• Journal of computational fluids engineering
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• v.22 no.1
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• pp.67-80
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• 2017

The high-speed bypass effect on the heat exchanger performance has been investigated numerically. The plate-fin type heat exchanger was modeled using two-dimensional porous approximation for the fin region. Governing equations of mass, momentum, and energy equations for compressible turbulent flow were solved using ideal-gas assumption for the air flow. Various bypass-channel height were considered for Mach numbers ranging 0.25-0.65. Due to the existence of the fin in the bypass channel, the main flow tends to turn into the core region of the channel, which results in the distorted velocity profile downstream of the fin region. The boundary layer thickness, displacement thickness, and the momentum thickness showed the variation of mass flow through the fin region. The mass flow variation along the fin region was also shown for various bypass heights and Mach numbers. The volumetric entropy generation was used to assess the loss mechanism inside the bypass duct and the fin region. Finally, the correlations of the friction factor and the Colburn j-factor are summarized.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.109-112
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• 1997

The Hydrodynamic performance of the trileaflet polymer prosthetic valves depends on the design of the leaflet and the physical properties of the leaflet membrane. In order to study the effect of leaflet membrane elasticity on the hemodynamic performance of trileaflet prosthetic valve, leaflet membranes are manufactured using two different polymers - Biospan and Tecoflex SG-93A. The hemodynamic performance parameters are measured under steady and physiological pulsatile flow, and compared with monoleaflet polymer valve(floating valve) and bileaflet mechanical valve(St. Jude Medical valve). Well designed trileaflet valve shows the lowest mean pressure drop among the tested valves. The trileaflet valves with Biospan membrane show lower pressure drop and back low comparing to those with Tecoflex membrane. More elastic membrane may provide wide opening area during systole and close membrane ree edge contact during diastole. Durability of trileaflet valves are also tested in vitro. Trileaflet valves with non-uniform membrane thickness ail within 17 days because of stress concentration. Trileaflet polymer valves with uniform membrane thickness perform well over 55 days without failure.

• Journal of Biomedical Engineering Research
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• v.17 no.1
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• pp.49-60
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• 1996

An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) withdifferent leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison test. Pressure drops of MLPVS are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of the polymer valve, the larger are the corresponding pressure drop. The velocity profiles for MLPs reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVS at a flow rate of $30{\ell}$/min are in the range 50-130 dyn/$cm^2$, and the corresponding maximum Reynolds shear stresses are in the range of 100-500 dyn/$cm^2$, respectively, which are beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it may be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the Important parameters.

• Journal of Biomedical Engineering Research
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• v.18 no.2
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• pp.147-156
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• 1997

Various prosthetic heart valves have been developed and used clinically, but they have problems, such as thrombogenecity, hemoltsis, high cost and low durability. New types of trileaflet polymer heart valves have been developed in order to use them as inlet and outlet valves in a ventricular assist device. The aim of this study is to determine the hydrodynamic effectiveness of the newly designed trileaflet polymer valves and their feasibility for temporary use in the blood pumps. Trileaflet polymer valves are made of polyurethane, because of its good blood compatibility, high tonsil strength and good resistance to fatigue. An in vitro experimental investigation was perf'ormed in order to ev91ua1e hydrodynamic performance of the trileaflet polymer valves having different design and fabrication tech- niques. The St. Jude Medical valve (SJMV) and floating-type monoleaflet polymer valve (MLPV) were also tested The pressure drop across the valve, leakage volume, and the flow patterns mere investigated for valves. The result of comparative tests showed that the trileaflet polymer valves had a better hydrodynamic performance than the others. TPV which has two stable membrane shape showed the lowest back flow. The pressure hops of TPVs were lower than that of MLPV, but slightly higher than SJMV. The hydrodynamic performance of valves under the pulastile flow showed the similar results as steady flow. The velocity profiles and turbulent intensities were measured at the distal sites of valves using a hot-film anemometer. Central flow was maintained in trileaflet polymer valves, and the maximum turbulent intensities were lower in TPVs comparing to MLPV.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.241-246
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• 1995

An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) with different leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison tests. Pressure drops of MLPVs are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of a polymer valve, the larger arc the corresponding press drop. The velocity profiles for MLPV reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVs at a flow rate of 30 l/min are in the range $54-130\;dyn/cm^2$, and the corresponding maximum. Reynolds shear stresses are in the range of $100-500\;dyn/cm^2$, respectively. Both arc beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it can be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the important parameters.

