• Title/Summary/Keyword: Low-flow

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The Numerical Study on Effect of the Droplet Sizes on Internal Mass Transfer in the Spray Type Scrubber (분무형 스크러버에 내에서 액적크기에 따른 물질전달에 관한 전산해석적 연구)

  • Lee, Chanhyun;Chang, Hyuksang
    • Clean Technology
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    • v.25 no.1
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    • pp.19-32
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    • 2019
  • As regional air pollution gets worse by the sulfur oxides emitted from various types of vessels passing through the many countries, the International Maritime Organization establishes the emission control areas and regulates sulfur dioxide in those areas. In order to satisfy these regional regulations, the fuel selection method and the exhaust gas post-treatment device are applied to the ships. Due to the economic reasons, the post-treatment method of exhaust gas for reducing the amount of sulfur oxides discharged is mainly preferred. The scrubber which is dominantly used in the ships are the spray type system where the sprayed liquid drops used for capturing the soluble sulfur dioxides in the exhaust gas. The performance of the spray type system depends on the size distribution of the sprayed droplets. In order to evaluate this performance, we designed counterflow type scrubber and cyclone scrubber and evaluated the desulfurization efficiency and the amount of droplet evaporation according to the size of each droplet by using computational fluid dynamics. The Eulerian-Eulerian analysis method was used because the scrubber had a gas-liquid two-phase flow inside the scrubber. When the diameter of the droplet was $100{\mu}m$, $300{\mu}m$, $500{\mu}m$ and $700{\mu}m$. As a result, both of scrubbers showed high desulfurization efficiency and low evaporation amount at $500{\mu}m$ and $700{\mu}m$.

Estimation of deep percolation using field moisture observations and HYDRUS-1D modeling in Haean basin (해안분지의 현장 토양수분 관측과 HYDRUS-1D 모델링을 이용한 지하수 함양 추정)

  • Kim, Jeong Jik;Jeon, Woo-Hyun;Lee, Jin-Yong
    • Journal of the Geological Society of Korea
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    • v.54 no.5
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    • pp.545-556
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    • 2018
  • This study was conducted to estimate the deep percolation using numerical modeling and field observation data based on rainfall in Haean basin. Soil moisture sensors were installed to monitoring at 30, 60 and 90 cm depths in four sites (YHS1-4) and automatic weather station was installed to around YHS3. Soil moisture and meteorological data was observed from March 25, 2017 to March 25, 2018 and May 06, 2016 to May 06, 2018, respectively. Numerical analysis was performed from June to August, 2017 using the HYDRUS-1D. Average soil moisture contents were high to generally in YHS3 for 0.300 to $0.334m^3/m^3$ and lowest in YHS1 for 0.129 to $0.265m^3/m^3$ during the soil moisture monitoring period. The results of soil moisture flow modeling showed that field observations and modeling values were similar but the peak values were larger in the modeling result. Correlation analysis between observation and modeling data showed that r, $r^2$ and RMSE were 0.88, 0.77, and 0.0096, respectively. This show high correlation and low error rate. The total deep percolation was 744.2 mm during the period of modelling at 500 cm depth. This showed that 61.3% of the precipitation amount (1,214 mm) was recharged in 2017. Deep percolation amount was high in the study area. This study is expected to provide basic data for the estimation of groundwater recharge through unsaturated zone.

Repetition and Inertia of Policy Failure -Focusing on the Case of Yangyang International Airport (정책실패의 반복과 관성에 관한 연구: 양양국제공항 사례를 중심으로)

  • Heo, Hyeok;Choi, Seonmi
    • The Journal of the Korea Contents Association
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    • v.18 no.12
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    • pp.456-467
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    • 2018
  • This study analyzed the repeated causes of policy failure focusing on Yangyang International Airport cases. Yangyang International Airport, which opened in 2002, was built with about 360 billion won, but it is considered as a representative example of policy failure of local airports. According to the policy failure theory, the failure factors of Yangyang International Airport are anlyzed by rationalistic, political, and environmental complexity viewpoint. The results are as follows. First, from a rationalist point of view, Yangyang Airport failed to achieve the policy goal of securing passengers and revitalizing local economy, This is due to the pressure of politics and the lack of geographical infrastructure. Second, the failure of the stakeholders to resolve conflicts in the flow of politics can be seen as the conflict between the airline and the airport, and the failure to reconcile conflicts between the government and the airports on the low cost airline permits and subsidies. Third, from the viewpoint of environmental complexity, Yangyang International Airport can be regarded as a failure to adapt to environmental changes such as the opening of nearby expressways and railway lines, and the sharp decline of Chinese tourists. This study sugeests the establishment of an independent organization that can prevent unreasonable business promotion by politics in the case of large scale national projects, the linkage with the surrounding infrastructure and related businesses in the case of transportation facilities such as airports and railways, and institutionalization of cooperative governance for coordinating conflict among stakeholders.

