• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1294-1298
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• 2005

In this study, combined micro press and surface finishing process are proposed to fabricate the micro nozzle array on a stainless steel sheet metal. In micro hole punching process the burr occurs inevitably, but the burr must be minimized in order to improve the quality and accuracy of the product. For this reason, subsequent magnetic field-assisted finishing technique is applied to remove the burr which exists around the nozzles for ink-jet printer head and proved to be a feasible for deburring by experiment. The deburring characteristics of sheet metals were investigated changing with polishing time and magnetic abrasive size. After the deburring, the burr size has remarkably reduced and roundness of the hole also has improved.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.201-202
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• 2012

The isothermal flow structure and mixing characteristics of a hybrid/dual swirl jet combustor for micro-gas turbine were numerically investigated. Location of pilot nozzle, angle and direction of swirl vane were varied as main parameters with constant fuel flow rates for each nozzle. As a result, the variation in location of pilot nozzle resulted in significant change in turbulent flow field near burner exit, in particular, center toroidal recirculation zone (CTRZ) as well as turbulent intensity, and thus flame stability and emission characteristics might be significantly changed. The swirl angle of $45^{\circ}$ provided similar recirculating flow patterns in a wide range of equivalence ratio (0.5~1.0). Compared to the co-swirl flow, the counter-swirl flow leaded to the reduction in CTRZ and fuel-air mixing near the burner exit and a weak interaction between the pilot partially premixed flame and the lean premixed flame. With the comparison of experimental results, it was confirmed that the case of co-swirl flow and swirl $angle=45^{\circ}$ would provided an optimized combustor performance in terms of flame stability and pollutant emissions.

• Polymer(Korea)
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• v.32 no.4
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• pp.334-339
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• 2008

Recently electro spinning is a widely used simple technique to prepared micro- to nanometer-sized fiber of various polymers. In general, a normal multiple-nozzle electro spinning system has been difficult to achieve high production-rate fabricating micro/nanofibers due to the interference of electric field between individual nozzles in the process. To reduce the interference effect of electric field between nozzles, we developed a multi-nozzle electrospinning system supplemented with auxiliary electrodes. Poly($\varepsilon$-carprolactone)(PCL), which has good mechanical property and biocompatibility, was electrospun by the multi-nozzle electro spinning system. Electrospinnability, product rate, and size uniformity of spun fibers for the system with and without auxiliary electrodes were characterized. As a result, the multi-nozzle electrospinning system supplemented with auxiliary electrodes provides excellently stable processability and showed high mass productivity of PCL-nanofibers relative to a normal multi-nozzle electro spinning system.

• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.232-238
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• 2001

We fabricated micro-pump using stereolithography technology. The pump was fabricated using PZT for its drive and used non-movable valve of diffuser/nozzle concept. Size of the pump chamber is, $14mm{\psi}$, narrow hole of diffuser/nozzle is $0.5mm{\psi}$ and wide hole $1mm{\psi}$ and chamber depth is 1.2mm, respectively. We confirmed its operation at frequency 100Hz, supply voltage $90{\sim}250Vp-p$. As the result of the pump working measurement, when ethanol is used, the pressure head difference between inlet and outlet of the pump is about 53mm in the frequency of 100Hz, 200V of Vp-p.

• Journal of the Korean Society of Combustion
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• v.19 no.4
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• pp.8-13
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• 2014

Flow distribution of fuel nozzles for a combustor in a micro gas turbine is numerically investigated. The fuel supply system for the present study has 12 single nozzles with a diameter of several hundred micrometers. A uniform temperature distribution of a combustor outlet should be achieved for maximizing the lives of the turbine blades and nozzle guide vanes. For this, it is very important to uniformly supply fuel to a combustor. In order to investigate flow distributions of fuel nozzles, numerical models for fuel nozzles are made and solved by a commercial code, ANSYS FLUENT. An effect of a fuel nozzle diameter and fuel flow rates on flow distribution of fuel nozzles is numerically investigated. As a result, non-uniformity is increasing as a diameter of a single fuel nozzle increases. Finally, an appropriate diameter of a single fuel nozzle is suggested.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.60-65
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• 2015

This paper deals with performance characteristics and efficiencies of Pelton turbine can be applied as one of ERDs (Energy Recovery Devices) of PRO (Pressure Retarded Osmosis) system for desalination. The objective of this study is experimentally estimating the performance of micro-scale Pelton turbine for PRO pilot plant. Especially the performance characteristics with variations of jet nozzle diameter of Pelton turbine are discussed in detail. In order to do this, lab scale test rig of Pelton turbine was made for performance test, which includes water tank, Pelton wheel with buckets, jet nozzle and torque brake and so on. The parameter effects related on Pelton turbine's efficiency were investigated and discussed on the influence of the variations of load and speed ratio.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.1
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• pp.8-13
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• 2016

The micro drill bit automatic regrinding in-line system is a system that refurbishes drill bits used in a PCB manufacturing process. This system is able to refurbish drill bits with a minimum size of ø0.15-0.075mm that have previously been discarded. Beyond the conventional manual cleaning process using ultrasound, this system adopts a water jet cleaning system, making it capable of cleaning drill bits with a minimum size of ø0.15-0.075mm. This paper analyses various contact pressures applied to the surface of drill bits depending on the shooting pressure of the cleaning device and fluid velocity in order to optimize the nozzle location and to detect structural instability caused by the contact pressures.

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.48-53
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• 2018

In this study, the effect of injection pressure on the column diameter and droplet velocity of liquid jet with the weakly turbulent Rayleigh-like breakup mode is experimentally studied using digital microscopic holography (DMH). The injection nozzle has the diameter of $50{\mu}m$ and injection pressure is varied from 0.1 to 0.4 MPa. When the micro liquid jet is injected into still air, the double-pulsed holograms was recorded on a CCD sensor and numerically reconstructed in order to obtain well focused images. In this study, the liquid column diameter from $50{\mu}m$ orifice nozzle is shown to be changed slightly but the droplet velocity is increased proportionally as the injection pressure is increased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.173-177
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• 2004

This paper presents a novel mechanism of electrostatic micro thruster using based on a layered electrode structure of nozzle. A comparison between experiment and simulation studies indicates that the proposed mechanism allows at less than 100 volt of operating voltage for the micro thruster.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.76-79
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• 2007

From the previous researches about flow characteristic of micro-nozzle， we found that viscosity and back pressure induced heavy losses in micro nozzle. To overcome thess losses, we began to study new conceptual micro propulsion system that is thermal transpiration based micro propulsion system. It has no moving parts and can pump the gaseous propellant by temperature gradient only (cold to hot). Most of previous research on thermal transpiration is in its early stage and mainly studied for application to small vacuum facility or gas chromatography in ambient condition using nanoporous material like aerogel. In this study, we focus on basic research of propulsion system based on thermal transpiration using polyimide material in vacuum conditions.