• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2460-2464
• /
• 2008

The present paper suggests new method to know the effects of molecular diffusion and the helicity of microchannel flows on mixing in passive micromixers, which are essential components of a microfluidic chip. In this study, 'Helix Index' is newly defined as the magnitude of chaotic advection. Relationship between Helix Index and Mixing Index is analyzed numerically such as the wide range of Peclet and Reynolds numbers in three dimensional serpentine microchannel when using soluble solutions (water/glycerol). As a result, a simple algebraic equation is derived by this relationship based on a regression analysis. The algebraic equation is found to be able to accurately predict the mixing performance without solving the coupled, complex momentum and mass transfer equations.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.6
• /
• pp.586-591
• /
• 2015

This study discusses numerically-explored thermal performances of hybrid fin heat sinks (HF HSs) for lightweight thermal management of LED modules under natural convection. A hollow hybrid fin heat sink (HHF HS) and a solid hybrid fin heat sink (SHF HS) are proposed as HF HSs. A 3-D CFD analysis has been carefully conducted to obtain reliable numerical results. The 3-D CFD study investigates the effects of both fin spacing and an internal channel diameter on performances of the HHF HS and the SHF HS. The study results show that the mass-based thermal resistance of the HHF HS is 20~32% smaller compared with the pin fin heat sink (PF HS). The results also show that the mass-based thermal resistance of the HHF HS decreases with the increase of the channel diameter. These results are mainly due to coupled effects of the mass reduction and heat pumping through an internal channel. Considerably superior mass-based thermal performances of the HHF HS to the conventional PF HS suggest the feasible application for the lightweight thermal management of the LED modules under natural convection.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.3
• /
• pp.285-290
• /
• 2003

An analytical method for the simultaneous determination of trace Ge, As and Se in biological samples by inductively coupled plasma/mass spectrometry has been investigated. The effects of added organic gas into the coolant argon gas on the analyte signal were studied to improve the detection limit, accuracy and precision. The addition of a small amount of methane (10 mL/min.) into the coolant gas channel improved the ionization of Ge, As and Se. The analytical sensitivity of the proposed Ar/CH₄system was superior by at least two-fold to that of the conventional Ar method. In the present method, the detection limits obtained for Ge, As and Se were 0.014, 0.012 and 0.064 ㎍/L, respectively. The analytical reliability of the proposed method was evaluated by analyzing the certified standard reference materials (SRM). Recoveries of 99.9% for Ge, 103% for As, 96.5% for Se were obtained for NIST SRM of freeze dried urine sample. The proposed method was also applied to the biological samples.

• Journal of Mechanical Science and Technology
• /
• v.20 no.10
• /
• pp.1741-1752
• /
• 2006

A combined Streamline Upwind Petrov-Galerkin method (SUPG) and segregated finite element algorithm for solving conjugate heat transfer problems where heat conduction in a solid is coupled with heat convection in viscous fluid flow is presented. The Streamline Upwind Petrov-Galerkin method is used for the analysis of viscous thermal flow in the fluid region, while the analysis of heat conduction in solid region is performed by the Galerkin method. The method uses the three-node triangular element with equal-order interpolation functions for all the variables of the velocity components, the pressure and the temperature. The main advantage of the presented method is to consistently couple heat transfer along the fluid-solid interface. Four test cases, which are the conjugate Couette flow problem in parallel plate channel, the counter-flow in heat exchanger, the conjugate natural convection in a square cavity with a conducting wall, and the conjugate natural convection and conduction from heated cylinder in square cavity, are selected to evaluate efficiency of the presented method.

• Journal of the Optical Society of Korea
• /
• v.15 no.2
• /
• pp.174-181
• /
• 2011

An airborne sensor is developed for remote sensing on an aerial vehicle (UV). The sensor is an optical payload for an eletro-optical/infrared (EO/IR) dual band camera that combines visible and IR imaging capabilities in a compact and lightweight package. It adopts a Ritchey-Chr$\'{e}$tien telescope for the common front end optics with several relay optics that divide and deliver EO and IR bands to a charge-coupled-device (CCD) and an IR detector, respectively. The EO/IR camera for dual bands is mounted on a two-axis gimbal that provides stabilized imaging and precision pointing in both the along and cross-track directions. We first investigate the mechanical deformations, displacements and stress of the EO/IR camera through finite element analysis (FEA) for five cases: three gravitational effects and two thermal conditions. For investigating gravitational effects, one gravitational acceleration (1 g) is given along each of the +x, +y and +z directions. The two thermal conditions are the overall temperature change to $30^{\circ}C$ from $20^{\circ}C$ and the temperature gradient across the primary mirror pupil from $-5^{\circ}C$ to $+5^{\circ}C$. Optical performance, represented by the modulation transfer function (MTF), is then predicted by integrating the FEA results into optics design/analysis software. This analysis shows the IR channel can sustain imaging performance as good as designed, i.e., MTF 38% at 13 line-pairs-per-mm (lpm), with refocus capability. Similarly, the EO channel can keep the designed performance (MTF 73% at 27.3 lpm) except in the case of the overall temperature change, in which the EO channel experiences slight performance degradation (MTF 16% drop) for $20^{\circ}C$ overall temperate change.

