In this study, numerical analysis is conducted to understand the flow characteristics of the radial impeller with the design parameters such as the blade shape and position using the ANSYS Fluent software. The shape of blade is divided into two types, a backward curved blade and an airfoil forward curved blade. To examine the fundamental flow characteristics near the blades, a rectangular flow field is modeled and analyzed. On the other hand, for the impeller rotation analysis, the simulation is performed by modeling the rotational region separately. As a result, the airfoil forward curved blade shows higher outlet flow rate than the backward curved blade. In addition, as the depth of the impeller and the attachment angle of blade increase, the higher flow rate appears.

Chemical decontamination of primary systems in a nuclear power plant (NPP) prior to commencing the main decommissioning activities is required to reduce radiation exposure during its process. The entire process is repeated until the desired decontamination factor is obtained. To achieve improved decontamination factors over a shorter time with fewer cycles, the appropriate flow characteristics are required. In addition, to prepare an operating procedure that is adaptable to various conditions and situations, the transient analysis results would be required for operator action and system impact assessment. In this study, the flow characteristics in the steady-state and transient conditions for the chemical decontamination operations of the Kori-1 NPP were analyzed and compared via the MARS-KS code simulation. Loss of residual heat removal (RHR) and steam generator tube rupture (SGTR) simulations were conducted for the postulated abnormal events. Loss of RHR results showed the reactor coolant system (RCS) temperature increase, which can damage the reactor coolant pump (RCP)s by its cavitation. The SGTR results indicated a void formation in the RCS interior by the decrease in pressurizer (PZR) pressure, which can cause surface exposure and tripping of the RCPs unless proper actions are taken before the required pressure limit is achieved.

본 연구의 목적은 슬리브 이음된 배관 사이의 간극과 Re가 변할 때 배관 내의 유동은 어떻게 변하는지 조사함으로써 조정관 설치 시에 압력손실과 난류 강도를 감소시킬 수 있는 배관 간극(Lp)을 파악하는 것이다. 슬리브 이음된 배관 두께(tp)는 5 mm로 고정 하고 Lp는 10, 50, 100 및 200 mm로 하여 슬리브 이음부의 속도, 압력 분포, 재순환 영역에서의 재부착점 길이 및 Re와의 상관관계를 해석하였다. 상용 프로그램인 Ansys fluent 18.1을 이용하였고, Re의 범위는 200 ≤ Re ≤ 5,000으로 하여 층류에서 난류까지 슬리브 이음부의 유동 특성을 파악하였다. 슬리브 이음부의 확대비와 축소비는 각각 1.2와 0.83이였고 Lp가 일정할 때 Re가 커질수록 슬리브 하류가 장자리(edge)의 난류 강도와 압력 변화가 크게 나타났다. 이는 슬리브 벽면에서의 유동이 tp에 의해 흐트러지고 속도 에너지의 손실이 발생하면서 슬리브 이음부의 가장자리에 영향을 미친 것으로 판단된다. Lp가 10 mm 이하의 경우, Re가 증가함에 따라 가장자리의 난류 강도에는 큰 변화가 없었다. 재순환 영역에서의 재부착점은 Lp가 10 mm 이하에서 나타나지 않았으며 와(vortex)의 영향도 없었다. 3,000 ≤ Re의 경우, Lp가 증가함에 따라 슬리브 이음부 벽면에서의 재부착점 길이는 거의 일정하였다.

The effect of flow direction on heat transfer in water cooling channel of lithium-ion battery is numerically investigated. Battery Design StudioⓇ software is used for modeling electro-chemical heat generation in the battery and the conjugated heat transfer is analyzed with the commercial package STAR-CCM+. The result shows that the maximum temperature and temperature difference of battery with Type 1 are the lowest because the heat transfer in the entrance region near the electrode is enhanced. As the inlet velocity is increased, the maximum temperature and temperature difference of battery decreases but the pressure loss increases. The pressure loss in Type 2 channel is the lowest due to the shortest channel length, while the pressure loss with Type 3 or 4 channel is the highest because of the longest channel length. Considering heat transfer performance and pressure loss, Type 1 is the best cooling channel.

