• The KSFM Journal of Fluid Machinery
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• v.20 no.1
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• pp.29-34
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• 2017

An analysis on pressure drop in vortex amplifier has been performed. Based on theoretical approach with flow physics on well-known firm ground from previous studies, two dimensional flow model, which is very useful to calculate pressure drop of vortex amplifier, is proposed. Parametric studies on inlet and outlet boundary conditions also have been performed so that it found the most influential parameter is the inlet swirl velocity condition. Finally, a simple formulation is given to calculate total pressure drop.

• Journal of Powder Materials
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• v.15 no.1
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• pp.46-52
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• 2008

The restrictor, which is a fluid channel from a reservoir to a chamber inside a thermal micro actuator, has been fabricated using ArF and KrF excimer lasers, Diode-Pumped Solid State Lasers (DPSSL) and femtosecond lasers for a feasibility study. A numerical model of fluid dynamics for the actuator chamber and restrictor is presented. The model includes bubble formation and growth, droplet ejection through nozzle, and dynamics of fluid refill through the restrictor from a reservoir. Since an optimized and well-fabricated restrictor is important for a high frequency actuator, some special beam delivery setups and post processing techniques have been researched and developed. The effects of variations of the restrictor length, diameter, and tapered shapes are simulated and the results are analyzed to determine the optimal design. The numerical results of droplet velocity and volume are compared with the experimental results of a cylindrical-shaped actuator. It is found that the micro actuators having tapered restrictors show better high frequency characteristics than those having a cylindrical shape without any notable decrease of droplet volume. The laser-fabricated restrictors demonstrate initial feasibility for the laser direct ablation technique although more development is required.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.3
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• pp.129-134
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• 2013

Sapphire wafers are used as an important substrate for the production of blue LED (light emitting diode) and the LED's performance largely depends on the quality of the sapphire single crystals. There are several crystal growth methods for sapphire crystals and Kyropoulos method is an efficient way to grow large diameter and high-quality sapphire single crystals with low dislocation density. During Kyropoulos growth, the convection of molten melt is largely influenced by the hot zone geometry such as crucible shape, heater and refractory arrangements. In this study, CFD (computational fluid dynamics) simulations were performed according to the bottom/side ratios (per unit of the crucible surface area) of heaters. And, based on the results of analysis, the molten alumina flows and remelting phenomena were analyzed.

• Journal of the Korean Solar Energy Society
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• v.28 no.1
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• pp.9-17
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• 2008

An experimental investigation has been carried out to study the effects of different working fluids on the behavior and thermal performance of a hi-directional thermodiode. The thermodiode was made up of two rectangular loops mounted between a collector plate and a radiator plate. Rotatable joints between the horizontal and inclined segments of the loops enable easy alteration of the direction of heat transfer. The loops and the tank were filled with a working fluid for effective heat transfer when the thermodiode was forwarded biased. Six different working fluids were tested with thermal conductivity values ranging from 0.1 to $0.56W/m-^{\circ}C$, thermal expansion coefficient values ranging from $1.8\;{\times}10^{-4}$ to $1.3\;{\times}\;10^{-3}\;K^{-1}$, and kinematic viscosity values ranging from $0.65\;{\times}\;10^{-6}$ to $100\;{\times}\;10^{-6}\;m^2/s$. Especially, mixtures of $Al_2O_3$ (30nm Particle) in deionized water have been tested for the volumetric ratios of 0.01, 0.02, 0.03, 0.1, 0.2%. Each experiment was carried out after the loop was filled with a working fluid for effective heat transfer and the thermodiode was forwarded biased. The solar thermodiode was heated by a radiant heater consisting of 20 halogen lamps that generated a heat flux of about $1000\;W/m^2$ on the collector surface. Results are given in terms of temperature development in different parts of the loop as heat is delivered from its hot end to the surrounding atmosphere by the radiator made of copper plates.

• Korean Journal of Optics and Photonics
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• v.27 no.6
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• pp.218-222
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• 2016

The thermal characteristics of a laser diode TO package has been analyzed using a commercial computational fluid dynamics (CFD) tool, and the thermal bypass structure was optimized. Comparison of device temperature and the estimated thermal resistance of the resultant structure showed that the bypass structure relieved the thermal bottleneck, and improved the thermal characteristics quite efficiently.

