• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.32-33
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• 2003

Mechanism of a periodic oscillation of shock-induced combustion over a two- dimensional wedges and axi-symmetric cones were investigated through a series of numerical simulations at off-attaching condition of oblique detonation waves(ODW). A same computational domain over 40 degree half-angle was considered for two-dimensional and axi-symmetric shock-induced combustion phenomena. For two-dimensional shock-induced combustion, a 2H2+02+17N2 mixture was considered at Mach number was 5.85with initial temperature 292 K and initial pressureof 12 KPa. The Rankine-Hugoniot relation has solution of attached waves at this condition. For axi-symmetric shock-induced combustion, a H2+2O2+2Ar mixture was considered at Mach number was 5.0 with initial temperature 288 K and initial pressure of 200 mmHg. The flow conditions were based on the conditions of similar experiments and numerical studies.[1, 3]Numerical simulation was carried out with a compressible fluid dynamics code with a detailed hydrogen-oxygen combustion mechanism.[4, 5] A series of calculations were carried out by changing the fluid dynamic time scale. The length wedge is varied as a simplest way of changing the fluid dynamic time scale. Result reveals that there is a chemical kinetic limit of the detached overdriven detonation wave, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. At the off-attaching condition of ODW the shock and reaction waves still attach at a wedge as a periodically oscillating oblique shock-induced combustion, if the Rankine-Hugoniot limit of detachment isbut the chemical kinetic limit is not.Mechanism of the periodic oscillation is considered as interactions between shock and reaction waves coupled with chemical kinetic effects. There were various regimes of the periodicmotion depending on the fluid dynamic time scales. The difference between the two-dimensional and axi-symmetric simulations were distinct because the flow path is parallel and uniform behind the oblique shock waves, but is not behind the conical shock waves. The shock-induced combustion behind the conical shockwaves showed much more violent and irregular characteristics.From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.221-221
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• 2014

The present work proposes an improved numerical simulator for design and modification of large area capacitively coupled plasma (CCP) processing chamber. CCP, as notoriously well-known, demands the tremendously huge computational cost for carrying out transient analyses in realistic multi-dimensional models, because electron dissociations take place in a much smaller time scale (${\Delta}t{\approx}10-8{\sim}10-10$) than time scale of those happened between neutrals (${\Delta}t{\approx}10-1{\sim}10-3$), due to the rf drive frequencies of external electric field. And also, for spatial discretization of electron flux (Je), exponential scheme such as Scharfetter-Gummel method needs to be used in order to alleviate the numerical stiffness and resolve exponential change of spatial distribution of electron temperature (Te) and electron number density (Ne) in the vicinity of electrodes. Due to such computational intractability, it is prohibited to simulate CCP deposition in a three-dimension within acceptable calculation runtimes (<24 h). Under the situation where process conditions require thickness non-uniformity below 5%, however, detailed flow features of reactive gases induced from three-dimensional geometric effects such as gas distribution through the perforated plates (showerhead) should be considered. Without considering plasma chemistry, we therefore simulated flow, temperature and species fields in three-dimensional geometry first, and then, based on that data, boundary conditions of two-dimensional plasma discharge model are set. In the particular case of SiH4-NH3-N2-He CCP discharge to produce deposition of SiNxHy thin film, a cylindrical showerhead electrode reactor was studied by numerical modeling of mass, momentum and energy transports for charged particles in an axi-symmetric geometry. By solving transport equations of electron and radicals simultaneously, we observed that the way how source gases are consumed in the non-isothermal flow field and such consequences on active species production were outlined as playing the leading parts in the processes. As an example of application of the model for the prediction of the deposited thickness uniformity in a 300 mm wafer plasma processing chamber, the results were compared with the experimentally measured deposition profiles along the radius of the wafer varying inter-electrode gap. The simulation results were in good agreement with experimental data.

• Korean Chemical Engineering Research
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• v.45 no.1
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• pp.39-45
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• 2007

This paper proposed a shortcut method for the structure design of dividing wall column based on the Fen-ske-Underwood equation by applying it on three conventional simple column configuration. It is shown that the proposed shortcut method can design the column structure including the feed tray, dividing wall section, and side-stream tray in a simple and efficient way in the initial design stage. Simulation study using HYSYS to compare the energy saving performance between the conventional sequential two column system and the dividing wall column designed by the proposed method shows that the proposed dividing wall column system saves from 16% to 65% more over the condepends on the composition of intermediate component while the optimal energy consumption pattern to internal flow distribution on the dividing wall section is characterized by the ESI factor of the feed mixture.

• Journal of Korea Water Resources Association
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• v.45 no.1
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• pp.39-52
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• 2012

Surface-subsurface interactions are an intrinsic component of the hydrologic response within a watershed. In general, these interactions are considered to be one of the most difficult areas of the discipline, particularly for the modeler who intends simulate the dynamic relations between these two major domains of the hydrological cycle. In essence, one major complexity is the spatial and temporal variations in the dynamically interacting system behavior. The proper simulation of these variations requires the need for providing an appropriate coupling mechanism between the surface and subsurface components of the system. In this study, an approach for modelling surface-subsurface flow and transport in a fully intergrated way is presented. The model uses the 2-dimensional diffusion wave equation for sheet surface water flow, and the Boussinesq equation with the Darcy's law and Dupuit-Forchheimer's assumption for variably saturated subsurface water flow. The coupled system of equations governing surface and subsurface flows is discretized using the finite volume method with central differencing in space and the Crank-Nicolson method in time. The interactions between surface and subsurface flows are considered mass balance based on the continuity conditions of pressure head and exchange flux. The major module consists of four sub-module (SUBFA, SFA, IA and NS module) is developed.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.6
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• pp.586-599
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• 2014

During the last two decades, indoor air quality and volatile organic compounds (VOCs) have been of concern in Korean society due to their nature of potential health impacts. In order to investigate the pollution levels of VOCss in indoor environments, establishment of a solid test method for monitoring the airborne VOCss is essential. In Korea, a method based on adsorbent sampling and GC analysis coupled with thermal desorption was proclaimed as the Korea Standard Method for Indoor Air Quality Test. This study was carried out to examine some inherent problems of the VOCs measurement method. The VOCs method does not describe in detail preparing the standard samples. The standard samples may be prepared by impregnation of either liquid standard solutions or a mixture of standard gases. In this study, we investigated the optimal temperature condition for transferring the liquid standards onto a standard adsorbent tube. As a result, keeping the impregnation temperature at $250^{\circ}C$ will be recommended in regard of the boiling points of multiple target analytes and the thermal stability of the adsorbent. We also demonstrated some problems associated with handling of a syringe used for transferring the standard solutions onto the adsorbent tubes, and a best way to get rid of the syringe problems was suggested. Finally, a number of field works were conducted to evaluate the performance of adsorbent sampling methods. Comparison of different adsorbent tubes, i.e. tube packed with single sorbent (Tenax) and double sorbents (Tenax with Carbotrap), revealed that 30 to 40% differences between the two groups, implying that sampling efficiency is depending on the volatility and the strength of adsorbents. However, duplicate precisions for VOCs sampling with a same type of adsorbent and at same flow rates appeared to be satisfactory to be all within 20%, which is a quality control guideline. Distributed volume precisions were also found to be within a guideline value, 25%, although the precision was in general inferior to the duplicate precision. The Korea indoor VOCs test method should be more refined and improved in many aspects, particularly procedure and instrumentation for preparing the standard samples and specification of quality control assessment.