reflection points furthest from the focal point are intercepted by the receiver to be 2σ, i.e. all the spread half-angles smaller than 2σ, and at a system edge angle of 90 degrees, where the nearest reflection point is only half the furthest from the focal point, i.e. the intercept half-angle of the nearest reflection point is 4σ, the average intercept ratio can be estimated approximately (95.4% +100%)/2=97.7%). Thus, we derive the tubular receiver radius R as:

here, theIs the trough mirror edge angle and λ is the angle of incidence of sunlight on the trough system. On the other hand, half width of the trough mirror +.>After substitution, the method comprises the following steps:

the light concentration ratio GR is calculated as:

obviously, edge angleWhen the degree is high, the condensing ratio is maximum.

When using a cavity or flat receiver, we derive the receiver half-width as:

the maximum light concentration ratio is:

obviously, edge angleWhen the degree is high, the condensing ratio is maximum. The following theory is used to compare the condensing ratio of a common parabolic trough system and a cylindrical mirror spliced parabolic trough system, and the difference between the two is that the optical gradient error of the cylindrical mirror spliced trough system is 1mrad, and the common parabolic trough system is about 2.5 mrad. First, calculate the variance of Gaussian distribution of reflected light intensity

Referring to the actual measurement data provided by the groove system research report Optical analysis and optimization of line focus solar collectors issued by Bendt et al, assuming that the system is installed on Qinghai-Tibet plateau, the variance sigma of the solar light intensity distribution is taken _sun Is 3.4mrad, sigma _slope The slope error distribution variance of the groove type reflector is that the distribution of the parabolic reflector in two directions is respectively 2.5mrad and 1mrad, and the cylindrical reflector is 1mrad; sigma (sigma) _tracking Taking 1mrad from the tracking error Gaussian distribution variance; sigma (sigma) _disp Taking 1mrad from the Gaussian distribution variance of the system installation error; sigma (sigma) _specular Is the error Gaussian distribution variance of the reflector material and the like, which is ignored here; respectively calculated to obtainTo a common parabolic trough system sigma= 6.263mrad, a cylindrical surface spliced trough system sigma=4.27 mrad is used, the pressing angle is 30 degrees, and the light concentration ratio is calculated respectively as follows:

the light concentration ratio gr=22.0 of a common parabolic trough system;

the cylindrical surface spliced parabolic trough system has a light concentration ratio gr=32.3.

When the two groove systems respectively adopt the light collecting ratios, the interception rates are similar, the performance difference is mainly reflected on heat loss, the radius of a receiver of the common parabolic groove system is about 50% larger than that of a cylindrical surface spliced parabolic groove system, and the heat loss is about 50% larger than that of the spliced parabolic under the same working condition. If the two groove systems use receivers with the same radius, and the two groove systems are spliced groove system receiver radii, the maximum distribution angle of complete interception under the working condition of 30 degrees of sunlight incidence angle is 4.27 x 2mrad, which is only 1.36 times of the Gaussian distribution variance sigma= 6.263mrad of the common groove system, the system interception rate is the average value of interception rates when the interception distribution variances are 1.36 sigma and 2.72 sigma respectively, and the average interception rate= (82.6% +99.3%)/2=90.9% is obtained by looking up the Gaussian error distribution table, which is lower than the interception rate of the cylindrical surface spliced parabolic groove system by 6.8%. Therefore, when the same condensing ratio design is adopted, the intercepted energy is 6.8% lower than that of a cylindrical surface spliced parabolic trough system due to the large optical error of a common parabolic trough system. In summary, we demonstrate that the use of cylindrical surface stitched parabolic trough systems performs significantly better than conventional parabolic trough systems.

Using equation (17), when the edge angleThe trough system with the cavity receiver has the greatest light concentration ratio when the radian is the radian, and when the incident angle lambda takes pi/6 radian, sigma=5 mrad, the light concentration ratio is 27.6 compared with the trough system with the tube receiver; the slot system using the cavity receiver had a light collection ratio of 43.3, which is significantly better than the slot system using the tube receiver. On the other hand, the use of a cavity receiver is superior to a tube receiver and a flat receiver in that the cavity receiver has a high absorption rate, and after light enters the cavity,substantially all of the solar energy is absorbed by the receiver, but the tube and flat receivers reflect a portion of the intercepted solar rays, typically about 5% -10%, resulting in a lower absorption rate.

The cavity receiver and the cylindrical surface spliced parabolic trough system are practically used, the optimal edge angle is pi/4 radian only, so that the maximum optical error of the system is reduced, and the maximum design light concentration ratio is 51.4 when the typical optical error data are adopted, so that the reflection solar Gaussian distribution variance sigma=4.21 mrad can be obtained.

