• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.4
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• pp.556-562
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• 2012

Micro electrical discharge machining (${\mu}EDM$) has been used for non-conventional material removal. One drawback of ${\mu}EDM$ is low productivity. In this study, we tried to find the optimal machining conditions to manufacture the micro hole with an optimal machining time without loss of accuracy. Taguchi method was used to figure out the relation between machining parameters and characteristics of the process. It was found that the electrode wear, the entrance and exit clearance gave a significant effect on the diameter of the micro hole when the diameter of the electrode was identical. Grey relational analysis was used to determine the optimal machining condition for minimum machining time without loss of accuracy. The obtained optimal machining condition was the input voltage of 80V, the capacitance of 680pF, the resistance of $500{\Omega}$, the feed rate of $1.5{\mu}m$/s and the spindle speed of 2900rpm. The machining time was reduced to 48% without loss of accuracy under the optimal machining condition.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.2
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• pp.180-186
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• 2011

This paper describes a micro electrical discharge machining (MEDM) technique that uses an insulated tool in combination with ultrasonic vibration to drill micro holes. As the machining depth becomes deeper, the dispersion of debris and circulation of the dielectric fluid are difficult to occur. Consequently, machining becomes unstable in the machining region and unnecessary electrochemical dissolution and secondary discharge sparking occur at the tool side face. To reduce the amount of unnecessary side machining, an insulated tool was used. Ultrasonic vibration was applied to the MEDM work fluid to better remove debris. Through these methods, a $1000\;{\mu}m$ thick stainless steel plate was machined by using a $73\;{\mu}m$ diameter electrode. The diameters of the hole entrance and exit were $96\;{\mu}m$ and $88\;{\mu}m$, respectively. It took only 351s to completely drill one hole.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.170-178
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• 2005

Multi-hole type oxygen combustion burner was developed for industrial gasification and smelting furnace. We investigated characteristics of flame, radiation transfer, and soot emission in the convectional oxygen burner with respect to the feeding condition of fuel and oxygen. Regarding the results of the conventional burner, we designed new burners which have larger fuel consumption rate and radiation heat transfer. We changed the size and hole number and shape of the exit plane of the burner. In addition, the performance of the burner was tested with respect to the feeding condition of the fuel and air: Normal Diffusion flame(NDF) and Inverse Diffusion Flame(IDF). We investigated the flame configuration, radiation heat transfer, and soot formation by using a CCD camera, heat flux meter, and Laser Induced Incadescence(LII), respectively. The stable operating condition was obtained by the flame configuration and the flame of the burner which has dented exit plane was more stable in whole operating conditions. The characteristics of radiative heat transfer were sensitive to the feeding condition of reactants and the flame of 75% primary oxygen and 25% secondary oxygen of the IDF case shows maximum radiation heat transfer. The soot volume fraction of the flame was measured in the axial direction of the flame and the amount of soot volume fraction is proportion to the radiation heat transfer. As a result, we can get the optimal operating condition of the newly designed burner which enhances the characteristics of flame stabilization and radiation heat transfer.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2066-2070
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• 2003

This experimental study describes the propagation characteristics and suppression of the impulse noise emitted from the exit of a perforated pipe attached to the open end of a simple shock tube. The experiment is performed through the systematic change of the shock wave Mach number and the geometrical parameters such as the porosity, hole diameter and length of the perforated pipe. The experimental results for the near and far sound field are presented and explained in comparison with those for a straight pipe. The results obtained show that for the near sound field the impulse noise strongly propagates toward to the pipe axis, but for the far sound field the impulse noise uniformly propagates toward to the all directions, indicating that the directivity pattern is almost same regardless of the pipe type. Moreover, the noise reduction performance of perforated pipe depends upon the condition of sound field. For the near sound field the perforated pipe has a little performance to suppress the impulse noise, but for the far sound field the perforated pipe has little performance to suppress the impulse noise.

