Analysis of thermal conductivity in HI-LEDs lighting materials

Rong-Tsu Wang,Jung-Chang Wang 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.6

The present study devised a measurement system to estimate the thermal conductivity of electronic product materials, especially in HILEDslighting materials, exhibiting distinct thermal characteristics by conducting thermal performance experiments and theoreticalanalyses. First, steady-state conduction analysis with thermal resistance method was investigated on three composite material substratesof unknown heat conduction coefficients through a substrate material named Bakelite of low thermal conductivity revealing stable quality. Second, one-dimension semi-infinite transient conduction analysis was utilized to investigate metal materials with high thermal conductivities. Results showed that the Bakelite experimental module was verified for 62.5 % of the original wattages, which closest to thethermal conductivity 0.233 W/m-K of the Bakelite. And these composite materials M1, M2 and M3 composed of polymer and epoxywere 1.311, 0.844 and 2.403 W/m-K, respectively. The thermal performance experiments were investigated and the results have provedthe correctness of the theoretical model. According to the experimental results, calculating the temperature value of the metal materialscomprising cotton insulation and the transient analysis, this study determined the temperature error to be less 20 %. Consequently, a transientmeasurement system and method for metal materials with high heat conduction coefficients was established. Finally, the results ofthis work are the useful thermal conductivity method to facilitate rapid analysis in the future.

Utilization of high carbon fly ash and copper slag in electrically conductive controlled low strength material

Lim, S.,Lee, W.,Choo, H.,Lee, C. Elsevier BV 2017 Construction and Building Materials Vol.157 No.-

<P><B>Abstract</B></P> <P>The aim of this experimental investigation is to develop electrically conductive controlled low strength materials (CLSM) using both fly ash with high content of unburned carbon particles (HCFA) and copper slag as a fine aggregate, both of which are waste materials with low reuse rate. Various experiments, including flow consistency test, bulk density measurement, unconfined compression test, and electrical conductivity (<I>σ<SUB>mix</SUB> </I>) measurement were performed on the developed electrically conductive CLSM. For comparison with the results of the developed conductive CLSM, various experiments were also performed on CLSM containing electrically nonconductive particles (low carbon fly ash (LCFA) and sand). The results of this study demonstrate that <I>σ<SUB>mix</SUB> </I> of the tested CLSM specimens increases with increasing copper slag fraction in aggregate and the measured <I>σ<SUB>mix</SUB> </I> of the CLSM based on HCFA is greater than that with LCFA because both HCFA (or unburned carbon particles) and copper slag are electrically conductive. The measured flow consistency, bulk density, and unconfined compressive strength (UCS) of conductive CLSM were comparable with those of nonconductive CLSM. Therefore, the electrically conductive CLSM can be developed using both HCFA and copper slag. Finally, the relationship between UCS and 1/<I>σ<SUB>mix</SUB> </I> was also investigated in this study.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Both high carbon fly ash (HCFA) and copper slag (CS) are electrically conductive. </LI> <LI> Both HCFA and CS are waste materials with low reuse rate. </LI> <LI> CS was reused as a substitute for a fine aggregate in the CLSM. </LI> <LI> Electrically conductive CLSM was developed using both HCFA and CS. </LI> <LI> Various experiments were performed on the developed CLSM. </LI> </UL> </P>

CNT 연속섬유와 전도성 물질 복합체의 제조와 전기적 성질

이일재,김경은,마한솔,백두현 한국섬유공학회 2019 한국섬유공학회지 Vol.56 No.1

To improve the electrical conductivity of the carbon nanotube (CNT) fibers produced by the continuous spinning method, conductive materials such as silver nanoparticles, gold nanoparticles, and silver nanowires were added. The structures of the CNT fiber/conductive materials composites were observed using scanning electron microscopy. Raman spectroscopy was used for identifying the possible damages to the CNT fiber during the process of adding the conductive materials. Electrical conductivities of the CNT fiber/conductive materials composites were measured by the four-probe method. The Raman spectroscopic results indicated that there was no significant damage in the CNT fibers of the CNT fiber/conductive materials composites. The electrical conductivity of the CNT fibers increased up to 54% after the addition of the conductive materials.

석탄회를 활용한 CLSM의 열전도도에 관한 실험적 연구

이승준(Lee Seung Jun),이종휘(Lee Jong Hwi),조현수(Cho Hyun Soo),천병식(Chun Byung Sik) 대한토목학회 2012 대한토목학회논문집 C Vol.32 No.3

