• Journal of Bio-Environment Control
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• v.19 no.4
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• pp.195-202
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• 2010

Cooling air-conditioning of APC (Agricultural Products processing Center) workplace is important to improve the working environment in the summer season. As existing cooling systems for air-conditioning of whole workplace are inefficient because of their high equipment operating costs, relatively inexpensive cooling system is required. The objectives of this study were to simulate the thermal flow fields in APC workplace having the positive and negative pressure type fan and pad systems and spot cooling system by using CFD software (FLUENT, 6.2) and estimate the cooling effectiveness of respective cooling systems. The results showed that the negative pressure type fan and pad system was inappropriate for the present APC workplace because of excessive outside air influx from open gateway and the positive pressure type fan and pad system created relatively low temperature field but non-uniform velocity field at worker positions. The spot cooling system could supply cool air to worker positions with relatively constant air velocity and temperature.

• Membrane Journal
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• v.17 no.4
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• pp.352-358
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• 2007

A nonporous hollow fiber membrane contactor was used to control the concentration of oxygen dissolved in an aqueous solution, which was predicted along the hollow fiber membrane using a computer simulation. The governing ordinary differential equations were derived for the occurrent flows of the feed aqueous solution and the feed gas mixture in a membrane contactor and they were numerically solved using the 5th Runge-Kutta-Verner method with a personal computer, where the program was coded utilizing a software of the Compaq Visual Fortran 6.6. It is found that the concentration of oxygen dissolved in water increases from 30 to 64 ppm as the length of the hollow fiber increases from 0.4 to 1.2 m when the membrane of fibers are equal to be 16,000; the flow rate of the feed gas is kept to be 0.536 mol/sec; its pressure is maintained to be 486 kPa; the flow rate of the water is 16.69 mol/sec. As the flow rate of the water increases from 9.26 to 26.85 mol/sec, the concentration of oxygen decreases from 40 to 20 ppm with the constant fiber length of 0.4 m. Finally, it is observed that the concentration of oxygen increases from 33 to 69 ppm as the pressure of the feed gas increases from 298 to 847 kPa.

• Journal of the Korean Society of Radiology
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• v.14 no.7
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• pp.965-973
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• 2020

The purpose of this study was to quantitatively correlate the change of flow velocity and signal voiding in TOF-MRA. We made our phantom to control the flow velocity, and changed the flow velocity in 16 steps from 8.0 to 127.3 mc/s. The TOF-MRA test was performed using a 3.0T MRI system and the signal intensity was measured by classifying the signal voiding length and image into the In flow, Mid flow, and Out flow. The length of signal voiding was the longest when the flow velocity was 127.3 cm/s and the signal intensity decreased with increasing flow velocity(p<0.05). In flow(-.547) and Mid flow(-.643) were negatively correlated with flow velocitys(p<0.05). In conclusion, it was confirmed that the increase in flow velocity was a major factor causing signal voiding in TOF-MRA. In the future, this study will provide basic data when studying sequences and parameters to reduce signal voiding in models with a high flow velocity.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.335-341
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• 2019

In order to provide basic data for uniformization of temperature distribution in heating greenhouses, heating experiments were performed in two greenhouses with a hot water heating system. By analyzing heat transfer characteristics and improving pipes layout, measures to reduce the variation of pipe surface temperature and to improve the uniformity were derived. As a result of analyzing the temperature distributions of two different greenhouses and examining the maximum deviation and uniformity, it was found that the temperature deviation of greenhouses with a large amount of hot water flow and a short heating pipe was small and the uniformity was high. And it was confirmed that the temperature deviation was reduced and the uniformity was improved when the circulating fan was operated. The correlation between the surface temperature of the heating pipe and the indoor air temperature was a positive correlation and statistically significant(p<0.01) in both greenhouses. It was confirmed that the indoor temperature distribution in a hot water heating greenhouse was influenced by the surface temperature distribution of heating pipe, and the uniformity of indoor temperature distribution could be improved by arranging the heating pipe to minimize the temperature deviation. Analysis of the heat transfer characteristics of heating pipe showed that the temperature deviation increased as the pipe length became longer and the temperature deviation became smaller as the flow rate in pipe increased. Therefore, it was considered that the temperature distribution and the uniformity of environment in a greenhouse could be improved by arranging the heating pipe to shorten the length and controlling the flow velocity in pipe. In order to control the temperature deviation of one branch pipe within $3^{\circ}C$ in the tube rail type hot water heating system most used in domestic greenhouses, when the flow velocity in the pipe is 0.2, 0.4, 0.6, 0.8, $1.0m{\cdot}s^{-1}$, the length of a heating pipe should be limited to 40, 80, 120, 160, 200m, respectively.

