• 한국식품과학회지
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• 제47권4호
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• pp.474-479
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• 2015

연속식 옴가열 장치를 이용한 고추장을 베이스로 한 모델 식품에 대한 가열 살균 연구를 진행하여, 옴가열을 이용한 소스 살균에 필요한 기초 데이터를 수집하였다. 옴가열 시 점도에 상관없이 $100^{\circ}C$까지 고르게 상승하였으나, 점도가 높을수록 전기전도도와 가열속도가 낮아져 살균력이 감소하는 것으로 나타나, 저점도 식품이 옴가열을 이용한 가열 및 살균에 있어 더 유용하다는 것을 알 수 있었다(13,14). 재래가열 후의 살균도는 65.4-75.4%, 옴가열 시는 89.5-95.0%로 살균력이 더 우수하였다. 향후 연속식 옴가열 장치의 살균효과를 더 높이기 위해서는 여러 개의 셀 연결 방식을 통해 한 개의 셀에서 온도를 조금씩 상승시켜 스케일 생성을 방지하는 연구와 셀 통과시 빠른 온도 상승에 의한 점도 변화로 살균 처리량이 변하기 때문에 최적 셀 조합 및 가열살균 조건에 대한 충분한 고찰이 필요할 것으로 생각된다.

• 한국기계가공학회지
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• 제17권1호
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• pp.108-115
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• 2018

In bone tissue engineering, polycaprolactone (PCL) is one of the most widely used biomaterials to manufacture scaffolds as a synthetic polymer with biodegradability and biocompatibility. The polymer deposition system (PDS) with four axis heads, which can dispense bio-polymers, has been used in scaffold fabrication for tissue engineering applications. A dual-head deposition technology of PDS is an effective technique to fabricate 3D scaffolds. The electrospinning technology has been widely used to fabricate porous and highly interconnected polymer fibers. Thus, PDS can fabricate nanofiber-combined hybrid scaffolds using fused deposition modeling (FDM) and electrospinning methods. This study aims to fabricate nanofiber-combined scaffolds with uniform nanofibers using PDS. The PCL nanofibers were fabricated and evaluated according to the fabrication process parameters. PCL nanofibers were successfully fabricated when the applied voltage, tip-to-collector distance, flow rate, and solution concentration were 5 kV, 1 cm, 0.1 ml/h, and 8 wt%, respectively. The cell proliferation was evaluated according to the electrospinning time. Scanning electron microscopy was used to acquire images of the cross-sectioned hybrid scaffolds. The cell proliferation test of the PCL and nanofiber-combined hybrid scaffolds was performed using a CCK-8 assay according to the electrospinning time. The result of in-vitro cell proliferation using osteosarcoma MG-63 cells shows that the hybrid scaffold has good potential for bone regeneration.

• Selected Papers of The Society of Naval Architects of Korea
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• 제1권1호
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• pp.76-90
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• 1993

A new propeller series is developed using the newly developed blade section (KH 18 section) which has better cavitation characteristics and higher lift-drag ratio at wade angle-of-attack range than a conventional section. The radial patch distribution of the new series propellers is variable stance they were designed adaptively to a typical wake distribution. Basic geometric particulars of the series propellers. such as chord length, thickness, skew and rake distributions, are determined on the basis of recent full scale propeller geometric data. The series is developed for propellers having 4 blades, and blade area ratios of 0.3, 0.45, 0.6 and 0.75. Mean pitch ratios are varied as 0.5, 0.6, 0.7, 0.95 and 1.1 for each blade area ratio. The new propeller series consists of 20 propellers and is named as the KD(KRISO-DAEWOO)-propeller series. Propeller open-water tests are performed at the towing tank, and cavitation observation tests and fluctuating pressure tests are carried out at the cavitation tunnel of KRISO. $B_{p}-\delta$ curves, which can be used to select the optimum propeller diameter at the preliminary design stage, are derived from a regression analysis of the propeller open-water test results. The KD-cavitation chart is derived from the cavitation observation test results by choosing the local maximum lift coefficient and the local cavitation number as parameters. The cavity extent predicted by the KD-cavitation chart would be more accurate compared to that by an existing cavitation charts, such as the Burrll's cavitation chart, since the former is derived from the cavitation observation test results in a typical ship's wake, while the lather is derived from the test results in a uniform flow.