In order to satisfy the strengthening automobile exhaust gas regulation and CO2 regulation, the development of eco-friendly vehicles is actively progressing. To cope with these regulations, research on alternative fuel vehicles is being actively conducted. Alternative fuels are one of the best ways to reduce dependence on fossil fuels and respond to emissions and CO2 regulations. Natural gas, one of many alternative fuels, contains methane (CH4) as a main component and has abundant reserves, so it is attracting attention as a fuel that can provide stable long-term supply by replacing fossil fuels. In addition, natural gas has a high octane number, so there is room for improvement in combustion characteristics when used in SI engines, and it has the advantage of reducing harmful emissions and carbon dioxide (CO2) compared to conventional fossil fuels. When using a low-pressure injector in a turbo engine, it is difficult to secure the flow rate of fuel because the pressure difference between the injector and the manifold is small. Therefore, it is necessary to develop a high-pressure injector to improve this. Natural gas is a gaseous fuel and should be developed in consideration of compressible flow, Although the use of a CNG high-pressure injector is required, it is difficult to stabilize the flow due to the Mach disk and shock wave interference caused by compressible flow. If the flow is not stabilized, it is difficult to precisely control the flow. Therefore, it is necessary to develop an injector in consideration of flow characteristics. In this paper, the flow analysis according to the shape change of the injector was conducted to improve the fuel flow rate injected from the 800 kPa high pressure CNG injector.

본 연구는 산악형 설악산 국립공원지역에서 발생한 토석류 발생지 263개소를 대상지로 선정하여 다양한 산림환경 인자별로 조사하고 토석류발생지 특성을 분석하였다. 토석류 평균(침식량, 길이, 폭, 면적)은 각각 1,935㎥, 103.7m, 14.4m, 1,728㎡로 나타났다. 산림환경 인자가 토석류 발생 빈도에 미치는 영향을 분석한 결과, 경사도(31∼40°), 사면방위(남사면), 종단사면(오목凹), 횡단사면(오목凹), 표고(801∼1,200m), 사면위치(산록), 하천차수 (1차), 임상(혼효림), 모암(화강암), 토심(15cm 이하)에서 발생빈도가 높은 것으로 조사되었다. 토석류가 발생한 피해지에서의 침식량과 산림환경 인자와의 상관관계를 분석한 결과는, 종단사면(오목凹, 복합凹凸), 표고(1,201m 이상), 토심(46cm 이상)에서 1% 수준 내에서 정의 상관관계를 보였다.

The effect of the change in air inflow velocity has been investigated at the opening of the malodor emission source to determine its influence on the Complex odor concentration. Both the Complex odor collection efficiency and concentrations were measured according to the change in airflow velocity. When the air inflow velocity was 0.1 m/s, it was observed that some of the generated gas streams were diffused to the outside due to low collection efficiency. In contrast, only the increased gas collection volume up to 0.5 m/s showed no substantial reduction of the Complex odor concentration, which indicates an increase in the size of the local exhaust system as well as the operation cost for the Complex odor control device. When the air inflow velocity reached 0.3 m/s, the Complex odor concentrations not only were the lowest, but the odorous gas could also be collected efficiently. The air inflow velocity at the opening of the malodor emission source was considered the key factor in determining the gas collection volume. Therefore, based on the results of this study, an optimal air inflow velocity might be suggestive to be 0.3 m/s.

우리나라 서남해 연안역에서 해수유동을 재현하기 위해 모든 분조를 포함하고 절점변조진폭, 위상보정인자 및 천문인수를 적용한 완전한 형태의 실조석(Real Tide)을 도입하였다. 실조석으로 해수유동을 재현한 결과, 조석의 관측치와 계산치의 상관계수는 1.0으로 진폭 및 위상의 정확도가 매우 우수하였고, U성분 및 V성분으로 구분하여 나타낸 조류는 각각 평균 0.883과 0.936의 높은 상관도를 보여 실조석으로 재현하는 것이 타당한 것으로 보였다. 그리고 잔차류의 관측치와 계산치의 차는 평균 0.006 m/s로 유의미하지 않았고, 그 진 행방향은 서로 매우 유사하였다. 그리고 본 연구의 계산결과에서 관측치와 계산치 간에 나타난 유속성분 오차는 주로 고파랑이나 폭풍을 비롯한 남풍계열의 강한 바람과 같은 기상적 요인에 의한 것이 원인으로 분석되었다. 향후 해수유동 수치모형 실험에서 하나의 변수로 작용하는 기상적 요인을 고려하고 본 연구의 실조석을 재현한다면 계산결과는 더욱 향상될 것으로 기대된다.