• Journal of Environmental Impact Assessment
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• v.28 no.6
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• pp.507-524
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• 2019

The purpose of this study was to validate the EFDC model for the weir pool of Gangjeong-Goryong Weir located in Nakdong River, and evaluate the effect of flow control and phosphate loading reduction on the water quality and algae biomass by group (Diatom, Green, Cyanobacteria). As a result of model validation using 2018 experimental data,the time series of water level and vertical distribution of water temperature, DO, organic matter, nitrogen, and phosphorus time series were properly simulated. Seasonal fluctuations of algae biomass by group were adequately reproduced, but the deviations between measured and simulated values were significant in some periods. As a result of scenario simulations to control the water level and flow rate, the thermal stratification was resolved as the water level was lowered and the flow rate increased. The flow velocity at which the water temperature stratification was resolved was about 0.1 m/s, which is consistent with the previous study results of Baekje Weir in Geum River. Simulations of the 2Q flow scenario showed that Chl-a decreased by 8.7% and the cell density of diatom and green algae declined. The cell density of cyanobacteria increased, however, because the high concentrations of cyanobacteria in the upstream boundary conditions directly affected downstream due to increased flow velocity. In the scenario simulation of reducing the influent phosphate load concentration (average 0.056 mg/L) to 50%, Chl-a decreased by 13.6%.The results suggest that the upstream algae concentration and phosphorus load reduction should be considered simultaneously with hydraulic control to prevent algal overgrowth of Gangjeong-Goryong Weir.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.1
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• pp.33-43
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• 2003

The midwater pair trawl which is being used at present in Korea have several problems. Firstly, it is difficult to control the net height on high towing speed. Secondly, net breaking often occurs owing to floats and thirdly, the volume of net on the net drum is so large. This study is aiming for examining the possibility of application for the Korean midwater pair trawl through the model experiment of non-float midwater pair trawl. The model of non-float midwater pair trawl was manufactured as 1/100 of the full scale net which is being used in bottom pair trawl for 850ps class considering the Tauti's Similarity law. The model experiment was carried out to analyze the opening efficiency according to the variation of lower warp length and the opening efficiency was investigated between th proto type and non-float type. The results obtained can be summarized as follows ; 1. The hydrodynamic resistance of non-float type was about 10~20% smaller than that of the proto type and it increased about 1ton according to the increase of dL at the condition of the same flow speed. The resistance acting on the lower warp decreased about 5% but that of the upper warp increased according to the increase of lower warp length (dL) at the condition of the same flow speed. 2. The net height of the non-float type decreased almost linearly according as the increased of flow speed and it increased in a logarithmic functional form with the increase of the lower warp length at the condition of the same flow speed. On the decreasing rate of the net height, the non-float type was lower than the proto type and the difference of the decreasing rate was about 12% at 3.0 knot, 25% at 4.0 knot, 25% at 4.0 knot respectively when dL was 30m. 3. The net width of non-float type was not varied so much as only 2m range and was larger than that of proto type. 4. The mouth area of non-float type decreased in a exponential functional form. On the decreasing rate of the mouth area, the non-float type was lower than the proto type. The filtering volume increased in a logarithmic functional form with increasing flow speed and the filtering volume of proto type decreased steeply over 3.0knot, but that of non-float type increased until 4.0knot. 5. The optimal length of lower warp was when the value of dL was about 30m and the optimal position of front weight was at the connection point of four net pendants.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.386-398
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• 1998

The present experiment is conducted to investigate heat transfer characteristics on the impinging surface with secondary flows around circular nozzle jets. The changed vortex pattern around jet affects significantly the flow characteristics and heat transfer coefficients on the impinging surface. The effects of the jet vortex control are also considered with jet nozzle-to-plate distances and main jet velocities. The vortex pattern around a jet is changed from a convective instability to an absolute instability with a velocity suction ratio of the main jet and the secondary counterflow. With the absolute instability condition, the jet potential core length increases and the heat transfer on the impinging surface is increased by small scale eddies. The region of high heat transfer coefficients is enlarged with the high Reynolds number due to increasing secondary peak values. The effect of suction flows is influenced largely with collars attached the exit of the jet nozzle because the attached collar guides well the counterflow around the main jet.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.71-71
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• 2017

