• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.91-91
• /
• 2022

하천 합류부에서 수체의 흐름은 매우 역동적으로 변화하며 합류부의 복잡한 3차원 흐름과 난류 구조는 2차류(secondary currents)의 강도변화, 전단층(shear layer)의 뒤틀림 그리고 재순환구역(recirculation zone)의 발생 등 합류부에서의 독특한 특징을 형성한다. 이러한 특징들의 변화는 수체의 흐름구조 뿐만 아니라 하천으로 유입된 오염물의 거동에도 영향을 준다. 기존의 합류부 연구들은 주로 본류와 지류의 합류각이나 유량비에 차이를 두어 합류부의 특징 변화를 모의하였다. 하지만 실제 자연하천에서 홍수방지를 위한 수심확보, 건축자재의 골재수집 등 다양한 목적으로 수행되는 본류의 준설작업으로 인해 발생하는 본류와 지류의 하상면 단차 또한 합류부의 특성에 영향을 미치는 주요한 인자 중 하나이다. 단차가 커짐에 따라 증가하는 지류수체의 낙차는 이차류의 강화를 야기하며 이는 합류부에서의 유속구조를 변화시켜 흐름을 가속시키거나 지체시키며 오염물의 혼합에 영향을 미친다. 본 연구에서는 3차원 수치모의를 통해 90도로 합류되는 수로에서의 흐름구조와 오염물의 혼합에 단차비와 유량비가 미치는 영향을 모의하였다. 유동장 해석을 위해 3차원 RANS (Reynolds-averaged Navier-Stoke) 방정식을 사용하였으며 난류해석은 k-𝜔 SST 모델을 이용하였다. 본류의 경우 11.4m의 수로 연장을 갖고, 하폭은 0.3m이며 수심은 단차의 크기에 따라 변화한다. 지류의 경우는 수로연장 1m, 하폭 및 수로깊이는 0.1m이다. 수치결과의 검증을 위해 이주하(2013)이 수행한 실내 합류수로의 실험결과를 이용하였다. 모의결과를 통해 파악한 합류부의 흐름특성을 이용하여 적절한 2차원 분산계수를 산정한다. 자연하천에서 오염물의 혼합거동을 효과적으로 모의하기 위해 수심 평균된 2차원 이송-분산모형을 이용하는데 이때 적절한 분산계수의 산정이 필수적이다. 본 연구에서는 합류 후 흐름방향에 따라 분산특성이 상이한 구간을 구분하여 분산계수를 산정하였으며 이를 통해 오염물의 거동을 정확하게 모의하였다.

• Journal of Korean Neurosurgical Society
• /
• v.29 no.7
• /
• pp.853-860
• /
• 2000

Objective : The purpose of our experimental study was to analysis the advantages and disadvantages in the reversible and irreversible cerebral ischemic models with rats by staining with Neutral Red(NR) solusion, 2% 2,3,5-triphenyltetrazolium chloride(TTC) and Hematoxylin & Eosin(H & E). Methods : We have measured the range of cerebral infarction in the rat to get a suitable ischemic model along the object of study with and without craniectomy. With craniectomy, 9 rats were sacrificed for irreversible cerebral ischemic model by means of ligation at proximal(group I) and distal(group II), and coagulation at proximal(group III) middle cerebral artery. Also, 6 rats were sacrificed for irreversible(group IV) and reversible(group V) cerebral ischemic model using nylon thread without craniectomy. The sizes of infarction were measured by staining the coronal sections of the brain with NR solusion, TTC and H & E. Results : There are no difference of physiological parameters comparing the each group. Cerebral infarction was not observed in group II, but it's volume was largest in group IV. Disadvantages of craniectomy group(I, II, III) are the long duration of operation and cortical damage by procedure. It's advantage is confirmation of the middle cerebral artery occlusion and cessation of blood flow through the operative microscope. In case of ischemic models using nylon thread (group IV, V), it is hard to identify the interruption or recirculation of blood flow through the middle cerebral artery, but the advantage is the simplicity of operative technique which reduces the operation time and minimizes the cerebral damage due to craniectomy. Therefore, it seems important to set up the reversible and irreversible ischemic models by carefully considering advantages and disadvantages listed above. Conclusion : TTC staining seems to be effective since it reflects the histological damage sufficiently and quickly. It is hoped that researches focused on ischemic penumbra, which became popular recently, will be further carried on with use of NR staining, optical microscope and electron microscope.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.2
• /
• pp.527-539
• /
• 2018