• Journal of ILASS-Korea
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• v.21 no.1
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• pp.20-28
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• 2016

This paper presents an experimental study on the GDI injector with Bosch method. The injection characteristics, such as the injection quantity, the injection rate, the maximum velocity of the nozzle exit and the injection delay were studied through the change of the injection pressure, the tube pressure and energizing duration in injection rate measurement device using nheptane. The injection quantity is increased by increasing injection pressure, decreasing tube pressure or increasing energizing duration. As the difference of the injection quantity changed, the shape of injection rate was moved with a constant form. The maximum velocity of the nozzle exit showed a tendency to increase as the injection pressure is increased. However, tube pressure did not affect. Overall, it was confirmed that the closing delay is longer than the opening delay in all conditions. As the injection pressure increased, the result has a tendency to decrease the closing delay, it did not affect the opening delay. Reduction of the closing delay showed the reduction of the injection duration. the tube pressure and energizing duration did not affect the injection delay (opening delay, closing delay).

• Journal of Conservation Science
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• v.25 no.3
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• pp.317-322
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• 2009

Nicobium castaneum belonging to the family Anobiidae of Coleoptera was found in Jeju Folk Museum in 2006, Miribeol Folk Museum in 2007, and a bier preserved in the bier house of Jeju in 2008. We found that this species did considerable damage to the several wooden cultural properties. For Identification and pest management to conserve wooden cultural properties from this anobiid species, we report morphology of adult and damage pattern (shape of exit holes from the host, tunnels and their excrements etc).

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.102-105
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• 2001

The bending process for the curved tube can be developed by the hot metal extrusion machine with the multiple punches moving in the different velocity. The bending phenomenon has been studied to be occurred by the different of velocity at the die extrusion. The difference of velocity at the die exit section can be obtained by the different velocity of billets through the multi-hole container and by the welding of billets inside the porthole die chamber. The multiple billets are moving differently by the multiple extrusion punches controlled by PLC with the servo mechanism units. The results of the experiments show that the curved tube can be bended by the extrusion process and that the defects such as the distortion of section and the thickness change of thick tube, tile folding and wrinkling of thin tube can not be shown after the bending processing by the extrusion bending machine.

• Journal of ILASS-Korea
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• v.22 no.3
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• pp.146-152
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• 2017

An experimental study was carried out to investigate the spray characteristics of non-circular effervescent twin-fluid nozzles. For this purpose, two types of non-circular nozzles (E1, E2) and circular nozzle (C) were used. Three types of aerorators with hole diameters of 1.2, 1.7 and 2.1 mm were used. Each aerorator has a total of 12 holes. It is defined by area ratio which is ratio of exit orifice area and aerator hole area. Experiments were carried out by controlling the amount of air flowing after fixing the flow rate of the liquid, and the nozzle internal pressure and SMD were measured, and the jet image was taken from the nozzles. The discharge coefficients of the three kinds of nozzles were compared with the used in plain orifice's equation and the Jedelsky's equation, and the Jedelsky's equation was found to be about 3 times larger. In addition, empirical formula based on ALR, which is the largest variable in Jedelsky's equation, was derived. The droplet sizes(SMD) were found to be smaller in the non-circular shape than in the circular shape, which is concluded to be caused by the difference of the discharge coefficients.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1606-1615
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• 2001

The present study has been conducted to investigate heat/mass transfer characteristics on a target plate fur arrays of circular impingement jets with and without effusion holes. A naphthalene sublimation method is employed to determine local heat/mass transfer coefficients on the target plate. The effusion holes are located at the center of four injection holes in the injection plate where the spent air is discharged through the effusion hole after impingement on the target plate. For the array jet impingement without effusion holes, the array jets are injected into the crossflow formed by upstream spent air because the impinged jets must flow to the open exit. For small gap distances, heat/mass transfer coefficients without effusion holes are very non-uniform due to crossflow effects and re-entrainments of spent air. However, uniform distributions and enhanced values of heat/mass transfer coefficients are obtained by installing the effusion holes. For large gap distances, the crossflow has little influence on heat/mass transfer characteristics on the target palate due to the large cross-sectional open area between the injection and target plates. Therefore, the distributions and levels of heat/mass transfer coefficients are almost the same for both cases.