• 공업화학
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• 제22권6호
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• pp.703-710
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• 2011

분리막 모듈 내 스페이서는 용액의 원활한 흐름을 위한 공간 확보와 더불어 유체의 난류를 형성시키므로 농도분극화 현상을 감소시키고 막 표면에 축적되는 오염물을 용액 내로 혼합하여 높은 투과유속과 분리막 모듈을 장기간 운전하는데 도움을 준다. 본 연구에서는 분리막 모듈 내 원형, 십자형, 다이아몬드형 및 육각형 단면의 스페이서와 스페이서의 배열 각도, 용질 배제율 및 투과유속에 대한 농도 변화를 "COMSOL Multiphysics" 프로그램으로 수치 해석하여 최적화하였다. 4가지 형태의 스페이서 중에서 십자형 단면 스페이서를 포함한 모듈의 경우가 분리막 표면 농도를 가장 낮게 유지하였으며 스페이서의 배열 각도는 $30^{\circ}$가 효율적이었다. 스페이서가 없는 모듈 출구에서 분리막 표면의 농도는 입구보다 약 2.09배까지 증가하였으나 가장 효율적인 십자형 스페이서를 $30^{\circ}$로 배열할 경우 약 1.29배로서 최대 37% 낮았다. 또한 투과유속이 증가할수록 십자형 스페이서의 농도분극 감소효과는 급격히 증가하였다.

• Wind and Structures
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• 제23권1호
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• pp.45-57
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• 2016

Open-cross-section composite beam (OCB) tends to suffer vortex-induced vibration (VIV) due to its bluff aerodynamic shape. A cable-stayed bridge equipped with typical OCB is taken as an example in this paper to conduct sectional model wind tunnel test. Vortex-induced vibration is observed and maximum vibration amplitudes are obtained. CFD approach is employed to calculate the flow field around original cross sections in service stage and construction stage, as well as sections added with three different countermeasures: splitters, slabs and wind fairings. Results show that flow separate on the upstream edge and cause vortex shedding on original section. Splitters can only smooth the flow field on the upper surface, while slabs cannot smooth flow field on the upper or lower surface too much. Thus, splitters or slabs cannot serve as valid aerodynamic means. Wind tunnel test results show that VIV can only be mitigated when wind fairings are mounted, by which the flow field above and below the bridge deck are accelerated simultaneously.

• 한국재료학회지
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• 제32권6호
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• pp.301-306
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• 2022

This study explored the possibility of forming a coating layer containing alginic acid on the surface of a magnesium alloy to be used as a biomaterial. We formed a coating layer on the surface of a magnesium alloy using a plasma electrolytic oxidation process in an electrolytic solution with different amounts of alginic acid (0 g/L ~ 8 g/L). The surface morphology of all samples was observed, and craters and nodules typical of the PEO process were formed. The cross-sectional shape of the samples confirmed that the thickness of the coating layer became thicker as the alginic acid concentration increased. It was confirmed that the thickness and hardness of the sample significantly increase with increasing alginic acid concentration. The porosity of the surface and cross section tended to decrease as the alginic acid concentration increased. The XRD patterns of all samples revealed the formation of MgO, Mg₂SiO₄, and MgF₂ complex phases. Polarization tests were conducted in a Stimulate Body Fluid solution similar to the body's plasma. We found that a high amount of alginic acid concentration in the electrolyte improved the degree of corrosion resistance of the coating layer.

• 소성∙가공
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• 제21권3호
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• pp.172-178
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• 2012

We performed a shot peening test and used a 2-D finite element model which predicts the compressive residual stress distribution below the material's surface. In this study, the concept of 'impact cycle' is introduced to account for the irregularity in the shot's impact position during testing. The impact cycle was imbedded in the finite element model. In the shot peening test, shot bombarded a type-A Almen strip surface with different impact velocities. To verify the proposed finite element model, we compared the deformed cross sectional shape of the Almen strips with the shapes computed by the proposed finite element model. Good agreement was noted between measurements and the finite element model predictions. With the verified finite element model, a series of finite element simulations was conducted to compute the residual stress distribution below the material's surface and the characteristics of these distributions are discussed.

• 설비공학논문집
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• 제23권10호
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• pp.670-677
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• 2011

Direct numerical simulation are performed in order to investigate the effect of the circular cylinder shape on the forced convection around a circular cylinder at the Reynolds number of 300 and Prandtl number of 0.71. Three-dimensional characteristics of fluid flow and heat transfer around the smooth, wavy and torsional cylinders are investigated. A wavy cylinder has the sinusoidal variation in the cross sectional area along the spanwise direction with the wave length of ${\pi}/3$ and wavy amplitude of 0.1. A torsional cylinder has the twisted elliptic cross section with a torsional period of ${\pi}/2$ and an axis ratio of 1.35 corresponding to the major axis of 1.15 and the minor axis of 0.85. The value of time-and surface-averaged drag coefficient for the smooth cylinder is similar to that for the wavy cylinder, but larger than that for the torsional cylinder. The time and surface-averaged lift coefficient for the smooth cylinder is larger than that for the wavy and torsional cylinders. The time-averaged local heat transfer rate for the wavy and torsional cylinders shows different distribution along the circumferential direction, compared to that for the smooth cylinder because of the shape change in the spanwise direction for the cases of the wavy and torsional cylinders.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.273-280
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• 1997

