• 한국방재학회 논문집
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• 제9권4호
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• pp.107-113
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• 2009

본 연구는 점착성 미립자의 침전률에 대한 플록의 영향에 관한 것이다. 연구 진행시 플록 밀도와 입경변화의 영향도 고려하였다. 플록입자의 침전속도는 정지수면에서 측정되었다. 플록 입경과 밀도는 수정된 Stokes방정식에 유체의 밀도, 입자의 밀도, 점성계수 및 측정된 침전속도와 입경과의 관계식으로부터 얻은 플록 차원을 이용하여 분석되었다. 석영과 알루미나의 플록지름은 초기농도가 증가함에 따라 증가되었으며, 염도농도의 증가에 따른 석영의 플록된 입경은 $0.8{\sim}10$ ${\mu}m$이다. 플록밀도는 입경이 증가함에 따라 감소하였다. 플록 침전속도와 입경의 관계는 로그표위에 직선식으로 표현된다. 플록 차원($=n_f$)은 초기농도가 증가할 경우 2.65이며, 염도가 증가할 때 2.93이다. 침전속도를 예측하기 위한 비례상수(n)는 제시되었으며, 그 범위는 $1{\sim}1.93$이다.

• 폴리머
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• 제26권3호
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• pp.316-325
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• 2002

비상용성 LDPE/PS 블렌드계 (86.5/l3.5 vol%)를 내부 혼합기를 사용하여 만들었고 레오미터 (rheometer)와 scanning electron microscope (SEM)으로 분산상인 droplet들의 변형과 합체 (coalescence)거동에 대하여 살펴보았다. 혼합 초기에 일정한 크기의 droplet들이 서로 뭉쳐졌고 큰 변형 하에서 실모양 (thread-like)을 나타냈다. 본 실험에 사용한 LDPE/PS 블렌드계의 critical capillary number를 De Bruijn의 실험식으로 계산한 결과 0.96이었고 local capillary number는 3.867이었다. 또한 블렌드 시편을 $200^{\circ}C$에서 다양한 시간으로 서냉한 후 서냉 시간에 따른 형태의 변화를 관찰하였다. $200^{\circ}C$에서 ${\gamma}$=1789일 때 최대 크기의 droplet이 관찰되었고 특히 서냉 시간이 15분일 때 형태의 파괴 (break-up)가 일어났다. Droplet의 합체에 결정적인 영향을 미치는 것은 기질의 점도이다.

• 에너지공학
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• 제2권3호
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• pp.268-275
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• 1993

수치해석 방법에 의해 큐백시의 스토커 소각로 유동장을 분석하였다. 수치모사의 변수는 큐백시의 스토커 소각로를 중심으로 한 5가지 내부 형상, 1차공기 속도, 2차공기 속도 및 주입각, 출구면적을 고려하였다. 검사체적에 기초한 Patankar의 유한차분 방법을 사용한 본 논문에서는 power-law scheme과 SIMPLEC 알고리즘을 사용했으며 난류 유동은 표준 k-e 모델을 이용했다. 소각로 유동장 분석을 위해서 재순환 영역의 크기, 난류 점성계수 및 이차공기의 질량분율 분포, 압력강하를 계산했다. 계산 결과는 물리적 의미에 잘 맞게 나타났으며, 큐백시의 스토커 소각로가 다른 내부 형상의 소각로에 비해 상부에 강한 난류를 가진 재순환 영역을 형성하였다.

• 한국산학기술학회논문지
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• 제14권8호
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• pp.3611-3616
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• 2013

MR 유체의 물리특성은 자기장에 의해 영향을 받는다. 본 연구에서는 MR 유체의 자기장에 의한 유동변화를 실험적으로 조사하고자, MR 유체의 밀도와 점도를 변경하면서 자기장에 의한 유동 가시화와 전단응력 변화를 측정하였다. 이를 위해 밀도 3종, 점도 3종에 대한 MR 유체를 제조하였고 MR 유체 가시화 실험장치를 제작하였다. 자기장이 인가되면, MR 유체 파우더의 유동흐름은 띠를 형성하면서 자기장이 인가되지 않은 경우와는 다른 유동흐름을 보여주었다. 또한 전단응력은 인가전류와 밀도가 높을수록 더 크게 증가하였으며, 인가전류 2.0A에서 MR 유체의 밀도가 $1300kg/m^3$에서 $1700kg/m^3$ 로 변하면 전단응력은 33% 정도 증가하였다.

• 한국추진공학회지
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• 제21권5호
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• pp.1-9
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• 2017

초임계 환경에서 와류형 분사기의 극저온 질소 분무 동적 특성 분석을 위하여 3차원 LES 난류 모델을 적용하였다. 초임계 상태에서 질소의 상태량들을 정확하게 예측하기 위해 SRK 실기체 상태방정식을 사용하였고, 점성계수와 열전도도는 Chung의 고압 상태 혼합물에 대한 방정식, 그리고 확산 계수는 Fuller의 이론에 Takahashi의 보정식을 적용하였다. 질소 분무 결과, 분사기 내, 외부에서 유동장과 음향장 사이의 상호작용으로 복잡한 유동구조가 형성된다. 복잡한 유동 현상을 분석하기 위해 FFT, POD 그리고 DMD 기법을 적용하여 해석을 수행하였다. FFT 해석을 수행하여 분사기 내, 외부에서 나타나는 특정 주파수를 파악하였으며, POD와 DMD를 통해 각 주파수가 어떠한 유동 구조를 갖는지에 대한 연구를 수행하였다. 또한, DMD를 통해 각 주파수의 감쇠 계수를 파악하여 이를 실험 결과와 비교하였다.

