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Paved phonon transport route in graphene by vapor phase process
Kim, Duckjong,Kim, Woochang,Lee, Seung-Mo,Luo, Tengfei,Moon, Choongman,Kim, Jae-Hyun,Lee, Hak-Joo,Park, Jinsung,Lee, Joo-Hyoung Elsevier 2018 INTERNATIONAL JOURNAL OF THERMAL SCIENCES Vol.133 No.-
<P><B>Abstract</B></P> <P>Various atomistic defects ever-present in graphene have triggered unwanted phonon scattering, thereby significantly deteriorating the heat transport property of the graphene. Consequently, continuous endeavors have been made to minimize these atomistic defects. Here, we first experimentally show that defect healing based on atomic layer deposition (ALD) can significantly mitigate the degradation in the thermal conductivity of the graphene. After defect healing with Pt and Al<SUB>2</SUB>O<SUB>3</SUB> ALD, the thermal conductivities of graphene synthesized by conventional chemical vapor deposition were improved by ∼83% and ∼64%, respectively. It is speculated that the healing atoms facilitate heat transfer across the defects, by eliminating the influence of vacancy in the graphene layer, which likely increases the phonon lifetime (leading to a noticeable improvement in thermal conductivity). This study provides an understanding of how defect engineering could affect phonon transport in 2D materials and sheds light on affordable graphene with excellent thermal conductivity.</P>
Dimensional dependence of phonon transport in freestanding atomic layer systems.
Kim, Duckjong,Hwangbo, Yun,Zhu, Lijing,Mag-Isa, Alexander E,Kim, Kwang-Seop,Kim, Jae-Hyun RSC Pub 2013 Nanoscale Vol.5 No.23
<P>Due to the fast development of nanotechnology, we have the capability of manipulating atomic layer systems such as graphene, hexagonal boron nitride and dichalcogenides. The major concern in the 2-dimensional nanostructures is how to preserve their exceptional single-layer properties in 3-dimensional bulk structures. In this study, we report that the extreme phonon transport in graphene is highly affected by the graphitic layer stacking based on experimental investigation of the thermal conduction in few-layer graphene, 1-7 layers thick, suspended over holes of various diameters. We fabricate freestanding axisymmetric graphene structures without any perturbing substrate, and measure the in-plane transport property in terms of thermal conduction by using Raman spectroscopy. From the difference in susceptibility to substrate effect, size effect on hot-spot temperature variation and layer number dependence of thermal conductivity, we show that the graphitic membranes with 2 or more layers have characteristics similar to 3-dimensional graphite, which are very different from those of 2-dimensional graphene membranes. This implies that the scattering of out-of-plane phonons by interlayer atomic coupling could be a key mechanism governing the intrinsic thermal property.</P>
Kim, Duckjong,Kim, Chihyun,Park, Jinsung,Kim, Tae Young Elsevier 2019 Energy conversion and management Vol.183 No.-
<P><B>Abstract</B></P> <P>Thermoelectricity is regarded as one of the promising waste heat recovery candidates. A fundamental but effective method for the best use of thermoelectric generators (TEGs) is to maximize the heat flow crossing thermoelectric materials. The main focus of the present study was to develop a thermal interface material (TIM) with high thermal conductivity and temperature resistance as the key to minimizing the overall thermal resistance of the heat flow path of a TEG module operating under high-temperature conditions. In combination with a polyimide matrix and a multi-dimensional filler compound, a new TIM having stable heat conduction behavior at high temperatures was produced. The developed TIM was stable without losing mass up to ∼500 °C, and its thermal conductivity reached 81.4 W/m·K. It was applied to the interface between a TEG and a heat source whose temperature ranged from 100 to 300 °C and, the effect of the thermal conductivity and interface thermal resistance of the TIM on thermoelectric power generation performance during onsite curing of the TIM was investigated. Reduction of the interface thermal resistance by the new TIM improved the power generation by, at most, 132.3 and 38.6% compared to cases without a TIM and with a conventional graphite foil TIM, respectively. In terms of energy conversion efficiency, the TEG with the new TIM showed maximum improvements of 73.2 and 20.9% over the cases without a TIM and with a graphite TIM for the same temperature difference across the TEG, respectively. In addition, thermal cyclic testing confirmed the long-lasting heat-conducting feature of the developed TIM. The present work clearly shows the potentially significant influence that TIMs have on the waste heat recovery performance of TEGs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We developed a TIM paste with high thermal conductivity and temperature resistance. </LI> <LI> Compared to graphite foil, we reduced interface thermal resistance by at most 80.9%. </LI> <LI> The reduced thermal resistance enhanced the thermoelectric power by at most 38.6%. </LI> <LI> Thermal cyclic test confirmed long-lasting heat conducting feature of the TIM. </LI> <LI> This study shows significant influence that TIMs have on the waste heat recovery. </LI> </UL> </P>
Manifold Design for Uniform Flow Distribution to Parallel Microchannels
duckjong Kim(김덕종),Seok Ho Yoon(윤석호),Jun Seok Choi(최준석) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
For efficient scale up of microchannel devices, uniform flow distribution to parallel microchannels is very important. In the present work, a dimensionless geometric parameter indicating the optimal manifold configuration is derived through a numerical parametric study and validated by micro particle image velocimetry. It is clearly shown that the flow uniformity is maximized when the dimensionless parameter is about 0.8. This study presents a simple and systematic design methodology for a uniform flow distribution to multiple microchannels operating in parallel.
