• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.5
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• pp.43-55
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• 2020

The effect of cutted pin in front of pin-fin array was analyzed for increasing the cooling performance of gas turbine blade. The numerical simulations were conducted to figure out the flow and thermal characteristics. The base case which is staggered pin-fin array, cut pin case 1 which has X₂/D_p=1.25 cut pin and cut pin case 2 which has X₃/D_p=1.75 cut pin were compared. The results showed that cut pin increases the strength of the horseshoe vortex which occurred at the leading edge of pin-fin array. Furthermore, the wake effect is reduced at the trailing edge of pin-fin array. As a result, the heat transfer distribution on the endwall increases. However, the friction factor increases owing to the installation of cut pin, but the thermal performance factor is increased maximum 23.8% in cut pin case 2. Therefore, installation of cut pin will be helpful for increasing the cooling performance of pin-fin array of gas turbine blade.

• Journal of Software Assessment and Valuation
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• v.15 no.1
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• pp.109-114
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• 2019

In this paper, simulations of S-parameter and characteristic impedance for the probe pin are performed and its high-frequency performance is analyzed. The probe pins are arranged with one signal pin in the center and four ground pins on the top, bottom, left and right sides. The insertion loss and return loss of the probe pin are calculated while increasing the separation between the probe pins to 0.35 mm, 0.40 mm, and 0.50 mm, respectively. It is confirmed that the probe pin has different features of the insertion loss due to its periodic resonance phenomenon. Effect of the characteristic impedance on pitch and assignment of the probe pin is also analyzed. It is verified that there are a number of ground pins whose characteristic impedance is close to 50 Ω.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.12
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• pp.1084-1096
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• 2016

This paper presents method of design and analysis of a high-speed serial interface connector with a data rate of 12.5 Gbps. A high-speed serial interface connector is composed of various material and complex structures. It is very difficult to match the impedance of each discontinuous portion of connector. Therefore, this paper proposes the structure of a connector line that be simplified a connector. In the structure of proposed connector line, this research presents a method for extracting R, L, C and G parameters, analyzing the differential mode impedance, and minimizing the impedance discontinuity using time domain transmissometry and time domain reflectometry. This paper applies the proposed methods in the connector line to the high-speed serial interface connector. The proposed high-speed serial interface connector, which consists of forty-four pins, is analyzed signal transmission characteristics by changing the width and spacing of the four pins. According to the analysis result, as the width of the ground pin increases, the impedance decreases slightly. And as the distance between the ground pin and the signal pin increases, the impedance increases. In addition, as the width of the signal pin increases, the impedance decreases. And as the distance between the signal pin and the signal pin increases, the impedance decreases. The impedance characteristic of initial connector presents ranges from 96 to $139{\Omega}$. Impedance characteristic after applying the structure of proposed connector is shown as a value between 92.6 to $107.5{\Omega}$. This value satisfies the design objective $100{\Omega}{\pm}10%$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.2
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• pp.79-86
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• 2017

In this study, the flow and heat transfer characteristics of the finned annular passage were investigated numerically. The annular passage simulates co-axial geothermal heat exchanger, and fins are installed on its inner wall to reduce heat loss from the production passage (annulus) to injection passage (inner pipe). A commercial CFD program, Ansys Fluent, was used with SST $k-{\omega}$ turbulence model. The effects of the geometric parameters of the fin on the inner tube were analyzed under the periodic boundary condition. The result indicated that most parameters had a tendency to increase with an increase in the height and angle of the fin. However, it was confirmed that the Nusselt number of the inner tube on the coaxial 15, 5, 0.3 was lower than that of the smooth tube. Additionally, the Nusselt number of the inner tube exhibited a tendency of decreasing with a decrease in the spacing in Coaxial 15, $S_f$, 0.3.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1168-1177
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• 2004

This paper presents the characteristics of the electromagnetically coupled small broadband disk-loaded monopole antenna with multiple shorting pins. The electromagnetically coupled monopole antenna can achieve broad bandwidth by controlling resonant frequency of the rectangular disk-loaded monopole and a probe with the spiral strip line monopole. The number and arrangement of the shorting pin affect the capacitance of the disk. The variation of the capacitance changes resonant frequency of the antenna, and therefore, its electrical sizes and frequency bandwidth are also affected. The antenna with three shorting pins has a volume of $0.094\lambda_0{\times}0.094\lambda_0{\times}0.094\lambda_0$ in electrical length and the frequency bandwidth of $26.8\%\;for\;VSWR\leq2$ with the center frequency at 2.556 GHz.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1089-1095
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• 2011

