• Nuclear Engineering and Technology
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• 제45권5호
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• pp.613-624
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• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

• 한국해양학회지
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• 제30권1호
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• pp.57-63
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• 1995

$\beta$-효과를 포함한 원통 용기 내의 상하층유체의 하충운동을 하충수와 같은 밀도를 갖는 외부유체를 주입하여 야기시키고 상층수와 같은 유체를 유입 및 유출시켜 지형류 조절에 의한 경계면의 변형 및 이에 따른 상층운동 특성을 실험적으로 관찰하였다. 특 히 유입-유출 위치를 변경시키고 동시에 유입과 유출양을 다르게 하여 상층수에 해상 풍의 효과를 첨가하였다. 실험의 목적은 극전선 형성과 관련하여 유입-유출 경로(대만 난류의 유입-쓰가루, 쏘야 유출)를 결정짓는 외부 인자를 파악하고자 함이다. 유입, 유출양이 같은 경우 유입수의 경로는 서안에 따라 북상하다가 이안후 위도에 평행하게 유출된 반면 상층수에 해상풍의 영향을 주었을시 서안 경계류의 분기(negative curl of wind stress 효과시), 남향의 서안 경계류에 의한 유입수의 내부로 침투(positive curl of wind stress 효과시) 등의 현상을 보여준다. 한편 유입-유출의 위치를 변경 시켜 유입수의 위치를 서안경계에 두었을 시 유입수의 경로가 경계면의 지형류 조절에 의한 서안에 근접하게 북상후 유출 (negative curl), 동안에 근접하게 북상후 유출 (positive curl)의 특성을 보여준다. 북부의 반시계방향의 흐름이 유입수의 북방 한계 를 결정짓는 역할을 하고 있음도 관찰되었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1476-1477
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• 2008

This paper reports on a flexible flap valve actuated by electromagnetic force under a constant pressure source. The flexible flap valve consists of the three main components: a flexible flap with a steel disk embedded in PDMS, an electromagnetic actuator and two glass plates with inlet and outlet. Sealing lip structures for improving the valve characteristics are added on the outlet of the bottom glass substrate. The flap valve is fabricated by the spin-coating process, the EDM process, SU-8 mold process and oxygen plasma treatment. The dimension of an assembled flap valve is $12mm{\times}20mm{\times}28mm$. The stroke volume of the flap valve is measured for various pressures and open times. When the input voltage of 30 V is applied for 0.33 s, the minimum stroke volume of the flap valve is 70 ${\mu}L$ at 50 kPa.

• 설비공학논문집
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• 제29권8호
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• pp.401-407
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• 2017

The effect of different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on local heat transfer distributions and pressure drops in a divergent channel with $30^{\circ}$ inclined ribs on one wall or two walls was investigated for Reynolds numbers from 22,000 to 75,000. Top and bottom walls were insulated; two side walls were uniformly heated in the divergent channel. Heated walls were composed of 10 isolated coper sections and length-to-outlet hydraulic diameter ratio of 10. Rib height-to-outlet hydraulic diameter ratio was 0.1, and rib pitch-to-height ratio equaled 10. Results revealed that V-shaped continuous rib (case A) produced approximately 1.4 times higher average Nussselt number than in the parallel broken rib (case B), and V-shaped broken rib (case C) in the channel with two ribbed walls at Re = 54,000.

• 한국농공학회논문집
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• 제60권3호
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• pp.71-81
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• 2018

$CO_2$ concentration has a significant effect on quality of cold-stored apples. High indoor $CO_2$ concentrations above 10,000 ppm cause the browning of apples and result in economic loss for farmers. The purpose of this study is to evaluate $CO_2$ concentrations and their distribution in a controlled atmosphere (CA) storage and provide better structural designs to improve the $CO_2$ environment using computational fluid dynamics (CFD) simulations. The CFD model was developed for a real CA storage for apples and applied to investigate the effect of changing the inlet and outlet locations and the aspect ratio of the floor of the CA storage on the spatial distributions of $CO_2$ concentration and the browning of the apples. The lowest $CO_2$ concentrations in existing CA storage with a high aspect ratio of the floor were achieved from the combination of the inlet located at the top of the right side and the outlet located at the bottom of the left side. In modified CA storage with a low aspect ratio, the combination of the inlet and outlet located at top and bottom of left side respectively achieved the lowest $CO_2$ concentrations. The proposed case enhanced the storage performance by reducing total browned apples by 3.6% in storage duration of 210 days. This study is expected to reduce the browning damages of apples in CA storage, and thus greatly prevent economic losses.

