• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.1022-1030
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• 2002

The experiments were performed with a $31{\times}31{\times}7mm^3$ simulated 3-dimensional module on the thermal conductive board of a parallel plate channel. The convective thermal conductance for the path from the module surface directly to airflow and conjugate thermal conductance for the path leading from the module to the floor by way of a module support, then, to the airflow were determined with several combinations of module-support-construction(210, 0.32, 0.021 K/W)/floor-material(398, 0.236W/mK) and channel height(15-30mm). As the result, it was found that the conjugate thermal conductance and the temperature distribution around the module depend on the thermal resistance of the module support, and the channel height. These configurations were designed to investigate on the feasibility of using the substrate as an effective heat spreader in the forced convective air-cooling of surface mounted heat source. The experimental results were discussed in the light of interactive nature of heat transfer through two paths, one directed from the module to the airflow and the other via the module support and the floor to the air.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2448-2453
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• 2008

The present study numerically investigates the flow and heat transfer characteristics of rib-induced secondary flow in a cooling channel with staggered V-shaped ribs, extruded on both walls. The rib-height-to-hydraulic diameter ration (h/$D_h$) is 0.17; the rib pitch-to-height ratio (p/h) equals 2.8; the Reynolds number is 50,000. Shear stress transport (SST) turbulence model is used as a turbulence closure. The present results are compared with those for a continuous V-shaped rib. Computational results show that, for average heat transfer rate the staggered V-shaped rib gives about 2.5 times higher values than the continuous V-shaped rib, while, for the streamwise pressure drop the former gives about 5 times higher values than the latter. Consequently, for the thermal performances, based on the equal pumping power condition, the staggered one gives about 2 times higher values than the continuous one. Also, for the staggered V-shaped rib, complex secondary flow patterns are generated in the duct due to the snaking flow in the streamwise direction, and more uniform heat transfer distributions are obtained.

• Journal of the Korean Solar Energy Society
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• v.31 no.4
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• pp.57-65
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• 2011

This study proposes a Passive Solar Chamber System (PSCS) as a passive method for reduction of building energy consumption. Through numerical analysis, the study quantitatively analyzes system performance and aims to provide foundational data for system design. For this purpose, the study configures different system operation modes seasonally and also computes thermal and ventilation performance of the system in accordance with design factors(solar radiation, air channel height and distance). System and ventilation efficiency increases along with increase in solar radiation and air channel distance; however, as the air channel height increases, the efficiencies showed a tendency to decrease. Upon installation of PSCS, an average of $98.23W/m^2$ of heat flux was introduced in the daytime for the month of January in comparison to walls with no PSCS installed. For the month of August, natural ventilation of $56.68m^3/h$ was shown to be supplied to the room.

• Journal of Korea Water Resources Association
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• v.36 no.4
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• pp.623-631
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• 2003

A large scale hydrological laboratory model tests for the geotextile tube were conducted to investigate the stability of geotextile tube and the capability of breakwater with variations of significant wave height, percentage of soil filling, and the water level above geotextile tube. The sliding displacement of geotextile tube is measured to check the stability of geotextile tube for given the various significant wane heights. The marked mash was laid out at the bottom of water channel to measure the displacement of geotextile tube. The bench mark was furnished in the upper part of water channel and the initial location was marked every 10cm interval to measure the displacement of geotextile tube. The wane transmit ratios are analyzed with the variations of soil filling of tube and of the top crown height wave above the geotextile tube in order to study the performance of brekwater before and after the installation of geotextile tube.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.94-103
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• 2015

The turbulent flow characteristics in the channel flow are investigated using large eddy simulation(LES) of FDS code, built in NIST(USA), in which the near-wall flow is solved by Werner-Wengle wall function. The periodic flow condition is applied in streamwise direction to get the fully developed turbulent flow and symmetric condition is applied in lateral direction. The height of the channel is H=1m, and the length of the channel is 6H, and the lateral length is H. The total grid is $32{\times}32{\times}32$ and $y^+$ is kept above 11 to fulfill the near-wall flow requirement. The Smagorinsky model is used to solve the sub-grid scale stress. Smagorinsky constant $C_s$ is 0.2(default in FDS). Three cases of Reynolds number(10,700, 26,000, 49,000.), based on the channel height, are analyzed. The simulated results are compared with direct numerical simulation(DNS) and particle image velocimetry(PIV) experimental data. The linear low-Re eddy viscosity model of Launder & Sharma and non-linear low-Re eddy viscosity model of Abe-Jang-Leschziner are utilized to compare the results with LES of FDS. Reynolds normal stresses, Reynolds shear stresses, turbulent kinetic energys and mean velocity flows are well compared with DNS and PIV data.