• 한국재료학회지
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• 제25권7호
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• pp.336-340
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• 2015

For rear metallization with Al paste, Al back contacts require good passivation, high reflectance, and a processing temperature window compatible with the front metal. In this paper, the effect of the firing ambient during the metallization process on the formation of Al rear metal was investigated. We chose three different gases as ambient gases during the firing process. Using SEM, we observed the formation of a back surface field in $N_2$, $O_2$, and Air ambients. To determine the effect of the ambient on Voc, the suns-Voc tool was used. In this study, we described the mechanism of burn-out of organic materials in Al paste during the firing process. The oxygen ambient plays an important role in the burn-out process. We calculated the efficiency with obtained the back surface recombination velocities using PC1D simulation. It was found that the presence of oxygen during the firing process influenced the uniform back surface field because the organic materials in the Al paste were efficiently burned out during heating. The optimized temperature with oxygen flow shows an absolute efficiency of 19.1% at PC1D simulation.

• 한국해양환경ㆍ에너지학회지
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• 제4권1호
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• pp.38-46
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• 2001

조류 중에 설치한 이중 유벽의 유효성을 검증하기 위하여 유벽 전후 및 유벽사이에서의 유적(oil droplet)의 거동을 실험적 및 수치적으로 연구하였다. 이 연구에는 단일 유벽의 경우 유벽의 유연성이 포유성능에 미치는 영향도 포함되었다. 실험은 유적의 밀도와 근사한 구형의 고체입자가 전방 유벽의 상류 한 지점에서 방류되었을 때 그 궤적을 추적하는 것이 내용이었다. 입자는 방류되었을 때 유동장의 상태에 따라 자유표면으로 부상하거나, 유벽에 충돌 또는 유벽하로 빠져나가는 현상을 나타내게 된다. 본 논문에는 이러한 유적의 이동 경위를 해석함으로써, 이러한 유적의 유적이 운동을 시작하는 영역이 어딘가에 따라 전방유벽하로 기름이 누출될 것인지 아닌지를 판단할 수 있는 방법과 전후 유벽의 흘수의 차 그리고 수심이 이중유벽의 포유성능에 미치는 영향을 해석할 수 있는 방법을 제시하였다.

• 설비공학논문집
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• 제8권1호
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• pp.1-12
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• 1996

In lots of application to heat exchanger systems, closed two-phase thermosyphons are tilted from a horizontal. If the tilt angle, especially, is less than 30$^{\circ}$, the operational performances of thermosyphon are highly dependent on tilt angle. The present study was conducted to better understand such operational behaviors as mech-anni는 of phase change, and flow patterns inside a tilted thermosyphon. For experiment, an ethanol thermosyphon with a 35% of fill charge rate was designed and manufactured, using a copper tube with a diameter 19mm and a length 1500mm. Through a series of test, the tilt angle was kept constant at each of 4 different values in the range 10~25deg. and the heat supply to the evaporator was stepwisely increased up to 30㎾/$m^2$. When a steady state was established to the thermosyphon for each step of thermal loads, the wall temperature distribution and vapor temperature at the condenser were measured. The wall temperature distributions demonstrated a formation of dry patch in the top end zone of the evaporator, with a values of temperature 20~4$0^{\circ}C$ higher than the wetted surface for a moderate heat flux q≒20㎾/$m^2$. Inspite of the presence of hot dry patch, however, the mean values of boiling heat transfer coefficient at the evaporator wall were still in a good agreement with those predicted by Rohsenow's formula, which was based on nucleate boiling. For the condenser, the wall temperatures were practically uniform, and the measured values of condensation heat transfer coefficient were 1.7 times higher than the predicted values obtained from Nusselt's film condensation theory on tilted plate. Using those two expressions, a correlation was formulated as a function of heat flux and tilt angle, to determine the total thermal resistance of a tilted thermosyphon. The correlation formula showed a good agreement with the experimental data within 20%.

