• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.4
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• pp.563-567
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• 2009

The polymer electrolyte membrane fuel cell(PEMFC) with the advantages of low-operating temperature, high current density, low cost and volume, fast start-up ability, and suitability for discontinuous operation becomes the most reasonable and attractive power system for transportation vehicle and micro-grid power plant in a household. 200W PEM-type FCs system was integrated by this study, then the electrical characteristics and diagnosis of the fuel cell were analyzed with variations on mass flow rate and stack temperature. The ranges of the variations are 1~8L/min on $H_2$ volume and $20{\sim}70^{\circ}C$ on stack temperature.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.56-61
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• 2003

Nanocrystalline hydrogenated silicon (nc-Si : H) thin films were deposited at room temperature by plasma enhanced chemical vapor deposition (PECVD): a mixture of SiH₄ and H₂ gas was introduced into the evacuated reaction chamber. When the H₂ gas flow rate was low, the density of Si-H₃ bonds was high in the films. On the other hand, when the H₂ gas flow rate was high, e.g., 100 sccm, a large number of Si-H bonds contributed to the passivation of the surface of the large volume of Si nanocrystallites. The relative fraction of the Si-H₃ and Si-H₂ bonds in the amorphous matrix varied sensitively with the H₂ gas flow rate. The variation was associated with the change in the intensity as well as the wavelength of the main PL peaks, indicating the change in the total volume as well as the size of the Si nanocrystallites in the films.

• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.200-209
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• 2012

The current of the water body is very important information for the water quality management on reservoirs. It is applied to hydraulics and water quality model for simulation. In this regard, the current characteristic of water body is the basic information that can be used to predict various conditions. However, it is very slow flowing and is affected by the reservoir operations and external factors. As such, an accurate measurement of the current is a difficult problem. In order to measure the water current, we constructed a drifter. According to the result of flow survey at Yongdam reservoir, 5m and 10 m depth layer flow was investigated from the upstream to the downstream, during a flood period. Maximum flow rate of 5 m depth is 13.8 cm $sec^{-1}$ and 10 m depth shows 4 cm $sec^{-1}$, respectively. But 2m depth shows a backward flow and maximum flow rate is 4 cm $sec^{-1}$. Density currents flow plays the role of back flow in reservoirs. Flow velocity in the reservoir was measured in the range of 1~2 cm $sec^{-1}$, at normal flow season, and the flow direction were different for each survey. This phenomenon occurs because the reservoir volume is very large, compared to the inflow and outflow volume.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.295-300
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• 2002

The construction of the T-shaped post-column flow cell has been changed to enhance the practicability as a UV-visible absorbance detector for capillary electrophoresis. In this new design, a rectangular cube-shaped inner structure is employed, which completely fits the outer rectangular tubing. This arrangement has greatly facilitated the fabrication of the T-cells. In addition, the volume for the auxiliary flow has been dramatically reduced down to 300 ${\mu}L$, and its volume flow rate is optimized at 4.2 ${\mu}L$/min. The short optical path length in the sheath flows (500 ${\mu}m$ on each side) minimizes background absorption, and thus enhances its performance in low-UV wavelengths. We have optimized the auxiliary flow rate at 50 ${\mu}m$/s, so that migration times are insensitive to the flow rate. This optimization has improved repeatabilities in migration times and peak heights. A double-beam detection scheme using a pair of photodiodes is employed to increase the signal-to-noise ratio.

• Proceedings of the KSR Conference
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• 2000.05a
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• pp.634-644
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• 2000

The study was carried out about the roof hood structure of power car for Korean High Speed Train. The compatibility for applied material and volume of hood duct was studied using analysis about heat and flow distributions. The materials and volume of duct were mainly determined by output air temperature and flow rate of each electric blocks. This report was described, which focuses on pressure distribution and air temperature within engine compartment of power car.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.1-7
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• 2005

Tidal circulation in a closed bay using a variation of bottom roughness was investigated through the numerical experiments based on a finite difference multi-level model. Various distributions of bottom roughness in the bay were implemented to determine their effects. It hadbeen determined that residual currents can be generated from the differences of the bottom roughness between streaming and reverse flow directions. The magnitude of residual currents and volume flow rate increase when the relative ratio of bottom roughness between streaming and reverse flow directions increase. Circulation in the closed bay is also improved by the employment of the change of bottom roughness.

