KR101229772B1 - Surface structure of solar thermal absorber - Google Patents

Surface structure of solar thermal absorber Download PDF

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KR101229772B1
KR101229772B1 KR1020110113111A KR20110113111A KR101229772B1 KR 101229772 B1 KR101229772 B1 KR 101229772B1 KR 1020110113111 A KR1020110113111 A KR 1020110113111A KR 20110113111 A KR20110113111 A KR 20110113111A KR 101229772 B1 KR101229772 B1 KR 101229772B1
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absorber
wavelength
surface structure
solar
energy
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KR1020110113111A
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Korean (ko)
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이현진
김종규
이상남
강용혁
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한국에너지기술연구원
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S70/00—Details of absorbing elements
    • F24S70/60—Details of absorbing elements characterised by the structure or construction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/40—Solar thermal energy, e.g. solar towers

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  • Life Sciences & Earth Sciences (AREA)
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Abstract

PURPOSE: A surface structure of a solar receiver is provided to effectively improve energy efficiency by having a surface roughness with a wavelength longer than the wavelength of radiant energy of sunlight and shorter than the wavelength of radiant energy emitted from the receiver. CONSTITUTION: A surface structure of a solar receiver(1) comprises a surface roughness with a wavelength longer than the wavelength of radiant energy of sunlight and shorter than the wavelength of radiant energy emitted from the receiver. The surface structure of the solar receiver is formed by sand blasting, etching, brushing, or rolling.

Description

태양열 흡수기의 표면 구조물{Surface Structure of Solar Thermal Absorber}Surface Structure of Solar Thermal Absorber

본 발명은 태양열 흡수기의 표면 구조물에 관한 것으로서, 더욱 상세하게는 태양에너지의 흡수율을 높여 효율을 증가시킬 수 있는 태양열 흡수기의 표면 구조물에 관한 것이다. The present invention relates to a surface structure of the solar heat absorber, and more particularly to a surface structure of the solar heat absorber that can increase the efficiency by increasing the absorption rate of solar energy.

일반적으로 태양열 흡수기는 태양 에너지에 대한 흡수율이 높고 자체 온도에서 방사율은 낮은 것이 좋기 때문에, 이를 만족시키기 위해 다양한 방법이 시도되고 있다. 일례로, 태양에너지의 흡수율을 높이고 방사율을 낮추기 위해 흡수기의 표면을 특정 소재로 선택 코팅하는 기술이 있으나, 아직까지는 코팅이 안정적이지 못하며 고온 상태에서는 코팅이 박리되면서 그 성질을 잃는 경우가 발생하고 있다.In general, solar absorbers have high absorption of solar energy and low emissivity at their own temperature, and various methods have been tried to satisfy them. For example, there is a technique of selectively coating the surface of the absorber with a specific material to increase the absorption rate of the solar energy and lower the emissivity, but the coating is not stable until now, and the coating is peeled off at a high temperature, thereby losing its properties. .

본 발명은 상술한 종래 기술에 착안한 것으로서, 본 발명의 목적은 태양열 흡수기의 에너지 효율을 높이는 표면 구조물을 제공하는 데 있다.The present invention has been made in view of the above-described prior art, and an object of the present invention is to provide a surface structure for enhancing the energy efficiency of a solar heat absorber.

상기 목적을 달성하기 위한 본 발명에 따른 태양열 흡수기의 표면 구조물은 태양광의 복사에너지 파장보다는 길고 흡수기로부터 방사되는 복사에너지의 파장보다는 짧은 파장의 표면 거칠기를 갖는다. The surface structure of the solar heat absorber according to the present invention for achieving the above object has a surface roughness of a wavelength longer than the wavelength of the radiation of sunlight and shorter than the wavelength of the radiation emitted from the absorber.

또한, 본 발명에 따른 태양열 흡수기의 표면 구조물의 상기 표면 거칠기(R)는 0.5㎛ ≤ R ≤

Figure 112011086126942-pat00001
㎛이다. Further, the surface roughness R of the surface structure of the solar heat absorber according to the present invention is 0.5 μm ≦ R ≦
Figure 112011086126942-pat00001
[Mu] m.

또한, 본 발명에 따른 태양열 흡수기의 표면 구조물의 거칠기 값은 제곱평균제곱근이다. In addition, the roughness value of the surface structure of the solar absorber according to the present invention is the root mean square.

또한, 본 발명에 따른 태양열 흡수기의 표면 구조물은 샌드 블래스팅(sand blasting), 에칭, 브러슁, 롤링 중 하나에 의해 형성되는 태양열 흡수기의 표면 구조물.In addition, the surface structure of the solar absorber according to the present invention is a surface structure of the solar absorber is formed by one of sand blasting, etching, brushing, rolling.

