• International Journal of Vascular Biomedical Engineering
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• 제4권1호
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• pp.1-8
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• 2006

The x-ray PIV method was improved for measuring quantitative velocity fields of real blood flows using a coherent synchrotron x-ray source. Without using any contrast media or seeding particles, this method can visualize flow pattern of blood by enhancing the phase-contrast and interference characteristics of blood cells based on a synchrotron x-ray imaging mechanism. The enhanced x-ray images were achieved by optimizing the sample-to-scintillator distance, the sample thickness, and hematocrit. The quantitative velocity fields of blood flows inside opaque tubes were obtained by applying a 2-frame PIV algorithm to the x-ray images of the blood flows. The measured velocity field data show typical features of blood flows such as the yield stress effect. The non-Newtonian flow characteristics of blood flows were analyzed using the x-ray PIV method and the experimental results were compared with hemodynamic models.

• International Journal of Vascular Biomedical Engineering
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• 제4권2호
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• pp.13-18
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• 2006

Direct injection of a fibrinolytic agent to the intra-arterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. Computational fluid dynamic methods were used in order to predict clot lysis for different jet velocities and nozzle arrangements. Firstly, thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about 20% increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. Secondly, thrombolysis was modeled based on the enzyme transport and the fluid flow equations, and quasi steady numerical analysis was performed. Clot lysis efficiency was also increased as injection velocity increased.

• E2M - 전기 전자와 첨단 소재
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• 제10권4호
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• pp.334-341
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• 1997

Streaming electrification on insulating paper and pressboard under D.C. and A.C. electric field was investigated by using paper tubes and oil circulation apparatus. At first, flowing of static charges as measured with no electric field. As the temperature of oil increased, the measured current curve hows peak. As the velocity increased, it shows increasing exponential curve. Then, we applied A.C. and D.C. electric field on paper tube and the current from relaxation tank to earth was measured, which other factors such as temperature and velocity were varied like case of no electric field. The ions in oil carry the charges. So electric field makes asymmetry effect, and electrophoretic effect on ions in oil. We find that as the electric field intensity increased, the charges which were made by electric double layer were increased. The charge vs. velocity curve made peak point at a velocity.

• 설비공학논문집
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• 제15권9호
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• pp.727-732
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• 2003

In the present study, a PIV measurement and image processing technique were applied in order to investigate the flow characteristics in the gas injected liquid bath. The circulation of liquid was induced by upward bubble flow. Due to the centrifugal force, the flow was well developed near both wall sides than in the center of a bath. The vortex flow irregularly repeated generation and disappearance which helped to accelerate the mixing process. The bubble rise velocity in the bottom region was relatively lower than in the upper region because the energy generated by bubbles' behavior in the region near the nozzle was almost converted into kinetic energy But bubble rise velocity increases with the increase of the axial distance since kinetic energy of rising bubbles is added to buoyancy force. In conclusion, the flow increased bubble rise velocity and the flow of the bottom region became more active.

• 대한토목학회논문집
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• 제9권4호
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• pp.135-143
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• 1989

깊이 32m인 심층포기장치에서 기포(氣泡)의 형태(形態)와 거동(擧動)에 관하여 실험연구(實驗硏究)를 실시하였다. 연구(硏究) 결과(結果)에 의하면, 심층포기장치의 하향관(下向管)에 설치된 0.06cm의 단일(單一) 오리피스경(經)에서 발생되는 기포(氣泡)의 구체적(球體積) 상당경(相當經)(Dv)은 0.422-0.722cm이고 기포(氣泡)의 형상(形狀)은 타원체(橢圓體)이었다. 기포(氣泡) 체류량(滯留量) 기(氣)-액(液) 접촉면적(接觸面積)은 심층포기장치의 수심(水深) 증가(增加)할수록 감소(減少)하였으며, 기포(氣泡)의 하강속도(下降速度)는 액체(液體)의 순환(循環)유속보다 작고, 기포(氣泡)의 상승속도(上昇速度)는 액체(液體)의 순환(循環)유속보다 약간 크게 나타났다. 심층포기장치내의 기포분포(氣泡分布)는 거의 대수정정규분포(代數定定規分布)를 나타내고 있으며, 또한 기포(氣泡)의 갯수는 수심(水深)이 증가(增加)할수록 감소(減少)하며, 하향관(下向管)이 상향관(上向管)에 비하여 많았다.

