Phase report of Sino-Danish Research Project: “Optimization of solar space heating & water heating combisystems in buildings”, 2012

Phase report of Sino-Danish Research Project: “Optimization of solar space heating & water heating combisystems in buildings”, 2012

Beijing Solar Energy Research Institute Co., Ltd.

1. Project activities of BSERI in 2011

1) Flat plate solar collector with 2-covers testing

We have developed a flat plate collector with 2-covers, a glass and a Teflon film in order to improve efficiency. The collector has be tested compared with a flat plate collector with single glass cover at BSERI experimental base.

The National Center for Quality Supervision and Testing of Solar Heating

System(NCQST) also tested the thermal performance of the two kinds of collectors and the results are consistent with our testing.

Fig.1 1-covers collector Fig.2 2-cover collector

Fig.3 1-cover collector instantaneous efficiency curve based on the aperture area and collector inlet temperature

Fig.4 2-covers collector instantaneous efficiency curve based on the aperture area and collector inlet temperature

Results: the 1-cover collector testing results : η_0,a =0.75 U=5.1（W/㎡·K）

the 2-covers collector testing results: η_0,a =0.78 U=4.9（W/㎡·K）

（Appendix. 1 is the detailed results）

So from the testing results, it can be seen that the efficiency and performance of 2-covers collector do not get good improvement.

2) The numerical simulation of the tank in solar heating system The tank paramters:

Height: 1600mm External diameter:620mm Internal diameter: 520mm Insulation thickness: 50mm

Diameter of the collector tubes: φ₁ =20mm; 25mm; 32mm; 40mm V₁=0.4m³/h Q₁=50kWh

Diameter of the boiler tubes: φ₂ =25mm Q₂=70kWh ∆T₂=25℃

Diameter of the heating tubes: φ₃ =25mm Q₃=120kWh ∆T₃=10℃

Fig .5 CFD model of the tank Fig.6 The grid of the tank

Fig.7 φ₁ =20mm thermal stratification

Fig.8 φ₁ =25mm Thermal stratification

Results: The thermal stratification of the tank is quite obvious, the maximum temperature difference is 24.97℃. However, among the simulation results of four different collector inlet and outlet diameters, there is a little change of the thermal stratification in the tank.(Appendix. 2 is the detailed results)

3) Study on antireflective glass by liquid-phase etching

Our researchers have finished the study on antireflective glass by liquid-phase etching.

The methods used and results are as follows:

First : Sodium oxide, calcium oxide and metal oxide composed the glass were selectively etched by fluorosilicic acid saturated by silicon dioxide, leaving the surface of the glass substantially consisted of silicon dioxide. Thus, an antireflective film was formed on the appearance of the glass.

Second: The properties of the as-gained antireflective glass were measured by scanning electron microscope, spectrophotometer and then theoretically analyzed.

The results indicate that the glass has a porous antireflective film and its transmittance increases by 2.8%~7.0% ,over the wavelength range of 350nm~1000nm, with 3.0%, 7.0% and 2.8% at 350nm, 550nm, 1000nm respectively. The finally thickness and refractive index of the antireflective film on the as-gained glass were theoretically calculated.

Fig. 9 Shearing-off of the antireflective by SEM Fig. 10 Surface of the antireflective film by SEM

Fig.11 Transmittance of the antireflective glass and common glass

From figure 11, it can be seen that within the wavelengh range of 300nm~1000nm, spectral transmittance keep increased and then decreased, the maximum at about

500nm.Glass transmittance at 350nm~1000nm increased by 2.8%~7.0%, and at 350nm and 1000nm, the value-added were 3.0% and 2.8%, at 550nm, the value-added was 7.0%.

The researchers have published a paper in 2011 Chinese Materials Conference.

(Appendix. 3 is the paper)

2. Project Plans of BSERI in 2012

1）2012.03~2012.06 Thermal stratification study and performance test of heat storage tank

2）2012.06~2012.09 Design and performance analysis of the improved solar heating system

3）2012.09~2012.12 Reaearch and development of solar air collector heating system

Fig .1 CFD model of the tank Fig.2 The grid of the tank

Fig.3 φ₁ =20mm Thermal stratification

Fig.4 φ₁ =25mm Thermal stratification

Fig.5 φ₁ =32mm Thermal stratification

Fig.6 φ₁ =40mm Thermal stratification

Fig .7 φ₁ =25mm Moved down the outlet pipe 50mm

Fig .8 φ₁ =25mm Moved up the outlet pipe 50mm

Fig .9 φ₁ =25mm Moved down the inlet pipe 50mm

Fig .10 φ₁ =25mm Moved up the inlet pipe 50mm

Fig.11 φ₁ =20mm Velocity distribution in the X ditrction

Fig.12 φ₁ =25mm Velocity distribution in the X ditrction

Fig.13 φ₁ =32mm Velocity distribution in the X ditrction

Fig.14 φ₁ =40mm Velocity distribution in the X ditrction

Fig .15 φ₁ =25mm Moved down the outlet pipe 50mm velocity distribution in the X ditrction

