• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.10-12
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• 2008

Hemodynamic features of blood flow in the abdominal aorta aneurysm (AAA) are very important, because they are closely related with the rupture of aneurysm to death. It has been considered that the wall shear stress of blood flows influences the formation, growth, and rupture of AAA. On this account, it is important to understand the flow structure of blood in the aneurysm. In this study, the whole velocity field information inside a typical AAA was measured using an in vitro AAA model under the pulsatile flow condition. The vessel geometry was reconstructed based on the computerized tomography (CT) data of a patient. The AAA model was made by using a rapid prototyping (RP) method, based on the reconstructed vessel geometry. Velocity fields in the AAA model were measured at different pulsatile phases using a PIV (particle image velocimetry) system. As experimental results, a large-scale vortex is formed inside the AAA model and the vortices located near the AAA wall are supposed to increase the local pressure and wall shear stress. In this study, the AAA wall stress found to be was one of the most important governing parameters giving rise to the ruptured aneurysm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.239-244
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• 2003

This study concerns the performance of condensing heat transfer in two-phase closed thermosyphons with various helical grooves. Distilled water, methanol, ethanol have been used as the working fluid. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A experimental study was carried out for analyzing the performances of having 50, 60, 70, 80, 90 helical grooves. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphons is also tested for the comparison. The type of working fluid and the numbers of grooves of the thermosyphons with various helical grooves have been used as the experimental parameters. The experimental results have been assessed and compared with existing theories. The results show that the type of working fluids are very important factors for the operation of thermosyphons. And the maximum enhancement (i.e. the ratio of the heat transfer coefficients the helical thermosyphons to plain thermosyphons) is $1.5{\sim}2$ for condensation.

• KSBB Journal
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• 제11권1호
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• pp.52-57
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• 1996

평활근 세포에 대한 shear stress의 영향을 알아보기 위해 슬라이드 글라스위에 배양된 牛 대통맥의 평활근 세포를 120시간 동안 0~26 dyn/$cm^2$의 각기 다른 일정한 shear stress의 유체에 노출하였다. 실험 장치를 순환하는 배지의 lactate dehydrogen­a ase의 농도측정 결과, 본 연구에서 적용된 shear stress 범위에서는 유체의 흐름으로 인하여 세포가 슬라이드 글라스 표면으로부터 이탈되는 현상은 없었다. 표면 $cm^2$ 당 존재하는 세포의 수를 측정한 결과, 평활근 세포는 정체배양시 가장 빨리 성장하였다. 표변에서의 shear stress가 증가할수록 i영활근 세포의 성장은 늦었으며, shear stress가 17 dyn/$cm^2$ 이상에서는 세포의 성장이 관찰되지 않았다.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.5-10
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• 2012

The effect of pressure-side opening length on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-tochord ratio of $h_{st}/c$ = 5.05% and h/c = 2.0% respectively. The opening length-to-camber ratio is changed to be $OL/c_c$ = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7 The results show that longer OL leads not only to weaker secondary flow but also to lower aerodynamic loss in the tip leakage vortex region, while it significantly widens the area with high aerodynamic loss in the passage vortex region. The aerodynamic loss coefficient mass-averaged all over the measurement plane is kept almost constant for $0.0{\leq}OL/c_c{\leq}0.3$, whereas it increases rapidly for $OL/c_c$ > 0.3 in proportion to $OL/c_c$. There is little deterioration in flow turning with increasing $OL/c_c$.

• 한국유체기계학회 논문집
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• 제14권6호
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• pp.35-44
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• 2011

Membrane filtration has become firmly established as a primary process for ensuring the purity, safety and efficiency of treatment of water or effluents. Several researches have been performed to develop and design membrane systems in order to increase the accuracy and performance of the processes. In this study, a lattice Boltzmann method for the cake layer has been developed using particle dynamics based on an immersed boundary method and the cake layer formation process on membrane has been numerically simulated. Case studies including various particle sizes were also performed for a microfiltration process. The growth rate of the cake layer thickness and the permeation flow rate along the membranes were predicted. The results of this study agreed well with that of previous experiments. Effects of various particle diameters on the membrane performance were studied. The cake layer of a large particle tended to be growing fast and the permeation flow going down rapidly at the beginning. The layer thickness of a small particle increased constantly and the flow rate was smaller than that of the large particle at the end of simulation time.

