• Journal of Korean Society of Environmental Engineers
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• v.35 no.10
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• pp.710-716
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• 2013

New and renewable energy sources have drawn attention because of climate change. Many studies have been carried out in waste-to-energy field. Fast pyrolysis of waste lignocelluosic biomass is one of the waste-to-energy technologies. Bubbling fluidized bed (BFB) reactor is widely used for fast pyrolysis of the biomass. In BFB pyrolyzer, bubble behavior influences on the chemical reaction. Accordingly, in the present study, hydrodynamic characteristics and fast pyrolysis reaction of waste lignocellulosic biomass occurring in a BFB pyrolyzer are scrutinized. The computational fluid dynamics (CFD) simulation of the fast pyrolysis reactor is carried out by using Eulerian-Granular approach. And two-stage semi-global kinetics is applied for modeling the fast pyrolysis reaction of waste lignocellulosic biomass. To summarize, generation and ascendant motion of bubbles in the bed affect particle behavior. Thus biomass particles are well mixed with hot sand and consequent rapid heat transfer occurs from sand to biomass particles. As a result, primary reaction is observed throughout the bed. And reaction rate of tar formation is the highest. Consequently, tar accounts for 66wt.% of the product gas. However, secondary reaction occurs mostly in the freeboard. Therefore, it is considered that bubble behavior and particle motions hardly influences on the secondary reaction.

• Journal of Navigation and Port Research
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• v.39 no.6
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• pp.539-544
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• 2015

There is drift toward moving offshore structures operating sites to deep water that brings subsea systems and types of apparatus to meet more severe environment than onshore. At this moment, climatic condition and seabed state affect trenching efficiency so trenching process is need to make steady progress in a short time. This paper is research on estimation about construction performance of waterjet trenching machine mounted on ROV trencher. Optimal number of nozzles that can maximize trenching efficiency is selected by considering clearance and angle of nozzles through CFD. Then verified effectiveness of waterjet apparatus on the result of trenching depth and velocity by model test analogized performance for construction work of waterjet trenching machine.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.593-593
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• 2012

본 연구는 화력 및 원자력 발전소로 취입된 냉각수(circulating and essential service water)가 복수기로부터 온배수 형태의 개수로 흐름으로 표층배수 될 경우 수온을 저감시키기 위해 주입하는 희석수(by-pass cooling water)와의 혼합효과의 효율성을 증대시키고, 불리한 수리현상을 야기하지 않으며, 경제적인 배수로 구조물을 고찰하기 위한 목적으로 시도되었다. 배수로 구조물 내 온배수와 희석수가 혼합되는 구간을 혼합지(mixing basin)라 하는데, 본 과업에서는 ${\bigcirc}{\bigcirc}$발전소의 배수로 구간 중 혼합지를 대상으로 FLOW-3D$^{(R)}$를 이용한 3차원 수치모형을 구축하고, 총 9개에 해당하는 각 대안별 현상을 분석하고 비교하였다. 각 대안들의 차이점은 배수로에 설치되는 보조구조물들의 형상과 배열 등이며, 복수기로부터 나오는 배출수의 수온은 $42^{\circ}C$, 희석수는 $35^{\circ}C$이고, 본 과업의 주요 관심대상 물리량은 유속과 온도이다. 배수로에 아무런 보조 구조물이 없는 형태인 기본 계획안을 검토한 결과, 평균 $3.31^{\circ}C$의 수온강하가 이루어졌으나, 우안 쪽으로 강한 흐름이 발생하여 수온의 좌우편차가 $4.61^{\circ}C$ 가량 발생하는 것으로 나타났다. 기본 계획안의 검토결과를 보완하기 위한 대안으로 연직 흐름의 소산을 위해 고안된 잠형 소파블록(baffle block) 설치안은 평균 $3.06^{\circ}C$의 수온강하가 이루어지고 $4.44^{\circ}C$의 수온 좌우편차가 발생했다. 지그재그(zigzag) 형태의 흐름을 만들어 혼합효과를 올리기 위한 미로형 수제(labyrinth groin) 설치안은 평균 $5.33^{\circ}C$의 수온강하가 이루어지고, $1.43^{\circ}C$의 수온 좌우편차를 보여줘 검토했던 대안들 중 가장 좋은 결과를 보여주었다. V자 배열 소파블럭(deformed block) 설치안은 연직 및 수평방향의 소산을 기대했으나 평균 $3.00^{\circ}C$의 수온 강하와 $4.41^{\circ}C$의 수온 좌우편차를 나타냈다. 벤츄리(Venturi) 형태의 흐름을 발생시키기 위한 병목형(bottleneck) 수로안은 평균 $3.18^{\circ}C$의 수온강하와 $3.94^{\circ}C$의 수온 좌우편차, 흐름의 소산과 흐름방향을 변화시키기 위한 와형 수제(swirl groin) 설치안은 평균 $2.24^{\circ}C$의 수온강하와 $1.48^{\circ}C$의 수온좌우편차, 우안 흐름을 지연시키기 위한 물방석(water cushion) 수로안은 평균 $3.03^{\circ}C$의 수온강하와 $4.50^{\circ}C$의 수온 좌우편차, 우안의 흐름을 좌안으로 보내기 위한 분사형(injector) 수로안은 평균 $3.13^{\circ}C$의 수온강하와 $4.45^{\circ}C$의 수온 좌우편차, 우안의 흐름을 막기 위한 외팔형 수제(cantilever groin) 설치안은 평균 $3.11^{\circ}C$의 수온강하와 $3.02^{\circ}C$의 수온 좌우편차가 발생하는 것으로 나타났다.