플라즈마를 이용하는 건식 식각 또는 박막 증착 장비(PECVD)의 경우 웨이퍼에 rf bias를 인가하여 이온의 에너지와 입사각을 조절한다. 종래에는 웨이퍼의 가장 자리 3 mm영역을 공정 대상에서 제외하는 exclusion area로 지정하였으나 점차 공정 기술의 발달로 2 mm 이내로 감소하고 있다. 따라서 웨이퍼의 가장 자리에서 발생하는 전기장의 방향 및 크기 변화를 조절할 수 있는 기술의 개발이 필요하게 되었으며 그중 핵심적인 부품이 Si 또는 SiC로 제작되는 edge ring이다. Focus ring이라고도 불리는 이 부품은 웨이퍼 상에서 반경 방향으로 흐르는 가스의 유속이 가장 자리에 근접하면 빨라지는 현상과 이에 의해 식각/증착 화학 반응 속도가 증가하는 문제를 완화하기 위한 것과 적절한 전기 전도도를 부여함으로써 가장 자리의 전기장 분포를 최적화 할 수 있는 새로운 설계 변수로 활용할 수 있다. 스퍼터링의 경우에도 웨이퍼 중앙과 주변 부는 마그네트론 음극의 회전 링과의 입체각이 차이가 나므로 가장 자리의 경우 트렌치나 홀의 내측이 외측에 비해서 증착막의 두께가 얇아지는 문제가 있으며 건식 식각의 경우 홀의 형상이 수직에서 벗어나는 경향이 발생할 수 있다. 또한 사용 시간에 비례해서 edge ring의 형상이 변화하는데 상대적으로 고가품이어서 교체 주기를 설정하는 보다 합리적 기준이 필요하다. 본 연구에서는 전산 유체 역학 모델을 사용하는 ESI사의 CFD-ACE+를 활용하여 edge ring의 형상과 재질이 갖는 영향을 전산 모사하기 위한 기초 작업을 그림 1과 같이 진행하였다. 2D-CCP model에 Ar 가스를 가정하고 비유 전율 10내외 전도도 $0.1/Ohm{\cdot}m$정도의 재질에 대한 용량성 결합 플라즈마에 대해서 계산을 하고 이 때 기판에 인가되는 고주파 전력에 의한 이온의 입사 에너지 분포 및 각도 분포를 Monte Carlo 방법으로 처리하여 계산하였다.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.590-595
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• 1998

차세대 원자로(KNGR : Korea Next Generation Reactor)에는 새로운 안전개념으로서 피동형 안전주입탱크(Safety Injection Tank. SIT)의 도입을 고려하고 있는데, 이러한 피동형 유량조절기능은 안전주입탱크내의 유체기구(Fluidic device)인 볼텍스챔버(vortex chamber)에 의해 이루어진다. 볼텍스챔버는 내부에서 발생되는 와류강도에 따라 유동저항의 강도가 달라짐을 이용하여 유량을 피동적으로 조절할 수 있는 유체기구이다. 본 연구에서는 볼텍스챔버의 유동특성을 관찰하기 위하여 소규모 실험장치를 구축하고, 이를 이용하여 실험을 수행하였다. 본 연구는 두 단계로 수행되었다. 제1단계 실험에서는 볼텍스챔버의 기하학적 특성이 안전주입탱크의 안전주입수 방출특성에 미치는 영향에 대한 거시적 관점에서의 연구로서. 볼텍스챔버의 기하학적 변수(유입구 및 방출구의 직경)가 안전주입수의 방출과정에서 발생되는 SIT 내의수위 거동, 안전주입수의 방출유량 특성등에 미치는 영향에 대해 중점적으로 고찰하였다 제2단계 실험에서는 1단계 실험에서 관찰된 안전주입탱크의 여러 가지 방출특성과 볼텍스챔버 내부 유동장의 유동특성과의 관련성을 규명하기 위해 PIV (Particle Image Velocimetry)를 이용하여 볼텍스챔버의 기하학적 변수에 따른 유동장 내부의 국소 유속분포를 측정하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1011-1015
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• 2010

하천의 이용과 관리적 측면에서 가장 빈번하게 발생하는 하도의 직선화, 홍수량의 변화, 하상굴착, 하폭의 확대 축소 및 횡단구조물 등은 중규모 스케일의 하천지형을 인위적으로 교란시키는 대표적인 사례이다. 따라서, 이러한 인위적 교란은 하천생태계의 기반인 하천의 물리적 구조를 크게 변화시키므로 하도지형의 응답방향을 규명할 필요가 있다. 하천 유역의 지형은 여러 가지 스케일의 지형단위가 조직화되어 있는 것이므로 대(大) 중(中) 소(小)의 3가지 스케일 지형단위로서 계(系, system)를 계층화하고, 작은 계층의 계(系)에서는 큰 계층의 계(系)를 고정적인 경계조건으로 하여, 그 내부의 여러 가지 특징이나 변화를 규정하는 주요 인자를 이용하여 분석해야 한다. 또한 대(大) 스케일은 유역스케일의 지형스케일이며, 하도의 수계망이나 하도종단형 형상 등이다. 중(中) 스케일은 segment에서 reach 스케일의 지형이며 사행형상, 하천 폭 등이다. 소(小)스케일은 수심의 10배 정도이하의 지형스케일이며, 소규모 하상파 등의 미지형(微地形)이다. 따라서, 본 연구에서는 남강과 황강을 대상하천으로 유량 조절과 유사공급이 차단되는 댐하류 및 골재채취와 같은 인위적 교란요인에 의한 중규모(segment scale) 하도지형의 변화와 응답방향을 조사, 분석하였다. 연구결과 유량 및 유사공급량의 변동의 크기에 따라 전체적인 하상저하와 더불어 사주와 소가 소멸되면서 여울과 소가 사라지는 현상이 동조하는 것으로 분석되었으며, 하상의 평탄화에 의하여 저수로의 폭이 넓어져 복열사주가 발달하면서 수심 및 유속의 다양성이 감소되는 것으로 분석되었다.