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정원석(Won Seok Chung),권오명(Ohmyoung Kwon),최두선(Du Seon Choi),이준식(Joon Sik Lee) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper suggests and demonstrates a novel flow measurement technique, tunable AC mode hotwire<br/> anemometry that allows simple integration, robust measurement, and extremely high accuracy. The principle<br/> and simple theoretical analysis of the technique are shown. To find the optimal frequency at which the phase<br/> lag becomes most sensitive to flow speed change, the phase lag was measured scanning the heating frequency<br/> from 1 to 100 Hz, while the flow speed of ethanol was increased stepwise from 0 to 10 mm/s. To optimize the<br/> sensitivity of technique, the periodic thermal characteristic of the hotwire should be understood and is<br/> currently under study.
3 ω 방법을 이용한 다중벽 탄소나노튜브 나노유체의 열확산율 측정
오동욱(Dong-Wook Oh),권오명(Ohmyoung Kwon),이준식(Joon Sik Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The 3-omega (3ω) method is utilized to measure the effective thermal diffusivity of nanofluids. Metal lines which work as either a heater or a temperature sensor on a pyrex wafer are microfabricated. Thermal modeling of the traditional 3ω method is modified so that the thermal property of a droplet of the fluid that is placed on top of the two parallel thin film heaters can be calculated. Sinusoidal heat pulses are given to the heater and the induced temperature oscillation at a known distance is measured to calculate the thermal diffusivity of the surrounding fluid. The thermal diffusivity of the nanofluid containing multi-wall carbon nanotubes (MWCNTs) is measured with the fabricated 3ω device. The thermal conductivity and the heat capacity of the nanofluids can simultaneously be measured by the proposed method.
장건세(Gun Se Chang),권오명(Ohmyoung Kwon) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
High resolution dopant profiling in semiconductor device has been an intense research topic because of its practical importance in semiconductor industry. Although several techniques have already been developed. it still requires extremely expensive tools to achieve nanometer scale resolution. In this study we demonstrated a novel dopant profiling technique with nanometer resolution using very simple setup. The newly developed technique measures the thermoelectric voltage generated in the contact point of the SPM probe tip and MOSFET surface instead of electrical signals widely adopted in previous techniques like Scanning Capacitance Microscopy. The spatial resolution of our measurement technique is limited by the size of contact size between SPM probe tip and MOSFET surface. Experiment results were compared with theoretical analysis to estimate the contact size.
주기적 정상상태 대류 열전달 현상의 수치해석을 통한 교류 방식 열선 유속측정법 특성분석
김병조(Byung Jo Kim),권오명(Ohmyoung Kwon),이준식(Joon Sik Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Recently a novel flow measurement technique, a tunable AC thermal anemometry, was proposed and experimentally demonstrated. The technique measures the flow speed by using the phase lag of the temperature oscillation induced by the periodic heat generation imposed on the hotwire. In this study, nondimensional governing equations for the steady periodic heat transfer phenomenon from a hotwire with internal periodic heat generation to the surrounding flow are derived and solved numerically to find the dominant parameters affecting the measurement accuracy of the technique. The results show the phase lag of the sensor is determined by flow speed, thermal diffusivity of the fluid and heating frequency. The measurement sensitivity can be improved by modulating the heating frequency. This anemometry can resolve flow speed as low as 0.07 ㎜/s at 0.1 ㎐ when R22 is the working fluid.
평형점 주사탐침열현미경을 이용한 변형률에 따른 그래핀의 열전도도 변화 측정
정재훈(Jaehun Chung),황광석(Gwangseok Hwang),권오명(Ohmyoung Kwon) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
Recently, many studies for enhancing the thermoelectric performance by tuning the phonon dispersion and introducing the phonon scattering via nano-structuring have been reported. For example, simulations have predicted that the thermal conductivity of graphene can be tuned by strain. However, they have shown the contradictory results and the measurement results of thermal conductivity of strained graphene are hard to find. In this study, we experimentally measure the strain effect on the thermal conductivity of suspended graphene by utilizing the null point scanning thermal microscopy, which can directly apply the strain to the graphene and simultaneously measure the change of the spreading resistance which is inversely proportional to the thermal conductivity. The strain is applied to the graphene by pushing the thermocouple probe, whose T.C. junction is locally heated, to the center of the suspended graphene disk. The change of spreading resistance of the graphene is obtained by monitoring the temperature signals measured at T.C. junction and ultimately, we can observe the strain effect on the thermal conductivity of the graphene.