• Journal of Internet Computing and Services
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• v.17 no.6
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• pp.71-79
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• 2016

As computer technology continues to evolve, the Computational Sciences utilized in Physics, Chemistry, Materials Science, and Life Sciences have been attracting more attention. In Korea, to compensate for the drawbacks in Computational Science, students and researchers have been using the EDISON platform. The EDISON platform provides a web portal service for education and research and an environment for addressing complex issues involving five fields, e.g., Computational Fluid Dynamics (CFD), Nanophysics, Computational Chemistry, Structural Dynamics, and Computational Design. As the platform and user scale increase beyond service provision, the need for efficient operation of its currently running data management system is on the rise. In this study, we resolve the data synchronization issues between the existing EDISON platform and web portal. As the EDISON platform is integrated with the web portal, a file management service is implemented to integrate the management of user data and files, which ultimately improves the overall efficiency of file management.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.618-627
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• 2016

This study numerically analyzes the characteristics of the velocity distribution for each location of a square-sectional $180^{\circ}$ bent duct using a Reynolds Stress Turbulent model. The flow parameters were varied, including the working fluids, inlet velocity, surface roughness, radius of curvature, and hydraulic diameter. The boundary conditions for computational fluid dynamics analysis were inlet temperatures of air and water of 288 K and 293 K, inlet air velocity of 3-15 m/s, inner surface roughness of 0-0.001 mm, radius of curvature of 2.5-4.5 D, and hydraulic diameter of 70-100 mm. The working fluid characteristics were highly affected by changes in the viscous force. The maximum velocity profiles in the bent duct were indicated when the $90^{\circ}$ section was in the region of X/D=0.8 and the $180^{\circ}$ section was in the region of Y/D=0.8. Lower surface roughness and higher radius of curvature resulted in a higher rate of velocity change. Also, an efficient measuring location downstream of the bent duct is suggested since the flow deviations were the most stable when the straight duct length was in the region of L/D=30. The minimum deviations at the same velocity conditions according to the hydraulic diameter were mostly indicated in the range of L/D=15-30 based on the standard deviation characteristics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.126-132
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• 2016

This study numerically investigates the characteristics of chemical reactions and thermal deformation in a steam reformer. These phenomena are significantly affected by the high-temperature burner gas and the process gas conditions. Because the high temperature of the burner gas ranges from 800 to 1000 K, the reformer tubes undergo substantial thermal deformation, eventually resulting in structural failure. Thus, it is necessary to understand the characteristics of the reaction and thermal deformation under the operating conditions to evaluate the reformer tubes for sustainable, stable operation. Extensive numerical simulations were carried out using commercial CFD code (ANSYS FLUENT/MECHANICA Ver. 13.0) while considering three-dimensional turbulent flows and combined heat transfer including conduction, convection, and radiation. Structural analysis considering conjugated heat transfer between solid tubes and fluid flows was conducted using the Fluid-Solid Interaction (FSI) method. The results show that when the injection temperature of the process gas and burner gas decreased, the hydrogen production rate decreased significantly, and thermal deformation decreased by at least 15 to 20%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.527-535
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• 2017

Heat management is one of the most critical issues in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) installed inside the fuel cell power pack of a fuel cell battery hybrid UPS. If the heat generated by the chemical reaction in the fuel cell is not rapidly removed, the durability and performance of the fuel cell may be affected, which may shorten its lifetime. Therefore, the objective of this study is to select and propose a proper cooling method for the fuel cells used in the fuel cell power pack of a UPS. In order to find the most appropriate cooling method, the various design factors affecting the cooling performance were studied. The numerical analysis was performed by a commercial program, i.e., COMSOL Multiphysics. Firstly, the surface temperature of the 1 kW class fuel cell stack with the cooling fans placed at the top was compared with the one with the cooling fans placed at the bottom. Various rotation speeds of the cooling fan, viz. 2,500, 3,000, 3,500, and 4,000 RPM, were tested to determine the proper cooling fan speed. In addition, the influence of the inhaled air flow rate was investigated by changing the porous area of the grille, which is the entrance of the air flowing from the outside to the inside of the power pack. As a result, it was found that for the operating conditions of the 1 kW class PEMFC to be acceptable, the cooling fan was required to have a minimum rotating speed of 3500 RPM to maintain the fuel cell surface temperature within an acceptable range. The results of this study can be effectively applied to the development of thermal management technology for the fuel cells inside the fuel cell power pack of a UPS.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.671-679
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• 2008