본 발명에 따른 태양열 흡수기는 표면에 태양광의 복사에너지 파장보다는 길고 흡수기로부터 방사되는 복사에너지의 파장보다는 짧은 거친 구조물을 형성함으로써 흡수율은 증가시키되 방사율은 증가하지 않도록 하여 에너지 효율을 효과적으로 높일 수 있다. The solar heat absorber according to the present invention can effectively increase energy efficiency by increasing the absorption rate but not increasing the emissivity by forming a rough structure on the surface longer than the wavelength of the radiation of sunlight and shorter than the wavelength of the radiation emitted from the absorber.

도 1은 복사에너지와 파장 사이의 관계를 도시한 그래프이다.
도 2는 본 발명의 일 실시예에 따른 태양열 흡수기의 표면을 확대 도시한 도면이다. 1 is a graph showing the relationship between radiant energy and wavelength.
2 is an enlarged view of a surface of a solar absorber according to an embodiment of the present invention.

이하, 본 발명의 바람직한 실시예를 첨부한 도면을 참조하여 상세히 설명하기로 한다.Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

흑체 복사(Black body;공동 복사체) 이론에 따르면 모든 물체는 전자기파 형태로 에너지를 방출한다. 흑체에서 방출되는 전자기파 에너지는 파장에 따른 분포를 갖는데 이를 플랑크 분포(Plank's distribution)라 부른다. According to Black body theory, all objects emit energy in the form of electromagnetic waves. The electromagnetic energy emitted from the blackbody has a wavelength distribution, which is called Plank's distribution.

Figure 112011086126942-pat00002
Figure 112011086126942-pat00002

Figure 112011086126942-pat00003
Figure 112011086126942-pat00003

Figure 112011086126942-pat00004
Figure 112011086126942-pat00004

λ : 복사에너지의 파장λ: wavelength of radiant energy

T : 흑체 온도
T: black body temperature

도 1은 플랑크 분포에 따른 복사에너지와 파장의 관계를 도시한 그래프이다. 파란 실선과 빨간 점선은 온도가 각각 5800K와 1000K 흑체에서 방사되는 복사에너지의 파장에 따른 분포이다. 1 is a graph showing the relationship between the radiant energy and the wavelength according to the Planck distribution. The solid blue line and the dotted red line are the temperature distributions of the radiant energy emitted from the 5800K and 1000K black bodies, respectively.

플랑크 분포에 따르면 일반적으로 흑체의 온도가 높아질수록 낮은 파장의 전자기파에서 에너지가 주로 방사된다. 그리고, 최대 에너지가 방사되는 파장은 아래 빈의 법칙(Wien's law)에 의해 구할 수 있다. According to Planck's distribution, in general, the higher the temperature of the blackbody, the more energy is emitted from low-frequency electromagnetic waves. The wavelength at which the maximum energy is emitted can be determined by Wien's law below.

Figure 112011086126942-pat00005
Figure 112011086126942-pat00005

λmax : 최대 에너지가 방사되는 파장
λmax: wavelength at which maximum energy is emitted

태양 온도는 약 5800K이므로 최대 에너지가 방사되는 파장은 도 1에서 같이 0.5 μm이다. 즉, 태양의 복사에너지 중에 0.5 μm 근방의 복사에너지에 대해 흡수율이 높을수록 흡수기 효율은 증가한다.Since the solar temperature is about 5800K, the wavelength at which the maximum energy is radiated is 0.5 μm as shown in FIG. That is, the higher the absorption rate for the radiation energy around 0.5 μm of the sun's radiation energy, the higher the absorber efficiency.

한편, 도 2에 확대 도시한 바와 같이 흡수기(1)의 표면이 거칠면 다수의 반사를 통해 에너지 흡수율을 높일 수 있다. 즉, 흡수기(1)의 표면 거칠기가 상술한 최대 태양 복사에너지가 발생하는 파장 0.5μm보다 크면 그만큼 많은 다중 반사를 만들 수 있으므로 흡수율을 증가시켜 흡수기의 효율을 높일 수 있게 된다. On the other hand, when the surface of the absorber 1 is rough, as shown in an enlarged view in FIG. 2, the energy absorption rate may be increased through multiple reflections. In other words, when the surface roughness of the absorber 1 is larger than the wavelength of 0.5 μm at which the maximum solar radiation occurs, the multiple reflections can be made. Therefore, the absorption efficiency can be increased by increasing the absorption rate.

