Absorption characteristics of nanoparticles with sharp edges for a direct-absorption solar collector

Qin, Caiyan,Kim, Joong Bae,Gonome, Hiroki,Lee, Bong Jae Elsevier 2020 RENEWABLE ENERGY Vol.145 No.-

<P><B>Abstract</B></P> <P>Plasmonic nanofluids has been reported beneficial for enhancing absorption of the solar energy in a direct-absorption solar collector (DASC). In order to overcome the shortage of narrow absorption band associated with the localized surface plasmon, two strategies can be adopted. One is to blend nanoparticles with different absorption peaks, and the other is to develop nanoparticles capable of exhibiting multiple absorption peaks at different wavelengths. In this study, the latter strategy is explored systematically by investigating the absorption efficiency of metallic nanoparticles with sharp edges. The results show that the Ag nanoparticles with sharp edges can induce multiple absorption peaks due to both localized surface plasmon resonance and lightning rod effect. We also show that the sharper edges (i.e., with either smaller radius of curvature or smaller edge angle) can greatly enhance the lightning rod effect. In addition, the study of SiO<SUB>2</SUB>-core/Ag-shell suggests that the core/shell configuration is beneficial for further broadening the absorption band compared to the Ag nanoparticle. Further investigation shows that the solar-weighted absorption coefficient of a DASC using the four-edge nanoparticle is 35% and 20% point higher than the nanosphere and the nanorod respectively with a fixed volume fraction of <SUP> 10 − 6 </SUP> .</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ag nanoparticles with sharp edges can generate multiple absorption peaks. </LI> <LI> Multiple peaks are due to the localized surface plasmon and the lightning rod effect. </LI> <LI> More edges do not necessarily result in broader absorption. </LI> <LI> Core/shell nanoparticles exhibit broader absorption band than the Ag nanoparticles. </LI> <LI> Performance of a DASC with edged particles is much higher than smooth particles. </LI> </UL> </P>

Optical absorption characteristics of brown carbon aerosols during the KORUS-AQ campaign at an urban site

Park, Seungshik,Yu, Geun-Hye,Lee, Sangil Elsevier 2018 Atmospheric research Vol.203 No.-

<P><B>Abstract</B></P> <P>This study investigates the absorption characteristics of brown carbon (BrC) obtained from water and methanol extracts of fine particulate matter measured at an urban site in Gwangju, Korea during the KOREA U.S. – Air Quality campaign (May 2–June 11, 2016). The measurement period was classified into two intervals: biomass burning (BB) and non-BB periods. During the non-BB period, water-soluble organic carbon (WSOC) and humic-like substances (HULIS) primarily resulted from secondary organic aerosol (SOA) formation and primary vehicle emissions. Water-soluble organic aerosols during the BB period, meanwhile, were closely related to SOA formation and regionally transported BB emissions.</P> <P>The light absorption coefficient measured at 365nm (b<SUB>abs,365</SUB>) by methanol extracts was 2.6 and 6.1 times higher than the coefficients from the water and HULIS extracts, respectively, indicating the importance of BrC absorption by water-insoluble organic carbon. This was demonstrated by a good correlation between the water-insoluble BrC absorption and the elemental carbon concentration. A comparison of b<SUB>abs,365</SUB> between the methanol- and water-extracted BrC indicated that water-insoluble BrC accounted for approximately 61% (33–86%) of the total BrC absorption. The contributions of SOA, primary BB emissions, and traffic emissions to the water extract b<SUB>abs,365</SUB> were estimated using a stepwise multiple linear regression (MLR) analysis and found to be 1.17±0.55, 0.65±0.62, and 0.25±0.09Mm<SUP>−1</SUP>, respectively, accounting for 59.6, 26.1, and 14.3% of the absorption coefficient by the water-soluble BrC. Further, it was determined that the contribution of the BB emissions to the water-soluble BrC absorption was approximately two times higher in the BB period than in the non-BB period.</P> <P>The average absorption Ångstrӧm exponent was 4.8±0.3, 5.3±0.7, and 6.8±0.8 for the methanol, water, and HULIS extracts, respectively. The average mass absorption efficiency (MAE<SUB>365</SUB>) of methanol extracted BrC was 1.3±0.4m<SUP>2</SUP>/g·C. Water- and HULIS-extracted BrC had a MAE<SUB>365</SUB> of 1.0±0.3 and 0.8±0.3m<SUP>2</SUP>/g·C, respectively. These results suggest that methanol-extracted BrC could provide a better estimation of BrC absorption compared to WSOC and HULIS.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heterogeneous processes were a dominant contributor to NO<SUB>3</SUB> <SUP>-</SUP> and SO<SUB>4</SUB> <SUP>2-</SUP> formation during the non-biomass burning (BB) period. </LI> <LI> Regional transport and high O<SUB>3</SUB> could be important factors for the enhanced NO<SUB>3</SUB> <SUP>-</SUP> and SO<SUB>4</SUB> <SUP>2-</SUP> during the BB period. </LI> <LI> Water-soluble organic aerosols were associated with SOA, regionally transported BB, and traffic emissions. </LI> <LI> About 60% of total brown carbon (BrC) absorption comes from water-insoluble BrC. </LI> <LI> Contribution of BB source to water-soluble BrC absorption was two times higher in the BB period than in the non-BB period. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

