• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4322-4328
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• 2022

The two-fluid model is widely used to describe two-phase flows in complex systems such as nuclear reactors. Although the two-phase flow was successfully simulated, the standard two-fluid model suffers from an ill-posed nature. There are several remedies for the ill-posedness of the one-dimensional (1D) two-fluid model; among those, artificial viscosity is the focus of this study. Some previous works added artificial diffusion terms to both mass and momentum equations to render the two-fluid model well-posed and demonstrated that this method provided a numerically converging model. However, they did not consider mass conservation, which is crucial for analyzing a closed reactor system. In fact, the total mass is not conserved in the previous models. This study improves the artificial viscosity model such that the 1D incompressible two-fluid model is well-posed, and the total mass is conserved. The water faucet and Kelvin-Helmholtz instability flows were simulated to test the effect of the proposed artificial viscosity model. The results indicate that the proposed artificial viscosity model effectively remedies the ill-posedness of the two-fluid model while maintaining a negligible total mass error.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.395-402
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• 2002

This paper shows how to formulate the transient analysis of 2-dimensional Hagen-Poiseuille flow using smoothed particle hydrodynamics (SPH). Treatments of viscosity, particle approximation and boundary conditions are explained. Numerical tests are calculated to examine effects caused by the number of particles, the number of particles per smoothing length, artificial viscosity and time increments for 2-dimensional Hagen-Poiseuille flow. Artificial viscosity for reducing the numerical instability directly affects the velocity of the flow, though effects of the other parameters do not produce as much effect as artificial viscosity. Numerical solutions using SPH show close agreement with the exact ones for the model flow, but SPH parameter must be chosen carefully Numerical solutions indicate that SPH is also an effective method for the analysis of 2-dimensional Hagen-Poiseuille flow.

• 한국세라믹학회지
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• 제43권4호
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• pp.203-206
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• 2006

Polyacrylonitrile (PAN) nanofibers, which are pH-sensitive and exhibit soft actuation as a linear actuator and artificial muscles, were prepared by electrospinning to investigate the effect of viscosity on the morphology of PAN fibers. Experimental results revealed that higher viscosity is critical for the formation of unbeaded nanofibers because surface tension is almost constant throughout the experiment. Uniform, smooth, and continuous fibers with diameters of about 700 nm were achieved for the 10 wt% PAN fibers at a flow rate of 0.5 mL/h and an electric field of 0.875 kV/cm.

• Journal of Oral Medicine and Pain
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• 제32권4호
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• pp.365-373
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• 2007

구강건조증 환자에서 자주 발생하는 구강 연조직과 경조직의 손상은 구강건조증 환자의 삶의 질에 심각한 문제를 일으킨다. 타액선의 기능을 완전히 상실한 구강건조증 환자의 경우 인공타액은 유일한 처치법임에도 불구하고, 현재 통용되고 있는 인공타액은 환자들의 기대치에 비해 많이 부족한 실정이다. 본 연구는 CMC 용액과 인공타액의 점도와 습윤성을 비교함으로써 향후 이상적인 인공타액의 개발에 필요한 정보를 얻고자 시행되었다. CMC를 타액모방완충용액(simulated salivary buffer, SSB)과 증류수에 용해시켜 동물 mucin 용액을 완성한 후, 이를 인체 전타액, 인체 개별 타액선 타액, 그리고 CMC를 주성분으로 하는 인공타액인 Salivart 및 Moi-Stir와 비교 분석하였다. 점도는 cone-and-plate digital viscometer로 검체 당 6개의 전단율에서 측정하였고, 습윤성은 아크릴릭 레진과 Co-Cr alloy 표면 위에서의 접촉각 측정을 통해 평가하여 다음과 같은 결론을 얻었다. 1. CMC 용액의 점도는 CMC 농도에 비례하여 증가하였으며, 0.5% CMC 용액의 점도는 비자극성 전타액의 점도와 유사하였다. 반면에 CMC 용액의 접촉각은 점도와는 반대로 CMC 농도를 증가시킴에 따라 감소하였다. 2. 인체 타액의 점도는 전단율 증가에 따라 감소하는 non-Newtonian fluid의 특성을 나타내었다. 다양한 전단율에서의 평균 점도는 자극성 이하선 타액, 자극성 전타액, 비자극성 전타액, 자극성 악하선-설하선 타액의 순으로 증가하였다. 3. 인체 타액의 접촉각은 점도와는 반대로 자극성 이하선 타액, 자극성 전타액, 비자극성 전타액, 자극성 악하선-설하선 타액의 순으로 감소하였다. 4. 타액모방완충용액에 용해시킨 CMC를 가열하여 변성시킨 경우 점도가 감소하였다 (P < 0.01, 전단율 $90s^{-1}$). 5. 인체 타액의 아크릴릭 레진 표면에서의 접촉각은 인체 타액의 Co-Cr alloy 표면에서의 접촉각보다 유의하게 작은 것으로 나타났다 (P < 0.01). 6. 인체 타액의 아크릴릭 레진 표면에서의 접촉각은 CMC 용액의 아크릴릭 레진 표면에서의 접촉각보다 유의하게 작은 것으로 나타났다 (P < 0.01). 이번 연구에서 CMC 용액의 유동학적 성질을 객관적으로 확인할 수 있었으며, 이상의 결과를 종합하여 보면 CMC는 향후 효과적인 인공타액의 개발에 있어서도 중요한 역할을 수행 할 것으로 기대된다.

