Evidence for the importance of particle distribution in effective medium theory: a model study

진재식,이준식 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.8

This study investigates the fundamental effects of particle distribution in a heterogeneous composite, which has never been revealed before. This work is based on the Laplace equation in cylindrical coordinates and shows that the effective thermal conductivity has a different value even at the same volume fraction depending on the particle distribution configuration. Consequently, applying the effective medium approximation without using detailed information about the particle spatial distribution can result in considerable error. This is especially true for the case of augmented conduction by insertion particles.

A simple model for the prediction of thermal conductivity of Ge2Sb2Te5 thin film

진재식 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.9

A modified version of the Mayadas-Shatzkes (MS) model is proposed for the prediction of the thermal conductivity of both amorphous and crystalline of Ge2Sb2Te5 (GST) phase-change materials at room temperature. The structural parameters of the original MS model are extended to describe the additional disorder scattering effects caused by the ternary components of the GST. The effect of disorder due to the alloy composition on the grain boundary scattering can be interpreted with the aid of thermal models. It is also found that for all phases of GST, the contribution of disorder scattering to the thermal resistance is nearly uniform. This is consistent with the fact that the GST phase changes without any destruction of the structural basis such as the building blocks.

유동 경계층이 다공성물질내 대류 열전달에 미치는 영향

진재식,이대영,강병하,Jin, Jae-Seek,Lee, Dae-Young,Kang, Byung-Ha 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.8

Convective heat transfer in a channel filled with porous media has been analyzed in this paper. The two-equation model is applied for the heat transfer analysis with the velocity profile, considering both the inertia and viscous effects. Based on a theoretical solution, the effect of the velocity profile on the convective heat transfer is investigated in detail. The Nusselt number is obtained in terms of the relevant physical parameters, such as the Biot number for the internal heat exchange, the ratio of effective conductivities between the fluid and solid phases, and hydraulic boundary layer thickness. The results indicate that the influence of the velocity profile is characterized within two regimes according to the two parameters, the Biot number and the conductivity ratio between the phases. The decrease in the heat transfer due to the hydraulic boundary layer thickness is 15% at most within a practical range of the pertinent parameters.

Prediction of phonon and electron contributions to thermal conduction in doped silicon films

진재식 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6

The modified electron-phonon interaction model is proposed, and the relative contributions of phonons and electrons to the thermalconduction in doped silicon films are investigated quantitatively. The carrier contributions in sub-micro scale heat conduction are validatedby an order of magnitude analysis and comparison with previous data. The simulation results show that the electron contribution inSi-layer is not negligible when the doping concentration is higher than 1019 cm−3, which can be classified as semimetal or metal by thevalue of its electrical resistivity at 300 K. The electron thermal conductivity increases with increasing doping density, and its fraction isabout 57.2% of the total thermal conductivity when the doping concentration is 5.0 ´ 10²⁰ cm−3 and silicon film thickness 100 nm.

온도 영향을 고려한 실리콘 내 포논 열전달 특성에 대한 실험 기반 연구

진재식 대한기계학회 2021 大韓機械學會論文集B Vol.45 No.6

The heat transfer characteristics for each phonon mode, which plays a key role in various thermal engineering applications, were examined with varying temperatures. By employing the results of existing experimental data on the ability of heat transfer by each phonon mode based on the phonon mean free path, its spectral distributions in silicon were discussed under the conditions of 100K, 300K, and 500K. As temperature increased, the contribution of the LA phonon mode to the thermal conductivity increased, and at a temperature of 100K, a critical frequency existed owing to the relative influence between the phonon-phonon scattering and impurity–phonon scattering processes. It was also shown that at a temperature of 500K the heat transfer contribution of the phonon mode of about 8.1 THz or more was decreased owing to the increase in high-order phonon scattering such as a four-phonon scattering process. 포논 전달 특성을 활용한 공학적 응용에 핵심적인 역할을 하는 포논 모드별 열전달 특성을 온도 변화에 대해 살펴봤다. 기존 실험적 연구 결과 기반에 수치적 연구 결과를 적용하여, 온도 100K, 300K, 500K 조건에서 실리콘 내 포논 전달의 주파수 스펙트럼 특성에 대해 논했다. 온도가 상승하면서 LA 포논 모드의 열전도 기여도가 증가했으며, 온도 100K에서는 포논-포논 산란과 불순물-포논 산란 과정의 상대적 크기 변화의 영향으로 임계 주파수가 존재함을 보였고, 온도 500K에서는 4-포논-포논 산란 과정으로 인한 포논 산란의 증가로 약 8.1 THz 이상의 포논 모드의 열전달 기여도가 작아짐을 보였다.