레이저 흡수에 의해 발생하는 열 효과의 빔 직경 및 흡수 계수 의존성

장경민 ( Kyungmin Jang ),백준혁 ( Jun-hyeok Baek ),양승진 ( Seung-jin Yang ),정재훈 ( Jae Hoon Jung ),권민기 ( Min-ki Kwon ),박종락 ( Jong-rak Park ) 조선대학교 공학기술연구원 2016 공학기술논문지 Vol.9 No.2

The thermal effects induced by pulsed laser absorption in an optical medium were simulated. In particular, the dependences of maximum temperature increase and decay time constant on the laser beam diameter and the medium absorption coefficient were investigated. The maximum temperature increase showed the inverse square dependence on the laser beam diameter, and the decay time constant was found to be almost independent of the laser beam diameter for relatively large absorption coefficients. As the absorption coefficient increased, the maximum temperature increase increased and the decay time constant decreased. The maximum temperature increase was directly proportional to the absorption coefficient, and the decay time constant was found to be almost independent of the absorption coefficient for relatively small laser beam diameters.

Sound Absorption Capability of Medicine Herb Residues Mat

Eun-Suk Jang,Nam-Ho Lee,Chun-Won Kang 한국펄프·종이공학회 2023 펄프.종이기술 Vol.55 No.4

This study investigated the sound-absorbing properties of herbal medicine waste (HMW) as a promising eco-friendly material for sound absorption. The authors examined the sound absorption coefficient by filling impedance tubes with varying heights of HMW (4 cm, 6 cm, 8 cm, and 10 cm). The results revealed that at a filling height of 4 cm, the optimal sound absorption frequency was found to be 1416 Hz, with a sound absorption coefficient of 0.999. Similarly, at a filling height of 12 cm, the optimal sound absorption coefficient was 0.965 at 456 Hz. It was observed that the sound-absorbing performance at lower frequencies improved as the thickness of the sound-absorbing material increased. Based on the standards established in KS F 3503, HMW would receive a sound absorption grade of 0.5M to 0.7M, depending on the filling height. In conclusion, HMW showed excellent potential as a sound-absorbing material, and the results of our testing showed that it can be used as an alternative to synthetic fibers.

생체조직의 광학적 흡수계수 측정에 관한 연구

임현수,김남중 대한의용생체공학회 1999 의공학회지 Vol.20 No.2

본 연구는 쥐의 뇌, 심장, 간, 근육 및 근육부위의 종양조직과 인간의 뇌 조직과 뇌 종양 조직의 광학적 흡수계수를 500nm~900nm 범위의 파장에서 측정하고 비교분석하였다. 광학적 흡수계수는 물질마다 가지고 있는 고유한 성질을 나타내므로 생체조직의 광학계수를 측정하면, 생체 조직의 고유한 특성을 나타낼 수 있다. Spectrograph monometer와 PDA를 이용하여, 동결절편으로 제작한 시편에 대하여 실험하였다. 실험결과, 쥐 조직과 인체의 뇌 조직의 흡수계수는 정상적인 일반 조직과 종양 조직에서 차이가 분명하게 있음을 알 수 있었다. 정상 뇌 조직의 흡수계수는 파장이 변화함에 따라 0.1~0.2$cm^{-1}$사이의 비교적 균일한 값을 보이는데 반하여, 뇌종양 조직의 흡수계수는 파장에 따라서 크게는 약 0.4~0.5$cm^{-1}$정도의 변화가 있다. 본 실험 결과들은 다양한 조직에서의 광학계수 중에서 흡수계수를 측정함으로써, 생체조직의 흡수계수의 변화를 감지하여 질병진단의 지표로 삼을 수 있다. In this study, we measured the absorption coefficient of the tissues of mouse (brain, heart, liver, muscle and tumor) and human brain (normal and tumor) in the wavelength between 500nm~900nm. The optical coefficient is a representative of the characteristics of the materials. So, we can characterize the biological tissue with the optical coefficients. Using the spectrograph monometer and PDA(Photo Diode Array), we experimented with quick-frozen sectioned specimens. Because the optical coefficient is concerned with the conformation and biochemical component of the biological tissue, we experimented as the wavelength between 500nm~900nm on the normal and tumor samples of the animal and human. For the mouse, there are distinctive differences of the absorption coefficients between normal tissues and tumor. The absorption coefficient of the normal tissue varies 0.1~0.2cm$^{-1}$ with wavelength. But, the absorption coefficient of the brain tumor is changed round about 0.4~0.5cm$^{-1}$ as the wavelength. The absorption coefficients we measured can be a useful implement to detect diseases.