• Journal of Korea Water Resources Association
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• v.43 no.6
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• pp.517-524
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• 2010

In this study, the 1D apparent shear stress model for vegetated compound open-channel flows was suggested. To consider the effect of momentum exchange between main channel and floodplain, the eddy viscosity concept was used in the present model. The interfacial eddy viscosity in the interface of main channel and floodplain was determined from the 3D Reynolds stress model. The evaluated interfacial eddy viscosity appears to be good agreement with those proposed previously. To investigate the effect of interfacial eddy viscosity, sensitive analysis was carried out. the computed backwater profiles are nearly identical with respect to the value of the interfacial eddy viscosity. However, the discharge conveyed by the floodplain changes is proportional to the interfacial eddy viscosity. Finally, the changes of the interfacial eddy viscosity due to the vegetation density and vegetation height were examined. The computed results of interfacial eddy viscosity are in proportion to the vegetation density and vegetation height, and the interfacial eddy viscosity has a range of $(2-5)\;{\times}\;10^{-4}$.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.303-308
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• 2003

In this paper, wave numerical modeling was experimented for the analysis of impact factors for the wave transmission as the incident wave and topographic conditions in the narrow channel sea. Recently, Although the results of many researcher for the wave modelling, numerical equations have limited to simulation of wave transformation effects. Despite of thispresent problems, the models was used to design the coastal structures in barrow channel sites. Finally, this paper estimated the wave model(mild slope eq. model) as the analysis of the wave energy transmission according to changing of impact factors(width of channel, bottom slope in channel, incident wave angle, wave period). As the results of numerical experiment, the major impact factors which influence to wave energy transmission were the width of channel and incident wave direction. But in the case that the width of channel is larger than 3L(L=Length of wave), the reduction of wave energy was small.

• Journal of Korean Society of Forest Science
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• v.100 no.2
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• pp.202-211
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• 2011

The geometric characteristics of step-pool structures and how they are influenced by channel characteristics were investigated in a steep mountain stream in the Experimental Forests of Kangwon National University in Chuncheon, Gangwon-do. Average values of steps for the study reaches were as follows: step spacing, 4.69 m; step height, 0.47 m; step drop, 0.71 m; step-forming particle sizes, 0.68 m; number, 21steps/ 100 m; the ratio of step spacing to channel width, 0.5; and step steepness, 0.13. Relationships between spacing and height of steps and channel gradient showed a negative- and positive correlation, respectively, whereas all geometric variables of steps manifested poor correlation with channel width. Therefore, step steepness, expressed as the ratio of step height to step spacing, increased as channel gradient increased. The ratio of step steepness to channel gradient representing the criterion of maximum flow resistance was 1.2, indicating the channel bed's stable condition. In particular, the relationship between the ratio of step drop to step height and channel gradient showed a significant negative correlation, suggesting the influence of step-pool geometry in trapping sediment and providing an aquatic habitat. Positive correlations also exist between spacing and drop of steps and step particles. Our findings suggest that the dynamics of step-pool structures may strongly control physical and ecological environments in steep mountain streams, so understanding them is essential for stream management.

• Membrane Journal
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• v.6 no.1
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• pp.44-52
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• 1996

For the purpose of the optimal design of a frame and plate type of pervaporation module, model equations which can predict the effects of feed flow condition on the temperature distribution of the feed developed in the module were established and the temperature distribution with feed flow condition was investigated through the model si$$\mu$ation. With increasing the Reynolds number of feed flow in the module, the flow velocity gradient in the channel height-direction as well as the volume rate of feed which acts as energy source for the evaporation of perrneants on the permeate-side surface of a membrane increased to such an extent that both mass and heat flux in the channel height direction could increase and the temperature drop of feed due to the evaporation of the permeant could be reduced correspondingly. A decrease in channel height caused the temperature drop of feed because of decreasing feed flow in the module. It was observed that the si$$\mu$ation result on the effect of Re on the temperature distribution of feed in the module has an agreement with experiment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.133-133
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• 2008

Recently, as the down-scailing of field-effect transistor devices continues, Schottky-barrier field-effect transistors (SB-FETs) have attracted much attention as an alternative to conventional MOSFETs. SB-FETs have advantages over conventional devices, such as low parasitic source/drain resistance due to their metallic characteristics, low temperature processing for source/drain formation and physical scalability to the sub-10nm regime. The good scalability of SB-FETs is due to their metallic characteristics of source/drain, which leads to the low resistance and the atomically abrupt junctions at metal (silicide)-silicon interface. Nevertheless, some reports show that SB-FETs suffer from short channel effect (SCE) that would cause severe problems in the sub 20nm regime.[Ouyang et al. IEEE Trans. Electron Devices 53, 8, 1732 (2007)] Because source/drain barriers induce a depletion region, it is possible that the barriers are overlapped in short channel SB-FETs. In order to analyze the SCE of SB-FETs, we carried out systematic studies on the Schottky barrier overlapping in short channel SB-FETs using a SILVACO ATLAS numerical simulator. We have investigated the variation of surface channel band profiles depending on the doping, barrier height and the effective channel length using 2D simulation. Because the source/drain depletion regions start to be overlapped each other in the condition of the $L_{ch}$~80nm with $N_D{\sim}1\times10^{18}cm^{-3}$ and $\phi_{Bn}$ $\approx$ 0.6eV, the band profile varies as the decrease of effective channel length $L_{ch}$. With the $L_{ch}$~80nm as a starting point, the built-in potential of source/drain schottky contacts gradually decreases as the decrease of $L_{ch}$, then the conduction and valence band edges are consequently flattened at $L_{ch}$~5nm. These results may allow us to understand the performance related interdependent parameters in nanoscale SB-FETs such as channel length, the barrier height and channel doping.