• 한국분무공학회지
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• 제13권4호
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• pp.212-219
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• 2008

To develop the twin-fluid atomizer having the excellent performance of painting, the spray characteristics of how a wide area can be painted efficiently by one time spraying were studied in this paper. Spray phenomena are affected by the many factors determining the spray field such as the spraying pressure of gas, the spraying pressure and viscosity of liquid paints, the opening duration of needle valve, the design dimension of nozzle, and so on. As the results of experiments, these factors affecting on spray characteristics were suggested as followings; 1) The optimum spraying pressure of gas was $0.015{\sim}0.02\;kPa$, and the appropriate spraying pressure of liquid paint was 0.01kPa, In these situations, the setting up pressures must be compensated as much as the losing amount of pressure because a decompression occurred when operating valves. 2) The duration of opening the needle valve must be sustained for $1{\sim}2$ seconds to inject gas after spraying the liquid paint. This operating of the needle valve was necessary to avoid the affect on the changing of liquid column length, and to prevent the droplet deposit at the initial time of spraying. 3) The spray tip penetration was gained form the experimental equation, and the effective spraying angle was $85^{\circ}{\pm}5^{\circ}$ just at he appropriate spraying pressure of gas. The distribution of the area sprayed had the variation in $350{\pm}50\;mm$ because of the spraying pressure of gas, the its distance from the spray tip, and the lift of the needle valve.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.327-330
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• 2006

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at $20^{\circ}C$. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard $k-{\omega}$ high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various $\eta$, and the traveling distance for wavy vortex have the critical traveling distance for each case.

• Advances in concrete construction
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• 제9권6호
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• pp.547-556
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• 2020

This study aimed to develop reference materials (RMs) that are chemically stable and can simulate the flow characteristics of cement paste. To this end, the candidate components of RMs were selected considering the currently required properties of RMs. Limestone, slag, silica, and kaolin were selected as substitutes for cement, while glycerol and corn syrup were selected as matrix fluids. Moreover, distilled water was used for mixing. To select the combinations of materials that meet all the required properties of RMs, flow characteristics were first analyzed. The results revealed that silica and kaolin exhibited bilateral nonlinearity. When an analysis was conducted over time, slag exhibited chemical reactions, including strength development. Moreover, fungi were observed in all mixtures with corn syrup. On the other hand, the combination of limestone, glycerol, and water exhibited a performance that met all the required properties of RMs. Thus, limestone, glycerol, and water were selected as the components of the RMs. When the influence of each component of the RMs on flow characteristics was analyzed, it was found that limestone affects the yield value, while the ratio of water and glycerol affects the plastic viscosity. Based on this, it was possible to select the mixing ratios for the RMs that can simulate the flow characteristics of cement paste under each mixing ratio. This relationship was established as an equation, which was verified under various mixing ratios. Finally, when the flow characteristics were analyzed under various temperature conditions, cement paste and the RMs exhibited similar tendencies in terms of flow characteristics. This indicated that the combinations of the selected materials could be used as RMs that can simulate the flow characteristics of cement paste with constant quality under various mixing ratio conditions and construction environment conditions.

• 한국수산과학회지
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• 제53권5호
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• pp.681-687
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• 2020

Physicochemical properties of fucoidan and alginate extracted from Sargassium horneri were investigated. The alginates were extracted and purified via three different routes (CaCl₂, HCl and ethanol routes), and their rheological properties at various concentrations and temperatures were determined. The yield of fucoidan was 3.08%, and it was mainly composed of fucose and galactose. Fourier-transform infrared spectrum of fucoidan showed strong absorption band at 1,254 and 827 cm^-1 corresponding to the sulfate group. Flow behavior of the alginate solution was characterized using the power-law model. The consistency index increased with increasing concentrations. The sodium alginate solution (1.5%) exhibited Newtonian behavior when extracted via the CaCl₂ and HCl routes, while it exhibited pseudoplastic behavior when extracted via the ethanol route. The effect of temperature on the flow behavior was investigated in terms of the activation energy (E_a), which was obtained using the Arrhenius equation. The E_a value corresponding to the alginate solution decreased with increasing shear rates. The E_a values corresponding to the alginate solutions purified via the CaCl₂, HCl, and ethanol routes were 13.54-18.64 kJ/mol, 13.42-19.21 kJ/mol, and 9.51-10.67 kJ/mol, respectively. The low E_a values corresponding to the solutions extracted via the ethanol route suggest that the flow behavior does not depend significantly on temperature.

• 한국전산유체공학회지
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• 제18권4호
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• pp.25-34
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• 2013

A numerical study of a laminar natural convection of the CuO-water nanofluid in a square cavity using the Buongiorno's nonhomogeneous model is presented. All the governing equations including the volume fraction equation are discretized on a cell-centered, non-uniform grid employing the finite-volume method with a primitive variable formulation. Calculations are performed over a range of Rayleigh numbers and volume fractions of the nanopartile. From the computed results, it is shown that both the homogeneous and nonhomogeneous models predict the deterioration of the natural convection heat transfer well with an increase of the volume fraction of nanoparticle at the same Rayleigh number, which was observed in the previous experimental studies. It is also shown that the differences in the computed results of the average Nusselt number at the wall between the homogeneous and nonhomogeneous models are very small, and this indicates that the slip mechanism of the Brown diffusion and thermophoresis effects are negligible in the laminar natural convection of the nanofluid. The degradation of the heat transfer with an increase of the volume fraction of the nanoparticle in the natural convection of nanofluid is due to the increase of the viscosity and the decrease of the thermal expansion coefficient and the specific heat. It is clarified in the present study that the previous controversies between the numerical and experimental studies are owing to the different definitions of the Nusselt number.