• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.12-17
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• 2023

Aortic valve stenosis is a heart valve disease caused by the accumulation of calcium in the valve, which can divide into tricuspid aortic valve (TAV) stenosis and bicuspid aortic valve (BAV) stenosis depending on the shape of natural valve. In this study, pig heart-based TAV and BAV ex vivo models were fabricated, and the flow characteristics behind a valve were analyzed using 4D flow MRI. Flow behind normal TAV was uniformly distributed, while BAV asymmetrically opened with an eccentric strong jet. Especially, BAV ex vivo model exhibited a secondary flow in the region where the valve closed. In addition, BAV had a 26% higher peak velocity while maintaining similar stroke volume compared with normal TAV. This study would be helpful for understanding the flow characteristics for BAV AS patients.

• Journal of the Korean Vacuum Society
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• v.22 no.5
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• pp.238-244
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• 2013

Doping process using laser is an important process in fabrication of solar cell for heat treatment. However, the process of using the furnace is difficult to form a selective emitter doping region. The case of using a selective emitter laser doping is required an expensive laser equipment and induce the wafer's structure damage due to high temperature. This study, we fabricated a new costly plasma source. Through this, we research the selective emitter doping. We fabricated that the atmospheric pressure plasma jet injected Ar gas is inputted a low frequency (a few tens kHz). We used shallow doping wafers existing PSG (Phosphorus Silicate Glass) on the shallow doping CZ P-type wafer. Atmospheric plasma treatment time was 15 s and 30 s, and current for making the plasma is 40 mA and 70 mA. We investigated a doping profile by using SIMS (Secondary Ion Mass Spectroscopy) and we grasp the sheet resistance of electrical character by using doping profile. As result of experiment, prolonged doping process time and highly plasma current occur a deeper doping depth, moreover improve sheet resistance. We grasped the wafer's surface damage after atmospheric pressure plasma doping by using SEM (Scanning Electron Microscopy). We check that wafer's surface is not changed after plasma doping and atmospheric pressure doping width is broaden by increase of plasma treatment time and current.

• Solar Energy
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• v.13 no.1
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• pp.1-10
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• 1993

The purpose of this research is to investigate the characteristics of heat transfer in the downward axisymmetric free water jet system impinged on a flat oblique plate which has the uniform heat flux. Experimental conditions considered were Reynolds number, distance between nozzle and Bat plate, inclination angle of heater surface and nozzle exit velocity. Local Nusselt number was subjected to the influence of Re number, Pr number, oblique angle of heating surface and local position of flat plate. In the wall region of downward surface, The secondary peak point of heat transfer appeared at the local point of X/D=-8 from the stagnation point. The stagnation heat transfer rate of this experimental study augments 2.4 times than that of laminar theorical solution. The stagnation nusselt number is function of Reynolds number, nozzle-plate spacing Prandtl number and oblique angle of impinging plate.

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.104-108
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• 2001

Naphthalene derived mesophase pitch WP) was spun into short fibers by using melt-blown technology. The pitch fibers oxidative stabilization were carried out heating rates of $2^{\circ}C/min,\;5^{\circ}C/min\;and\; 10^{\circ}/min$. The heating rate was a key factor to maximate the capacity of the Li-ion secondary battery through controlling the morphology of the graphitized fiber. The diameters of the melt-blown fibers prepared were in the range of $4{\mu}m\~16{\mu}m$ with functions of air jet speed, air temperature and the temperature of the nozzle. The graphitized fibers of $10{\mu}m$ diameters showed various morphological structure with heating rate of the stabilization. Radial, radial-random and skin-core cross-sectional structure of the fibers were observed at the respective heating rate of $2^{\circ}C/min\;5^{\circ}C/min\;and\;10^{\circ}C/min$. Most crystalline structure of graphite was obtained from the fiber stabilized at heating rate of $10^{\circ}C/min$ exhibiting the best anode performance with 400 mAh/g of capacitance and $96.8\%$ of charge/discharge efficiency.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3068-3073
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the performance study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and shadow graph. Numerical simulation was also performed to study flow characteristics and interactions between ramp tabs. This paper provides to analyze the location of normal shock wave and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Journal of Navigation and Port Research
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• v.28 no.3
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• pp.259-268
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• 2004

For the last years, it has become hot issue such as disposal of the treated wastewater, which caused by increment of a population and industrial development at the coastal areas. The ocean outfall system discharges primary or secondary treated effluent into coastline or at the deep water, or between these two. The effluent, which has a density similar to that of fresh water, rises to the see, surface forming plume or jet, together with entraining the surrounding salt water and becomes very dilute. This paper deals ocean outfall design which effects to decision-making about marine environment management and wastewater treatment. In order to make predictions of dilution of discharged water and the trajectory of a plume, CORMIX has been used considering several elements including a seasonal and tidal changes. These solutions are strung together to provide basic data and general drawings for effective management of outfall.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.870-879
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• 2000

An experimental investigation is conducted to improve a slot film cooling system which can be used for the cooling of gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal-, parallel-, and counter-flow paths to the mainstream direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot with various injection types and coolant feeding directions. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The secondary flow at the lip exit has uniform velocity distributions for the parallel and vertical injection types, which are similar to the results of a two-dimensional slot injection. In the results of local heat/mass transfer coefficient, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effect of jet impingement. The lateral distributions of Sh with the parallel- and counter-flow paths are more uniform than the normal flow path. The averaged Sh with the injection holes are $2{\sim}5$ times higher than that of a smooth two-dimensional slot path.

• The KSFM Journal of Fluid Machinery
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• v.10 no.6
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• pp.32-37
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and schlieren system. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.2
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• pp.115-124
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• 2009

Cryogenic cutting technology is one of the most suitable technologies for dismantling nuclear facilities due to the fact that a secondary waste is not generated during the cutting process. In this paper, the feasibility of cryogenic cutting technology was investigated by using a computer simulation. In the computer simulation, a hybrid method combined with the SPH (smoothed particle hydrodynamics) method and the FE (finite element) method was used. And also, a penetration depth equation, for the design of the cryogenic cutting system, was used and the design variables and operation conditions to cut a 10 mm thickness for steel were determined. Finally, the main components of the cryogenic cutting system were manufactures on the basis of the obtained design variables and operation conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.109-112
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• 2004

Of late, the thrust vectoring control, using fluidic co-flow and counter-flow concepts, has been received much attention since it not only improves the maneuverability of propulsive engine but also reduces an additional material load due to the trailing control wings, which in turn reduce the aerodynamic drag. However, the control effects are not understood well since the flow field involves very complicated non: physics such as shock wave/boundary layer interaction, separation and significant unsteadiness. Existing data are not enough to achieve the effectiveness and usefulness of the thrust vectoring control, and systematic work is required for the purpose of practical applications In the present study, computational study has been performed to investigate the effects of the thrust vector control using the fluidic co-and counter-flow concepts. The results obtained show that, for a given pressure ratio, the thrust deflection angle has a maximum value at a certain suction flow rate, which is at less than $5\%$ of the mass flow rate of the primary jet. With a longer collar, the same vector angle is achievable with smaller mass flow rate.