• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.98-104
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• 2007

The carbon fiber reinforced carbon composite (CFRC) materials are necessary for the advanced industries that require the thermal resistance. And the development and research for CFRC has been in progress in the field of aerospace and defense industry. CFRC have several advantages and special properties such as excellent anti ablation, outstanding strength retention at very high temperature, high heat capacity and thermal transport, high specific stiffness and strength, and high thermal shock resistance. They have been used as aircraft brake, rocket nozzle, nose cones, jet engine turbine wheels, and high speed craft. Since the technology related to CFRC was prohibited from importing and exporting, we developed our own technology to produce F-16 B32 brake disk made out of CFRC, and then we performed various tests to observe the characteristics of CFRC-based brake disk developed in this study in view of density, strength, friction, specific heat, and heat conductivity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.887-890
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• 1997

Recently micromachining using DPSSL(Diode Pumped Solid State Laser) with 3rd harmonic wavelength is actively studied in laser machining area. Micromachining using DPSSL have outstanding advantages as UV source comparing with excimer laser in various aspect such a maintenance cost, maskless machining, high repetition rate and so on. In this study micro-drilling of PCB type substrate which consists of Cu-PI-Cu layer was performed using DPSS Nd:YAG laser(355nm, wavelength) in vector scanning method. Experimental and numerical method(Matlab simulation, FEM) are used to optimize process parameter and control machining depth. The man mechanism of this process is laser ablation. It is known that there is large gap between energy threshold of copper and that of PI. Matlab simulation considering energy threshold of material is performed to effect of duplication of pulse and FEM thermal analysis is used to predict the ablation depth of copper. This study could be widely used in various laser micromachining including via hole microdrilling of PCB, and micromachining of semiconductor components, medical parts and printer nozzle and so on.

• Laser Solutions
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• v.2 no.3
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• pp.11-18
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• 1999

This paper describes the weldability of carbon steel and stainless steel using 5㎾ $CO_2$ laser system with nearly multi-mode beam and a parabolic focusing mirror. In the laser welding of steels, major welding parameters are focal point, travel speed, beam power, shield gas and gap tolerance, etc.. Two kinds of gases(Ar, He) were used as a assist gas and supplied through the external nozzle. It is very important for optimum condition to remove plasma plume which absorbs laser beam and to obtain deep penetration and sound weld bead. Bead-on-plate welding tests were carried out for the experiments. Penetration data were obtained with various welding parameters and the effects of welding parameters were discussed. Butt welding tests were performed with various conditions. Only the optimum laser parameters assured good weld quality As a result of this study, We achieve the fundamental weldabilities using a high power $CO_2$ laser for carbon steel and stainless steel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1061-1073
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• 1996

Vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream without any chemical reactions. The phenomena of energy separation taking place in a vortex tube has been investigated experimentally. Recently, vortex tube is widely used to local cooler of industrial equipments and air conditioner of special purpose. In this study, experimental study on vortex tube efficiency was performed with various cold end orifices and nozzles type. The experimental results indicate that there is an optimum diameter of cold end orifice and nozzle type for the best cooling performance. The variation of the maximum wall temperature along the vortex tube surface provides useful information about the location of the stagnation point of the flow field at the axis of the vortex tube. The similarity relation for the prediction of the temperature of the cold exit air was obtained.

• Journal of ILASS-Korea
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• v.19 no.2
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• pp.75-81
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• 2014

Swirl flow in the gun type burner has a decisive effect on the stabilization of the flame, improvement of the combustion efficiency, and also a reduction of NOx. This swirl flow is created by the spinner which is inside the airtube that guide the combustion air. Gun type burner has generally the inner devices composed nozzle adapter, spark gap ignitor, and spinner. These inner components change the air flow behavior passing through air tube. Meanwhile, turbulent characteristics of this air flow are important to understand the combustion phenomena in the gun type burner, because the mixture of fuel and air are depended on. However, nearly all of the studies have been analyzed the turbulent flow of simplified combustion formation without the inner devices. So, this study conducted the measurement using by hot-wire anemometer and analyzed turbulent flow characteristics of the swirl flow discharged from the air tube with inner devices. Turbulence characteristics come up in this study were turbulence intensity, kinetic energy and shear stress of the air flow with the change of the distance of axial direction from the exit of the air tube.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.3
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• pp.215-222
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• 2014