A Study on the Drop-in Tests of a Small Ice Maker Using R-404A Replacements R-448A and R-449A (소형 제빙기에 사용되는 R-404A 대체 R-448A, R-449A의 Drop-in Test에 대한 연구)

  • Lee, Byungmoo;Kim, Nae-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.1
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    • pp.21-27
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    • 2019
  • R-404A, which is used widely in small-scale ice makers, is scheduled to be phased out because of its high global warming potential. In this study, drop-in tests were conducted using R-448A and R-449A, which replace R-404A, to modify the outdoor air and supply water temperatures. The results showed that the daily ice production rate of R-404A was 5.3% higher than that of R-448A and 4.2% higher than that of R-449A. This was attributed to the larger vapor density of R-404A, which resulted in a larger mass flow rate in the system. Between R-448A and R-449A, R-448A yielded a larger amount of ice at low air and water temperatures, whereas R-449A yielded a larger amount of ice at high air and water temperatures. The daily power consumption of R-404A was approximately 10% larger than those of R-448A and R-449A. The resulting COPs of R-448A and R-449A was similar, only 3.0% larger than that of R-404A. The literature survey showed that the condensation or evaporation data of R-448A or R-449A are very limited, and research on this issue is recommended.

Occurrence and Chemical Composition of Minerals from the Pallancata Ag Mine, Peru (페루 Pallancata 은 광산에서 산출되는 광물들의 산상 및 화학조성)

  • Yoo, Bong Chul;Acosta, Jorge
    • Journal of the Mineralogical Society of Korea
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    • v.32 no.2
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    • pp.87-102
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    • 2019
  • Pallancata Ag mine is located at the Ayacucho region 520 km southeast of Lima. The geology of mine area consists of mainly Cenozoic volcanic-intrusive rocks, which are composed of tuff, andesitic lava, andesitic tuff, pyroclastic flow, volcano clasts, rhyolite and quartz monzonite. This mine have about 100 quartz veins in tuff filling regional faults orienting NW, NE and EW directions. The Ag grades in quartz veins are from 40 to 1,000 g/t. Quartz veins vary from 0.1 m to 25 m in thickness and extend to about 3,000 m in strike length. Quartz veins show following textures including zonation, cavity, massive, breccia, crustiform, colloform and comb textures. Wallrock alteration features including silicification, sericitization, pyritization, chloritization and argillitization are obvious. The quartz veins contain calcite, chalcedony, adularia, fluorite, rutile, zircon, apatite, Fe oxide, REE mineral, Cr oxide, Al-Si-O mineral, pyrite, sphalerite, chalcopyrite, galena, electrum, proustite-pyrargyrite, pearceite-polybasite and acanthite. The temperature and sulfur fugacity ($f_{s2}$) of the Ag mineralization estimated from the mineral assemblages and mineral compositions are ranging from 118 to $222^{\circ}C$ and from $10^{-20.8}$ to $10^{-13.2}atm$, respectively. The relatively low temperature and sulfur-oxygen fugacities in the hydrothermal fluids during the Ag mineralization in Pallancata might be due to cooling and/or boiling of Ag-bearing fluids by mixing of meteoric water in the relatively shallow hydrothermal environment. The hydrothermal condition may be corresponding to an intermediate sulfidation epithermal mineralization.

Soil Properties of Granitic Weathered Soils in the Landslide-prone Areas in Seoul (서울지역 화강암 풍화토 토층지반의 토질특성)

  • Kim, Kyeong-Su
    • The Journal of Engineering Geology
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    • v.29 no.1
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    • pp.23-35
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    • 2019
  • Landslides occur due to heavy rainfall in the summer season. Some of water may infiltrate into the ground; it causes a high saturation condition capable of causing a landslide. Soil properties are crucial in estimating slope stability and debris flow occurrence. The main study areas are Gwanaksan, Suraksan and Bukhansan (Mountain) in Seoul. A total of 44 soil samples were taken from the study area; and a series of geotechnical tests were performed. Physical and mechanical properties were obtained and compared based on region. As a result, among well-graded soils, they are classified as a clayey sand. Coarse-grained and fine-grained contents are approximately 95% and 5%, respectively, with very low amount of clay content. Density, liquid limit and dry unit weight are ranged in $2.62{\sim}2.67g/cm^3$, 27.93~38.15% and $1.092{\sim}1.814g/cm^3$. Cohesion and internal friction angle are 4 kPa and $35^{\circ}$ regardless of mountain area. Coefficient of permeability is varied between $3.07{\times}10^{-3}{\sim}4.61{\times}10^{-2}cm/sec$; it means that it results in great seepage. Permeability is inversely proportional to the uniformity coefficient and is proportional to the effective particle size. In the formal case, there was a difference by mountain area, while in the latter, the tendency was almost similar.