The effect of Pre-cooled Turbojet Engine installation and nozzle exhaust jet on Hypersonic Turbojet EXperimental aircraft(HYTEX aircraft) were investigated by three-dimensional numerical analyses to obtain aerodynamic characteristics of the aircraft during its in-flight condition. First, simulations of wind tunnel experiment using small scale model of the aircraft with and without the rectangular duct reproducing engine was performed at M=5.1 condition in order to validate the calculation code. Here, good agreements with experimental data were obtained regarding centerline wall pressures on the aircraft and aerodynamic coefficients of forces and moments acting on the aircraft. Next, full scale integrated analysis of the aircraft and the engine were conducted for flight Mach numbers of M=5.0, 4.0, 3.5, 3.0, and 2.0. Increasing the angle of attack $\alpha$ of the aircraft in M=5.0 flight increased the mass flow rate of the air captured at the intake due to pre-compression effect of the nose shockwave, also increasing the thrust obtained at the engine plug nozzle. Sufficient thrust for acceleration were obtained at $\alpha=3$ and 5 degrees. Increase of flight Mach number at $\alpha=0$ degrees resulted in decrease of mass flow rate captured at the engine intake, and thus decrease in thrust at the nozzle. The thrust was sufficient for acceleration at M=3.5 and lower cases. Lift force on the aircraft was increased by the integration of engine on the aircraft for all varying angles of attack or flight Mach numbers. However, the slope of lift increase when increasing flight Mach number showed decrease as flight Mach number reach to M=5.0, due to the separation shockwave at the upper surface of the aircraft. Pitch moment of the aircraft was not affected by the installation of the engines for all angles of attack at M=5.0 condition. In low Mach number cases at $\alpha=0$ degrees, installation of the engines increased the pitch moment compared to no engine configuration. Installation of the engines increased the frictional drag on the aircraft, and its percentage to the total drag ranged between 30-50% for varying angle of attack in M=5.0 flight.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.613-620
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• 2021

A flow channel shape of PEMFC has an influence on the internal flow uniformity. If the reactant distribution in a flow path is not uniform during operation, both catalyst deactivation and mechanical damage of membrane could occur resulting in decreasing the membrane electrode assembly (MEA) durability. Numerous studies concerning flow design have been conducted to make smooth supply and uniform distribution of reactants in fuel cells. The baffle of flow path could improve fuel cell performance through the forced convection effect. A sub-channel, as an additional air flow path, could increase the reactant concentration and reduce the mass transfer loss via a smooth water discharge. In this study, computational fluid dynamics (CFD) was used to analyze the effect of blocks and sub-channels on the current density and oxygen concentration of the fuel cell. As a result, the limit current density and oxygen concentration at a rear block increased when using blocks and sub-channels in a flow channel. In particular, the current density increased significantly when the sub-channel was placed between two blocks. Also, the sub-channel position was optimized by analyzing the oxygen concentration, and the oxygen concentration was recovered at a rear block in the fuel cell.

• Clean Technology
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• v.25 no.2
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• pp.153-160
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• 2019

As air pollution becomes more serious due to the increased number of diesel vessel operations, ship regulations on harmful emissions strengthen. Therefore, the development of a diesel exhaust after-treatment system for ships is required, and the higher the flow uniformity of the exhaust treatment system, the higher the treatment efficiency. With the computer software ANSYS Fluent, pressure drop and flow uniformity were used in this study to simulate flow rate with and without a baffle in both a Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) system. The system pressure drop was found to be 38 to 40 mbar in the existing system condition, and the flow uniformity was approximately 84 to 92% at the inlet and outlet of the DOC. When the baffle was installed inside the system, the pressure increased and the flow uniformity was lowered due to an increase in flow rate. When the exhaust gas flow was reduced by 50% from $7,548kg\;h^{-1}$ to $3,772kg\;h^{-1}$, the flow uniformity at the inlet and outlet of the DOC increased by approximately 1 to 3% due to the low flow rate. In the case of DPF, the flow uniformity of exhaust gas was 98 to 99% because the uneven flow proceeded after uniformly flowing from the DOC.