This paper presents an experimental study of a vibration-assisted dry micro-wire electrical discharge machining (${\mu}$-WEDM) utilized in high precision and micro-manufacturing area. The assisted vibration was applied to the workpiece using a piezoelectric actuator, and high pressure air was injected directly into the machining gap through a nozzle. Investigation experiments were performed to estimate the importance of input parameters and it was observed from experiment results that the width (kerf) of the cutting slot and the machining time were significantly affected by the air injection pressure and input energy. Moreover, it was also observed that there exists an optimal relationship between the machining time and input parameters including the air pressure and vibration frequency and amplitude. Central composite design based experiments were also carried out, and empirical models of the machining time and cutting slot kerf have been developed using the response surface methodology to analyze and optimize the process.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.6
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• pp.233-241
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• 2005

The present model of a SF6 arc accounts for the copper vapour contamination from the electrodes inside a Laval nozzle of a circuit breaker. Steady state simulations have been done for the arc with electrode gap of 60mm and DC electric current of 500A, 1000A and 1500A for both cases with and without copper contamination. The effects of electrode polarity are considered for the arc current of 1000A. It was found out that evaporation of copper from the anode results in a cooling of the arc in a region close to the electrodes. The electrical potential across the electrodes is not sensitive to the presence of copper vapour, typically less than $4\%$ difference. Transient analysis has been done in order to obtain the arc properties at current zero. The arc current is increased linearly from -1000 to 0A when the upstream electrode is cathode with constant dI/dt of $27.0A/{\mu}s$ (or decreased linearly from 1000 to 0A when upstream electrode is anode). It has been predicted that the presence of copper vapour reduces the interruption capability of the breaker.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.215-221
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• 2023

Proton treatment may deliver a larger dose to a patient's skin than traditional photon therapy, especially when a range shifter (RS) is inserted in the beam path. This study investigated the effects of an RS on skin dose while considering RS with different thicknesses, airgaps and materials. First, the physical model of the scanning nozzle with RS was established in the TOol for PArticle Simulation (TOPAS) code, and the effects of the RS on the skin dose were studied. Second, the variations in the skin dose and isocenter beam size were examined by reducing the air gap. Finally, the effects of different RS materials, such as polymethylmethacrylate (PMMA), Lexan, polyethylene and polystyrene, on the skin dose were analysed. The results demonstrated that the current RS design had a negligible effect on the skin dose, whereas the RS significantly impacted the isocenter beam size. The skin dose was increased considerably when the RS was placed close to the phantom. Moreover, the magnitude of the increase was related to the thickness of the inserted RS. Meanwhile, the results also revealed that the secondary proton primarily contributed to the increased skin dose.

• Clean Technology
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• v.27 no.1
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• pp.61-68
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• 2021

Selective catalytic reduction (SCR) is widely used as a method of removing nitrogen oxide in large-capacity thermal power generation systems. Uniform mixing of the injected ammonia and the inlet flue gas is very important to the performance of the denitrification reduction process in the catalyst bed. In the present study, a computational analysis technique was applied to the ammonia injection system design process of a denitrification facility. The applied model is the denitrification facility of an 800 MW class coal-fired power plant currently in operation. The flow field to be solved ranges from the inlet of the ammonia injection system to the end of the catalyst bed. The flow was analyzed in the two-dimensional domain assuming incompressible. The steady-state turbulent flow was solved with the commercial software named ANSYS-Fluent. The nozzle arrangement gap and injection flow rate in the ammonia injection system were chosen as the design parameters. A total of four (4) cases were simulated and compared. The root mean square of the NH3/NO molar ratio at the inlet of the catalyst layer was chosen as the optimization parameter and the design of the experiment was used as the base of the optimization algorithm. The case where the nozzle pitch and flow rate were adjusted at the same time was the best in terms of flow uniformity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.8
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• pp.671-676
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• 2014

The vortex cup is proposed as a method to transport sensitive products such as silicon wafers in manufacturing. Air through the inlet nozzle located at the top of the vortex cup flows to form a swirl in the cylinder. The flow located in the lower part of the thin gap between the vortex cup and the bottom surface escapes and generates a negative pressure that can lift objects. In this research, three-dimensional numerical simulation of the air flow field in a vortex cup is performed, and a comparison of the simulation and experimental results shows very good agreement. In addition, the vortex cup length and shape that affect the negative pressure were applied to the analysis. Through the simulation results, optimum conditions for the vortex cup shape were proposed.