• Journal of Mechanical Science and Technology
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• 제15권6호
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• pp.764-775
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• 2001

Oscillartory thermocapillary flow of high Prandtl number fluids in the half-zone configuration is investigated. Based on experimental observations, one oscillation cycle consists of an active period where the surface flow is strong and the hot corner region is extended and a slow period where the opposite occurs. It is found that during oscillations the deformation of free surface plays an important role and a surface deformation parameter S correlates the experimental data well on the onset of oscillations. A scaling analysis is performed to analyze the basic steady flow in the parametric ranges of previous ground-based experiments and shows that the flow is viscous dominant and is mainly driven in the hot corner. The predicted scaling laws agree well with the numerical results. It is postulated that the oscillations are caused by a time lag between the surface and return flows. A deformation parameter S represents the response time of the return flow to the surface flow.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.93-96
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• 2006

The heat transfer enhancement by pulsatile flow in the plate heat exchanger has been investigated numerically in the present study. The numerical study was performed in the range of the mass flux from 0.04 to 0.12 kg/s. The results showed that the pulsatile flow produces resonating vortex shedding at the groove sharp edges and a strong transient vortex rotation within the grooved channels. As a result, the mixing between the trapped volume in the grooved cavity and the main stream was enhanced. Good agreements between the predictions and measured data are obtained in steady flow. And the heat transfer of pulsatile flow is about 2.4 times than steady flow when frequency is 10 Hz and the mass flux of cold side is 0.04 kg/s.

• 설비공학논문집
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• 제3권1호
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• pp.34-41
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• 1991

The effect of flow conditions on flow measurement is difficult to identify from the inherent characteristics of the flowmeters and flow standard system. A new experimental approach has been attempted to detect the turbine meter error due to inlet flow conditions. In this try not only the design of the turbine meter package but also the data analysis method was altered. It was found that k factor slope of the turbine meter responds to the change of flow conditions in the test line with higher sensitivity than the degree of the data scattering. The flow standard system of $0.1m^3/s$ was chosen for the investigation. The systematic and random error of the system were less than ${\pm}0.08%$ and ${\pm}0.13%$ respectively.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.43-48
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• 2003

When the Eulerian-Lagrangian method is used to analyze the particle laden two-phase flow, a large number of particles should be used to obtain statistically meaningful solutions. Then it takes too much time to track the particles and to average the particle properties in the numerical analysis of two-phase flow. The purpose of this paper is to reduce the computation time by means of a set of particle gird separate to the flow grid. Particle motion equation here is the simplified B-B-O equation, which is integrated to get the particle trajectories. Particle turbulent dispersion, wall collision, and wall roughness effects are considered but the two-way coupling effects between gas and particles are neglected. Particle laden 2-D channel flow is solved and it is shown that the computational efficiency is indeed improved by using the current method

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.280-288
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• 2000

In this study, flow factors are evaluated in terms of kurtosis using random rough surface generated numerically. As h/$\sigma$become large øx, øy, øfp approach to 1 and øs, øfs to 0 asymptotically regardless of kurtosis. øx, øy, øfp increase with increasing kurtosis in the mixed lubrication regime. øs, øfs is associated with an additional flow transport due to the combined effect of sliding and roughness. As h/$\sigma$ decreases øs, øfs increase up to a certain point, and then decrease toward zero. This behavior can be attributed to the increasing number of contacts in the mixed lubrication regime. øx in the presence of elastic deformation on the surface is larger than øx in the absence of it because local film thickness( h$\_$T/) increases by elastic deformation.

• 한국수자원학회논문집
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• 제37권5호
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• pp.375-386
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• 2004

갈수량은 수자원의 개발 및 관리에 매우 중요한 인자중의 하나이다. 신뢰성 높은 갈수량을 측정하기 위해 한국수자원공사는 2000년도에 용담댐 시험유역에 5피트 규격의 파샬플륨을 설치하였다. 파샬플륨은 유량측정을 하기 위해 독특한 모양을 가지고 있으며, 부정확한 유량관측을 유발하는 퇴사문제를 거의 해결한 시설물이다. 본 연구에서는 3차원 CFD (Computational Fluid Dynamics) 모형으로 5가지 수위에 대해서 완전월류(free flow)시 파샬플륨의 유동을 해석하였다. CFD모형에 의해 산정된 결과와 ISO에 제시된 유량공식, USBR에 제시된 유량공식 및 수위-유량관계식으로 산정한 유량을 비교하였다. 그 결과 ISO와 USBR의 공식에 의해 산정된 유량은 거의 동일했으나, 3차원 CFD모형에 의한 유량은 경험공식에 의한 유량보다 9%정도 크게 나타났고 수위-유량관계식에 의한 유량은 경험공식에 의한 유량보다 16%정도 작게 나타났다.

