• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.3
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• pp.285-291
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• 2017

Micro-needles are used as transferring devices for sampling of tiny constitute substances from biological bodies. Typically, nickel is used as a coating to improve the rigidity of micro-needles. This study introduces the methodology to manufacture a WC needle with very high hardness and toughness. Micro-EDM technology was used to manufacture micro-needles with holes $130{\mu}m$ in diameter and $2300{\mu}m$ in length. A micro-needle was aligned to the micro-EDM electrode using a custom two degree-of-freedom alignment system. A three-step manufacturing technique was developed to drill a micro-hole using a WC electrode. In the first process, an electrode $105{\mu}m$ in diameter was used to make a hole. Electrodes of 90 and $105{\mu}m$ diameters were used in the second and third process, respectively. Consequently, a WC micro-needle with an inner hole of $135{\mu}m$ diameter, length of $2300{\mu}m$, and outer diameter of $300{\mu}m$ was developed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.338-348
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• 2004

The present study is conducted to investigate the effect of rib arrangements on an impingement/effusion cooling system with initial crossflow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of tile hole diameter. Initial crossflow passes between the injection and effusion plates, and the square ribs (3mm) are installed on the effusion plate. Both the injection and effusion hole diameters are 10mmand Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and 6 times of the hole diameter, respectively. To investigate the effects of rib arrangements, various rib arrangements, such as 90$^{\circ}$transverse and 45$^{\circ}$angled rib arrangements, are used. Also, the effects of flow rate ratio of crossflow to impinging jets are investigated. With the initial crossflow, locally low transfer regions are formed because the wall jets are swept away, and level of heat transfer rate get decreased with increasing flow rate of crossflow. When the ribs are installed on the effusion plate, the local distributions of heat/mass transfer coefficients around the effusion holes are changed. The local heat/mass transfer around the stagnation regions and the effusion holes are affected by the rib positions, angle of attack and rib spacing. For low blowing ratio, the ribs have adverse effects on heat/mass transfer, but for higher blowing ratios, higher and more uniform heat transfer coefficient distributions are obtained than the case without ribs because the ribs prevent the wall jets from being swept away by the crossflow and increase local turbulence of the flow near the surface. Average heat transfer coefficients with rib turbulators are approximately 10% higher than that without ribs, and the higher values are obtained with small pitch of ribs. However, the attack angle of the rib has little influence on the average heat/mass transfer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.150-157
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• 1985

In terms of behavior of fatigue cracks propagated after build-up around the artificial drilled miro-hole, this study has been made of the build-up process of slips and micro cracks, behavior of micro-crack propagation and the definition of fatigue limit under the rotating bending stress with low carbon steel. The results of this study are as follows: (1) The fatigue limit is the repropagating critical stress for the nonpropagating cracks which have grown to some limit around the micro-hole in regard of the magnitude of micro-hole. (2) Behavior of the slips and micro-cracks initiation are occurring simultaneously in front and in rear of micro-hole tips in the view of the rotational direction, regardless of the magnitude of micro-hole. (3) Behavior of fatigue crack propagation is different from magnitude of micro-hole, its behavior is propagation of single crack about respectively large hole, but about respectively small hole, fatigue crack propagated joining phenomena of micro-cracks. (4) The behavior of fatigue fracture is affected by the factor of its defects in the view of magnitude of micro-hole when the diameter of the micro-holes are smaller than 50.mu.m, and this is also affected with the size effect of micro-hole diameter.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.76-80
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• 1989

Spatial filters were designed for 1 TW high power phosphate glass laser development. Laser beam should be expanded from 1 mm diameter to 200mm diameter. Pin hole size should be determined and most of incident energy should be transmitted through out to final spatial filter. Each pin hole size is determined by calculating encircled energy for Gaussian beam from the oscillator. The optical tube length of each spatial filter is corrected to have the best collimating quality by scew raytracing through the total system.