Due to current interest in creation of urban space and urban landscape, more emphasis has been placed on underground space development. With increasing number of underground power cables and its importance, a study of backfill materials for pipe is now imperative. Backfill materials require outstanding thermal characteristics since breakdown of cable insulation can be caused if heat generated from transmission of underground power cables had not been effectively discharged through backfill materials. Also, coal ash, which are industrial by-products, is being produced in high volume every year. Among them, ponded ash (PA) is not recycled and instead, mostly buried. Therefore in this study, thermal conductivity test based on mixture ratio (PA, ponded ash : FA, fly ash) was performed to evaluate the thermal conductivity characteristics of CLSM (controlled low strength materials) with coal ash. The results indicate that the mixture ratio (PA, ponded ash : FA, fly ash) of 80:20, water contents of 28~30%, and cement contents of 7~11% showed the highest conductivity at 0.796~0.884W/mK and thus, considered optimal in terms of recycling ponded ash (PA) as well as tor maximizing utilization as backfill materials for pipe in underground. 라이프라인의 공간 창출 및 미관 등의 이유로 지하공간의 개발이 활발해짐에 따라 지중하부에 매설되는 관(pipe)은 점차 증가하고 있으며 새로운 재료를 활용한 관거 뒤채움용 CLSM(Controlled Low Strength Materials)에 관한 연구의 비중은 점점 증가하고 있는 추세에 있다. 그리고 지중송전케이블에서 송전으로 인하여 발생된 열을 뒤채움재가 효과적으로 방출시키지 않으면 절연파괴에 이를 수 있으므로 뒤채움재는 반드시 우수한 열적 특성을 필요로 한다. 한편, 산업부산물인 석탄회는 매년 상당한 양이 발생되고 있으며, 그 중 매립회(ponded ash, PA)는 재활용되지 못하고 회처리장에 매립되고 있다. 본 연구에서는 산업폐기물인 석탄회를 활용한 관거 뒤채움용 CLSM의 열전도도 특성을 규명하기 위하여 배합비에 따른 열전도도(thermal conductivity) 시험을 실시하여 값의 변화를 검토하였다. 시험결과, 배합비(PA:FA) = 80:20, water contents = 28~30%, cement contents = 7, 9, 11%에서 0.796~0.884W/mK을 나타냈으며 이는 타 배합비보다 높은 열전도도를 나타내었으며 현재 폐기물로 처리되고 있는 매립회를 대량 유효 활용하는 측면에서 적합할 뿐 아니라 전력 및 통신 등 관거 뒤채움재로서의 활용이 클 것으로 판단된다.

Electric Field Intensity Factors for Conducting Paths in Anisotropic Dielectric Bimaterials

Song Lin,범현규,Cheng Bin Cui 한국정밀공학회 2013 International Journal of Precision Engineering and Vol.14 No.3

Conducting paths in an anisotropic dielectric bimaterial as well as in a homogeneous anisotropic material subjected to electric loading are investigated. The conducting path problems are formulated by using a linear transformation method. Electric field intensity factors are obtained for conducting paths emanating from a surface electrode in an orthotropic material. The asymptotic problem of a kinked conducting path in dissimilar anisotropic dielectric materials is considered. The electric field intensity factor for the asymptotic problem is obtained in the infinite product form. To ascertain validity of the solution obtained from the linear transform method, numerical computations are carried out by using finite element method. The electric field intensity factor for a conducting path emanating from the vertex of a bimaterial wedge with a tilt boundary is also obtained in the closed form.

Prediction Model for Saturated Hydraulic Conductivity of Bentonite Buffer Materials for an Engineered-Barrier System in a High-Level Radioactive Waste Repository

이기준,윤석,김봉주 한국방사성폐기물학회 2023 방사성폐기물학회지 Vol.21 No.2

In the design of HLW repositories, it is important to confirm the performance and safety of buffer materials at high temperatures. Most existing models for predicting hydraulic conductivity of bentonite buffer materials have been derived using the results of tests conducted below 100°C. However, they cannot be applied to temperatures above 100°C. This study suggests a prediction model for the hydraulic conductivity of bentonite buffer materials, valid at temperatures between 100°C and 125°C, based on different test results and values reported in literature. Among several factors, dry density and temperature were the most relevant to hydraulic conductivity and were used as important independent variables for the prediction model. The effect of temperature, which positively correlates with hydraulic conductivity, was greater than that of dry density, which negatively correlates with hydraulic conductivity. Finally, to enhance the prediction accuracy, a new parameter reflecting the effect of dry density and temperature was proposed and included in the final prediction model. Compared to the existing model, the predicted result of the final suggested model was closer to the measured values.

탄소재료가 내첨된 열전도성 복합재의 연구 동향

안동해 ( Donghae An ),김경훈 ( Kyung Hoon Kim ),김지욱 ( Ji-wook Kim ),이영석 ( Young-seak Lee ) 한국공업화학회 2020 공업화학 Vol.31 No.1