In order to design a diesel engine system and predict its performance, it is necessary to analyze the gas flow of the intake and exhaust system. A gas flow analysis in three-dimensional (3D) format needs a high-resolution workstation and enormous time for analysis. Therefore, the method of characteristics (MOC) was used for a gas flow analysis with a fast calculation time and a low-resolution workstation. An experiment was conducted on a single cylinder diesel engine to measure pressure in cylinder, intake pipe and exhaust pipe. The one-dimensional (1D) gas flow was analyzed under the same conditions as the experiment. The engine speed, valve timing and compression ratio were the same conditions and the intake pressure was inputted as the experimental results. Bent pipe such as an exhaust port that cannot be realized in 1D was omitted. As results of validation, the cylinder pressure showed accuracy, but the exhaust pipe pressure exhibited inaccuracy. This is considered as an error caused by the failure to implement a bent pipe such as an exhaust port. When analyzed in 3D, calculation time required 61 hours more based on a model of this study. In the future, we intend to implement a bent pipe that cannot be realized in 1D using 3D and prepare a method to supplement reliability by using 1D-3D coupling.

The concentrations of odor and volatile organic compound (VOC)-inducing substances were measured using selected ion flow tube mass spectrometers (SIFT-MS). SIFT-MS can continuously measure the concentration of odor-causing substances and VOCs in real time without pre-treatment steps. Measurements were conducted during the day and at night at 10 spots in the chemical block of the Sihwa industrial complex. Similar measurement results were observed in the daytime and nighttime for materials except methyl ethyl ketone with high concentrations. A high concentration of hydrogen sulfide was also measured at night. It is expected that an amount of emissions of VOCs and odor-causing substances under the absence of inspection can be traced if measured at other industrial complexes in vulnerable times.

Numerical analysis has been carried out to analyze seawater flow field and power generation characteristics of the tidal current power generation system for various multi channel shroud systems. Geometrical multi channel arrangement largely affects the flow field characteristics in the shroud system which power generation performance through turbine blade depends on. Sectional averaged velocity in front of the turbine blade which increases more than 2 times compared with channel inlet is much influenced as well as the flow from the rear with curl. And flow variation results in high inlet velocity in horizontal arrangements of multi channels with mechanical output of the turbine. These results are expected to be used as applicable data for the development of the tidal power generation system with shrouds.

When oil spill disaster on sea takes place, the most effective measure is to use oil fence with vertical wall. It has been big challenges that suitable oil fence in consideration of variety of variables such as wind speed, height of wave and current direction is chosen. And current characteristics below two of vertical wall was studied by PIV experiment with utilizing technic of visualized analysis like velocity distribution, contour of velocity and streamline pattern in flow characteristic between vertical wall of oil fence. In this study it is purposed to identify characteristics of inside water flow between two vertical walls depending on respective various water speeds to minimize outflow of floating article below bottom of vertical wall and observed that re-circulation flow and irregular vortex at certain places between two vertical walls occurred. Consequently, the study showed that failure of oil fence such as entrainment failure and submergence failure can be largely lessen by means of optimizing length between two vertical walls with water speeds.