흡수기(1)의 표면 거칠기는 KS B 0161 : 1999의 규격에 따르면 중심선 평균 거칠기(Ra), 최대높이(Rmax), 10점평균거칠기(Rz), 제곱평균거칠기(Rq), 제곱평균제곱근(Rrms), 요철의 평균 간격(Sm), 국부 산봉우리의 평균 간격(S) 부하 길이율(tp) 등 다양한 방법을 채택하고 있다. 이러한 거칠기를 계산하는 방법은 이미 공지되어 있으며 측정기에서 자동적으로 계산되므로 자세한 설명은 생략한다. 다양한 거칠기 대표 값 중에서 제곱평균제곱근(Rrms) 값은 불규칙인 표면이나 규칙적인 표면에 모두 적용 가능하며 표면 거칠기에 의한 빛의 산란을 설명하는데 가장 바람직하다. The surface roughness of the absorber 1 is in accordance with the standard of KS B 0161: 1999. ), The average spacing of unevenness (Sm), the average spacing of local peaks (S), and the load length ratio (tp). The method of calculating such roughness is already known and is automatically calculated by the measuring instrument, so a detailed description thereof will be omitted. Of the various roughness representative values, the root mean square (Rrms) value is applicable to both irregular and regular surfaces and is most preferable for explaining scattering of light due to surface roughness.

표면 거칠기의 단위는 ㎛로, 이는 파장의 단위인 ㎛와 같다. 따라서, 흡수기(1)의 표면 거칠기를 흡수기로 입사되는 태양의 복사에너지 최대 파장 0.5㎛ 보다 길게 하면, 다수의 난반사로 인해 태양열 흡수율이 증가되므로, 최종적으로 흡수기의 에너지 효율을 높일 수 있게 된다. The unit of surface roughness is μm, which is equal to the unit of wavelength μm. Therefore, when the surface roughness of the absorber 1 is made longer than the maximum wavelength of 0.5 nm of the radiant energy incident to the absorber, the solar heat absorption rate is increased due to the large number of diffuse reflections, thereby finally increasing the energy efficiency of the absorber.

한편, 태양열 흡수기의 에너지 효율을 높이기 위해서는 흡수기에서 흡수되는 에너지도 높여야 하지만, 방출되는 에너지를 줄이거나 최소한 증가하지 않도록 해야 한다. 키리히호프(Kirchhoff)의 열복사 법칙에 따르면, 일정한 온도에서 같은 파장의 복사에 대한 물체의 흡수율과 방사율은 동일한 값을 갖는다. 만일 표면 거칠기가 0.5μm 이상의 모든 파장에 대해 흡수율을 높이는 효과를 준다면, 흡수기의 방사율도 증가하게 되고 흡수기 효율이 감소할 수도 있다. 따라서, 태양 에너지에 대한 흡수율은 높이지만, 자체 온도에서 방사율을 높이지 않는 방법이 필요하다.On the other hand, in order to increase the energy efficiency of the solar absorber, the energy absorbed by the absorber must be increased, but the energy emitted must be reduced or at least not increased. According to Kirchhoff's law of thermal radiation, the absorption and emissivity of an object for radiation of the same wavelength at a constant temperature have the same value. If the surface roughness has the effect of increasing the absorption for all wavelengths of 0.5 mu m or more, the emissivity of the absorber may also increase and the absorber efficiency may decrease. Therefore, there is a need for a method of increasing the absorption to solar energy but not increasing the emissivity at its own temperature.

광학적으로 전자기파의 파장이 표면 거칠기보다 커질수록, 비록 표면이 거칠더라도 도 2에서 보여주는 다중 반사의 효과가 줄어든다. 즉, 아래 조건에서는 표면 거칠기에 의한 흡수율 또는 방사율 변화가 작아서 그 값이 매끄러운 표면의 값과 비슷해진다. Optically, the greater the wavelength of the electromagnetic wave than the surface roughness, the less the effect of multiple reflections shown in FIG. 2, even if the surface is rough. That is, under the following conditions, the change in absorption or emissivity due to surface roughness is small, so that the value is similar to that of a smooth surface.