Fig .16 φ₁ =25mm Moved up the outlet pipe 50mm velocity distribution in the X ditrction

Fig .17 φ₁ =25mm Moved down the inlet pipe 50mm velocity distribution in the X ditrction

Fig .18 φ₁ =25mm Moved up the inlet pipe 50mm velocity distribution in the X ditrction

Procedia Engineering 27 (2012) 1 – 5 Available online at www.sciencedirect.com

Procedia Engineering

Procedia Engineering 00 (2011) 000–000

www.elsevier.com/locate/procedia

2011 Chinese Materials Conference

Study on antireflective glass by liquid-phase etching

Qi Wang, Yingchao Zhang, Dunzhi Zhu, Guangming Xie^*

Beijing Solar Energy Research Institute Co.,Ltd No.3 Huayuan Rd.Haidian District.Beijing,China,100191

Abstract

Sodium oxide, calcium oxide and metal oxide composed the glass was selectively etched by fluorosilicic acid saturated by silicon dioxide, leaving the surface of the glass substantially consisted of silicon dioxide. Thus, an antireflective film was formed on the appearance of the glass. The properties of the as-gained antireflective glass were measured by scanning electron microscope, spectrophotometer and then theoretically analyzed. The results indicates that the glass has a porous antireflective film and its transmittance increases by 2.8~7.0% by the light wavelength in the range of 350~1000nm, with 3.0%, 7.0% and 2.8% at 350nm, 550nm, 1000nm. Finally, the thickness and refractive index of the antireflective film on the as-gained glass were theoretically calculated.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Chinese Materials Research Society

Keywords: liquid-phase etching; antireflective glass; reflectance; transmittance; refractive index

浸蚀法减反射玻璃研究

王启，朱敦智，张英超，谢光明

北京市太阳能研究所有限公司 中国 北京市海淀区花园路₃号 ₁₀₀₁₉₁

*Corresponding author. Tel.: +86-10-62001057.

E-mail address: wang056112@163.com.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Chinese Materials Research Society

2 Q. Wang, et al. / Procedia Engineering 00 (2011) 000–000 Qi Wang et al. / Procedia Engineering 27 (2012) 1 – 5

摘要

利用氟硅酸的二氧化硅饱和溶液把玻璃表层的氧化钠、氧化钙以及金属氧化物进行有选择的刻蚀，只保 留二氧化硅，从而在玻璃表面形成一层二氧化硅减反射膜。通过扫描电镜、分光光度计和理论分析研究了制 备的减反射玻璃的性能，研究结果表明二氧化硅减反射膜呈多孔结构；玻璃透过率在350～1000nm增加了2.8

～7.0%，其中在350nm、550nm和1000nm的增值分别为3.0%、7.0%和2.8%；从理论上计算出二氧化硅减反射 膜的厚度和折射率。

关键词：浸蚀；减反射玻璃；反射率；透过率；折射率

目前国内外减反射玻璃都是通过在玻璃表面涂镀减反射膜实现的，减反射膜一般由两种方式 实现^[1]：一种是通过溶液有选择的浸蚀玻璃表面，使其形成一层多孔二氧化硅膜^[2,5-8]；另一种是 通过物理或化学的方法沉积、溅射等在玻璃形成减反射膜^[3,4]。本文是利用含二氧化硅的氟硅酸溶 液对玻璃表面进行选择性刻蚀，即把玻璃表面反射率较高的氧化钠、氧化钙以及其他金属氧化物 进行有选择的腐蚀而保留反射率较低的二氧化硅骨架，使玻璃表面形成一层多孔二氧化硅膜，当 腐蚀达到一定厚度时，一定波长的光在多孔二氧化硅表面会发生相消干涉，达到降低玻璃反射率 提高透过率的目的。

尽管 Thomsen^[5]早在 1951年就提出可以通过浸蚀的方法在玻璃表面实现多孔二氧化硅膜，但

该方法国内外的研究少之又少。丹麦 Sunarc 公司是目前唯一掌握该浸蚀技术并实现产业化的单 位，但一直将技术保密，没有公开发表文章和专利。北京市太阳能研究所谢光明研究员对丹麦减 反射玻璃制备方法、经济性能做了简介^[6]。Furbo^[7]通过对比 Sunarc 的减反射玻璃和普通玻璃，发 现浸蚀后的玻璃透过率提高了 5~9%，采用该减反射玻璃的集热器集热效率提高了 4~6%；San

Vicente^[8]在 50℃温度下对浸蚀减反射玻璃的耐候性进行了研究，14个月后减反射膜依然牢固附着

在玻璃表面，玻璃透过率可以达到0.96。

1. 实验

1.1. 抛光

抛光分为 a.水洗。用清水将玻璃表面的尘、垢等反复清洗至玻璃表面无明显污物；b.醇洗。

把用水清洗干净的玻璃放入盛有无水乙醇的容器中，并使醇液没过玻璃，超声波清洗 5～10min， 以清除玻璃表面的有机物，然后将玻璃表面醇液用热风吹干；c.酸洗。将玻璃放入 2% HF和20%

