JPS5916241B2 - Reflector device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cylindrical parabolic reflector that reflects solar radiant energy, in which absorption capsules that absorb the reflected energy are arranged to most efficiently absorb the reflected energy. be.

A typical type of electromagnetic wave energy is solar radiation energy, and the average solar radiation intensity in Earth's orbit is approximately O, IW/c- (energy per million watts in Ikm squared), and its spectral curve is As shown by curve I in FIG. 1, the maximum value is near the wavelength of 0.5 μm, and the black body temperature (color temperature) is 5900°.

If the solar radiation energy near 59,000 can be converted into thermal energy with high efficiency, high-temperature heat can be obtained. Further, the characteristic when the black body temperature (color temperature) is i and oo degrees is shown as a curve (■). The wavelength that gives the maximum energy intensity corresponding to 700° is 4.5 μm, and the intensity of 5 at this wavelength is extremely small compared to the maximum intensity of solar radiant energy (O, near 5ttm), and the Most are 0.3-2.0μm
concentrated in the wavelengths of

Furthermore, for these two curves I and ■, the wavelength of the electromagnetic waves that gives the maximum radiant intensity differs depending on the black body temperature (color temperature), and if the black body temperature (color temperature) is low, the wavelength that gives the maximum radiant intensity differs depending on the black body temperature (color temperature). In Figure 1, the horizontal axis shows wavelength (μm) and the vertical axis shows relative intensity. By the way, it can be said that solar radiant energy is inexhaustible. If it can be absorbed efficiently, it can be directly converted into high-temperature heat and used as a non-polluting, permanent thermal energy source.

In order to efficiently absorb such solar radiant energy, it is important to absorb the reflected energy without letting it escape.

This invention was made in consideration of the above points, and it is based on the most efficient relationship between the positions of the cylindrical parabolic reflector that reflects solar radiation energy and the absorption capsule that absorbs it. This was discovered as a result of various studies.

The absorption efficiency of solar radiant energy is usually considered to be most efficient by placing it at the focal point of the paraboloid, but in reality, it is affected by the curvature error (tilt error) of the reflective mirror surface, the tracking error of solar radiant energy, and the reflectance of the mirror surface. Since it is determined by three factors, the efficiency differs significantly depending on the shape of the mirror surface even when the focal point is the same.

For the above reasons, it is necessary to consider the curved shape of the cylindrical parabolic reflecting mirror. First, the manufacturing characteristics of the curved surface that becomes the cylindrical parabolic reflecting mirror will be explained.

The mirror surface of a cylindrical parabolic reflector is a parabola y=-
It consists of a curved surface that is part of a paraboloid consisting of The curvature of a curved surface is determined by the accuracy of its shape.

That is, the precision of the mold is that the outer periphery (curved surface) is formed by polishing or the like using a mechanical method, so the curved surface is formed uniformly. Therefore, as shown in FIG. 2, each of the subdivided curved surface portions Ml, m2, . . . of the cylindrical parabolic reflecting mirror 1 squeezed out by this curved surface is approximately a straight line. You can think about it. Also,
These curved surface portions Ml, m2, . . . all have the same curvature error (tilt error). In other words, the machining accuracy of the curved surface portions Ml, m2, . . . has a constant characteristic. Such curved surface portion Ml, m2,・
As mentioned above, because the processing accuracy is constant, the curvature error (tilt error) is also constant, and in some cases, the reflection angle of the reflected energy of the solar radiant energy irradiated on it may vary greatly. may occur.

Therefore, depending on the position of the absorption capsule, most of the absorption capsule will not be focused, and as a result, the absorption efficiency will decrease. FIGS. 3a to 3c show an embodiment of the present invention, which shows an example of the arrangement of a reflecting mirror and an absorption capsule.

In these figures, 1 is a cylindrical parabolic reflector that reflects solar radiant energy E, and 2 is an absorption capsule that absorbs solar radiant energy, which contains an absorber having a selective absorption film. θ is the opening angle when the absorption capsule 2 is placed on the reflecting mirror 1, and Ml, m2, . . . are the same curved portions as shown in FIG. Here, changes in the aperture angle θ will be explained using FIG. 4.

The parabola M1 representing the curved surface of the cross section of the reflecting mirror 1 to the size D of the eyebrow opening are kept constant and the focal length a is gradually increased, and the angle formed by the parabola M1 to M4 and the focal point F, i.e. The opening angle θ is sequentially 3000, 2300, 18
00 and 900, which shows that by changing the focal length a, the aperture angle θ between each of the parabolas M1 to Fox and the focal point F changes.