• Journal of Korean Society of Disaster and Security
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• v.16 no.1
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• pp.81-89
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• 2023

Recently, due to global warming and urbanization due to the influence of abnormal weather, weather changes are increasing worldwide. Various measures have been proposed to reduce flood damage as flood volume increases due to problems such as an increase in impermeable area due to urbanization and reckless development. In this study, flow characteristics and overflow volume were analyzed using FLOW-3D, a three-dimensional CFD model, in accordance with changes in the cross-flow weir inlet angle installed in the meandering river section, and a basic study was conducted to evaluate the overflow capacity and calculate the flow coefficient. As a result of the analysis, the smaller the inflow angle of the transverse overflow, the lower the water level and flow rate of the main water flow after passing the transverse overflow, and the higher the inflow angle, the higher the water level and the flow rate. In addition, it was confirmed that the direct downstream flow rate decreased compared to the upstream flow rate when the inflow angle of the transverse overflow was 40° or higher.

• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.1
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• pp.169-177
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• 2006

In this study, it was studied that the removal rate of VOC by the catalytic combustion. The combustion temperature was changed by the contact type of VOC(space velocity and catalyst depth) and the space velocity(SV) was defined by the rate of gas volume flow rate(Q, $m^3/hr$) over volume(V, $m^3$) of catalyst (SV=Q/V). The space velocity of catalytic combustor is maintained $10,000{\sim}50,000hr^{-1}$. it was studied that the conversion rate of VOC by the catalytic combustion. The combustion temperature was changed by the contact type of VOC and catalyst and the space velocity was defined by the rate of gas volume flow rate over volume of catalyst. The VOC which pass thru the heat exchanger was measured by the hydro ionic detector and measured the VOC removal rate by the activated catalyst in the reaction temperature range of 373K-423K. The removal rate was measured over 100 times. In the automobile painting booth The VOC concentration was 63.37ppm and the removal rate was 70 % at 373K and 78.92% at 423K. The removal rate was increased as increased the temperature.

• Nuclear Engineering and Technology
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• v.38 no.4
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• pp.343-352
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• 2006

Convenient analytical tools for evaluation of the aperiodic and the fluctuating instabilities of the passive residual heat removal system (PRHRS) of an integral reactor are developed and results are discussed from the viewpoint of the system design. First, a static model for the aperiodic instability using the system hydraulic loss relation and the downcomer feedwater heating equations is developed. The calculated hydraulic relation between the pressure drop and the feedwater flow rate shows that several static states can exist with various numbers of water-mode feedwater module pipes. It is shown that the most probable state can exist by basic physical reasoning, that there is no flow rate through the steam-mode feedwater module pipes. Second, a dynamic model for the fluctuating instability due to steam generation retardation in the steam generator and the dynamic interaction of two compressible volumes, that is, the steam volume of the main steam pipe lines and the gas volume of the compensating tank is formulated and the D-decomposition method is applied after linearization of the governing equations. The results show that the PRHRS becomes stabilized with a smaller volume compensating tank, a larger volume steam space and higher hydraulic resistance of the path $a_{ct}$. Increasing the operating steam pressure has a stabilizing effect. The analytical model and the results obtained from this study will be utilized for PRHRS performance improvement.

• 한국연소학회:학술대회논문집
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• 1998.10a
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• pp.139-154
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• 1998

Under certain circumstance, premixed turbulent flame can be treated as wrinkled thin laminar flame and its motion in a hydrodynamic flow field has been investigated by employing G-equation. Past studies on G-equation successfully described certain aspects of laminar flame propagation such as effects of stretch on flame speed. In those studies, flames were regarded as a passive interface that does not influence the flow field. The experimental evidences, however, indicate that flow field can be significantly modified by the propagation of flames through the volume expansion of burned gas. In the present study, a new method to be used with G -equation is described to include the effect of volume expansion in the flame dynamics. The effect of volume expansion on the flow field is approximated by Biot-Savart law. The newly developed model is validated by comparison with existing analytical solutions of G -equation to predict flames propagating in hydrodynamic flow field without volume expansion. To further investigate the influence of volume expansion, present method was applied to initially wrinkled or planar flame propagating in an imposed velocity field and the average flame speed was evaluated from the ratio of flame surface area and projected area of unburned stream channel. It was observed that the initial wrinkling of flame cannot sustain itself without velocity disturbance and wrinkled structure decays into planar flame as the flame propagates. The rate of decay of the structure increased with volume expansion. The asymptotic change in the average burning speed occurs only with disturbed velocity field. Because volume expansion acts directly on the velocity field, the average burning speed is affected at all time when its effect is included. With relatively small temperature ratio of 3, the average flame speed increased 10%. The combined effect of volume expansion and flame stretch is also considered and the result implied that the effect of stretch is independent of volume release.