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Numerical simulations of supersonic gas atomization of liquid metal droplets
Firmansyah, Dudi Adi,Kaiser, Rashed,Zahaf, Riyan,Coker, Zach,Choi, Tae-Youl,Lee, Donggeun Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>Computational fluid dynamics simulations incorporating supersonic turbulent gas flow models and a droplet breakup model are performed to study supersonic gas atomization for producing micron-sized metal powder particles. Generally such atomization occurs in two stages: a primary breakup and a secondary breakup. Since the final droplet size is primarily determined by the secondary breakup, parent droplets of certain sizes (1 to 5 mm) typically resulting from the primary breakup are released at the corner of the nozzle and undergo the secondary breakup. A comparison of flow patterns with and without the introduction of a liquid melt clearly indicates that the mass loading effect is quite significant as a result of the gas-droplet interactions. The flow pattern change reasonably explains why the final droplets have a bimodal mass size distribution. The transient size changes of the droplets are well described by the behavior of the Weber number. The present results based on the 1 mm parent droplets best fit previous experimental results. Moreover, the effects of inlet gas pressure and temperature are investigated in an attempt to further reduce droplet size. (C) 2014 The Japan Society of Applied Physics</P>
Firmansyah, Dudi Adi,Sullivan, Kyle,Lee, Kwang-Sung,Kim, Yong Ho,Zahaf, Riyan,Zachariah, Michael R.,Lee, Donggeun American Chemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.1
<P>The oxidation mechanism of nanoaluminum particles, nominally employed as fuel component, is still an unsettled problem, because of the complex nature of thermomechanical properties of the oxide shell surrounding the elemental core. Although mechanical breakage of the alumina shell upon or after melting of aluminum core has been thought to play a key role in the combustion of aluminum nanoparticles, there has been little direct evidence. In this study, the microstructural behaviors of Al core and alumina shell lattices were investigated with increasing temperatures. Three in situ techniques, high-temperature X-ray diffraction analysis, hot-stage transmission electron microscopy, and high-resolution transmission electron microscopy for heat-treated samples, were employed to probe the thermal behaviors of aluminum and alumina lattices before and after melting of the aluminum core. High-temperature X-ray diffraction analysis revealed that nano aluminum lattice was initially expanded under tension at room temperature, and then when heated passed through a zero-strain state at ∼300 °C. Upon further heating above the bulk melting temperature of aluminum, the aluminum lattice expanded under almost no constraint. This interesting observation, which is contrary to almost all of the previous results and models, was ascribed to the inhomogeneous (localized) crystalline phase transformation of amorphous alumina. High-resolution transmission electron microscopy and in situ hot-stage transmission electron microscopy evidenced localized phase transformation accompanied by a significant shell thickening, presumably resulting from diffusion processes of Al cations and O anions, which is to absorb the pressure built in aluminum core, by creating a more ductile shell.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-1/jp2095483/production/images/medium/jp-2011-095483_0009.gif'></P>
무함마드하피드펄만샤(Firmansyah Muhammad Hafidh),남혜빈(Hye-Been Nam),고석주(Seok-Joo Koh) 한국정보과학회 2021 한국정보과학회 학술발표논문집 Vol.2021 No.6
오랜 기간 웹 서비스의 성능을 향상시키기 위해 연구해온 Google에 의해 개발된 QUIC은 현재 가장 주목받는 차세대 수송 프로토콜로, HTTP/3는 이미 QUIC을 기반으로 개발되고 있다. 하지만 QUIC은 아직 초기 단계라 다중 경로와 같은 부가적인 기능에 관한 연구는 활발히 진행되고 있지 않다. 다중 경로는 수송 프로토콜 본질적인 핵심 기능은 아니지만 최근 출시되는 대부분의 이동 단말들은 2개 이상의 인터페이스를 가져 다중 경로를 이용한 통신을 사용할 수 있으며, 다중 경로 기반 통신을 수행할 경우 기본 경로 외에 백업 경로를 가지기 때문에 향상된 QoS를 제공받을 수 있다. 또한, QUIC은 커널이 아닌 사용자 영역에 구현되어 있어 새로운 다중 경로 알고리즘을 적용하기에 자유롭다. 본 논문에서는 효율적인 QoS 지원을 위한 MP-QUIC 기법을 제안하였으며, 간단한 테스트베드를 통해 이를 검증하였다.
Exchange of Copper Nanoparticles Properties During Spray Pyrolysis
Dudi Adi Firmansyah,김태일(Tae Il Kim),이동근(Donggeun Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
A continuous manufacturing process of copper nano particles by spray pyrolysis has been developed recently. Copper pure-phase nano particles were produced by spray pyrolysis of copper nitrates with ethanol as co-solvent over temperature of 450-600℃. The final products showed the properties exchanges as ethanol added as co-solvent. We found ethanol addition shifted the copper nanoparticles to smaller size that confirmed by DMA measurement results. Copper nanoparticles also experienced the morphological change from shell like to solid like as effect of ethanol addition, which was confirmed by TEM. The Energy Dispersive Spectroscopy (EDS) measurement showed that shell-like particles contained copper with high level of oxygen while the solid-like particle only consisted of copper. The XRD measurements revealed that ethanol addition induced the reduction of Cu₂O at isothermal spray pyrolysis of 600℃ and copper metallic phase were started to form at a 525℃ at a constant ethanol addition experiments. Thus, it can be assumed that copper nitrate involve the solid-state reaction to produce copper (Ⅰ) oxide and subsequently reduced to its metallic phase under reducing atmosphere result of ethanol decomposition.
Putra Arfis Maydino Firmansyah,Suzuki Hiroyoshi 대한조선학회 2024 International Journal of Naval Architecture and Oc Vol.16 No.-
Efforts to improve the hydrodynamic performance of high-speed ships have been underway for a long time. There are different approaches, one of which is to take advantage of an interceptor. Conventionally, the interceptor blades are mounted vertically on the ship’s bottom transom, oriented at a zero-degree angle of attack (AoA). This study comprehensively explores high-speed ships’ hulls with and without interceptor configurations, encompassing both negative and positive AoA of the interceptor, conducted through experimental and numerical methods using a fully captive model. The interceptors are strategically positioned and configured. Each configuration was examined under varying AoA settings, with uniform interceptor depths and systematic trim angle adjustments. The Computational Fluid Dynamics (CFD) approach simulates the local flow dynamics around the hull, thoroughly analyzing resistance, pressure distribution, lift force, wave profile, and trim moment. The results indicate that interceptor placement near the keel with AoA adjustments significantly reduces hydrodynamic resistance, while AoA changes have limited impact in other positions. Lift force analysis shows interceptors improve lift compared to the bare hull, but this improvement is not linear across positions. Furthermore, it is observed that adjustments in AoA influence lift, with a negative AoA generally being considered favorable. In summary, carefully considering placement, AoA, and height-to-length ratio is necessary to maximize interceptor advantages.
Dutta, Ranjan,Firmansyah, Dikhi,Kim, Jihoon,Jo, Hongil,Ok, Kang Min,Lee, Chang-Hee The Royal Society of Chemistry 2018 Chemical communications Vol.54 No.57
<P><I>meso</I>-Ethynyl extended aryl-picket calix[4]pyrroles 2 and 3 are designed and synthesized by directly anchoring arylethynyl groups at diametrically opposed <I>meso</I>-positions. The critical roles of direct ethynyl linkers are manifested through the isolation of unexpected host-anion conformers of <I>meso</I>-arylethynyl calix[4]pyrroles and a significant enhancement in halide binding affinities.</P>