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최선락(Sun Rock Choi),김동식(Dongsik Kim),좌성훈(Sung-Hoon Choa) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In the present study, the thermal conductivity and diffusivity of a variety of thin film materials, which are commonly used in MEMS applications, are measured. The samples include Au, Sn, Mo, Al/Ti alloy, anodized alumina, SiO₂, AlN, and SiC. In the experiment, the thermal diffusivities of metallic thin films are measured by two independent methods - the AC calorimetric method and photothermal mirage technique. The thermal conductivities of dielectric thin films are measured by the 3 omega technique. The results show that the thermal transport properties of some of the films are significantly smaller than those of the same material in bulk form. Especially, the AlN and SiC thin films exhibit pronounced thermal conductivity reduction because of the size effect. The results are analyzed based on the XRD (X-Ray diffraction) and AFM (Atomic Force Microscope) measurement.
마이크로 채널 내 액체 시료의 실시간 열분석 기법 개발
최선락(Sun Rock Choi),홍종간(Jonggan Hong),김동식(Dongsik Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
This work introduces a novel method for real-time measurement of the thermal conductivity and heat capacity of nanoliter-scale liquid samples. The device uses a micromachined thermal sensor composed of a microchannel and a thin-film probe. The method, based on the 3w technique, employs a multiparameter-fitting scheme to determine the thermal properties with numerical computation of heat transfer. The results demonstrate that the sensor can measure the thermal conductivity and heat capacity of 12 nl samples simultaneously. Furthermore, real-time thermal characterization of fluid samples flowing in a microchannel has been demonstrated, manifesting strong potential of the proposed technique as an in-situ probe in various microfluidic applications.
최선락,이주철,김동식,Choi, Sun-Rock,Lee, Joo-Chul,Kim, Dong-Sik 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.9
The mirage technique is proved to be powerful in measuring the thermal diffusivity of materials. In particular, its contactless nature makes it suitable for delicate samples and microscale structures. In this study, thermal-wave-coupling method is developed in a general form for both thermally thin and thick samples. In the suggested measuring scheme, the probe beam can be positioned close to the pump beam and the absolute position need not be measured. Therefore the new scheme provides a relatively simple yet effective way to determine the thermal diffusivity of thermally thick samples. Thermal diffusivities of bulk samples like Ni and Al were measured and the characteristics of mirage signal for a thin film were observed by using the mirage experimental setup. The apparent thermal diffusivity was measured by varying such parameters as probe beam height, size of pump beam, power of pump beam, and surface condition of sample. From the practical standpoint, it is shown that the size of the pump beam is the most important factor for accurate thermaldiffusivity measurement. Experiments using thin-film samples show that the thermal diffusivity of a substrate covered with thin film can be measured by photothermal mirage signals.
김동식(Dongsik Kim),최선락(Sun Rock Choi),이주철(Joochul Lee) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper introduces a novel scheme for determining the thermal diffusivity of solids<br/> using the photothermal mirage technique. The suggested scheme extends the thermal-wave<br/> coupling method, employing the solution to the heat conduction equation in close proximity<br/> to the pump beam. Therefore, determination of thermal diffusivity is possible by detecting<br/> the mirage signal with small separation between the probe and pump beams, with enhanced<br/> intensity of the mirage signal. Though the method requires information about the probebeam<br/> height, the absolute transverse position of the probe beam need not be known as it is<br/> automatically evaluated by the iterative-computation procedure. The thermal diffusivity of<br/> Ni is measured by the proposed scheme and the result demonstrates good agreement with<br/> the literature value to within 5 %.
홍종간(Jonggan Hong),최선락(Sun Rock Choi),김동식(Dongsik Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
This work reports development of novel liquid-level sensors based on the 3ω method. The sensors determine the liquid level by measuring the thermal response as in the conventional hot-wire technique. However the sensors employ an AC heating method to enhance the sensitivity, noise resistance and time response. Also, the microfabricated thin-film structure of the sensor provides mass-producibility as well as improved sensor performance owing to the increase in the surface-volume ratio of the sensor. Two different types of the sensor are developed: one for point detection of the fluid phase and the other for monitoring continuous variation of liquid level. Notable is that the performance of the sensor is not considerably affected by the liquid flow.
MMS 코드를 이용한 소듐냉각고속로의 출력변동운전 모의
김의광(Eui-Kwang Kim),최선락(Sun-Rock Choi),한지웅(Ji-Woong Han),이태호(Tae-Ho Lee) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.5-3
The MMS model for KALIMER-600 plant dynamics analysis are developed. The models include NSSS, BOP, BOP controls, and the supervisory plant controls. The NSSS model is subdivided into component models, such as a CORE, IHXs, Pumps, SGs, and the rest of the NSSS loop model. The BOP model is subdivided into a steam subsystem, feedwater subsystem, and preheater subsystem. All these models have been incorporated into the Master model to simulate transients in the plant. Representative results for power ramp change from 100% to 25% with a demanded load reduction of 25% at 5% per minute in 2000 sec demonstrate the suitability of this model for study of power maneuvering without severe oscillation.
입자크기와 레이저 조사가 나노유체의 열전도율 향상에 미치는 영향
김상현(Sang Hyun Kim),최선락(Sun Rock Choi),홍종간(Jonggan Hong),김동식(Dongsik Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
In this study, the effects of particle size and laser irradiation on thermal-conductivity of nanofluids are investigated experimentally. The thermal conductivity of nanofluids is measured by the transient hot-wire method using an anodized tantalum wire and the results are compared with theoretical models. Three different metallic oxide particles, alumina (Al₂O₃), zinc oxide (ZnO) and titanium dioxide (TiO₂) with three different mean diameters, are dispersed in distilled water and ethylene glycol to form nanofluids. Enhancement of the thermal conductivity of nanofluids is analyzed for ZnO nanofluids by varying the incident laser energy.