In addition, the line focusing parabolic trough reflector has a very uneven energy flow density distribution on the tubular receiver, so that the temperature distribution of the receiving surface is uneven, and the heat loss is larger, and the thermal stability is poor. Compared with a cavity receiver, the internal receiving surface structure of the receiver can be adjusted, and the uniform cavity energy fluid density distribution and temperature distribution can be maintained, so that the heat loss is smaller than that of a tubular receiver, the thermal performance is stable, and the heat collection efficiency is high.

The utility model increases the secondary condensation of the V-shaped groove type reflection condenser. In a focusing solar heat collector, a compound parabolic surface is often used for secondary focusing, so that the performance and the light concentration ratio are improved, but the compound parabolic surface used by the system can reflect light for many times, and high processing precision is required, otherwise, the error of the reflected light can increase linearly along with the reflection times, so that the system performance is reduced, and the scheme is poor in economical efficiency.

The V-shaped groove type reflection condensing lens has a light condensation multiple slightly lower than that of the compound paraboloid, but has a simple structure, and the incident light rays in a certain direction can be focused by using two inclined plane reflecting mirrors. The plane reflecting mirror used by the V-shaped groove is easy to process, and the optical error can be small, so that adverse effects caused by multiple reflections are eliminated. We propose to use a V-groove reflective condenser to mount it at the receiver entrance such that the V-groove entrance half-width is equal to the receiver half-width or radius R in the design method, and if the V-groove two mirrors tilt at θ, the exit half-width is R', which can be calculated as follows:

θ may be 5-10 degrees, using a bar-shaped cavity receiver, where the cavity receiver half width is R'; the radius of the vacuum heat collecting tube is R' when the vacuum heat collecting tube is used as a receiver. After the V-shaped groove type reflection condenser lens is added, the V-shaped groove type reflection condenser lens is matched with a cavity type or flat plate receiver for use, the performance is better, and the edge angle of the groove type system is the sameThe value range is about 45 degrees. The receiver width can then be reduced by half compared to if no V-groove mirror was added, thereby increasing the system condensing ratio to 100. The effect brought by adding the V-shaped groove type reflection condensing lens is obvious, heat loss can be reduced, the working temperature of the system is improved, the efficiency of a subsequent power generation system is improved, and the total efficiency and the performance of the groove type thermal power generation system are improved.

The utility model provides a design method of a parabolic trough type solar collector. The design method provided by the utility model can quickly and conveniently determine the design parameters of the parabolic trough solar collector spliced by using the cylindrical reflector. Generally, a tube type receiver is used in a slot type system, a vacuum heat collecting tube is used frequently, how to select various design parameters including edge angle and radius of the receiver, and often, the system performance under different conditions is calculated in a large amount by simulation, and the system performance can be determined by comprehensively considering the influence of various factors, for example, a slot type system research report Optical analysis and optimization of line focus solar collectors published by Bendt et al in the United states. The method has complex process and great workload, and an optimized design scheme is not necessarily obtained. According to the method, a light concentration ratio calculation formula is obtained according to a receiver size calculation formula provided by the inventor, so that the optimal edge angle and the receiver size can be determined, and each design parameter of the system is determined. In the aspect of splicing the parabolic trough reflectors by the cylindrical reflector, conditions and calculation formulas for eliminating spherical aberration and meridian coma are established, so that the parameters of the cylindrical reflector are determined. The design method provided by the utility model has the advantages of simple calculation process and clear thought, can easily obtain reliable design, and is superior to the design obtained by the traditional optical method.

The utility model has the beneficial effects that the cylindrical transparent glass cover plate is added to the opening of the cavity receiver, and firstly, the heat loss is reduced. The transparent glass material is selected to have high visible light transmittance and low infrared radiation transmittance, and is similar to the glass material used for the outer tube of the vacuum heat collecting tube, so that the heat loss is low. And secondly, the semi-circular structure is adopted, so that the sunlight of reflection loss can be reduced, and the absorptivity of the receiver to the sunlight is increased.

Claims

1. Novel cylindrical reflector splice groove type solar heat collection system is characterized in that: the device comprises a reflector group and a receiver, wherein the reflector group is formed by splicing a plurality of strip cylindrical surface reflectors, the centers of the strip cylindrical surface reflectors form parabolas, and the normal vector of the center of each strip cylindrical surface reflector is consistent with the normal vector of the parabolas of the installation position of the strip cylindrical surface reflector; the receiver is arranged on a parabolic focus formed by the centers of a plurality of strip-shaped cylindrical reflectors.

2. The novel cylindrical reflector splice trough solar thermal collection system of claim 1, wherein: when the receiver uses the bar-shaped cavity receiver, the cylindrical surface transparent glass cover plate is arranged at the opening of the bar-shaped cavity receiver, and the concave surface is arranged in the cavity receiver.