• 한국진공학회지
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• 제22권3호
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• pp.111-118
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• 2013

대기압 플라즈마 제트 장치의 유량 변화에 대한 플라즈마 방전 특성을 실험적으로 조사하고 이를 유체역학적으로 해석하였다. 유리관에 주입되는 아르곤 기체의 유량 변화에 대한 레이놀즈 수(Re)로 결정되는 기체 흐름의 형태 변화와 베르누이 정리에 의한 압력 변화가 플라즈마 발생에 영향을 준다. 유리관 내부에 발생하는 플라즈마의 길이 변화의 실험을 통하여, 아르곤 기체에 대한 레이놀즈 수가 Re<2,000이면 층류이고, Re>4,000이면 난류가 형성된다. 이는 일반 유체에서 알려진 결과와 일치한다. 층류에서 유량의 증가로 플라즈마의 길이가 증가한다. 층류와 난류의 전환 영역에서 플라즈마의 길이는 줄어든다. 난류 영역에서는 방전 기체의 흐름이 불규칙함으로서 방전 경로가 흐트러져 플라즈마 칼럼의 길이가 매우 짧아지고 급기야 플라즈마가 소멸된다. 층류에서 주입 유량의 증가로 유리관 내의 유속이 증가하면, 베르누이 정리에 의하여 유리관 내부의 압력이 낮아진다. 관내의 압력이 낮아지면, 파센 법칙에 의하여 관내의 전기장의 세기가 증가하여 방전 전압이 낮아진다. 따라서 주입 유량이 증가하면, 동일한 구동 전압에서 유리관에 발생하는 플라즈마의 길이는 길어진다. 층류의 방전은 유리관 밖에서도 층류의 흐름이 일정 길이로 유지되므로 시료 표면에 조사되는 플라즈마 빔의 직경은 유리관의 직경 이하로 유지된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.214-219
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• 2004

The HANARO, a multi-purpose research reactor of 30 MWth, open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. The HANARO is composed of inlet plenum, grid plate, core channel with flow tubes and chimney. The reactor core channel is located at about twelve m (12 m) depth of the reactor pool and cold by the upward flow that the coolant enters the lower inlet of the plenum, rises up through the grid plate and the core channel and exit through the outlet of chimney. A guide tube is extended from the reactor core to the top of the reactor chimney for easily un/loading a target under the reactor normal operation. But active coolant through the core can be Quickly raised up to the top of the chimney through the guide tube by jet flow. This paper is described an analytical analysis to study the flow behavior through the guide tube under reactor normal operation and unloading the target. As results, it was conformed through the analysis results that the flow rate, about fourteen kilogram per second (14 kg/s) suppressed the guide tube jet and met the design cooling flow rate in a circular flow tube, and that the fission moly target cooling flow rate met the minimum flow rate to cool the target.

• 에너지공학
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• 제23권4호
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• pp.73-88
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• 2014

Various studies on the critical flow models for sub-cooled and/or saturated water were reviewed, especially on Fauske, Moody, and Henry for basic theoretical models; Zaloudek for insight into physical phenomena for a critical flow in an orifice type flow path; Sozzi & Sutherland for a critical flow test of saturated and sub-cooled water at high pressure for orifice and nozzles; and a Marviken test on a full-scale critical flow test. In addition, critical flow tests of sub-cooled water for the break simulators in integral effect test (IET) facilities were also investigated, and a hybrid concept using Moody's and Fauske's models was considered by the authors. In the comparison of the models for the selected test data, discussions of the effect of the diameters, predictions of the critical flow models, and design aspects of break simulator for SBLOCA scenarios in the IET facilities were presented. In the effect of diameter on the critical flow rate with respect to all dimensional scales, it was concluded that the effect of diameter was found irrespective of diameter sizes. In addition, the diameter effect on slip ratio affecting the critical flow rate was suggested. From a comparison of the critical flow models and selected test data, the Henry-Fauske model of the MARS-KS code was found to be the best model predicting the critical flow rate for the selected test data under study.

• 대한기계학회논문집B
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• 제22권7호
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• pp.927-936
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• 1998

In the fully developed pipe flow, when jet is injected in cross to the flow there are complex transition flows caused by interaction of the cross flow and jet. These interactions are studied by means of the flow visualization methods and frequency analysis using a hot-wire anemometer. The velocity range of cross flow of the pipe is 0.3 m/s ~ 1.2 m/s and the corresponding Reynolds number, R$\sub$p/, based on the pipe diameter is 2.25 * 10$\^$3/ ~ 9.02 * 10$\^$3/. The velocity ratio (R), jet velocity/cross flow velocity, is chosen from 2 to 10. A circular cylinder is placed in the pipe instead of jet to observe the vortex shedding from the solid body. To compare the jet and circular cylinder flow, the vortical structure is analyzed in both cases and the structure of vortices and the origin of its formation are investigated, especially. The vortex shedding of the dominant coherent structure is compared between the jet flow and the circular cylinder flow. In the case of the jet flow, the Strouhal numbers are different depending on the existence of the upright vortex as well as the velocity ratio (R).