• Journal of the Korean Data and Information Science Society
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• 제21권6호
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• pp.1289-1303
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• 2010

The need for statistical process control to check the performance of a process is becoming more important in chemical and pharmaceutical industries. This study illustrates the method to determine whether a process is in control and how to produce and interpret control charts. In the experiment, a stream of green dyed water and a stream of pure water were continuously mixed in the process. The concentration of the dye solution was measured before and after the mixer via a spectrophotometer. The in-line mixer provided benefits to the dye and water mixture but not for the stock dye solution. The control charts were analyzed, and the pre-mixer process was in control for both the stock and mixed solutions. The R and X-bar charts showed virtually all of the points within control limits, and there were no patterns in the X-bar charts to suggest nonrandom data. However, the post-mixer process was shown to be out of control. While the R charts showed variability within the control limits, the X-bar charts were out of control and showed a steady increase in values, suggesting that the data was nonrandom. This steady increase in dye concentration was due to discontinuous, non-steady state flow. To improve the experiment in the future, a mixer could be inserted into the stock dye tank. The mixer would ensure that the dye concentration of the stock solution is more uniform prior to entering the pre-mixer ow cell. Overall, this would create a better standard to judge the water and dye mixture data against as well.

• 한국수소및신에너지학회논문집
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• 제22권6호
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• pp.842-851
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• 2011

A multi-cell test system with 25 independent cells is used to test different electrode materials simultaneously for polymer electrolyte membrane fuel cells (PEMFCs). Twenty-five segmented membrane electrode assemblies (MEAs) having the same or different Pt-loading are prepared to analyze the performance deviation of cells in the multi-cell test system. Improvements in the multi-cell test system are made by ensuring that the system performs voltage sensing for the cells individually and inserting optimum gaskets between the MEAs and the graphite plates. The cell performances are improved and their deviations are significantly decreased by these modifications. The performance deviations changed according to various cell configurations because the operating conditions of the cells, such as the gas flow and concentration, differed. This cell system can be used to test multiple electrodes simultaneously because it shows relatively uniform performance under the same conditions as well as linear correlation with various catalyst loadings.

• 대한기계학회논문집A
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• 제21권6호
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• pp.961-970
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• 1997

A numerical method is presented to predict and analyze the shape of a growing billet produced from the "spray forming process" which is a fairly new near-net shape manufacturing process. It is important to understand the mechanism of billet growing because one can obtain a billet with the desired final shape without secondary operations by accurate control of the billet shape, and it can also serve as a base for heat transfer and deformation analysis. The shape of a growing billet is determined by the flow rate of the alloy melt, the mode of nozzle scanning which is due to cam profile, the initial positio of the spray nozzle, scanning angle, and the withdrawal speed of the substrate. In the present study, a theoretical model is first established to predict the shape of the billet and next the effects of the most dominent processing conditions, such as withdrawal speed of the substrate and the cam profile, on the shape of the growing billet are studied. Process conditions are obtained to produce a billet with uniform diameter and flat top surface, and an ASP30 high speed steel billet is manufactured using the same process conditions established from the simulation.imulation.

• 한국세라믹학회지
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• 제35권11호
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• pp.1155-1161
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• 1998

브라운관 funnel glass 내며의 흑연 피막의 저항에 관하여 연구하기 위하여 흑연이 함유된 도전성 도료를 제조하여 flow coating 방법으로 28" wide TV용 funnel glass 내면에 도포하고 흑연피막의 특성과 브라운관의 동작 특성을 평가하였다. 고형분 농도가 증가함에 따라 도전성 도료의 점도와 흑연피막의 두께는 증가하였으며 흑연피막의 전기저항은 감소하였다. 도포 후 건조조건에 따라서도 도전막의 표면상태, 전기저항 및 브라운관의 초기동작 특성등이 다르게 나타났다. 도전성 도료의 고형분 농도는 27%, 점도는 13 cps 전후에서 안정한 흑연피막을 제조할 수 있었으며, 이 때 진공특성이 최적의 상태로 나타났다. 그리고 도전성 도료의 상태와 제조조건에 따라서 브라운관의 다른 전지적 특성들도 변할 수 있기 때문에 브라운관 전체의 특성을 동시에 평가를 해야한다고 생각한다. 그리고 funnel glass에서의 부의 별 저항산포 차리를 줄이기 위해서는 도포 시에 도전성 도료를 주입하는 위치, 건조 조건, funnel glass의 예열 온도 등에 대한 조사도 이루어져야 한다고 생각한다.