• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.385-390
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• 2011

In this study, we developed a micromixer based on the non-equilibrium electrokinetics at the junction of a microchannel and nanochannel. Two fluid streams were mixed by an electro-osmotic flow and a vortex flow created as a result of the non-equilibrium electrokinetics at the junction of the microchannel and nanochannel. Initially, the microchannel was fabricated using Polydimethylsiloxane (PDMS) by the general soft lithography process and the nanochannel was created at a specific position on the microchannel by applying a high voltage. To evaluate the mixing performance of the micromixer, fluorescent distribution was analyzed by using the fluorescent dye, Rhodamine B. About 90% mixing was achieved with this novel micromixer, and this micromixer can be used in microsystems for biochemical sample analysis.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.114-122
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• 2022

This paper explores three-dimensional unsteady computational fluid dynamic (CFD) analyses with an overset grid technique to analyse the wake effect created by a rotating propeller on a hand-launched unmanned aerial vehicle (UAV). Additionally, the influence of actual aileron deflection on the equilibrium condition of the rolling moment is examined in various hand-launched take-off conditions. The results of this study demonstrate the importance of initial aileron deflection in increasing the initial rolling stability during the hand-launched take-off process. Furthermore, an aerodynamic database is constructed to rapidly predict the aileron set values required for different take-off speeds and angle-of-attacks.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.9 no.1
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• pp.47-53
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• 1995

In this paper, the characteristics of breakdown voltage($\textrm{V}_{Brms}$) -temperature(T) for air insulated power installation in flowing air with variation of T(30[$^{\circ}C$] -180[$^{\circ}C$]) are presented. To study these subjects, needle-to-needle gap in the circular pipe(inner diameter 5[cm]) are used. Also, theories of gas discharge and hydrodynamics in pipe were used to analysis for the characteristics. The $\textrm{V}_{Brms}$ is proportional to flow velocity. At high velocity, $\textrm{V}_{Brms}$ is described the saturation. At high T(180[$^{\circ}C$]), $\textrm{V}_{Brms}$ is about 4.7(kV] lower than low T(30[$^{\circ}C$]). The empirical equation obtained from this study is $\textrm{V}_{Brms}=A\times{Log[Re}+B$. Where A, B : Constant.

• Journal of the Korean Electrochemical Society
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• v.14 no.4
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• pp.253-260
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• 2011

In this study, computational simulation was performed for thermal management of modules consisting of 10 batteries. Simplified structure and equivalent thermal resistance network was applied to maintain the thermal properties. Verification test of the mesh were in progress to ensure the reliability of 2.6 mm in the narrow gap between the battery, resulting in at least three divided mesh between the shape of the grid was required. Type of air from rear of the module, type of air from top of the module and type of air from bottom of the module were applied and effective cooling methods are discussed based on the location of fan and air intake of the modules. Maximum temperature and temperature differences of modules that directly affect the performance of the module were compared, and also behavior of the fluid was confirmed by comparing the air flow. The best maximum temperature is shown type of air from bottom of the module to $40.27^{\circ}C$ and type of air from top of the module shows smallest temperature difference $0.73^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1518-1528
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• 1995

The deformation and departure processes of a bubble attached to the wall are studied experimentally and numerically to understand the phenomena of the nucleate boiling heat transfer enhancement under DC electric field. An air-bubble is injected in a dielectric liquid with different electric fields generated by changing three types of electrode system (Type 1,2 and 3) in the bubble generator. Experimental variables are the electric field strength and the distance and the shape of the electrodes under DC electric field. From experimental results, it is observed that the bubble under Dc electric field is elongated in the same direction as the electric field and the contact angle increases. For the parallel plate electrode which generates a uniform electric field, bubble departure volume doesn't seem to decrease within our experimental range. However, when a needle is raised a few millimeters from the lower electrode to make a nonuniform electric field around the needle, bubble departure volume decreases continuously with the increase of an applied voltage. The reduction effect of bubble departure volume is the most effective under a strong nonuniform electric field generated with Type 3. As the nonuniformity of the electric field due to the shape of a electrode increases, the terminal velocity and the acceleration of a bubble increase largely. For the comparison with visualization results, the deformation of a bubble attached to the electrode is carried out by a numerical method. Numerical results show good agreement qualitatively with experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.403-408
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• 2016

Lithium-ion batteries are commonly employed in hybrid electric vehicles (HEVs), and achieving high energy density in the battery has been one of the most critical issues in the automotive industry. Because liquid cooling containing antifreeze is important in automotive batteries to enable cold starts, an effective geometric configuration for high-cooling performance should be carefully investigated. Battery cooling with antifreeze has also been considered to realize successful cold starts. In this article, we theoretically investigate a specific property of an antifreeze cooling battery system, and we perform numerical modeling to satisfy the required thermal specifications. Because a typical battery system in HEVs consists of multiple stacked battery cells, the cooling performance is determined mainly by the special properties of antifreeze in the coolant passage, which dissipates heat generated from the battery cells. We propose that the required cooling performance can be realized by performing numerical simulations of different geometric configurations for battery cooling. Furthermore, we perform a theoretical analysis as a design guideline to optimize the cooling performance with minimum power consumption by the cooling pump.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.112.2-112.2
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• 2011