Investigation of Spray Process for Carbon Nanotube Thin Films
Duckjong Kim(김덕종),Du Soon Choi(최두순) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Industrial use of carbon nanotube (CNT) films is in the spotlight due to their good physical properties and high economic feasibility. Spray coating process is one of feasible approaches for large area CNT films. Uniform spray coating is an important issue in applications requiring large area conductive films. In this work, we present a numerical model for the prediction of CNT deposition thickness distribution in the spray process and experimental data validating the numerical work. From the results, we can find that the pitch of the nozzle path is a key parameter affecting the deposition thickness uniformity and that there is optimal pitch value for unfirom and productive coating. We also discuss future research direction for improved numerical simulation tool.
Macrodispersion of multi-walled carbon nanotubes for conductive films.
Kim, Duckjong,Zhu, Lijing,Kim, Jae-Hyun,Han, Chang-Soo,Baik, Seunghyun American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4
<P>Understanding of the effect of the multi-walled carbon nanotube (MWCNT) dispersion process on physical properties of MWCNT film is crucial in process optimization of MWCNT film-based products. In the present work, the electrical conduction property of MWCNT films according to various conditions in MWCNT dispersion is investigated. Spectroscopic analysis of dispersed MWCNTs show that the electrical resistance of the MWCNT conductive film is affected by an increase in the electrical contacts between adjacent CNTs due to CNT debundling and physical damage caused by ultrasonic processing. Based on the two conflicting parameters, dispersion guidelines for highly conductive MWCNT film are presented.</P>
Continuous flow purification of nanocrystal quantum dots.
Kim, Duckjong,Park, Hye Kyung,Choi, Hyekyoung,Noh, Jaehong,Kim, Kyungnam,Jeong, Sohee RSC Pub 2014 Nanoscale Vol.6 No.23
<P>Colloidal quantum dot (QD) purification is typically conducted via repeating precipitation-redispersion involving massive amounts of organic solvents and has been the main obstacle in mass production of QDs with dependable surface properties. Our results show that the electric field apparently affects the streamlining of QDs and that we could continuously collect stably dispersed QDs by the electrophoretic purification process. The purification yield increases as the electric potential difference increases or the flow rate decreases, but reaches an asymptotic value. The yield can be further improved by raising the absolute magnitude of the mobility of QDs with the addition of solvents with high dielectric constants. The continuous purification process sheds light on industrial production of colloidal nanomaterials.</P>
Effects of manifold geometries on flow distribution to parallel microchannels
Duckjong Kim,유청환,윤석호,최준석 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.12
For efficient scale up of microchannel devices, uniform flow distribution to parallel microchannels is very important. In the present work, a dimensionless geometric parameter indicating the optimal manifold configuration is derived through a numerical parametric study and validated by micro particle image velocimetry. It is clearly shown that the flow uniformity is maximized when the dimensionless parameter is about 0.8. This study presents a simple and systematic design methodology for a uniform flow distribution to multiple microchannels operating in parallel.