• Journal of Veterinary Science
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• v.19 no.6
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• pp.835-839
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• 2018

Auditory tube diverticula, also known as guttural pouches, are naturally occurring dilations of the auditory tube in horses that communicate with the nasopharynx through a small ostium. Infection and select other conditions can result in inflammation and narrowing of the nasopharyngeal ostium, which prevents drainage of fluid or egress of air and can lead to persistent infection or guttural pouch tympany. Auditory tube diverticulotomy allows continuous egress from the auditory tube diverticula and is a feature of disease treatment in horses, in which medical treatment alone is not successful. Transpharyngeal endoscopic auditory tube diverticulotomy was performed using a diode laser either at a single dorsal pharyngeal recess location or bilaterally caudal to the nasopharyngeal ostium in 10 horse head specimens. Both methods resulted in clear communication between the nasopharynx and auditory tube diverticula. Diverticulotomy performed in the dorsal pharyngeal recess required less laser energy and activation time and had a shorter surgical duration than diverticulotomy performed caudal to the nasopharyngeal ostium. Further study related to the clinical application of both techniques is warranted.

• Journal of Biomedical Engineering Research
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• v.19 no.4
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• pp.369-377
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• 1998

This paper describes the results of investigations comparing the relative in vitro responses of different signal processing algorithms for laser Doppler flowmetry(LDF) using self-mixing effect of laser diode(LD). A versatile laser Doppler system is described which enabled complex signal processing to be implemented relatively simply using digital analysis. The flexibility of the system allowed a variety of processing algorithms to be studied by simply characterising the algorithm of interest under software control using a personal computer. Two in-vitro physical models are also presented which was used to maintain reproducible fluid flows Flows of particles were studied in two physical models using a 780nm laser diode source. The results show that frequency weighted algorithms(first and second moments, rate to zero moment) are responsive to particle velocity more than concentration, whereas non-weighted algorithm (zero moment responds to concentration and velocity.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.92-96
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• 2019

In the presence of ${\mu}-tip$ embedded in a slot-die head for stripe coatings, there arises the capillary flow that limits an increase of the stripe density, which is required for the potential applications in organic light-emitting diode displays. With an attempt to suppress it, we have employed a computational fluid dynamics software and performed simulations by varying the ${\mu}-tip$ length and the contact angles of the head lip and ${\mu}-tip$. We have first demonstrated that such a capillary flow phenomenon (a spread of solution along the head lip) observed experimentally can be reproduced by the computational fluid dynamics software. Through simulations, we have found that stronger capillary flow is observed in the hydrophilic head lip with a smaller contact angle and it is suppressed effectively as the contact angle increases. When the contact angle of the head lip increases from $16^{\circ}$ to $130^{\circ}$, the distance a solution can reach decreases sharply from $256{\mu}m$ to $44{\mu}m$. With increasing contact angle of the ${\mu}-tip$, however, the solution flow along the ${\mu}-tip$ is disturbed and thus the capillary flow phenomenon becomes more severe. If the ${\mu}-tip$ is long, the capillary flow also appears strong due to an increase of flow resistance (electronic-hydraulic analogy). It can be suppressed by reducing the ${\mu}-tip$ length, but not as effectively as reducing the contact angle of the head lip.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.443-444
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• 2006

The influence of the heat sources on LED junction temperature are Engine room air, Back plate, Electric power device, and so on. LED lamp cooling system is considered to be an important subject fur high light efficiency. Because LED Chip will be problem When LED junction temperature be over $135^{\circ}C$, In this Study, The Looped Heat Pipe System is considered to prevent LED Chip fall. The LHPS is consist of evaporator part, condenser part, heat pipe part. The working fluid of LHPS is HCFC-123. In this study, to prevent LED Chipfall, we study thermal characteristics for Looped Heat Pipe System with LED lamp.

• Journal of Biosystems Engineering
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• v.30 no.2 s.109
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• pp.114-120
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• 2005

In this study, a biological reaction and measurement control system was developed to rapidly measure the insecticide imidacloprid residues in agricultural products. The biological reaction part of the system was designed to include micro-pumps and valves for fluid transport, and a polystyrene covet as a reaction chamber. The measurement control part of the system consisted of a photodiode with a light-emitting diode for optical density measurement, and a control microcomputer to implement assay. Signal output was read as the rate of change in optical density at 645 nm. The sensitivity of the system was 2.2 ng/mL ($IC_50$). The system could execute a measurement cycle in about 19 minutes. Research will be continued to develop an automatic sampler fur imidacloprid residues from agricultural products.