Now, Fig. 3a shows the case where the absorption capsule 2 is placed very close to the cylindrical parabolic reflector 1, and the aperture angle θ is 3000, and Fig. 3b shows the case where the aperture angle θ is 3000.
is 900, cylindrical parabolic reflector 1
and the absorption capsule 2 are placed apart from each other.

In FIG. 3c, the aperture angle θ is set at 1800.

In these figures, solar radiant energy E is reflected by each curved surface portion Ml, m2, etc., which is a mirror surface of the cylindrical parabolic reflector 1, but according to the experimental results, the same curvature error ( Because of the curved surface portions Ml, m2, .

It was confirmed that the most efficient absorption occurs when the aperture angle θ is in the range of 1800 to 2600. This situation is shown in FIG. In this figure, the horizontal axis shows the aperture angle θ and the vertical axis shows the absorbed energy. Since this invention relates to a cylindrical parabolic reflector (hereinafter referred to as a "reflector") for the purpose of concentrating solar energy, it is practically efficient to use a reflector that takes in energy of a defined unit area. The following describes in detail how a good shape can be achieved.

First, for comparative consideration, the following points will be explained.

(1) Consider constant incident energy.

That is, the size D of the aperture is constant for any parabolic curved surface of any focal length a. (11) The reflectance of the subdivided mirror surface is constant for any part and for any parabolic curved surface of any focal length a.

(It is assumed that the degree of curvature of a subdivided mirror surface has a constant error from the true value at each point for any part and for any parabolic curved surface of any focal length a.

(Manufacturing methods that use molds have this characteristic.

) (5) What focal length a is the absorber at the focal point?
The parabolic curved surface of is also assumed to be a cylinder, and its diameter is constant.
(a) A very small subdivided partial mirror is a straight line or 1
or can be approximated by a plane.

(b) In the above case, if the small mirror is tilted with an error of Δθ from the true line of curvature, the reflected light will have an error of 2×Δθ.

(c) The focus of the reflected light from the partial mirror with this error angle
The shift at one point increases as the distance from the reflection point to the focal point (reflection optical path length) increases, and the relationship is proportional.

(d) For parabolic curved surfaces with different focal lengths a, the distance from the small mirror to the focal point (reflected optical path length) differs in total, and the average distance differs depending on the value of the focal length a. .

The above explanation is illustrated in FIG. 6, which is a more detailed version of FIG.

In order to determine the range of optimal design values for a reflector that condenses solar energy, we first set conditions and determine the condensed energy captured by the absorber based on general optical principles. By examining the relationship between the amount and the shape of , changing various design parameters, and performing an analysis, values as shown in FIG. 5 can be determined.

Part of the analysis that led to this result is shown below.

Assuming that the paraboloid is axially symmetric and considering the analytical half, as mentioned above, the energy captured by a certain absorber becomes smaller as the deviation of the reflected light increases, and the deviation of the reflected light increases with the reflected optical path length. Since it is proportional, the analysis example is to find the average value of the reflected optical path length for a paraboloid with a typical focal length,
The shortest average reflected optical path length means that the light is most efficiently focused on the absorber. Analysis 1 In Fig. 7, if the parabolic mirror has a focal length of a and a rim angle of θm (-θ), and the optical path length after specular reflection of sunlight (reflected optical path length) is ρ, then ρ
is the following formula.

Therefore, using the average reflected optical path length, the value becomes the following equation.

3,21L0m=6a7,.

. Moss sitting. ．． ．． ．． ．． ．． ．． ．． ．． ．． ．． ．． (9) Next, express a as a function of θm. [1] When 0m<θm×90s, the following equation holds true in FIG.

Here, when x=1 and substituting equations (3) and (4) into equation (5), when (2) θm〉90), in Figure 9, from equations (7) and (8), Therefore, poverty is [1] 0 from equations (2), (6), and (9).
When 〈θm〈900, 2 is the absorption capsule, and θ is the opening angle.

θ L? ? Figure 8 y″ Y Ol=10 02:20 03=30 04=40 a5=50 figure Figure 9

Claims (1)

[Claims] 1. In a reflecting mirror device that reflects solar radiant energy with a cylindrical parabolic reflecting mirror and makes it incident on an absorption capsule placed at a focal point, the mirror surface of the cylindrical parabolic reflecting mirror is formed into curved surface portions m_1, m_ with the same curvature error.
2. A reflecting mirror device characterized in that the angle formed by the straight line connecting both ends of the reflecting mirror and the focal point is in the range of 180° to 260°.