• Water Engineering Research
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• 제3권4호
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• pp.235-245
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• 2002

In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of flow of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in 0.3 $\leq$ x/$\l_q$ $\leq$ 17. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157~0.190.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.292-295
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• 2008

In a SCWR (SuperCritical pressure Water cooled Reactor), the coolant temperature initially at below the pseudo-critical temperature at the bottom of a reactor core increases as the coolant flows upward through the sub-channels of the fuel assemblies, and it finally becomes higher than the pseudo-critical temperature when it leaves the reactor core. At certain conditions, heat transfer deterioration occurs near the pseudo-critical temperature and it may cause a drastic rise of the fuel surface temperature resulting a fuel failure. Therefore, an accurate estimation of the heat transfer coefficient is very important for the thermal-hydraulic design of a reactor core. An experiment on heat transfer to the vertically upward flowing $CO_2$ at a supercritical pressure in a circular tube were performed at KAERI. The internal diameter of the test section is 6.32 mm, which corresponds to the hydraulic diameter of a sub-channel in the conceptional design proposed by KAERI. The test range of the mass flux is 285 to 1200 kg/m$^2$s and the maximum heat flux is 170 kW/m$^2$. The inlet pressure is maintained at 8.12 MPa, which is 1.1 times the critical pressure. A new correlation, which covers both the normal and deterioration heat transfer regimes was proposed and compared with the estimations by exiting correlations.

• 설비공학논문집
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• 제23권12호
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• pp.843-851
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• 2011

A two-dimensional immiscible water meniscus deformation phenomena on a moving tip in a channel has been investigated by using lattice Boltzmann method involving two-phase model. We studied the behavior of a water meniscus between the tip and a solid surface. The contact angles of the tip and a solid surface considered are in the range from $10^{\circ}$ to $170^{\circ}$. The velocity of the tip used in the study are 0.01, 0.001, and 0.0001. The shapes of tip considered are rectangular and circular. The behavior of water confined between the tip and a solid surface depends on the contact angles of the tip and a solid surface, and the tip velocity. When the tip is moving, we can observe the various behaviors of shear deformation of a water meniscus. As time goes on, the behavior of a water meniscus can be classified into three different patterns which are separated from the tip or adhered to the tip or sticked to a solid surface according to the contact angles and the tip velocity.

• 한국수자원학회논문집
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• 제48권11호
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• pp.891-903
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• 2015

본 연구는 식재된 개수로에서 흐름특성을 모의할 수 있는 수심 적분된 2차원 수치모형을 이용하여 원형 식생역 주변의 흐름을 수치모의하였다. 식생영향을 고려하기 위해 식생항력 항을 지배방정식에 추가하였고 다양한 식생체적비율(SVF) 조건에 따른 수치모의를 수행하였다. 흐름이 원형 식생역을 통과하고 하류에 저유속 구간인 후류영역(wake region)을 형성하며 식생체적비율이 0.08 이상이면 재순환 영역이 발생하였다. 재순환 발생위치는 식생체적비율이 감소하면 식생역에서 더욱 하류로 이동하였다. 후류영역을 지나 원형 식생역 양 측면에서 유발된 전단층들의 상호작용에 의해 von $K{\acute{a}}rm{\acute{a}}n$ 와열이 발생하였다. 원형 식생역 하류에서 발생하는 와류는 식생체적비율이 0.08 이상이 되면 나타나기 시작하였고 발생위치는 난류운동에너지가 최대값을 보이는 위치와 일치하였다. 최대 난류운동에너지는 식생체적비율이 감소하면 줄어드는 것으로 나타났고 최대값의 발생위치는 점점 하류로 이동하였다.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2007년도 추계학술발표회
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• pp.177-183
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• 2007

제어봉이 부착된 원관 후류의 유동특성을 관찰하기 위해 입자영상유속계(PIV)를 사용한 계측을 수행하였다. 실험은 소형회류수조에서 유업 유속을 0.lm/s, 0.2m/s, 0.4 m/s 로 하고, 원관(D=50mm) 에 제어봉이 없는 경우와 제어봉이 5mm, 10mm, 20mm 가 부착된 총 l27가지로 정하였고, 속도신호에 따른 주파수특성을 고찰하였다. 실험에서 제어봉의 영향으로 인하여 와류흘림 주파수가 작게 나타났으며, 유동제어의 지배변수로는 d/D와 레이놀즈수이며, 원관 후류의 주파수특성에 큰 영향을 미쳤다. 와류흘림 주파수는 제어봉이 0.20인 경우 가장 작게 나타났다.

