• Journal of Advanced Marine Engineering and Technology
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• v.38 no.2
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• pp.140-146
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• 2014

Stenosis is the drastic reduction in the cross-sectional area of blood vessel caused by accumulations of cholesterol. It affects the blood flow property and structure from the fluid dynamic point of view. To understand the flow phenomenon more clearly, a particle image velocimetry method is used and the fluid dynamic characteristics in a circular channel containing stenosis structure is investigated experimentally in this study. Different stenotic-structured models made of acrylic material are subjected to a pulsatile flow generated by an in-house designed pulsatile pump. The inner diameter of the tube inlet is 20 mm and the length of reduced area for stenosis ranges between 35mm and 40mm. It is circulated continuously through a circular channel by the pump system. Pressure is measured at four different sections during systolic and diastolic phase changes. The phase-averaged velocity field distribution shows a recirculation regime after the stenotic structure. The effects of the stenotic obstructions are found to be more severe when the aspect ratio is varied.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.705-706
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• 2002

Hemodynamics of the TPLS(Twin Pulse Life Support System) is numerically investigated to delineate the possibility of hemolysis in blood. Computational method employing finite element algorithm is utilized to solve the blood flow of the sac squeezed by moving actuator. We assume that the blood flow interacts with the sac material which is activated by the rigid body motion of the actuator. Valve dynamics at the ends of the sac is simplified as on/off type motion. We compute the transient viscous flow in the two-dimensional geometry of the blood sac. Incompressible laminar flow is simulated on the assumption of Newtonian fluid. Blood velocity has a step gradient near the throat of the sac formed by the moving actuator. According to the decrease of the gap size of blood passage, the magnitude of shear stress in the blood is dramatically increased. Numerical solutions show that the maximum value of shear stress in the blood flow in TPLS is relatively smaller than that of the roller type ECLS.

• Corrosion Science and Technology
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• v.16 no.1
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• pp.23-30
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• 2017

The inhibition effect of thioureido imidazoline inhibitor (TAI) for flow accelerated corrosion (FAC) at different locations for an X65 carbon steel elbow was studied by array electrode and computational fluid dynamics (CFD) simulations. The distribution of the inhibition efficiency measured by electrochemical impedance spectroscopy (EIS) is in good accordance with the distribution of the hydrodynamic parameters at the elbow. The inhibition efficiencies at the outer wall are higher than those at the inner wall meaning that the lower inhibition efficiency is associated with a higher flow velocity, shear stress, and turbulent kinetic energy at the inner wall of the elbow, as well as secondary flow at the elbow rather than the mass transport of inhibitor molecules. Compared to the static condition, the inhibition efficiency of TAI for FAC was relatively low. It is also due to a drastic turbulence flow and high wall shear stress during the FAC test, which prevents the adsorption of inhibitor and/or damages the adsorbed inhibitor film.

• Journal of Hydrogen and New Energy
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• v.25 no.4
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• pp.443-448
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• 2014

This paper describes thermal flow characteristics in various pipelines: straight pipeline and curved pipeline. In the permafrost area, pipelines are exposed to an extremely low temperature ($-40^{\circ}C$). In this situation, three-dimensional flow analysis should be analyzed to investigate thermal effects such as pressure drop, temperature change, velocity deficit and distribution change of liquid droplet of internal fluid. In this paper, multi-phase and multi-species analysis was introduced to analyze the flow characteristics of permafrost pipelines on the vertical support members above ground.

• International Journal of Advanced Culture Technology
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• v.10 no.3
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• pp.295-306
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• 2022

The NOx removal performance of the SCR process depends on various factors such as catalytic factors (catalyst composition, shape, space velocity, etc.), temperature and flow rate distribution of the exhaust gas. Among them, the uniformity of the flow flowing into the catalyst bed plays the most important role. In this study, the flow characteristics in the SCR reactor in the design stage were simulated using a three-dimensional numerical analysis technique to confirm the uniformity of the airflow. Due to the limitation of the installation space, the shape of the inlet duct was compared with the two types of inlet duct shape because there were many curved sections of the inlet duct and the duct size margin was not large. The effect of inlet duct shape, guide vane or mixer installation, and venturi shape change on SCR reactor internal flow, airflow uniformity, and space utilization rate of ammonia concentration were studied. It was found that the uniformity of the airflow reaching the catalyst layer was greatly improved when an inlet duct with a shape that could suppress drift was applied and guide vanes were installed in the curved part of the inlet duct to properly distribute the process gas. In addition, the space utilization rate was greatly improved when the duct at the rear of the nozzle was applied as a venturi type rather than a mixer for uniform distribution of ammonia gas.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.48-59
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• 2017