A Study on Heat Transfer and Pressure Drop Characteristics according to Block Size and Turbulence Generator's Placement in a Horizontal Channel (블록 크기 및 난류발생기 배치에 따른 수평채널내의 열전달 및 압력강하 특성에 관한 연구)

  • Seo, Kyu-Won;Lim, Jong-Han;Yoon, Jun-Kyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.4
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    • pp.639-647
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    • 2019
  • Recently, as the semiconductor integration technology due to miniaturization and high density of electronic equipment have developed, it is importantly recognized the application of thermal control system in order to release inner heat generated from chips, modules, In this study, we considered the heat transfer and pressure drop characteristics in a horizontal channel with four blocks using k-${\omega}$ SST turbulence model During CFD (Computational Fluid Dynamics) analysis, the parameters applied block width, block height, heat source and turbulence generator placement etc. As the boundary conditions of analysis, the channel inlet temperature and flow velocity were respectively 300 K and 3.84 m/s, the heat flux was $358W/m^2$. As a result, the heat transfer performance was decreased as the block width ratio (w/h) was increased, while it was increased as the block height ratio (h/w) was increased. In addition, as the arrangement of heat source size was increased to high heat flux from low heat flux, it was influenced by heat source size and the heat transfer coefficient showed a tendency to increase, When the turbulence generator was installed in the upper part of block No. 1 position the closely to the channel entrance, the heat transfer characteristics was greatly influenced on the whole of four heating blocks. and in oder to consider the pressure drop characteristics, we are able to select the most appropriate turbulence generator's position.

Suction Pressures with respect to the Operational Modes using the Multi-bore Capillary Membranes in the Membrane Bioreactor (생물막 반응기내 다공성 중공사형막을 이용한 운전방식에 따른 흡입 압력)

  • Kim, Min Hyeong;Koo, Eeung Mo;Lee, Min Soo;Chung, Kun Yong
    • Membrane Journal
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    • v.31 no.5
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    • pp.343-350
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    • 2021
  • In this study the suction pressure was measured with respect to operational time by submersing the multi-bore capillary membrane module in membrane bioreactor(MBR). The hexagonal shape capillary module which has the nominal pore size of 0.2 ㎛, outer diameter of 6.4 or 4.2 mm was immersed in MLSS 8,000 mg/L active sludge aqueous solution, and confirmed changes with respect to permeation flux and air flow rate. It was operated by the filtration/relaxation(FR), FR with backwashing(FR/BW), and sinusoidal flux continuous operation(SFCO) modes. The suction pressure for the SFCO and FR modes was lower at 30 and 50 L/m2·hr, respectively. In addition, the suction pressure of the module with a small outer diameter was relatively low. The suction pressure of a large outer diameter was greatly increased, but it could be reduced by more than 40% by backwashing.

Development of Noise and AI-based Pavement Condition Rating Evaluation System (소음도·인공지능 기반 포장상태등급 평가시스템 개발)

  • Han, Dae-Seok;Kim, Young-Rok
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.22 no.1
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    • pp.1-8
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    • 2021
  • This study developed low-cost and high-efficiency pavement condition monitoring technology to produce the key information required for pavement management. A noise and artificial intelligence-based monitoring system was devised to compensate for the shortcomings of existing high-end equipment that relies on visual information and high-end sensors. From idea establishment to system development, functional definition, information flow, architecture design, and finally, on-site field evaluations were carried out. As a result, confidence in the high level of artificial intelligence evaluation was secured. In addition, hardware and software elements and well-organized guidelines on system utilization were developed. The on-site evaluation process confirmed that non-experts could easily and quickly investigate and visualized the data. The evaluation results could support the management works of road managers. Furthermore, it could improve the completeness of the technologies, such as prior discriminating techniques for external conditions that are not considered in AI learning, system simplification, and variable speed response techniques. This paper presents a new paradigm for pavement monitoring technology that has lasted since the 1960s.

Towards a Transportation Support System for Off-site Construction : Identifying Key Functions and Diagramming Functional Blocks (오프사이트건설(Off-site Construction) 운반 시스템을 위한 핵심기능 도출 및 시스템 기능 전개도 개발)

  • Lee, Gangho;Kim, Minguk;Lee, Chansik;Koo, Choongwan;Kim, Taewan
    • Korean Journal of Construction Engineering and Management
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    • v.22 no.2
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    • pp.21-30
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    • 2021
  • The existing construction industry is classified into industries with low productivity compared to other industries. In order to solve the decline in productivity in the construction industry, the world is focusing on off-site construction (OSC), which is about 40% more productive than existing construction methods. This high productivity is possible because the three stages of production, transport to the site, and site assembly are consistently maintained in a continuous flow. This study conducted a functional survey through literature review, preliminary field survey, questionnaire, and expert interview. The surveyed function were classified into five categories: convenience, flexibility, manageability, communication, and safety, and the functional characteristics of flexibility, manageability, and communication were high. Because of the change according to the construction progress, the production schedule of the factory, and the variety of transportation time required. Finally, A functional block diagram was developed based on the 15 functions corresponding with an average score of 4 or more in the surveyed function score result. If the OSC transport system is established through this study, It can contribute to a successful construction OSC project and increase productivity.