• 한국안전학회지
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• 제28권5호
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• pp.54-60
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• 2013

In this study, a finite element model based on the SU/PG scheme was developed to solve shallow-water equations and the influences of parameters and internal boundary conditions on depth-averaged flow behavior were investigated. To analyze the effect of roughness coefficient and eddy viscosity on flow characteristics, the developed model was applied to rectangular meandering channel with two bends, and transverse velocities and water depth distributions were examined. As the roughness coefficient adjacent to wall increased, the velocities near the wall decreased, and the reduced velocities were compensated by the expanding mid-channel velocities. In addition, the flow characteristics around a circular cylinder were analyzed by varying the internal boundary conditions as free slip and no slip. The assignment of slip condition changed the velocity distribution on the cylinder surface and reduced the magnitude of the shear stress up to one third.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.710-716
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• 2006

Micro-PIV system with a high speed CCD camera is used to measure the flow field near the advancing meniscus of a water slug in microchannels. Image shifting technique combined with meniscus detecting technique is proposed to measure the relative velocity of the liquid near the meniscus in a moving reference frame. The proposed method is applied to an advancing front of a slug in microchannels with rectangular cross section. In the case of hydrophilic channel, strong flow from the center to the side wall along the meniscus occurs, while in the case of the hydrophobic channel, the fluid flows in the opposite direction. Further, the velocity near the side wall is higher than the center region velocity, exhibiting the characteristics of a strong shear-driven flow. This phenomenon is explained to be due to the existence of small gaps between the slug and the channel wall at each capillary corner so that the gas flows through the gaps inducing high shear on the slug surface. Simulation of the shape of a static droplet inside a cubic cell obtained by using the Surface Evolver program is supportive of the existence of the gap at the rectangular capillary corners. The flow fields in the circular capillary, in which no such gap exists, are also measured. The results show that a similar flow pattern to that of the hydrophilic rectangular capillary (i.e., center-to-wall flow) is always exhibited regardless of the wettability of the channel wall, which is also indicative of the validity of the above-mentioned assertion.

• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.1-10
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• 1999

In this study, a numerical analysis is made on the ice-formation for laminar water flow inside a stenotic tube. The study takes into account the interaction between the laminar flow and the stenotic port in the circular tube. The purpose of the present numerical investigation is to assess the effect of a stenotic shape on the instantaneous shape of the flow passage during freezing upstream/downstream of the stenotic channel. In the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the solid and liquid regions are resolved. In a channel flow between parallel plates, the agreement between the of predictions and the available experimental data is very good. Numerical analyses are performed for parametric variations of the position and heights of stenotic shape and flow rate. The results show that the stenotic shape has the great effect on the thickness of the solidification layer inside the tube. As the height of a stenosis grows and the length of a stenosis decreases, the ice layer thickness near the stenotic port is thinner, due to backward flow caused by the sudden expansion of a water tunnel. It is found that the flow passage has a slight uniform taper up to the stenotic channel, at which a sudden expansion is observed. It is also shown that the ice layer becomes more fat in accordance with its Reynolds number.

• 설비공학논문집
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• 제18권12호
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• pp.1007-1016
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• 2006

Although the advance in electronic technology enables a large number of circuity to be packed in a small volume, it is simultaneously required to remove the high heat load produced by them. In this study, the heat transfer and pressure drop characteristics of a mini-channel heat exchanger, which is designed for liquid cooling of electronic components, are investigated by varying operating conditions. Water and FC-72 were used as working fluids. The mini-channel heat exchanger was made with circular shape channels having din-meters of 2, 3, and 4 mm in regular intervals, and the channel length was 100 mm. The header and inlet guide pathway to provide uniform inflow were attached at the inlet of the test section. Copper block including the heaters was attached at the sidewall of the test section as a heat source, which provided the heat flux from 5 to $15W/cm^2$. The entrance effects enhanced the heat transfer coefficient in the mini-channel significantly. In addition, the single-phase pressure drop in the mini-channel was very similar to that predicted by the laminar flow correlation except that the transition Re decreased due to flow instability in the entrance region.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2009년도 학술발표회 초록집
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• pp.914-918
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• 2009

권 등(2008)은 수면보다 높은 정방형 다열기둥을 이용한 수리실험을 수행하여 수심과 이격거리에 따른 상당저항계수를 측정하였으며 이를 바탕으로 Manning 계수형태의 상당저항계수 이론식을 제안하였다. 본 연구는 수면보다 높은 원형 다열기둥을 이용한 수리실험을 수행하여 이격거리와 수심에 따른 상당저항계수를 측정하였다. 실험결과로부터 이격거리만의 함수로 가정한 항력상 호작용계수를 추정하여 이를 권 등(2008)의 이론식에 적용하여 실험결과와 비교하고 분석하였다. 정방형 다열기둥의 실험결과와 원형 다열기둥의 실험결과를 비교하여 흐름방향 이격거리가 큰 범위에서는 원형기둥의 저항계수가 정방형기둥의 저항계수보다 작게 측정되지만 흐름방향 이격거리가 감소할수록 원형기둥의 저항계수가 정방형기둥의 저항계수보다 증가하면서 원형기둥이 정방형 기둥보다 저항정도가 큰 상태가 되는 것을 알 수 있었다.