A model for the sound absorption coefficient of multi-layered elastic micro-perforated plates

Kim, Hyun-Sil,Ma, Pyung-Sik,Kim, Sang-Ryul,Lee, Seong-Hyun,Seo, Yun-Ho Academic Press 2018 Journal of Sound and Vibration Vol.430 No.-

<P><B>Abstract</B></P> <P>In this paper, a model for the sound absorption coefficient of multi-layered elastic micro-perforated plates (MPPs) in an impedance tube is developed using an analytical approach. Under the plane wave condition, a low-frequency solution is derived by including the symmetric modes of the plate vibration and the sound pressure field. The sound absorption model derived in this study can handle multi-layered structures composed of any combination of thin elastic plates with or without micro-perforations and rigid MPPs. The effects of the parameters of the plate thickness, hole diameter, perforation ratio, cavity depth, and damping on the sound absorption capabilities are described. For a single MPP, when the perforation ratio is very small, it is observed that the combined effect of the elastic behavior and micro-perforation results in a significant increase of the sound absorption coefficient compared to that of a rigid MPP. However, when the perforation ratio is order of a few percent, the effect of the elastic behavior is negligible compared to that of micro-perforations. Some guidelines for selecting optimum parameters to achieve the maximum average sound absorption coefficient for a given frequency band are discussed for double- and triple-elastic MPPs. It is important to ensure that the perforation ratio of the last MPP is small such that the elastic behavior is dominant, while for the first MPP (and for the second MPP in the triple configuration), the elastic behavior should not be dominant. In addition, maintaining equal cavity depths is beneficial for a high average sound absorption coefficient.</P>

방음판의 흡음률 측정방법 제안을 위한 기초 연구

오양기,김하근 한국음향학회 2023 韓國音響學會誌 Vol.42 No.2

Sound barrier walls are the most basic way to cope with noise problems in urban residential environments. The most important acoustic function of sound insulation board is represented by sound transmission loss and sound absorption coefficient. However, Korea has not yet established a standard for measuring the sound absorption rate of sound insulation boards. In addition, even in the European standard, where the overall acoustic standard of soundproofing boards has already been established, the sound absorption rate is applied only to the standard for measuring the sound absorption rate of general building finishing materials, and a separate measurement method considering the characteristics of soundproof walls and soundproofing boards is not presented. The sound absorption coefficient should be evaluated by summing up the energy absorbed into the material as well as the energy transmitted through the material, but the current European standard has a problem in that the transmitted sound energy is not taken into account. In this paper, we reviewed the sound absorption coefficient measurement standards of sound insulation boards currently being presented, and verified the difference between the results and the new measurement method considering transmission sound for sound insulation boards actually used in Korea. 방음벽은 도시 주거환경의 소음문제에 대응하기 위한 가장 기본적인 방법이다. 방음판의 가장 중요한 음향적기능은 음향투과손실과 흡음률로 표시된다. 특히 주거시설이 밀집되어있는 도심구간의 철도나 간선도로에서 원하지않는 반사음에 의한 2차 소음 문제를 최소화하기 위하여는 방음판의 흡음성능이 중요하다. 그러나 아직까지 우리나라는 방음판의 흡음률 측정방법에 관한 규격이 마련되어있지 않다. 또한 방음판의 전반적인 음향규격이 이미 만들어져있는 유럽규격에서조차 흡음률에 관해서는 일반적인 건축마감재료의 흡음률 측정기준을 준용하고 있을 뿐, 방음벽과방음판의 특성을 감안한 별도의 측정방법을 제시하지 못하고 있다. 흡음률은 재료의 내부로 흡수된 에너지 뿐 아니라재료를 투과한 에너지까지 합산하여 평가되어야 하는데 현재의 유럽규격은 투과음 에너지를 감안하지 못하고 있는문제를 안고 있다. 이 논문에서는 현재 제시되고 있는 방음판의 흡음률 측정 규격에 대해 고찰하고, 우리나라에서 실제 사용되고 있는 방음판을 대상으로 투과음을 감안한 새로운 측정방법과의 결과 차이를 검증하였다. 아울러 새로운 방음판 흡음률 측정규격의 마련을 위한 기초적 아이디어를 제시하였다.