• 센서학회지
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• 제20권5호
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• pp.357-362
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• 2011

This paper demonstrates a novel electrodynamic technique to remove particles from the wall of microchannels. Dielectrohporesis(DEP) is generated by applying alternating electric potentials to the interdigitated electrodes integrated at the bottom of the micro-channel. The proposed technique is applied to a general microfluidic channel as a feasibility test. To examine the wall loss reduction efficiency, 10 ${\mu}m$ diameter Polystyrene latexes(PSL) were supplied to the inlet of the device. Then, the concentration of collected particles through devices was measured. In the experiment for 10 ${\mu}m$ diameter PSL particles, the concentration of the injected particles was $174.25{\times}10^4$ particles/ml. However, the concentration of collected particles at the outlet was $52.25{\times}10^4$ particles/ml. Only 30 % of particles had arrived at the outlet and 70 % of particles had adhered to the wall of the microfluidic channel. By applying alternating electric potentials from 0 to 20 $V_{pp}$ at 3 MHz, the concentration of injected particles was 135.00${\times}10^4$ particles/ml, the concentration of collected particles was increased as $105.25{\times}10^4$ particles/ml at 20 $V_{pp}$ at the outlet. When the electric potential was 20 $V_{pp}$, the particle loss was decreased by 39 % (initial loss: 70 %, loss at 20 Vpp: 31 %) with 10 ${\mu}m$ particle. The particle loss was decreased along to the incensement of electric potentials and the enlargement of the diameter of particles. According to these measured results, it was confirmed that the proposal of using DEP technique could be a good candidate for particle loss reduction in micro-particle processing chip application. Moreover, it is expected that the proposed technique could enhance performance of microfluidic and biochip devices.

• 한국수자원학회논문집
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• 제30권5호
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• pp.467-475
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• 1997

본 연구에서는 실험개수로에 온수방류용 방류규가 있는 방파제의 모형을 설피하여 바닥\ulcorner의 유속분포를 측정하였다. 또한 3차원의 모형인 Fluent 모형을 이용하여 방파제의 방류구로부터 배출된 바닥젵의 유속구조를 수치모의하여 실험결과와 비교.검증하였으며 흐름특성을 규명하였다. 바닥젵은 자유젵에 비하여 흐름의 확립구간이 짧았으며, 종방향거리에 대한 젵 중앙유속의 감쇠율이 자유젵보다 크게 나타나고 있음이 밝혀졌다. 단순젵과 부력젵의 젵 중앙선에서의 종방향유속을 비교한 결과, 방류구 근처에서는 부력\ulcorner의 유속이 크게 발생하나 x/lQ가 15보다 큰 구간에는 도리어 작게 된다. 종방향유속의 연직분포를 비교한 결고, 방류구로부터 멀어질수록 저층에서는 단순젵의 유속이 크게 나타나며 상충에서는 단순젵의 부의 유속이 크게 나타나고 있음이 밝혀졌다. 또한 부력젵의 경우 자유수면에서의 유속의 분리가 단순젵보다 방류구로부터 가까운 거리에서 발생한다. 부력젵의 연직방향으로의 폭은 단순젵의 폭보다 빨리 확장된다.

• Tribology and Lubricants
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• 제14권1호
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• pp.7-13
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• 1998

The static characteristics of a five-pad tilting pad journal bearing of load on pad (LOP) type have been investigated experimentally under the different values of bearing load and shaft speed. The diameter and length of the bearing are 300.91 mrn and 149.8 mm, reslx;ctively. Circumferential distribution of the film pressure, film thickness, journal surface temperature and beating surface temperature are measured. A noticeable inlet pressure rise is observed at the entrance of each pad, especially the bottom pad. The inlet pressure is increased by the increase of shaft speed as well as bearing load. In the five-pad tilting pad joumal bearing of LOP type, almost all of beating load is being carried only by the bottom pad. The maximum bearing surface temperature is observed at near the minimum film thickness. It is observed that the metal temperature of the mid-plane is higher than that of the edge at the inlet region, while the metal temperature of the edge is higher than that of the mid-plane at the outlet region.

• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.134-141
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• 2000

In this study, a scaled model chamber was built to investigate ventilation characteristics of the Under floor Air-conditioning System. Experimental study was performed in model for cargo-oil pump room with inlet and outlet by visualization equipment with laser apparatus. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000) which adopted two-frame grey-level cross correlation algorithm. The flow pattern reveals the large scale counterclockwise forced-vortex rotation from upside louver to lower scupper toward diagonal corner and also found small eddies at bottom layer

• 한국주거학회논문집
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• 제16권2호
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• pp.75-82
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• 2005

The High-rise Residential Buildings are recently consuming a lot of energy because of the vertical height rise in case of supplying cold and hot water. It is required to a appropriate solution in occurring discomfortable use and unexpected conditions of High-rise Residential Buildings on account of the difference of water supply pressure on top and bottom floor, faucet outlet pressure rise. Thus, the purpose of this study is to research on practical use status of Cold and Hot Water Supply System through Question Survey in High-rise Residential Buildings and to analyze problems.