• 한국유체기계학회 논문집
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• 제17권2호
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• pp.30-34
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• 2014

Membrane distillation (MD) is a thermal driven separation process in which separation a hydrophobic membrane is a barrier for the liquid phase, letting the vapor phase pass through the membrane pores. Therefore, a porous and hydrophobic membrane should be used in membrane distillation. MD cannot work if water penetrates into the pores of the membrane (membrane wetting). Accordingly, it is necessary to prevent wetting of MD membranes and to remove water inside the pores of the wetted membranes if possible. In this context, our study aimed to develop methods to recover wetted membranes in MD processes. Poly-vinylidene fluoride (PVDF) membranes were used in this study. A laboratory-scale direct contact MD (DCMD) system was used to examine the effect of operating parameters on wetting. For dewetting the wetted membranes, specific techniques including the use of high temperature air were applied. The performances of the membranes before and after dewetting were compared in terms of flux, salt rejection and liquid entry pressure(LEP). The surface morphology of dewetted membrane was confirmed by scanning electron microscope (SEM).

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.497-498
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• 2006

Tribological properties of a Magneto-Rheological(MR) fluid in a polishing process are studied. For this polishing process, abrasive wear model is proposed as a function of shear force, normal force and actual mean velocity of MR particles at workpiece surface. Experimental conditions are changed by varying the gap distance between workpiece and tool and the rotational speed of tool. From the experimental results, a modified Stribeck curve is obtained, and the friction coefficient turns out to have linear relationship with a modified Sommerfeld number. The validity of the wear model is supported by additional experiments performed for measuring material removal rates.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.172-179
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• 2004

Average Bi-directional flow tube was suggested to measure single and two phase flow rate. Its working principle is similar with Pilot tube, however, it makes it possible to eliminate the cooling system which is normally needed to prevent from flashing in the pressure impulse line of Pilot tube when it is used in the depressurization condition. The suggested instrumentation was tested in the air-water vertical test section which has 80mm inner diameter and 10m length. The flow tube was installed at 120 of L/D from inlet of test section. From the test, single air and water flow rate was measured successfully. For the emasurement of two phase flow rate, Chexal drift-flux correlation was used. In the test a new correlation of momentum exchange factor was suggested. The test result shows that the suggested instrumentation using the measured void fraction and Chexal drift-flux correlation can predict the mass flow rates within $10\%$ error of measured data.

• 한국유체기계학회 논문집
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• 제16권6호
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• pp.32-39
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• 2013

In the present study, three-dimensional aerodynamic optimization of high pressure turbine nozzle for turbofan engine was performed. For this, Kriging surrogate model was built and refined iteratively by supplying additional experimental points until the surrogate model and CFX result has effective difference on objective function. When the surrogate model satisfied this reliability condition and developed enough, optimum point was investigated. Commercial program PIAnO was used for optimization process and evolutionary algorithm was used for searching optimum point. As a result, difference between estimated value from Kriging surrogate model and CFD result converges within 0.01% and the optimized nozzle shape has 0.83% improved aerodynamic efficiency.

• KSBB Journal
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• 제16권4호
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• pp.370-375
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• 2001

생물고분자 생산 균주를 분리하여 동정한 결과, 분리균주는 Gram 음성의 간균으로 내생포자를 형성하지 않았으며, nitrate 환원과 catalase 반응에서 양성이고, oxidase 반응에서 음성인 통성 혐기성의 한 균주로 분류학상의 위치를 검토한 결과, Enterobacter sp.로 판단하였다 이 균주가 생성하는 생물고분자는 정색반응, CPC 침전, IR 분석 등에 의해 우론산을 함유한 산성의 다당인 것으로 추정되었다. TLC 및 GC에 의해 조사한 결과, mannose, galactose 및 galacturonic acid로 구성된 hetero 다당이었으며, 분자량은 약 3.7$\times$$10^{5}$이었다. 이다당의 수용액(0.5-2.0%, w/v)은 비뉴우톤 유체로 항복응력을 갖는 의가소성 유체로서 거동하였으며, 1.5% 농도 이상의 낮은 농도에서 겔 형성능을 나타내었다.다.