PVT(Photovoltaic Thermal) 모듈은 태양광과 태양열 에너지를 동시 이용이 가능한 모듈로서 태양광전지(PV, Photovoltaic)모듈에 열교환기를 접합한 형태로 전기에너지뿐만 아니라 열에너지를 동시에 생산할 수 있는 시스템이다. 기존 PV 모듈은 일사량이 많으면 전력 생산량이 증가하는 동시에 PV모듈의 온도가 상승함에 따라 발전 효율이 감소하는 문제점이 있으며 일반적으로 $25^{\circ}C$이상 조건에서 모듈 온도가 $10^{\circ}C$ 증가할수록 발전효율의 약 4~5% 정도 감소하는 것으로 보고되고 있다. PVT 모듈은 기존 태양광모듈에 열교환기를 접합하여 냉각함으로써 PV모듈의 온도를 낮추어 발전효율을 증가시키는 동시에 부가적으로 발생하는 온수를 직접이용하거나 다양한 계통의 보조 열원으로 이용할 수 있는 장점이 있다. 본 연구에서는 수치해석기법(CFD)을 활용하여 PV모듈 냉각 및 온수 발생을 위한 열교환기를 설계하였으며 다양한 형상의 열교환기에 대해 유동해석을 수행하여 최적의 열흡수효율을 갖는 열교환기의 형상을 설계하였다. 또한 최적 설계된 PVT 모듈을 제작하여 실제 태양과 유사한 광원을 갖는 인공태양조건에서의 실내 실험을 통해 PVT 모듈의 성능을 검증하였으며 또한 실제 노상에 설치하여 ASHRAE 93-77의 실험기준과 ECN의 PVT 집열기 성능측정 가이드라인에 따라 옥외 시험평가를 하여 PVT 모듈의 성능 검증을 하였다. 최적 설계된 PVT모듈에 대한 성능평가 결과 기존 PV 모듈보다 발전효율이 약 15%(기존 발전효율 대비) 향상된 결과를 확인하였다.

• Nuclear Engineering and Technology
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• v.10 no.2
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• pp.79-86
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• 1978

The object of this study was to obtain data on air-distributions in two-phase up flow in vertical rod-bundle test-section. The test-section in this study was a hexagonal shaped 61-rod bundle where each rod was wrapped with helical spacers. The variables were flow rates of air and water and air inlet positions. Experimental data were obtained at the outlet of the test-section. The experiments were performed in two parts. Firstly, data were taken at increasing flow rates of air keeping water flow rates constant, and secondly, at simultaneous increase of air and water flow rates. At each flow condition, air supply position could be changed to 4 different positions. Data obtained by electrical void-needle technique were analyed and are presented here in graphical forms for comparison. The results of this study demonstrate qualitatively that air-distribution tends to be more uniform as water flow rates are increased. The air supply positions have noticeable effects on the pattern of air-distribution.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.7
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• pp.28-33
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• 2022

In this study, we analyze the flow characteristics according to the internal shape of a 700bar hydrogen charging gun for hydrogen electric vehicles. When charging hydrogen, it receives a high-pressure charging pressure. At this time, we analyze the flow characteristics according to the shape of the nozzle and find the shape of the nozzle that minimizes energy loss. Ultimately, the optimal design of the nozzle was obtained by comparing the pressure difference between the inlet pressure and outlet pressure under a fixed mass flow condition.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.4
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• pp.237-242
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• 2009

In the pyroprocessing of spent nuclear fuels, fuel materials are recovered by electrochemical reactions on the surface of electrodes as well as stirring the electrolyte in electrolytic cells such as electrorefiner, electroreducer and electrowinner. The system with this equipment should first be scaled-up in order to commercialize the pyroprocessing. So in this study, the scale-up for those electrolytic cells was studied to design a large-scale system which can be employed in a commercial process in the future. Basically the dimensions of both electrolytic cells and electrodes should be enlarged on the basis of the geometrical similarity. Then the criterion of constant power input per unit volume, characterizing the fluid behavior in the cells, was introduced in this study and a calculation process based on trial-and-error methode was derived, which makes it possible to seek a proper speed of agitation in the electrolytic cells. Consequently examples of scale-up for an arbitrary small scale system were shown when the criterion of constant power input per unit volume and another criterion of constant impeller tip speed were respectively applied.