전자기기의 고도화 및 소형화에 따라, 기기의 효율 및 수명에 영향을 미치는 발열 문제를 해결하는 것은 가장 큰 해결난제 중 하나가 되었다. 이를 해결하기 위하여 금속 및 세라믹 기반의 높은 열전도도를 가지는 재료가 많이 사용되어왔으나, 낮은 기계적 물성 및 높은 중량으로 인해 가벼우면서도 기계적 특성이 좋은 고분자를 기지재로 사용하고 높은 열전도도를 갖는 탄소재료를 필러로 사용한 열전도성 복합재가 주목받고 있다. 열전도성 복합재의 열전도도를 향상시키기 위해서는 효과적인 포논의 이동이 이루어지도록 포논 산란이 억제되야한다. 본 논문에서는 탄소재료/고분자복합재의 포논 이동 및 산란 억제에 관련된 연구를 분류하고, 열전도도 향상을 위하여 적용된 다양한 방법들에 대하여 논의하였다. As electronic devices become more advanced and smaller, one of the biggest problems to solve is the heat affecting the efficiency and lifetime of instruments. High thermal conductivity materials, in particular, metal or ceramic ones, have been used to reduce the heat generated from devices. However, due to their low mechanical properties and high weight, thermally conductive composites composed with polymers having a light-weight and good mechanical properties as a matrix and carbon materials having high thermal conductivity as a thermally conductive filler have been attracting great attention. To improve the thermal conductivity of the composites, a phonon scattering must be suppressed to move phonon effectively. In this review, we classified researches related to phonon migration and scattering inhibition of carbon/polymer composites, and discussed various methods to improve thermal conductivity.

Development of through-plane thermal conducting pathway via using of hybrid Al2O3/h-BN fillers in polymer composites

임민섭,류승한,좌용호 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

Heat dissipation polymer composites consists of polymer with high thermal conductivity filler such as carbon or ceramic (Al₂O₃, AlN, h-BN) material. One of the ceramic materials, h-BN is a promising filler material because of high thermal conductivity with insulate property. however in thermal interface materials and gap filler application, it is hard to apply as a filler because of its anisotropic thermal conductivity (∥: 600 W/mK, ⊥: 30 W/mK). In this study, in order to fabricate 3-dimensional thermal path and optimize through-plane thermal conductivity, composites were prepared using spherical Al₂O₃ and h-BN based on silicone rubber. structure of composite is designed to surround the Al₂O₃ of h-BN in order to dissipate heat well in vertical direction, and optimized thermal conductivity is obtained by controlling the content of Al₂O₃ and h-BN.

A Study of Futuristic Materials in Contemporary Fashion

Kim, Yoon-Hee,Choi, Yoon-Mi The Korea Society of Costume 2007 International journal of costume and fashion Vol.7 No.1

The systematic study of the future began with curiosity and imagination about the future; a unique trait of human mental effort-and this seems to be based on the idea that the future can be different depending on current choices or effort. In this sense, it would be seemly to encourage more interest and academic study on the progress of future fashion. In this study, we examine recent changes of fashion material; e.g. that which science and technology have more impact and importance in futuristic fashion since the 1990?s. The period analysed is from the1990's to the present and related data from recent fashion collections and fashion books has also been included The current prediction of the future is largely based on what was formed between the 19th Century and the 20th Century which has persisted until now and has been influenced by the view that science will play a bigger role in the future. This is especially reflected in fashion which chiefly represents material culture. New materials used for fashion are strong and permanently durable, in addition to being very light, thin, flexible, hygienic, ecological and comfortable to wear-almost like a second skin. These fashionable new materials roughly function in two different ways according to external and internal characteristics. First, they cause external change. Second, they exemplify or allow new functions. Examples of external change are the use of silver color, achromatic color, metallic material, smooth-to-the-touch shiny material and the use of luminous material. Examples of the extended function of clothing through the use of new materials are the use of conducting thread, the use of special material for blocking & opening and the use of material which changes colors as the surroundings change. These days, the use of new material which changes its appearance is a novelty unique to the fashion world but we also expect to witness the debut of diverse new materials with extended inner functions.

Anisotropic Thermal Interface Materials: Directional Heat Transfer in Uniaxially Oriented Liquid Crystal Networks

Kang, Dong-Gue,Ko, Hyeyoon,Koo, Jahyeon,Lim, Seok-In,Kim, Jin Soo,Yu, Yeon-Tae,Lee, Cheul-Ro,Kim, Namil,Jeong, Kwang-Un American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.41

<P>For the development of anisotropic thermal interface materials (TIMs), a rod-shaped reactive monomer PNP-6MA is newly designed and successfully synthesized. PNP-6MA reveals a smectic A (SmA) mesophase between crystalline (K) and isotropic (I) phases. PNP-6MA can be oriented under a magnetic field (<I>B</I> = 2 T), and its macroscopic orientation can be robustly stabilized by in situ polymerization. Even without macroscopic orientations, the fabricated thermal conducting liquid crystal (TCLC) films show the outstanding thermal conductivity of 1.21 W/m K, which is higher than conventional organic materials. The thermal conductivity of uniaxially and macroscopically oriented TCLC films can be 2.5 W/m K along the long axis of mesogenic core. The newly developed TCLC film can be used as a TIM between a high-power light-emitting diode and a heat sink.</P> [FIG OMISSION]</BR>