The subway used by many passengers is required to maintain a safe and comfortable environment and PSD (Platform Screen Door) must be installed in the platform after reinforcing the standard in 2003. In the previous research, in case of subway fire to control it, it is necessary to design the optimal ventilation and smoke exhaust system according to equipment capacity of the smoke exhaust system. Therefore, in this study, based on the results of previous research, three-dimensional numerical analysis was performed for the CO gas and smoke flow by the subway ventilation system in case of platform fire. As a result of this study, it was found that in case of emergency, if only the upper-level smoke exhaust system is activated, the risk of evacuation is high due to CO gas (653.8 ppm) and smoke concentration ($768.4mg/m^3$). And when all the smoke exhaust systems are activated and only the fire side PSD is opened, CO gas (36.0 ppm) and smoke concentration ($26.2mg/m^3$) are detected and the propagation range of smoke flow was reduced. When all the smoke exhaust systems are activated and only the fire side PSD is closed, it was analyzed as the most effective ventilation mode in the evacuation environment due to the absence of smoke-recirculation.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.21 no.5
• /
• pp.288-291
• /
• 1988

We have veen already reported the distribution of PSP of bivalve mollusca in southern coast of Korea and also analyzed their characteristics. The purpose of this study was to develop detoxification method for PSP infested sea mussel, Mytilus edulis, by rearing methods or processing treatments. There was no significant detoxification effect when the PSP infested sea mussel was reared in a tank with water recirculation system, but the toxicity of sea mussel rapidly decreased during the rearing time in a water flow system with filtered water. The detoxification rate of PSP during the rearing for 5 days in a water flow system tank with $15-17^{\circ}C$ of sea water was $94\%$ in case of high toxic sample with more than $2,600{\mu}g/100g$ and about $40\%$ in case of low toxic sample with less than $100{\mu}g/100g$. The toxicity of PSP extracted from the sample with 0.1N/ HCl solution was about 2-5 times higher than that extracted with distilled water. When sea mussel contained $100-150{\mu}g-PSP$ per 100g of edible meat was boiled for 30 min with tap water, the toxicity was destroyed as the level of PSP undetected by mouse assay. We can suggest that boiling of sea mussel with tap water was one of the most significant detoxification methods, but it was not enough to be safe in case of extremely high intoxicated sea mussel with PSP. For example, the digestive gland of sea mussel contained more than $9593{\mu}g/100g$ was heated in a can with tap water at $116^{\circ}C$ for 65 min. the residual PSP was more than $170{\mu}g$.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.21 no.5
• /
• pp.297-302
• /
• 1988

We have veen already reported the distribution of PSP of bivalve mollusca in southern coast of Korea and also analyzed their characteristics. The purpose of this study was to develop detoxification method for PSP infested sea mussel, Mytilus edulis, by rearing methods or processing treatments. There was no significant detoxification effect when the PSP infested sea mussel was reared in a tank with water recirculation system, but the toxicity of sea mussel rapidly decreased during the rearing time in a water flow system with filtered water. The detoxification rate of PSP during the rearing for 5 days in a water flow system tank with $15-17^{\circ}C$ of sea water was $94\%$ in case of high toxic sample with more than $2,600{\mu}g/100g$ and about $40\%$ in case of low toxic sample with less than $100{\mu}g/100g$. The toxicity of PSP extracted from the sample with 0.1N/ HCl solution was about 2-5 times higher than that extracted with distilled water. When sea mussel contained $100-150{\mu}g-PSP$ per 100g of edible meat was boiled for 30 min with tap water, the toxicity was destroyed as the level of PSP undetected by mouse assay. We can suggest that boiling of sea mussel with tap water was one of the most significant detoxification methods, but it was not enough to be safe in case of extremely high intoxicated sea mussel with PSP. For example, the digestive gland of sea mussel contained more than $9593{\mu}g/100g$ was heated in a can with tap water at $116^{\circ}C$ for 65 min. the residual PSP was more than $170{\mu}g$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.1
• /
• pp.103-110
• /
• 2012

The flow field, fuel-air mixing, and behaviors of turbulent flames have been investigated using the large eddy simulation (LES) numerical technique in a premixed swirl combustor equipped with EV double cone burners. Recirculation zones are generated by the swirl burner, and lean premixed flames are formed within a distance of 0.2 m from the tip of the burner. NOx emission of 0.46 ppm is predicted at 1 atm and an air/fuel ratio of 38.7. However, most of the CO generated in a flame front continues to be oxidized as it moves toward the exit, and CO emission of 5.45 ppm is predicted at the exit. The NOx emission can be reduced by decreasing the pressure and air/fuel ratio. The characteristics of NOx emission have been investigated through RANS simulations for various fuel injection types, and it is found thereby that five-lance-hole injection produces the lowest NOx emission rate.