In this study, an analysis of the thermo-fluid dynamic and missile-motion performance was carried out through a numerical simulation inside the missile canister. Calculation was made in an analytical volume using dynamic grid and evaporated water was used as a coolant. To analyze the interaction among the hot gas, coolant, and mixture flow, Realizable $k-{\varepsilon}$ turbulence and VOF (Volume Of Fluid) model were chosen and a parametric study was performed with the change of coolant flow rate. As a result of the analysis, pressure of the canister showed a large difference depending on the presence or absence of the coolant, and also showed a dependancy on the amount of coolant. Velocity and acceleration were dependent on the canister pressure.

• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.125-132
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• 2006

To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.66-74
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• 2011

The SCR catalyst in coal-fired power plant is eroded by the collision of fly ash on the catalyst surface. However the erosion of SCR catalyst by the collision of fly ash has not been fully studied, especially in terms of fluid dynamics. Hence, in the present study, we focus on the gas and solid flows inside the SCR catalyst duct and their consequent effect on the erosion characteristics. For this purpose, computational fluid dynamics is applied to investigate the two-phase flows and to evaluate the erosion rate for different flow and particle injection conditions. Also, the erosion rate and pressure drop of commonly used square shape are compared with equilateral triangle and hexagon shapes. The pressure drop of SCR catalyst is increased when SCR catalyst surface area per unit volume increases. The erosion rate of SCR catalyst is enhanced when the particle velocity, mass flow rate of particle, particle diameter and cell density of SCR catalyst are increased. From the results, the pressure drop and erosion rate at the catalyst surface can be minimized by reducing cell density of SCR catalyst to decrease particle velocity and number of particle impacts.

• Particle and aerosol research
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• v.11 no.2
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• pp.47-55
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• 2015

This study compares the results of collection efficiency of difference gas temperature in cyclone dust collector. The previous researcher's experiment results were used to confirm the reliability of CFD(Computational Fluid Dynamics) model. Based on this verified CFD model, we extended the analysis on the cyclone dust collectors. In CFD study, we used RNG k-epsilon model for analysis of turbulence flow, fluid is air, the velocity at inlet is 10 m/s, the temperature of air is $20^{\circ}C$, $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, $600^{\circ}C$ and $1000^{\circ}C$. As the temperature decreases, the average velocity of outer vortex and collection efficiency is increased, showed the highest collection efficiency at $20^{\circ}C$. It can be inferred smooth flow in cyclone dust collector is difficult because air viscosity increases as temperature increases. The power required at $1000^{\circ}C$ is almost 18 times greater than that of $20^{\circ}C$ to get the similar collection efficiency.

• Structural Engineering and Mechanics
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• v.68 no.3
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• pp.359-368
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• 2018

This paper deals with the dynamic stability of nanocomposite pipes conveying pulsating ferrofluid. The pipe is reinforced by carbon nanotubes (CNTs) where the agglomeration of CNTs are considered based on Mori-Tanaka model. Due to the existence of CNTs and ferrofluid flow, the structure and fluid are subjected to axial magnetic field. Based on Navier-Stokes equation and considering the body forced induced by magnetic field, the external force of fluid to the pipe is derived. For mathematical modeling of the pipe, the first order shear deformation theory (FSDT) is used where the energy method and Hamilton's principle are used for obtaining the motion equations. Using harmonic differential quadrature method (HDQM) and Bolotin's method, the motion equations are solved for calculating the excitation frequency and dynamic instability region (DIR) of the structure. The influences of different parameters such as volume fraction and agglomeration of CNTs, magnetic field, structural damping, viscoelastic medium, fluid velocity and boundary conditions are shown on the DIR of the structure. Results show that with considering agglomeration of CNTs, the DIR shifts to the lower excitation frequencies. In addition, the DIR of the structure will be happened at higher excitation frequencies with increasing the magnetic field.