• International Journal of Fluid Machinery and Systems
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• 제6권1호
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• pp.1-10
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• 2013

Jet pump is one type of artificial lifts and is used when depth and deviation of producing wells increases and pressure depletion occurs. In the present study, numerical analysis has been carried out to analyze the flow behavior and find the performance of the jet pump. Reynolds-averaged Navier Stokes equations were solved and k-${\varepsilon}$ turbulence model was used for simulations. Water and light oil as primary fluids were used to pump water, light oil and heavy oil. The ratios of area and length to diameter of the mixing tube were considered as design parameters. The pump efficiency was considered to maximize for the downhole conditions. It was found that the increase in viscosity and density of the secondary fluid reduced efficiency of the system. Water as primary fluid produced better efficiency than the light oil. It was also found that the longer throat length increased efficiency upto 40% if light oil was used as primary fluid and secondary fluid viscosity was 350 cSt.

• Journal of Mechanical Science and Technology
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• 제16권4호
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• pp.522-531
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• 2002

In order to study the thermal-hydraulic behavior of the cable-in-conduit-conductor (CICC), a numerical model has been developed. In the model, the high heat transfer approximation between superconducting strands and supercritical helium is adopted. The strong coupling of heat transfer at the front of normal zone generates a contact discontinuity in temperature and density. In order to obtain the converged numerical solutions, a moving mesh method is used to capture the contact discontinuity in the short front region of the normal zone. The coupled equation is solved using the finite element method with the artificial viscosity term. Details of the numerical implementation are discussed and the validation of the code is performed for comparison of the results with thse of GANDALF and QSAIT.

• 문화기술의 융합
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• 제9권4호
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• pp.331-335
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• 2023

혈액의 점도가 높아질수록 혈액은 더 끈적하고 흐름이 어려워지므로 혈전의 발생 가능성이 높아져 허혈성 뇌경색의 발생 확률이 증가한다. 혈액 점도 측정은 최근 순환기계 질환의 예방을 위하여 그 중요성이 강조되고 있으며 혈액의 점도를 쉽고 정확하게 측정할 수 있는 점도계의 필요성이 대두되고 있다. 본 연구에서는 평행판 점도계 ARS-Medi에 의한 점도표준액과 인공혈액의 측정값들을 국제적으로 정확성과 신뢰성을 인정받는 TA instrument의 Ares-G2로 측정한 값들과 비교하였다.. 뉴턴성 용액인 N44 표준용액의 점도는 모든 전단율에서 두 기기 간에 거의 완벽하게 일치하였다, 비뉴턴성 용액인 인공혈액의 경우 가장 낮은 전단율인 1 rad/s 에서는 약 10%의 차이를 보였으나, 임상적으로 유의한 전단율인 10 rad/s 이상에서는 두 기기간의 측정값이 오차범위 내에서 모두 일치하였다. 우리는 새로 개발한 혈액 전용 평행판형 점도계 ARS-Medi가 1회용 평행판을 사용하므로 혈액 점도 측정의 편의성과 위생성이 향상되어 임상에 매우 유용할 것으로 기대한다.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1470-1476
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• 2002

The goal of this work is to design and build an implantable artificial lung that can be inserted as a whole into a large vein in the body with the least effect on cardiovascular hemodynamics. The experimental results demonstrate that the pressure drop is not entirely related to viscosity effects. The friction factor decreases with an increase in the number of tied-hollow fibers at a constant Reynolds number A uniform flow pattern without stagnation is observed at all numbers of tied hollow fibers tested. The tied hollow fiber module, built in this study with 3 cm of outer diameter of module. 380 m of outer diameter of tied hollow fiber, and 700 number of tied hollow fiber with length of 60 cm, which shows a pressure drop of 13-16 mmHg, satisfies the required pressure drop qualifying 15 mmHg as an intravascular artificial lung.

• 대한조선학회논문집
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• 제31권1호
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• pp.63-70
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• 1994

항공유체의 계산에 주로 사용되는 음해법의 하나인 IAF(Implicit Approximate Factorization)법을 이용해 3차원 Wigley 선형 주위의 자유표면파 및 점성유동장을 해석하였다. IAF 법을 사용함으로서 기존 Euler 양해법의 계산 시간을 50% 이상 감소시키는데 성공하였다. 수치기법으로 국부선형화와 Euler 음해법을 사용하였으며 artificial viscosity의 생성을 위한 압력 구배항은 사용하지 않았다. 수치 계산은 Reynolds 수 $10^6$. Froude 수 0.25, 0.289 및 0.316에 대하여 수행하였고 난류 모형으로는 Baldwin-Lomax 모형을 사용하였으며 주요 계산 결과로는 자유표면화 형상 및 속도분포 등이었다. 본 연구에서는 그 중에서 자유표면파 형상에 대한 계산 결과를 실험값 및 Euler 양해법을 사용한 결과와 각각 비교 검토하였다.

• 펄프종이기술
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• 제45권5호
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• pp.49-55
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• 2013

To explore the paper materials for restoration of the Annals of the Joseon Dyansty, durability of the three type of the traditional Korean Papers were estimated in this study, through moist heat artificial aging test. Three types(D, F, and G) which showed the best preservation performance in dry heat and UV treatment in the previous study were selected and artificial accelerated aging treatment with moist-heat process was conducted; the viscosity change rate was D>G>F; folding endurance G>D>F; $L^*$ value F>D>G; $a^*$ and $b^*$ change rate D>G>F; brightness decrease rate D>G>F, suggesting paper F showed the least change rate in physical/optical properties. Also the CLSM image observation showed fair coherence among fibers and confirmed paper mulberry. And in FDI extraction from each sample, paper F showed the highest value. Overall, paper F (traditional glossy paper) showed the highest stability against thermal treatment. It confirms that paper F is suitable as restoration paper for tributary remains including the annals of the Joseon Dynasty for its steady strength/viscosity decrease rate and color change rate.