Rotary swaging is a process for reducing the cross-sectional area or changing the shape of bar, tube or wires by repeated radial blows with one or more parirs of opposed dies. The present study is concerned with investigation the effect of process parameters upon product quality(hardness, roughness, precision of dimension). To enhance the product quality, experimental works are carried out for some process parameters such as forming speed, billet shape, lubrication, reduction of area and ratio of t/D. Rod shift formed by RSM25 under cold conditions has good surface quality, hardness and precision of dimension. The recommendable process conditions are suggested for solid and tubular products.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권2호
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• pp.141-151
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• 2013

The study of environmental stress cracking (ESC) by contact with plastic rulers and PVC erasers which was artificially added to the external stress was carried out in order to accelerate the chemicals crack. To analyze a blooming plasticizer that migrates from the inside of blended eraser to the surface of the eraser, the ESC experiments were carried out at room temperature and $50^{\circ}C$ conditions. The chemicals crack shape caused by the plasticizer and the brittle fracture shape resulted from the external stress were observed in consequence with the cross-sectional surface analysis of the ruler crack by the ESC. The bending strength of the plastic rulers were fractured prior to the yield point and it had low bending flexure stress. We presented that ESC of polymer materials was affected by the polarity of the chemicals and polymer, the exposure time to chemicals, the exposure temperature and the level of strain on the polymer.

• Design & Manufacturing
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• 제14권4호
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• pp.11-16
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• 2020

In this study, forming of carbon composite parts was performed using an injection/compression molding process. An impregnation of matrix is determined by ability of wet and flow rate between the matrix and reinforcement. The flow rate of matrix passing through the reinforcements is a function of permeability of reinforcement, a viscosity of matrix and pressure gradient on molding, and the viscosity of the matrix depends on the mold temperature, molding pressure and shear strain of matrix. Therefore, compression molding experiment was conducted using a heating mold in order to confirm the possibility of matrix impregnation. The impregnation of the matrix through the porosities between the woven yarns was confirmed by the cross-sectional SEM image of compression molded parts. An injection molding process was also performed at a short cycle time, high molding pressure and low mold temperature than those of compression experiment conditions. Deterioration of impregnation on the surface of molded parts were caused by these injection conditions and it could be the reason of decreasing the maximum tensile strength. In order to improve impregnation of matrix on the surface, injection/compression molding and insert-over molding were applied. As a result of applying injection/compression molding and insert-over molding, it was shown that the improvement of impregnation on the surface and the maximum tensile strength was increased about 2.8 times than the virgin matrix.

• 한국재료학회지
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• 제2권1호
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• pp.19-26
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• 1992

$WF_6$와 $SiH_4$의 화학반옹으로부터 산화규소막 위에 텅스텐 핵이 형성되는 현상을 실험을 통해 관찰하였다. 핵이 생성되는 속도는 반응온도가 높고 운반기체의 유량이 적으며 반응기내의 압력이 높을수록 큰 것으로 나타났다. 또한 반응기체가 흘러가는 방향에서 아랫쪽으로 위치하는 표면에 핵이 생성되는 속도가 큰 것으로 나타났다. 산화막위에 생성된 텅스텐 핵의 형상과 파단면을 주사현미경으로 관찰하였으며 산화막위에 형성된 텅스텐 박막의 화학적 조성을 밝혀내었다.

• Carbon letters
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• 제4권4호
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• pp.168-174
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• 2003

Silver nitrate ($AgNO_3$) powder was mixed into a reformed pitch precursor. Then, the silver-containing pitch was melt spun to form round and "C" shape fibers. A wire mesh was inserted prior to the nozzle to improve the spinnability of the silvercontaining precursor pitch. Silver particles in the carbon fibers (CFs) were detected by XRD and TEM. These tests showed that silver particles were uniformly distributed and the total amount of silver remained constant during stabilization and carbonization. Next, the silver-containing CFs were activated by steam diluted in nitrogen gas. Silver particles accelerated the activation rate, but the specific surface areas of the silver-containing ACFs were similar to those of non-silver containing ACFs at the same burn-off levels. The specific surface area of the C-shaped activated carbon fibers was larger than that of the round activated carbon fibers. The likely reason is that the surface area of a C-shaped CF is about two times larger than that of a round CF when equivalent cross-sectional areas are compared. A small amount of silver particles in the periphery of the CFs was removed during the activation, but the remainder of silver was stayed within the ACFs.