• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.215-220
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• 2004

A mathematical formulation based on two-phase, two-fluid hyperbolic conservation laws is developed to investigate propagation of shock waves in one- and two-dimensions. We used a high resolution upwind scheme called the split-coefficient matrix method. Two extreme cases are computed for validation of the computer code: the states of a pure gas and a pure liquid. Computed results agreed well with the previous experimental and numerical results. It is studied how the shock wave propagation pattern is affected by the void fraction in the two-phase flow. The shock structure in a two-phase flow turned out, in fact, much deviated from the shape well known in the gas only phase.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.1
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• pp.39-49
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• 1999

Monolayer thick fluorocarbon films were characterized by the contact angle measurements. The contact angles of three different liquids, water, formamide and diiodomethane were measured on spun coated, vapor phased deposited films and Teflon surface. The highest contact angle over $130^{\circ}$was observed on fluorocarbon films deposited on Al substrates while the lowest angles below $70^{\circ}$deposited on oxide. The surface energies were calculated based on Lewis acid /base theory. The surface energies of Teflon and spin coated FC films were calculated to have 18 and 8.4 dynes /cm, respectively. Higher energies of 31 to .35 dynes /cm were calculated on vapor phase deposited films on silicon and oxide. However vapor phase deposited films on aluminum only showed a large Lewis base energy term. It might be explained by the surface roughness and heterogeneity as observed by dynamic contact angles and AFM measurements.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.321-326
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• 2021

This paper presents a technique to minimize damaged wafers during loading. A thin wafer used in solar cells and semiconductors can be damaged easily. This makes it difficult to separate the wafer due to surface tension between the loaded wafers. A technique for minimizing damaged wafers is to supply compressed air to the wafer and simultaneously apply a small horizontal movement mechanism. The main experimental factors used in this study were the supply speed of wafers, the nozzle pressure of the compressed air, and the suction time of a vacuum head. A higher supply speed of the wafer under the same nozzle pressure and lower nozzle pressure under the same supply speed resulted in a higher failure rate. Furthermore, the damage rate, according to the wafer supply speed, was unaffected by the suction time to grip a wafer. The optimal experiment conditions within the experimental range of this study are the wafer supply speed of 600 ea/hr, nozzle air pressure of 0.55 MPa, and suction time of 0.9 sec at the vacuum head. In addition, the technology improved by the repeatability performance tests can minimize the damaged wafer rate.

• Clean Technology
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• v.26 no.3
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• pp.204-210
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• 2020

In this study, the ignition characteristics of bio jet fuel (Bio-7629, Bio-5172) produced by F-T process and petroleum-based jet fuel (Jet A-1) were compared and analyzed. The ignition delay time of each fuel was measured by means of a combustion research unit (CRU) and the results were explained through an analysis of the properties and composition of the fuel. The ignition delay time of Bio-5172 was the shortest while that of Jet A-1 was the longest because Jet A-1 had the highest surface tension and Bio-5172 had the lowest viscosity in terms of fuel properties that could affect the physical ignition delay time. As a result of the analysis of the constituents' type and ratio, 22.8% aromatic compounds in Jet A-1 could generate benzyl radical, which had low reactivity during the oxidation reaction, affecting the increase of ignition delay time. Both Bio-7629 and Bio-5172 were composed of paraffin only, with the ratio of n-/iso- being 0.06 and 0.80, respectively. The lower the degree of branching is in paraffin, the faster the isomerization of peroxy radical is produced during oxidation, which could determine the propagation rate of the ignition. Therefore, Bio-5172, composed of more n-paraffin, possesses shorter ignition delay time compared with Bio-7629.

• Journal of the Korean Society for Marine Environment & Energy
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• v.20 no.1
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• pp.37-44
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• 2017

Complexity of multiphase flows due to existence of more than two interface including free-surface in one system, cannot be simulated easily. Since more than two fluids affect to flows and disturb interface, non-linearities such as instabilities can be appeared. Among several instabilities on multiphase flows, one of representative is Rayleigh-taylor instability. In order to examine in importance of density disparity, several cases with numerous Atwood number are set. Moreover, investigation of influence on initial disturbance were also considered. Moving particle simulation (MPS) method, which was employed in this paper, was not widely used for multiphase problem. In this study, by adding new particle interaction models such as self-buoyance correction, surface tension, and boundary condition at interface models, MPS were developed having more strength of physics and robust. By applying newly developed multiphase MPS, considered cases are performed and compared each other. Additionally, though existence of disagreement of magnitude of rising velocity between theoretical values from linear potential theory and that of numerical simulation, agreement of tendency can be proved of similarity of result. the discordance of magnitude can be explained due to non-linear effects on numerical simulation which was not considered in theoretical result.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.620-627
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• 2019

In this study, ignition delay characteristics of various bio aviation fuels (Bio-ADD, Bio-6308, Bio-7720) produced by HEFA process using different raw materials were compared and analyzed. In order to confirm the feasibility of applying bio aviation fuel to actual system, ignition delay characteristics of petroleum-based aviation fuel (Jet A-1) and blended aviation fuel (50:50, v:v) also analyzed. Ignition delay time of each aviation fuel was measured by using CRU, surface tension measurement and GC/MS and GC/FID analysis were performed to interpret the results. As a result, ignition delay time of Jet A-1 was the longest at all temperature because it contains aromatic compounds about 22.8%. The aromatic compounds can produce benzyl radical which is thermally stable and has low reactivity with oxygen during decomposition process. In the case of bio aviation fuels, ignition delay times were measured similarly because the ratio of n-paraffin/iso-paraffin constituting each aviation fuel is similar (about 0.12) and the composition ratio of cycloparaffin also has no difference. In addition, ignition delay times of blended aviation fuels (50:50, v:v) were measured close to the mean value those of each fuel so it was confirmed that it can be applied without any changing or improving of existing system.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.114-122
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• 2015

In the high convective gas flow condition, irregular shaped water waves from which droplet entrainment occurs are generated under horizontally stratified two-phase flow condition. KAERI proposed a new mechanistic droplet entrainment model based on the momentum balance equation consisting of the shear stress, surface tension, and gravity forces. However, this model requires correlation or experimental data of several physical parameters related to the wave characteristics. In the present study, we tried to measure the physical parameters such as wave slope, wave hypotenuse length, wave velocity, wave frequency, and wavelength experimentally. For this, an experiment was conducted in the horizontal rectangular channel of which width, height, and length are, respectively, 40 mm, 50 mm, and 4.2 m. In the present test, the working fluids are chosen as air and water. The PIV technique was applied not only to obtain images for phase interface waves but also to measure the velocity field of the water flow. Additionally, we developed the parallel wire conductance probe for the confirmation of wave height from PIV image. Finally, we measured the physical parameters to be used in the validation of new droplet entrainment model.