• Membrane Journal
• /
• v.24 no.3
• /
• pp.213-222
• /
• 2014

In this study, 2-stage recirculation membrane process was developed for purification of high purity bio-methane for the vehicle fuel application. Pure gas permeation and mixture gas permeation test were done as a function of methane content and pressure in the feed using polysulfone membrane modules. 2-stage membrane plant was designed, constructed in a food waste treatment cite. Dehumidification, dry desulfurization, and desiloxane plants are installed for the removal of $H_2O$, $H_2S$ and siloxane in the biogas. Permeation test were done with the pre-treated methane mixture in terms of methane purity and recovery by adjusting the ratio of membrane area (1:1, 1:3, 2:2) in the first and second membrane modules in the plant. When membrane area of 2 stage increased to $3m^2$ from $1m^2$ at 1-stage membrane area of $1m^2$, the feed rate and $CH_4$ recovery at 95% methane purity were increased from 47.1% to 92.5% respectively. When the membrane area increased two-fold (1:1 to 2:2), $CH_4$ recovery increased from 47.1% to 88.3%. When the feed flow rate was increased, in 1:3 ratio, final purity of the methane is reduced, the methane recovery is increased. When operating pressure was increased, the feed rate was increased and recovery was slightly decreased. From this result, membrane area, feed pressure and feed rate could be the important factor to the performance of the membrane process.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.8
• /
• pp.632-638
• /
• 2013

This paper describes on the flame stability and combustion instability of coal derived synthetic gas especially for gases of Buggenum IGCC in Netherlands and Taean IGCC in Korea. These combustion characteristics were observed by conducting ambient-pressure elevated-temperature combustion tests in GE7EA model combustor when varying heat input and nitrogen dilution ratio. Flame stability map is plotted according to the flame structure by dividing all regimes into six, and only regime I and II are identified to be stable. Both syngases of Taean and Buggenum with nitrogen integration corresponds to regime II in which syngas burnt stably and flame coupled with outer recirculation flow. Stable regime of Buggenum is larger than that of Taean when considering only $H_2$/CO ratio due to higher content of hydrogen. However, when considering nitrogen dilution, syngas of Taean is burnt more stably than that of Buggenum since more nitrogen in Buggenum has negative effect on the stability of flame.

• Journal of Korean Society of Environmental Engineers
• /
• v.36 no.5
• /
• pp.325-332
• /
• 2014

Growing concerns about harmful influence of radon on human body, many efforts are being made to decrease indoor radon concentration in advanced countries. To develop an indoor radon reduction technology, it is necessary to develop a technology to predict and evaluate indoor inflow and emission of radon. In line with that, the present study performed computational modelling of indoor dispersion of radon emitted from building materials. The computational model was validated by comparing computational results with analytical results. This study employed CFD (Computational Fluid Dynamics) analysis to evaluate the radon concentration and the airflow characteristics. Air change rate and ventilation condition were changed and several building materials having different radon emission characteristics were considered. From the results, the indoor radon concentration was high at flow recirculation zones and inversely proportional to the air change rate. For the different building materials, the indoor radon concentration was found to be highest in cement bricks, followed by eco-carats and plaster boards in the order. The findings from this study will be used as a method for selecting building materials and predicting and evaluating the amount of indoor radon in order to reduce indoor radon.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.1
• /
• pp.25-33
• /
• 2018

Renewable energy has been of interests in the area of modern alternative fuels. Biogas is produced in waste landfill sites through anaerobic digestion processes, including hydrolysis, acidogenesis, organic acid fermentation (acetogenesis), and methane fermentation (methanogenesis). High contents of fine dust and moisture limited its utilization for direct combustion, town gas and vehicle fuel. Thus, this study proposed a new design for a cooling device using a centrifugal cyclone for simultaneous removal of fine dust and moisture as a pretreatment in the purification processes. A heat exchanger and an ID fan, which are installed inside and outside of the cyclone, in order to cool the humid gas below the freezing point and form a foggy mist. Such an atmosphere enhanced to capture fine dust as recirculating the cold mist flow. The water removal rate was 80.8% at a relative humidity of 95%, and the particle removal efficiency was 98.3% for $2.5{\mu}m$. Simultaneous removal efficiency was 70.8% and 99.6% for particle and moisture respectively.