• Journal of Ocean Engineering and Technology
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• v.26 no.6
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• pp.39-45
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• 2012

Underwater robots are generally used for the construction of seabed structures, deep-sea ecosystem research, ocean energy development, etc. A ducted marine propulsor is widely used for the thruster of an underwater robot because of its collision protection, efficiency increase, cavitation reduction, etc. However, the flow of a ducted propeller is very complex because it involves strong flow interactions between the blade impeller and duct. The present work aimed to design a ducted propeller using 2-D strip theory and CFD analysis. The hydrodynamic forces (i.e. and ) were computed to set the local angle of attack in a spanwise direction of the propeller blade. After the propeller design, performance coefficients such as the thrust, torque, and efficiency were computed to check whether the designed performance was achieved. To validate the present analysis, the thrust was compared with experimental data and good agreement was obtained.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.88-93
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• 2017

For the control of pre-burner combustion pressure, the open angle of TTR(Throttle for Thrust Regulation) valve was varied from $143^{\circ}$ to $185^{\circ}$ while testing of cold flow, ignition, combustion. The major performance variables of rocket engine and hydraulic performance of TTR valve regarding the open angle was verified. However the controllability of pre-burner combustion pressure was not verified due to the limitations of test. The comprehensive research will be done after supplementing these problems.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.55-61
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• 2022

There is a major interest in diagnostic technology for multiple cancers worldwide. In order to reduce the difficulty of cancer diagnosis, a liquid biopsy technology based on a microfluidic device using trace amounts of biofluids such as blood is being studied. And optical biosensing, which measures the concentration of analytes through fluorescence imaging using biofluids, requires various strategies to improve sensitivity, and specialists and equipment are needed to carry out these strategies. This leads to an increase in diagnostic and production costs, and it is necessary to develop a technology to solve this problem. In this paper, we design and propose a fluorescent multi-cancer diagnostic sensing platform structure that implements passive self-separation technology and molecular recognition activation functions by fluid mixing, only with the geometry and microfluidic phenomena of microchannels based on self-driven flow by capillary force. In order to check the parameters affecting the performance of the plasma separation part of the designed sensor, the hydrodynamic diameter of the channel and the viscosity of the fluid were set as variables to confirm the formation of plasma separation flow through simulation. And finally, we propose an optimal sensor platform structure.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.535-543
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• 2022

A CPFD (Computational particle fluid dynamics) model of solar fluidized bed receiver of silicon carbide (SiC: average d_p=123 ㎛) particles was established, and the model was verified by comparing the simulation and experimental results to analyze the effect of particle behavior on the performance of the receiver. The relationship between the heat-absorbing performance and the particles behavior in the receiver was analyzed by simulating their behavior near bed surface, which is difficult to access experimentally. The CPFD simulation results showed good agreement with the experimental values on the solids holdup and its standard deviation under experimental condition in bed and freeboard regions. The local solid holdups near the bed surface, where particles primarily absorb solar heat energy and transfer it to the inside of the bed, showed a non-uniform distribution with a relatively low value at the center related with the bubble behavior in the bed. The local solid holdup increased the axial and radial non-uniformity in the freeboard region with the gas velocity, which explains well that the increase in the RSD (Relative standard deviation) of pressure drop across the freeboard region is responsible for the loss of solar energy reflected by the entrained particles in the particle receiver. The simulation results of local gas and particle velocities with gas velocity confirmed that the local particle behavior in the fluidized bed are closely related to the bubble behavior characterized by the properties of the Geldart B particles. The temperature difference of the fluidizing gas passing through the receiver per irradiance (∆T/I_DNI) was highly correlated with the RSD of the pressure drop across the bed surface and the freeboard regions. The CPFD simulation results can be used to improve the performance of the particle receiver through local particle behavior analysis.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.772-779
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• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.