• 순환기질환의공학회:학술대회논문집
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• 순환기질환의공학회 2006년도 제6회 학술대회
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• pp.34-35
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• 2006

• Korean Chemical Engineering Research
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• 제52권3호
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• pp.371-377
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• 2014

Characteristics of holdup and flow behavior of fluidized solid particles were investigated in a liquid-solid circulating fluidized bed ($0.102m{\times}3.5m$). Effects of liquid velocity ($U_L$), particle size ($d_P$) and solid circulation rate ($G_S$) on the solid holdup, overall particle rising velocity, slip velocity between liquid and particles and hydrodynamic energy dissipation rate in the riser were examined. The particle holdup increased with increasing $d_P$ or $G_S$ but decreased with increasing $U_L$. The overall particle rising velocity increased with increasing $U_L$ or $G_S$ but decreased with increasing $d_P$. The slip velocity increased with increasing $U_L$ or $d_P$ but did not change considerably with $G_S$. The energy dissipation rate, which was found to be closely related to the contacting frequency of micro eddies, increased with increasing $d_P$, $G_S$ or $U_L$. The solid particle holdup was well correlated with operating variables such as $U_L$, $d_P$ and $G_S$.

• 한국해양학회지:바다
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• 제12권3호
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• pp.219-224
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• 2007

광양만의 순환을 이해하기 위하여 2006년 봄철에 수심이 가장 깊은 두 지점을 선정하여 ADCP가 장착된 모니터링 부표 2대를 이용하여 유속관측을 하였다. 두 지점에서 공통적으로 북향류가 지배적인데, 이는 서쪽의 남향류를 동반하는 반시계 방향의 순환 이 있음을 뒷받침 하고 있다. 남쪽에서는 14 m 수심에서 유향이 반전되는 2층 구조가 뚜렷하며 저층의 북향류는 바닥에 가까운 36 m 수심까지 증가한다. 북쪽 지점에서는 북향류가 더욱 강해져서 북쪽의 단면적 감소에 따른 해류의 가속 효과가 있으며 상층부에서도 북향류가 우세하다. EOF 분석을 통한 연직구조에 있어서 첫 번째 모드는 북쪽 부표에서 전체 분산의 74%인데 비하여 남쪽 부표에서는 67%로 감소하고 상대적으로 2층 구조의 비중이 크다. 반시계 방향의 순환과 관련된 북향류의 전형적인 유속은 약 10 cm/s이다. 여기에 중첩되는 변동성으로서 국지적인 바람의 영향은 거의 받지 않는 반면에 동-서 방향의 바람에 의한 외해의 에크만 수송과 관련된 비국지적 영향은 주로 풍속이 강할 경우에 나타난다.

• 한국가시화정보학회지
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• 제12권1호
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• pp.18-24
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• 2014

The Korea Atomic Energy Research Institute (KAERI) has a scaled-down moderator test program to simulate the CANDU6 moderator circulation phenomena during steady state operation and accident conditions. In the present work a preliminary experiment using a 1/8 scaled-down moderator tank has been performed to identify the potential problems of the flow visualization and measurement in the scaled-down moderator test facility. With a transparent moderator tank model, a velocity field is measured with a Particle Image Velocimetry (PIV) technique under an isothermal state. The flow patterns from the inlet nozzles to the top region of the tank are investigated using PIV for a 1/8 scale moderator tank.

• 한국항공우주학회지
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• 제33권4호
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• pp.71-78
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• 2005

초임계 상태의 질소 유동 환경에서 헵탄 액적의 기화 특성을 수치적으로 연구하였다. 더불어 실기체 효과와 액적 내부 순환, 다양한 열역학적 물성치 및 고압 효과를 고려하였다. 또한 헵탄 액적 바로 근처에서의 저속 유동 문제를 풀기 위하여 예조건화 스킴을 적용한 시간 전진법을 수치 코드에 적용하였다. 주위 유동 속도와 주위 압력을 변화 시켜가면서 액적의 거동을 살펴보았다. 유동 속도 증가로 인한 레이놀즈수의 증가에 따라 액적의 변형이 활발히 이루어졌고, 동일한 레이놀즈수에 대해서는 압력이 높아질수록 액적의 변형이 약화되었다.