Figure 112011086126942-pat00006
Figure 112011086126942-pat00006

δ : 흡수기의 제곱평균거칠기(root mean square roughness, Rq)
δ: root mean square roughness (Rq) of the absorber

흡수기로부터 방출되는 복사에너지도 상술한 바와 같이 파장에 따른 특성으로 설명할 수 있다. 상기 빈의 법칙을 이용하여 흡수기(1)를 소정의 온도(Tr)를 갖는 흑체로 가정할 경우, 복사에너지가 최대로 방사되는 파장은 빈의 법칙에 따라 2898/Tr ㎛ 가 된다. 따라서, 흡수기 표면의 제곱평균거칠기가 2898/Tr ㎛ 보다 길면 흡수기 방사율도 높아지지만, 2898/Tr ㎛ 보다 짧으면 흡수기의 방사율은 높아지지 않는다. Radiation energy emitted from the absorber can also be described as a characteristic according to the wavelength as described above. Assuming that the absorber 1 is a black body having a predetermined temperature Tr using the bin's law, the wavelength at which the radiant energy is radiated to the maximum is 2898 / Tr μm according to the bin's law. Therefore, the absorber emissivity also increases when the square average roughness of the absorber surface is longer than 2898 / Tr μm, but the emissivity of the absorber does not increase when it is shorter than 2898 / Tr μm.

결과적으로 태양 에너지에 대한 흡수율은 높이지만 자체 온도에서 방사율 높이지 않으려면, 표면의 제곱평균거칠기는 0.5㎛ 보다 크고 2898/Tr ㎛ 보다 작아야 한다. 예를 들어 흡수기(1)의 평균온도가 1000K 라면, 최대 에너지가 방사되는 파장은 약 2.9㎛가 된다. 따라서, 흡수기(1)의 표면 거칠기가 0.5㎛ 와 2.9㎛ 사이의 값, 예를 들어 1㎛ 정도라면 태양의 복사에너지에 대해서는 광학적으로 표면이 거칠지만, 흡수기가 방사하는 복사에너지에 대해서는 표면은 거칠지 않다. 이는 다르게 표현하면, 태양 복사에너지에 대해 흡수율은 증가하지만 흡수기의 방사율은 변화가 없으므로, 최종적으로 태양열 흡수기의 에너지 효율은 증가됨을 의미한다. As a result, the surface root mean square roughness should be greater than 0.5 µm and less than 2898 / Tr µm, in order to increase solar energy absorption but not emissivity at its own temperature. For example, if the average temperature of the absorber 1 is 1000K, the wavelength at which the maximum energy is radiated is about 2.9 mu m. Therefore, if the surface roughness of the absorber 1 is between 0.5 μm and 2.9 μm, for example, about 1 μm, the surface is optically rough for the radiant energy of the sun, but the surface is rough for the radiant energy emitted by the absorber. not. In other words, the absorbance increases with respect to solar radiation but the emissivity of the absorber does not change, which means that the energy efficiency of the solar heat absorber is finally increased.

흡수기 표면의 거칠기(조도) 가공은 흡수기가 통상의 강판소재라 한다면 샌드 블래스팅(sand blasting), 에칭, 브러슁, 고온에서의 롤링 등이 가능하며, 불규칙적인 구조물은 물론 규칙적인 구조물도 포함할 수 있다.Roughness (absorption) processing of the absorber surface can be sand blasted, etched, brushed, rolled at high temperatures, etc., as long as the absorber is a conventional steel sheet, and can include irregular structures as well as regular structures. have.

1..태양열 흡수기1..Solar Heat Absorber

Claims (4)

태양광의 복사에너지 파장보다는 길고 흡수기로부터 방사되는 복사에너지의 파장보다는 짧은 파장의 표면 거칠기를 갖는 태양열 흡수기의 표면 구조물.A surface structure of a solar heat absorber having a surface roughness of a wavelength longer than that of sunlight and shorter than a wavelength of radiation radiated from the absorber. 제 1항에 있어서,
상기 표면 거칠기(R)는
0.5㎛ ≤ R ≤
Figure 112011086126942-pat00007
㎛인 태양열 흡수기의 표면 구조물.The method of claim 1,
The surface roughness (R) is
0.5 μm ≤ R ≤
Figure 112011086126942-pat00007
Surface structure of a solar absorber which is μm. 제 2항에 있어서,
상기 표면 거칠기는 제곱평균제곱근 값인 태양열 흡수기의 표면 구조물.The method of claim 2,
Wherein said surface roughness is a root mean square value. 제 1항 내지 제 3항 중 어느 한 항에 있어서,
상기 흡수기의 표면 구조물은 샌드 블래스팅(sand blasting), 에칭, 브러슁, 롤링 중 하나에 의해 형성되는 태양열 흡수기의 표면 구조물.4. The method according to any one of claims 1 to 3,
The surface structure of the absorber is a surface structure of the solar absorber is formed by one of sand blasting, etching, brushing, rolling.
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