Effect of the suspended ceiling with low-frequency resonant panel absorber on heavyweight floor impact sound in the building

Ryu, Jongkwan,Song, Hansol,Kim, Yonghee Elsevier 2018 Building and environment Vol.139 No.-

<P><B>Abstract</B></P> <P>This study investigated the effect of the suspended ceiling panel with low-frequency resonant panel absorber on heavyweight floor impact sound. The resonant panel absorber was designed with a perforated top panel, an air gap with or without glass wool, and a bottom panel to ensure a high absorption coefficient in the low-frequency range around 100 Hz. Absorption coefficient measurements were carried out first in the reverberation chamber for resonant panel absorbers varying with the hole diameter of the top panel, the thickness of the glass wool and the air gap between the top and bottom board. As a result, the glass wool had the greatest influence on the absorption coefficient, and the highest absorption coefficient of the resonant panel absorber was about 0.6 in the band of 100 Hz. Floor impact sounds after installing the suspended ceiling with the best resonant panel absorber were also measured in test building using heavyweight floor impact sound sources (bang machine and rubber ball) and compared with result for normal suspended ceiling with gypsum board. Heavyweight floor impact sound by the resonant panel absorber was decreased by 2 dB and 4 dB in single number quantity (<I>L</I> <SUB>i,Fmax,Aw</SUB>) for bang machine and rubber ball, respectively. In particular, the resonant panel absorber reduced by 6 dB in 125 Hz octave band with the largest absorption coefficient.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Suspended ceiling with resonant panel absorber reduces heavyweight floor impact sound. </LI> <LI> Glass wool has significant influence on resonance frequency of resonant panel absorber. </LI> <LI> Effect of glass wool in resonant panel absorber depends on hole diameter. </LI> <LI> Resonant panel absorber diminishes air-spring effect in space above ceiling. </LI> </UL> </P>

Sound Absorption Coefficients of Micro-fiber Fabrics by Reverberation Room Method

Na, YoungJoo,Lancaster, Jeff,Casali, John,Cho, Gilsoo Sage Publications 2007 Textile research journal Vol.77 No.5

<P>The sound absorption properties of materials are important not only for noise reduction, but also for controlling reverberation time for speech intelligibility in rooms and for promoting fuller sound in concert halls. Industrial textiles are focusing on these materials' application for sound absorption, thus new textiles were to be examined in relation to this performance. Micro-fiber fabric has fine fibers and a high surface area and it has been used in such applications as wipers, thermal insulator, filters or breathable layers. It can be also used for sound absorption. This paper examines the possibility of using micro-fiber fabrics as sound absorbent materials. We tested the sound absorption coefficients of five micro-fiber fabrics and one regular fiber fabric by the reverberation room method. The results showed that the micro-fiber fabrics' sound absorption is superior to that of conventional fabric with the same thickness or weight, and the micro-fiber fabrics' structure was found to be important for controlling sound absorption according to sound frequency. Fabric density was found to have more effect than fabric thickness or weight on sound absorption, and the Noise Reduction Coefficient increases to its highest value at a fabric density of about 0.14 g/cm3, and it decreases thereafter.</P>

Mass transfer analysis for CO₂ bubble absorption in methanol/Al₂O₃ nanoabsorbents

Torres Pineda, Israel,Kim, Dongmin,Kang, Yong Tae Elsevier 2017 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.114 No.-

<P><B>Abstract</B></P> <P>In this paper computational fluid dynamics (CFD) analysis is carried out to investigate CO<SUB>2</SUB> bubble absorption characteristics in methanol/Al₂O<SUB>3</SUB> nanoabsorbents. Bubble size, rising velocity and mass transfer rate are compared to the previous experimental results for validation. It is found that the distance traveled for each CO<SUB>2</SUB> bubble increases as the concentration of Al<SUB>2</SUB>O<SUB>3</SUB> increases, which, in consequence, increases the residence time between liquid and gas phases resulting in higher interfacial mass transfer rates. For the case of a bubble rising in the gap between walls, the wall shear stress has a major effect on the bubble diameter and rising velocity which in consequence affects the mass transfer coefficient. It is concluded that the mass transfer coefficient enhances by about 40% by adding Al₂O<SUB>3</SUB> nanoparticles (0.01vol%) compared with pure methanol absorbent from the experimental and simulation results. It is also concluded that the use of nanoparticles has a higher impact on mass transfer rate than it does on mass transfer amount, which depends on the residence time and travel distance of CO<SUB>2</SUB> bubbles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mass transfer analysis is carried out for CO<SUB>2</SUB> bubble absorption in nanoabsorbents. </LI> <LI> CO<SUB>2</SUB> absorption enhancement by nanoabsorbents is evaluated. </LI> <LI> Mass transfer coefficient enhances by about 40% by adding Al₂O<SUB>3</SUB> nanoparticles (0.01vol%). </LI> <LI> The use of nanoparticles has a higher impact on mass transfer rate than it does on mass transfer amount. </LI> </UL> </P>