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다양한 유체굴절률에서의 μ-DDPIV 적용을 위한 calibration보정기법
윤상열(Sang Youl Yoon),김경천(Kyung Chun Kim),Kenneth D. Kihm 한국가시화정보학회 2010 한국가시화정보학회 학술발표대회 논문집 Vol.2010 No.11
This study presents a calibration compensation method for various refractive indices of working fluids in using micro defocusing digital particle image velocimetry (μ-DDPIV). The μ-DDPIV has been considered as one of advanced techniques for 3D particle tracking in a microvolume and 3D microflow diagnostics. In using the μ-DDPIV, the fluid refractive index is one of the important parameters by which the defocusing imaging is affected seriously. Therefore, the calibration coefficient compensation method should be beneficial. This paper describes the effects of the fluid refractive index (RI) on the z-calibration, and correlations between fluidrefractive index and calibration coefficient, (dz/dD).
Kihm, Kenneth D,Chon, Chan Hee,Lee, Joon Sik,Choi, Stephen US Springer 2011 Nanoscale research letters Vol.6 No.1
<P>An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids. The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities. In contrast, the present model proposes a faster heat transfer velocity at the same order as the speed of sound, rooted in a modified kinetic principle. In addition, this model accounts for both nanoparticle heat dissipation as well as coagulation effects. This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.</P>
광파장 및 유체굴절률이 μ-DDPIV를 이용한 미세유동 3차원 측정에 미치는 영향
윤상열(Sang Youl Yoon),Kenneth D. Kihm,김경천(Kyung Chun Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
This study presents the effects of light wavelength and fluid refractive index on micro defocusing digital particle image velocimetry (μ-DDPIV). The μ-DDPIV has been considered as one of advanced techniques for 3D particle tracking in a microvolume and 3D microflow diagnostics. In using the μ-DDPIV, the light wavelength and fluid refractive index are one of the important parameters by which the defocusing imaging is affected seriously. This paper describes the effects of the fluid refractive index (RI) on the z-calibration, and a correlation between fluid refractive index and calibration coefficient, (dz/dD). In addition, the effects of light wavelength on image separation is demonstrated using optical bandpass filters with the central wavelengths of 480 ㎚, 540 ㎚, and 589㎚.
Kim, Iltai,Kihm, Kenneth D Optical Society of America 2010 Optics letters Vol.35 No.3
<P>Time-dependent and near-field nanoparticle concentrations are determined by correlating the surface plasmon resonance (SPR) reflectance intensities with the effective refractive index (ERI) of the nanofluid under evaporation. A critical angle measurement for total internal reflection identifies the ERI of the nanofluid at different nanoparticle concentrations. The corresponding SPR reflectance intensities correlate the nanofluidic ERI with the nanoparticle concentrations. Example applications for evaporating nanofluidic droplets containing 47 nmAl(2)O(3) particles demonstrate the feasibility of this new imaging tool for measuring time-resolved and full-field nanoparticle concentration profiles.</P>
화학증기 증착법으로 합성된 그래핀 위에서의 나노유체의 젖음성
이우림(Woorim Lee),Kenneth D. Kihm,박재성(Jae Sung Park),이준식(Joon Sik Lee) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In order to characterize the intrinsic nanofluid wettability on pristine graphene, contact angle measurements were conducted for the CVD-synthesized graphene on a copper substrate. All tests were conducted immediately after the graphene synthesis so that no surface contaminants can render the measurement uncertainties. Comparative studies were made for two different nanofluids containing alumina nanoparticles and silica nanoparticles, respectively. The hydrophobic effect of graphene is also investigated by measuring contact angles on annealed copper foil. The contact angle of the former continually increases with increasing alumina nanoparticle concentrations, whereas the contact angle of the latter gradually increases up to 1.25% silica volume concentration and then remains nearly unchanged thereafter. It is conjectured that the positive or attractive DLVO force of the silica nanofluid between nanoparticles and graphene substrate drives a rapid increase of silica nanoparticle population near the graphene surface and soon reaches the saturation level of nanoparticles that will slow down the contact angle increase for further increase of the nanoparticle concentration. In contrast, the alumina nanfluid with negative or repulsive DLVO force never reaches the saturation of nanoparticles near graphene and its contact angle increases consistently with increasing nanoparticle concentration since the nanoparticle effect is continually increasing.