본 연구는 전라북도지역에서 발생한 토석류 특성과 산림환경인자가 토석류에 미치는 영향을 분석하였다. 토석류 발생 수는 총 79개소였으며, 토석류 평균 발생면적은 3,383.2㎡, 평균 발생토사량은 5,879.7㎥, 평균 길이는 253.1m, 평균 폭 13.1m로 나타났다. 토석류가 비교적 많이 발생한 산림환경 인자는 사면 경사도(21~30° 이상), 북서사면, 해발(401m~500m 이하), 종단사면(오목), 횡단사면(오목), 침엽수, 화성암, 하천차수는(0차), 사면위치(산정), 임종(인공림), 수고(11~15m 이상), 흉고직경은 중경목(17cm 이상)에서 토석류 발생이 높은 것으로 조사되었다. 토석류 발생길이와 산림환경 인자와의 상관분석을 실시한 결과는 표고(501m 이상), 모암(화성암)에서 1% 수준 내에서 정의 상관관계를 보였고, 모암(퇴적암)에서 1% 수준 내에서 부의 상관관계를 보였다.

In this study, the temperature, the absolute humidity, and the turbulent flow characteristics of exhaust air and supply air in the mixer were studied while changing the shape of the mixer of the white smoke reducing heat exchange system. Using Solidworks, the mixer of the white smoke reduction heat exchange system was created by 3-D model. Also, the mixed flow of supply air and exhaust air inside the mixer under the uniform inlet conditions was computed, using the solidworks flow simulation. Two types of improvement models were selected by using a perforated plate and a guide vane as a turbulent mixing flow control method of the mixer. The mean temperature and mean absolute humidity of the mixture were greatly decreased according to the internal shapes of Case 1, 2, and 3. The temperature difference between the inlet and outlet of the mixer Case 3 was 26℃. The exit temperature and absolute humidity reduction rates of Case 3 were 26.2% and 48.1%, respectively, compared with Case 1.

In order to understand the tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea, numerical model experiments and vorticity analysis were carried out. The currents flow north at flood and south at ebb respectively and have the reversing form in the west channel. Topographical eddies are found in the surroundings of Dunbyong Island in the east of the channel. The flood currents flow from the waters near Naro Islands through the west channel and the coastal waters near Geumo Islands through the east channel. The ebb currents from the Yeoja Bay flow out along the west and the east channels separately. The south of Nang Island have weak flows because the island is located in the rear of main tidal stream. Currents are converged at ebb and diverged at flood in the northwest of Jeokgum Island. Tidal current ellipses show reversing form in the west channel but a kind of rotational form in the east channel. As the results of tide induced mean flows, cyclonic and anticyclonic topographical eddies at the northern tip but eddies with opposite spin at the southern tip are found in the west channel of Yeoja Bay. The topographical eddies around the islands and narrow channels are created from the vorticity formed at the land shore by the friction between tidal currents and the west channel.

The flow characteristics around the vertical wall with the flap were visualized in the water channel using PIV. And the effect of flap angle change was investigated to see how quickly the spreading can be prevented and confined if oil spill occurs at sea. As a result, the fluid in the front of the vertical wall flows constantly, Nearing a boundary layer on the vertical wall, and a flow separation phenomenon occurs. Thereafter, flow loss or depth loss to the bottom of the vertical wall was confirmed. Also, it was observed that irregular reverse circulation flow occurred due to flap angle change and pressure gradient at the back of vertical wall. In this study, it was analyzed that it is most effective at 20 degrees angle. In the future, it is necessary to confine the flow characteristics of PIV and CFD by assuming that there is a double vertical wall in which oil having a lower specific gravity than water is trapped in the oil fence.

In this study, the characteristics of the heat flow on SA(supply air) side of the white smoke reducing heat exchange system according to the change of SA velocity were analyzed in the winter condition (outside temperature 0℃). Also, the mixing process of SA and the EA(exhaust air) is presented in the psychrometric chart to confirm the possibility of reducing white smoke. Solidworks flow simulation was used to analyze the heat flow on the heat exchange system under uniform conditions. As the inflow velocity of SA increased, the temperature of SA decreased due to the convective heat transfer improvement due to the active flow in SA system. And the outlet temperature and absolute humidity of the mixing zone decreased significantly. At SA velocity 7 m/s, the outlet temperature and absolute humidity decreased to about 58% and 82%, respectively.