Numerical simulation is performed for nucleate boiling on a micro-finned surface, which has been widely used to enhance heat transfer, by solving the equations governing the conservation of mass, momentum, and energy in the liquid and vapor phases. The bubble motion is determined by a sharp-interface level-set method, which is modified to include the effect of phase change and to treat the no-slip and contact-angle conditions, as well as the evaporative heat flux from the liquid microlayer on immersed solid surfaces such as micro fins and cavities. The numerical results for bubble formation, growth, and departure on a microstructured surface including fins and cavities show that the bubble behavior during nucleate boiling is significantly influenced by the fin-cavity arrangement and the fin-fin spacing.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.1-7
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• 2014

This study is to analyze the local convective heat transfer for a circular cylinder with annular fins. The relation between wall heat transfer and three-dimensional flow is investigated for different distances of annular fins. Depending on the fin spacing, the flow structure is strongly changed by the variation of horseshoe vortices. As the fin spacing increases, the heat transfer rate is maximized at a certain condition. This is clearly obtained as the Reynolds number increases, and it is closely related to the development of horseshoe vortices.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.461-461
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• 2011

최근의 나노기술의 발전과 함께 나노미터크기의 물질들의 물성과 미세구조 등을 분석하기 위한 노력들이 활발히 이루어지고 있다. 투과전자현미경(transmission electron microscope; TEM)은 나노물질의 미세구조 관찰, 화학성분 분석, 전자기적 특성평가가 가능한 초정밀 분석장비이다. TEM 관찰을 위한 시편의 제작방법중 TEM 그리드(grid)를 사용하는 방법은, 분석하고자 하는 물질을 망(mesh) 형태의 그리드에 도포하여 샘플을 준비하는 방법으로 다른 방법에 비해 아주 빠르고 간편한 장점이 있다. 그러나 TEM 그리드에 나노물질을 분산/도포하여 공중에 떠있는 형태로 샘플을 제작하려면, 나노물질이 mesh 사이로 빠져나오지 않도록 그리드 mesh의 간격이 아주 미세하여야 하는데, 일반적으로 mesh의 크기가 미세할수록 그리드의 가격은 높아진다. 또한 기존에 사용되고 있는 비정질 탄소박막으로 덮여진 그리드는 극미세 크기의 나노물질 및 탄소나노물질을 분석할 경우, 고해상도의 TEM상을 얻는데 한계가 있다. 한편 그래핀은 2차원의 육각판상의 구조로 탄소원자가 빼곡히 채워진 흑연 한 층의 나노재료이다. 이는 원자단위 두께로 가장 얇은 물질로서 기계적 강도가 우수하여 지지막으로의 응용이 가능하다고 알려져 있다. 따라서 TEM grid막으로 사용할 경우 기존의 고가의 미세한 mesh가 형성된 그리드를 사용하지 않아도 나노물질을 효과적으로 분석할 수 있을 것으로 예상 된다. 본 연구에서는 열화학증기증착법(thermal chemical vapor deposition; TCVD)을 이용하여 300 nm 두께의 니켈박막이 증착된 기판위에 대면적으로 합성한 그래핀을 TEM 관찰용 그리드 위에 전사(transfer)함으로써 나노물질이 그리드 mesh사이로 빠져나오지 않는 저가의 TEM 그리드 제작 방법 및 응용 가능성에 대하여 보고한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.529-535
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• 2005

This study experimentally examines the air-side performance of spiral finned tube heat exchangers. The effects of fin spacing, fin height, and tube alignment were investigated. Reduction of fin spacing decreased the Colburn j factor. However, the effect of fin height on the Colburn j factor was negligible. An increase of tube row decreased the Nusselt number for both staggered and in-line tube alignments. However, the decrease of the Nusselt number for the in-line tube alignment was much more significant than that of the staggered tube alignment. The average Nusselt number of the staggered tube alignment was larger than that of the in-line tube alignment by $10\%$ when the Reynolds number ranged from 300 to 1700. An empirical correlation of the Nusselt number was developed by using geometric parameters of heat exchanger and correction factors. The correction factor considered the effects of tube alignment and number of tube rows on the heat transfer. The proposed correlation yielded a mean deviation of $4\%$ from the present data.

• Korean Journal of Agricultural Science
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• v.30 no.1
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• pp.76-88
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• 2003

This study exploits the robot system which is necessary in gene study, bio-technology industry. As well, it can achieve the job of DNA chip manufacturing whose use rate has been increased recently. The robot consists of DNA spotting device for spotting DNA on the silylated slide and well plate, bed for fixing well-plate, washing & drying device of washing and drying the pin part of DNA spotting device, distillation-water vessel, and discharge vessel of wash water. We made the term of sticking DNA to the pin on well plate to be 15 seconds. The spot size of DNA was set to be 0.28 mm on the average by bringing the slide into contact with pin for 1 second. At this rate, if DNA is spotted in the minimum space possible of about 0.32mm, it can stick about 8,100 DNA spots on the well plate. Analyzing the procedure: Movement starts. Pin washes, dries, and smears DNA on the well plate. Spots DNA onto 12 chips takes 2 minutes and 50 seconds.