• Journal of ILASS-Korea
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• v.7 no.1
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• pp.1-6
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• 2002

This study has focused on using fuel injections as variables for measuring performance and reducing exhaust gas in turbo-charger diesel engine. In experiments, we changed nozzle hole diameter, diameter of an injection pipe, and injection timing as variable. The results show that torque. fuel consumption and smoke are reduced as nozzle hole diameter decreases, while NOx increases. When the diameter of injector is reduced, torque, fuel consumption and smoke are deteriorated, but NOx is decreased. In addition, when the time for injection is advanced. torque, fuel consumption and smoke are improved, but the density of NOx is increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.393-396
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• 1997

Electro Discharge Machining (EDM) is a so-call non-conventional machining technique. This paper presents the experimental results of an EDM technique for the fabircation of microholes on #7440 pyrex glans. With various applied voltages and at various concentration of KOH solution, the glass substrate have been microdrilled using the copper electrodes of which diameters are 250$\mu\textrm{m}$ to 450$\mu\textrm{m}$, respectively. The machined throughholes have been observed the top diameter, the bottom diameter, hollow width and hole diameter of the hole, and machining time hale been measured. The experimental results show that the machining time decreases as the concentration of KOH solution increases or the applied voltage increase. Also, The top diameter increases as the concentration of KOH solution decreases or the allied voltage increases. The bottom and hollow width decreases as the of KOH solution increases or the applied voltage decreases.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.101-106
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• 2001

This paper presents experimental results for the confining characteristics of cylinder with center-hole and spiral reinforcements. The experiments have been conducted for the specimens with primary variables i.e., spiral reinforcement ratio and diameter of center-hole which affect the compressive strength and stress-strain relationship. Through this research, it was found that the compressive strength and ductility were increased with the ratio of spiral reinforcement because the lateral expansion of the concrete inside the spiral was restrained by the spiral, but dependent on the size of center-hole.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1185-1197
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• 1997

Three-dimensional flow within a film-cooling hole, which is normally oriented to the main flow, has been measured by using a straight five-hole probe for the blowing ratios of 1.0 and 2.0. The length-to-diameter ratio of the injection hole is fixed to be 1.0 throughout the whole experiments. The result shows that the secondary flow within the hole is strongly affected by the main flow and flow separation at the hole inlet. The higher blowing ratio provides less influence of the main flow on the injectant flow. The three-dimensional flow at the hole exit is considerably altered due to the strong interaction between the injectant and main flow. The aerodynamic loss produced inside the injection hole is mainly attributed to the inlet flow separation.

• Journal of KSNVE
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• v.9 no.5
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• pp.1005-1011
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• 1999

Generation of hole-tones and the instability of circular impinging jets are investigated based on the frequency characteristics and the radiated sound field. The experiment is carried out with varying hole sizes, jet speeds and impinging distances. It is found that hole-tones occur by both the low-speed laminar jet and the high-speed turbulent jet, but not by the transient jet, while plate-tones without holes are produced only in the high-speed turbulent impinging jet. When the diameter ratio of the hole to the nozzle is nearly one, hole-tones occur most easily. At low speed, it is found that hole-tones are due to the symmetrical unstable jet and the impinging distance decreases with jet speed. And the Strouhal number and the sound pressure level increase with jet speed. At high speed, hole-tones show the same characteristics as plate-tones. It is found that the ratio of the convection speed varies with the Strouhal number and the jet speed.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.489-496
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• 2001

Two perforated plates are used to investigate local heat/mass transfer characteristics in an impingement/effusion cooling system. A naphthalene sublimation method is conducted to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. The two plates are placed in parallel position with gap distances of 1, 2, 4 and 6 times of effusion hole diameter. The effects of hole arrangements of the plates are studied for staggered, square, and hexagonal arrays. The experiments are conducted at Reynolds number of 10,000 based on the effusion hole diameter. The results show that the smaller hole size in the staggered array has the higher transfer coefficients on the stagnation region due to the formation of higher momentum flows through the impingement holes. In the square array, heat/mass transfer on the target plate is more uniform as the number of impingement holes increases. High and uniform heat/mass transfer coefficients are obtained in the hexagonal array.