Effect of graphene-substrate conformity on the in-plane thermal conductivity of supported graphene
Kim, Hong Goo,Kihm, Kenneth D.,Lee, Woomin,Lim, Gyumin,Cheon, Sosan,Lee, Woorim,Pyun, Kyung Rok,Ko, Seung Hwan,Shin, Seungha Elsevier 2017 Carbon Vol.125 No.-
<P>Measuring the thermal conductivity k(g) of supported graphene is inherently complicated due to uncertainties associated with the heat dissipation into the substrate. We innovate the use of an ultra-thin 8-nm SiO2 substrate to alleviate these uncertainties and thus improve the accuracy of optothermal Raman technique to measure k(g) of supported graphene. As a result, we present an extensive k(g) database for a wide temperature range from 325 K to 575 K. Furthermore, we have found that the thermal conductivity of supported graphene before annealing is close to that of suspended graphene at 3000 W m(-1) K-1, which is attributable to graphene 'suspension' lightly on the substrate roughness, and then progressively decreases over repeated thermal annealing. We elaborate on this annealing-induced kg to occur mainly because of the thermally enhanced graphene-substrate conformity and interfacial scattering by probing the Raman spectroscopic characterization of charge carrier density in graphene and the thermal expansion mismatching strain between graphene and substrate. Repeated thermal annealing also expedites the depletion of intercalated impurities to reduce the graphene-substrate separation distance, which acts to further reduces k(g), ultimately to its lower bound under vacuum-annealing. Therefore, manipulating the thermo-mechanical affiliation can offer an alternative route to control the in-plane thermal conductivity of supported graphene. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Park, Jae S.,Kihm, Kenneth D.,Kim, Honggoo,Lim, Gyumin,Cheon, Sosan,Lee, Joon S. American Chemical Society 2014 Langmuir Vol.30 No.28
<P>The wetting and evaporative aggregation of alumina nanofluids (Al<SUB>2</SUB>O<SUB>3</SUB>) are examined for CVD-synthesized graphene-coated (GC) surfaces that are known as strongly hydrophobic (θ<SUB>contact</SUB> ≈ 90°). Our findings are compared to those associated with a hydrophilic cover glass (CG) substrate (θ<SUB>contact</SUB> ≈ 45°). The nanofluidic self-assemblies on the GC substrate are elaborately characterized in terms of the droplet wetting/crack formation, the particle migration time over the evaporative time (<I>C</I><SUB>R</SUB>), the Derjaguin–Landau–Verwey–Overbeek forces (<I>F</I><SUB>DLVO</SUB>), and the relative thermal conductivity (<I>K</I><SUB>R</SUB>). The GC substrate forms relatively thicker and larger cracks and requires a longer evaporation time. Both the GC and CG substrates share approximately the same time constant <I>C</I><SUB>R</SUB>, which suggests the formation of coffee-ring patterns for both substrates. The GC shows negative <I>F</I><SUB>DLVO</SUB>, which implies a repulsive force between the nanoparticles and the substrate, and the CG shows a positive <I>F</I><SUB>DLVO</SUB> of attraction. Furthermore, a more than 3 order of magnitude larger thermal conductivity of GC compared to that of CG drives significantly different particle/fluid motions near the drop edge areas between the two substrates.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2014/langd5.2014.30.issue-28/la404854z/production/images/medium/la-2013-04854z_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la404854z'>ACS Electronic Supporting Info</A></P>