H2SO4混合酸液中，室温清洗2min，以清除玻璃表面的无机物，并使玻璃露出新鲜的剖面。

1.2. 裂纹

裂纹所用溶液为 HF、NH4HF2、山梨醇混合溶液，裂纹温度为 45～55℃，裂纹时间为 18～ 25min。

1.3. 造孔

造孔所用溶液首先将 15～40% H2SiF6和0.5～2.0% SiO2混合成悬浊液，然后用真空泵抽滤得 清液，再在清液中加入其质量分数 4‰ 硼酸，即得造孔溶液。造孔温度为50～60℃，造孔时间为 25～33min。

Qi Wang et al. / Procedia Engineering 27 (2012) 1 – 5

Q. Wang, et al. / Procedia Engineering 00 (2011) 000–000 3

2. 2结果与讨论

2.1. 表面形貌

用扫描电镜对减反射膜的切面和表面形貌做了分析，如图1、2所示。从图1和2可以看出二 氧化硅减反射膜呈多孔疏松结构，厚度为 100~150nm；多孔疏松层为龟裂状，每个龟裂单元的直 径为30nm左右，龟裂间隙为10~15nm。

图1 电镜下减反射玻璃切面图 图2 电镜下减反射膜表面形貌

Fig.1. Shearing-off of the antireflective by SEM Fig.2. Surface of the antireflective film by SEM

2.2. 透过率

由图 3 可以看出，在 300～1000nm 波长范围内，玻璃透过率经历现增加后降低的过程，在 550nm附近有最大值。玻璃透过率在 350～1000nm增加了 2.8～7.0%，其中在 350nm和 1000nm 的增值分别为3.0%和2.8%，在550nm处增值达到7.0%。

300 400 500 600 700 800 900 1000 1100 30

40 50 60 70 80 90 100

Transmittance/%

Wavelength/nm

Common glass Antireflective glass

图3 浸蚀增透玻璃和普通玻璃的透过率

Fig.3. Transmittance of the antireflective glass and common glass

4 Q. Wang, et al. / Procedia Engineering 00 (2011) 000–000 Qi Wang et al. / Procedia Engineering 27 (2012) 1 – 5

2.3. 理论膜厚

单层膜的反射率：

) d n ( sin ) n n n ( ) d n ( cos ) n n ( n

) d n ( sin ) n n n ( ) d n ( cos ) n n ( R n

f f

g a f g

a f

f f

g a f g

a f 1







 







2 2

2 2

2 2 2 2

2 2

2 2 2 2

2 2











  (1)

式中：nf膜的折射率；

na，_ng膜两侧媒质空气、玻璃的折射率；d膜的厚度 当光线垂直入射时，

^{2 2}

2 2

) n n n (

) n n n R (

f g a

f g a



 

(2) 假设空气的折射率na=1，则发生干涉时：

R=0，即

g

f n

n 

当光垂直入射时，薄膜两表面反射光的光程差为 2nd，由于在膜的上、下表面反射时都有相 位突变，结果没有附加的相位差，两反射光干涉相消时应满足：

nd (k ) 2 2  1

(3) 单层增透膜的最小厚度应为（相应于k=0 ）

d n 4

 

因此，理想的单层增透膜的条件是：膜层的光学厚度为λ ／4，其折射率为入射媒质的折射率 与基片折射率二者乘积的平方根。

由图 3可知，在550nm附近减反射玻璃透过率增值达到最大，即反射光发生相消干涉对应的

波长为 550nm，所以理论上多孔二氧化硅减反射膜的厚度应为 137nm左右，与扫描电镜分析结果

一致。玻璃反射率按 1.52计算，多孔二氧化硅减反射膜的理论折射率为1.23，但目前未对这一理 论结果进行科学验证。

2.4. 多孔膜孔隙率

多孔二氧化硅薄膜的折射率在一定程度上由空隙率和薄膜组成成分所决定,多孔薄膜折射率与 孔隙率之间的关系可以表示为：

n pn_s(1p)n_v (4) 式中：p 为空隙密度；

ns 为空隙折射率；

nv 为薄膜成分折射率；

按照二氧化硅的实际折射率为 1.46，多孔二氧化硅减反射膜的理论折射率为 1.23计算，多孔 膜的孔隙率应为0.5左右。

3. 结论

Qi Wang et al. / Procedia Engineering 27 (2012) 1 – 5

Q. Wang, et al. / Procedia Engineering 00 (2011) 000–000 5

通过以上分析可以得到以下几点结论：

1. 二氧化硅减反射膜呈多孔疏松结构，厚度为100~150nm；多孔疏松层为龟裂状，每个龟裂单 元的直径为30nm左右，龟裂间隙为10~15nm。

2. 玻璃透过率在350～1000nm增加了2.8～7.0%，其中在350nm、550nm和1000nm的增值分 别为3.0%、7.0%和2.8%；

3. 理论上多孔二氧化硅减反射膜的厚度应为137nm左右，折射率为1.23，孔隙率为0.5。

参考文献

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