• Journal of Korea Water Resources Association
• /
• v.37 no.7
• /
• pp.599-612
• /
• 2004

The continuous long-term rainfall-runoff simulation model SWAT has the advantage of being able to account for various land use, however, SWAT lacks the capability of simulating the drainage characteristics of urban area. On the other hand, SWMM, which is the most popular model for runoff analysis of urban watershed, has the advantage of being capable of considering surface and drainage characteristics in urban area, but SWMM cannot easily account for land use other than urban area within a watershed. In this study, SWAT-SWMM model, which builds on the strengths of SWAT and SWMM, has been applied to the Osan River Watershed which is a tributary watershed to the Gyung-Ahn River. From the application, the results from coupled SWAT-SWMM model has been compared to the ones from SWAT for each hydrologic component such as evapotranspiration, surface runoff, groundwater flow, and watershed and channel discharge, and the runoff characteristics of two models for each hydrologic component has been discussed.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.11
• /
• pp.18-26
• /
• 1999

Recently, various simplified simulation techniques such as firite-difference beam propagation method and non-orthogonal coupled-mode theory have proposed to analyze the optical characteristics of tapered directional couplers supported by the coupling of two propagating modes. Although these approaches are often in sufficiently accurate, they do not provide the detailed solutions encountered in the analysis of tapered guiding structures. For this purpose, we introduce and utilize a newly developed modal transmission-line theory to analyze rigorously power transfer of the directional coupler. The numerical result reveals that the propagation constants of even and odd modes converge to a single value as increasing the spacer thickness between two symmetric tapered guides. Furthermore, 97% of the power incident into a guiding channel is transmitted to the other channel at the tapered angle ${\theta}=0.1^{\circ}$, and the efficiency of power transfer decreases dramatically as increasing the angle.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.41 no.8
• /
• pp.51-57
• /
• 2004

We have analyzed the effect of out-band dispersion in the cascaded fiber Bragg Elating(FBG) based optical add-drop multiplexers(OADM) when bypassed wavelengths contain SCM signals. In order to compute this impairment the dispersion characteristics of FBG have been analytically calculated by solving their coupled wave equations, and the Fourier method is applied to IMD analysis. The out-band dispersion effects over WDM/SCM signals are analyzed under different and common system situations as: ITU channel spacing(100, 50, 25 GHz), channel density parameter, frequency extension of the SCM plan, modulation characteristics, FBG length, etc. From this results, the transport of WDM/SCM signals in future DWDM transport networks could be limited by this effect which has to be taken into account for designing future networks.

• Korean Journal of Remote Sensing
• /
• v.18 no.1
• /
• pp.53-59
• /
• 2002

The MSC is a payload on the KOMPSAT-2 satellite to perform the earth remote sensing. The instrument images the earth using a push-broom motion with a swath width of 15 km and a GSD(Ground Sample Distance) of 1 m over the entire FOV(Field Of View) at altitude 685 km. The instrument is designed to haute an on-orbit operation duty cycle of 20% over the mission lifetime of 3 years with the functions of programmable gain/offset and on-board image data compression/storage. The MSC instrument has one channel for panchromatic imaging and four channel for multi-spectral imaging covering the spectral range from 450nm to 900nm using TDI(Time Belayed Integration) CCD(Charge Coupled Device) FPA(Focal Plane Assembly). The MSC hardware consists of three subsystem, EOS(Electro Optic camera Subsystem), PMU(Payload Management Unit) and PDTS(Payload Data Transmission Subsystem) and each subsystems are currently under development and will be integrated and verified through functional and space environment tests. Final verified MSC will be delivered to spacecraft bus for AIT(Assembly, Integration and Test) and then COMSAT-2 satellite will be launched after verification process through IST(Integrated Satellite Test). In this paper, the introduction of MSC, the configuration of MSC electronics including electrical interlace and design of CEU(Camera Electronic Unit) in EOS are described. MSC Operation parameters induced from the operation concept are discussed and analyzed to find the influence of system for on-orbit operation in future.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.1
• /
• pp.54-61
• /
• 2003

This paper shows the results of emissive electromagnetic field characteristics on medium voltage power line(22.9 kV). The measurements were taken when communications signals were coupled into the 22.9 kV main wire of medium voltage power-line in a frequency range of 9 kHz to 30 MHz. The results of the measurement are as follows-emissive electromagnetic Held characteristics from multi carrier signals were superior to a single carrier signal. And we confirmed the PLC transmission distance was 1.8 km when multi-carrier transmission power was 20 dBm. Electric field strength was under the 40 dBuV/m at 30 MHz when 10 m method was measured.