Investigation of the Full Spectrum Phonon Lifetime in Thin Silicon Films from the Bulk Spectral Phonon Mean-Free-Path Distribution by Using Kinetic Theory

진재식 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.5

Phonon dynamics in nanostructures is critically important to thermoelectric and optoelectronic devices because it determines the transport and other crucial properties. However, accurately evaluating the phonon lifetimes is extremely difficult. This study reports on the development of a new semi-empirical method to estimate the full-spectrum phonon lifetimes in thin silicon films at room temperature based on the experimental data on the phonon mean-free-path spectrum in bulk silicon and a phenomenological consideration of phonon transport in thin films. The bulk of this work describes the theory and the validation; then, we discuss the trend of the phonon lifetimes in thin silicon films when their thicknesses decrease.

Cobalt-Chromium 합금의 표면처리가 4-META/MMA-TBB 레진과의 접착에 미치는 영향

진재식 慶北大學校 齒科大學 1999 慶北齒大論文集 Vol.16 No.2

Thermal conduction of stable graphite suspensions considering structural characteristics of graphite aggregations

진재식 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.9

In this article, a new simple approach that can investigate thermal conduction of graphite suspensions is discussed. Using the threelevel homogenization model, the fractal dimension (df) of graphite suspensions is determined as df = 1.76 and 1.70 for graphite/EG and for graphite/PAO, respectively. From these values, the highly anisotropic heat conduction is expected to be dominant through aggregations of graphite flake. Based on these observations, a simple thermal expression is proposed to describe the anisotropic heat conduction of graphite suspensions incorporating the effect of the interfacial thermal resistance. The effects of aggregated sphere (AS) distribution on thermal irreversibilities of nanofluids are also investigated by comparing the entropy creations between spatially uniform and random distributions of AS.

Analysis of Phonon Transport in Silicon Nanowires Including Optical Phonons

진재식,이봉재,이현진 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.5

The present study identifies and investigates the dominant phonon contribution to the thermal conductivity of silicon nanowires at room temperature. We have employed the full phonon dispersion model including the heat transfer by optical phonons and have conducted a phonon band-to-band analysis in order to elucidate the energy transport mechanisms of each phonon band with a different polarization and frequency. The longitudinal acoustic phonon bands of 4 ∼ 8 THz is found to mainly contribute to the thermal conductivity of silicon nanowires (approximately 60%), whose diameters range from 37 to 115 nm. Although the contribution of optical phonons to the thermal conductivity is less than 10% even at nanometer-scale diameters, optical phonons can interact with acoustic phonons and modify their contribution to the thermal conductivity, especially at high frequencies. The results obtained from this study provide detailed information on which phonons of a certain polarization and frequency are dominant heat carriers in silicon nanowires.

Cobalt-Chromium 합금의 표면처리가 4-META/MMA-TBB 레진과의 접착에 미치는 영향

진재식,김교한,이청희,조광헌,Jin, Jae-Sik,Kim, Kyo-Han,Lee, Cheong-Hee,Jo, Kwang-Hun 대한치과보철학회 2000 대한치과보철학회지 Vol.38 No.4

The effects of pretreatment of Co-Cr alloy, including two adhesive primers that contain either MDP or MAC-10, and silicoating on the bond The result sobtained as follows; o Strength of 4-META/MMA-TBB resin were investigated using FT-IR, SEM, and EDAX. o In the SEM observation of surface morphologies, the sandblasted specimen exibited a very rough surface, whereas the surfaces of the two groups primed with either MDP or MAC-10 were covered with a layer of primer, and the surface morphology of the silicoated specimen remained almost the same after sandblasting. o Before the thermocycling tests, the group treated with MDP demonstrated the highest mean tensile bond strength and the sandblasted group showed the lowest bond strength. o After 20,000 thermocyling, the mean tensile bond strength of the sandblasted group exhibited a 50% reduction in bond strength, while the others showed a $20\sim30%$ reduction. o Observation of the metal-resin interface revealed that in all groups the resin permeated the rough surface formed by sandblasting thereby producing a mechanical bond between the metal and the resin. It was also found that thermocycling resulted in a gap formation at the metal-resin interface of the specimens, and the sandblasted group exhibited a larger gap width than the other groups. o In fracture mode, all specimens indicated a cohesive fracture within the resin before thermocycling. However, thermocyling produced adhesive failure at the edge of the resin-metal interface in most specimens. The sandblasted group, which exhibited the lowest bond strength after thormocycling, also demonstrated the largest area of adhesive failure.