• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.128-136
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• 2007

It is well known that two representative methods satisfy EURO-IV regulation from EURO-III. The first method is to achieve the regulation through the reduction of NOx in an engine by utilizing relatively high EGR rate and the elimination of subsequently increased PM by DPF. However, it results in the deterioration of fuel economy due to relatively high EGR rate. The second is to use the high combustion strategy to reduce PM emission by high oxidation rate and trap the high NOx emissions with DeNOx catalysts such as Urea-SCR. While it has good fuel economy relative to the first method mentioned above, its infrastructure is demanded. In this paper, the number distribution of nano PM has been evaluated by Electrical Low Pressure Impactor(ELPI) and CPC in case of Urea-SCR system in second method. From the results, the particle number was increased slightly in proportion to the amount of urea injection on Fine Particle Region, whether AOC is used or not. Especially, in case of different urea injection pressure, the trends of increasing was distinguished from low and high injection pressure. As low injection pressure, the particle number was increased largely in accordance with the amount of injected urea solution on Fine Particle Region. But Nano Particle Region was not. The other side, in case of high pressure, increasing rate of particle number was larger than low pressure injection on Nano Particle Region. From the results, the reason of particle number increase due to urea injection is supposed that new products are composited from HCNO, sulfate, NH3 on urea decomposition process.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.245-255
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• 2009

The low-rise buildings with gable roofs are commonly used in a number of industries. In order to study the characteristics of peak external pressure coefficient on low-rise buildings with gable roofs, wind-tunnel test have been carried out. Wind-induced pressures were measured simultaneously at many points on wind-pressure models, typical of simple low-rise buildings with gable roofs, which have seven different roof slope with constant width(D), height(H), and length(D). The pressure measurements were made in one kind of turbulent boundary layer, which simulated the natural winds over typical suburban terrains at a geometric scale of 1/150. The results indicate that peak external pressure coefficient on the roof and wall edges were increased. The results compared with wind standard of KBC-2005 and standards of various nations. The comparative resultant, experimental result appeared very similar at AIJ-2004. But the results were somewhat larger then wind standard of KBC-2005.

• Tunnel and Underground Space
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• v.25 no.6
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• pp.543-555
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• 2015

At present, local limestone mines with large opening employ auxiliary fans for workplace ventilation which have been used in coal mines with much smaller airways. Considering the low static pressure loss in the large-opening mines, high pressure auxiliary fans face serious economical limitations mainly due to their excessive capacity. The optimal fan selected for the ventilation in large-opening working places should supply air quantity enough for maintaining safe environment and keep its operating cost as low as possible. This study focuses on the development of a low pressure auxiliary fan designed to have smaller range of the static head but to have more potential for higher ventilation and energy efficiency. The flow characteristics of high and low pressure auxiliary fans were theoretical as well as experimentally investigated to assess the ventilation efficiency in term of environmental and economical aspects. Moreover, the low pressure fan was tested in two limestone mine sites with small and large cross-sectional areas for evaluating its ventilation efficiency. Results from this study can be applied to improve the economy and efficiency of auxiliary fan for ensuring better air quality and work environment management.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.2
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• pp.185-196
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• 2020

Low-pressure sodium lamps, high-pressure sodium lamps and fluorescent lamps etc are mainly used tunnel lighting in Rep. of Korea. Power rates for tunnel lighting are known to account for the highest percentage in the tunnel maintenance costs. Therefore, tunnel lights are being replaced by LED that have advantages such as low power consumption and longevity. To analysis effect of replacement low pressure sodium lamp with LED, illumination and monthly power usage for a year are investigated for 8 tunnels. Power usage for tunnel lighting is decreased by 26.1% to 59.6%, and illumination is increased by 34.1% to 293% replacing low pressure sodium lamp with LED.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.457-470
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• 2016

Most CFD codes, that mainly adopt the heat partitioning model as the wall boiling model, have shown low accuracies in predicting the two-phase flow parameters of subcooled boiling phenomena under low pressure conditions. In this study, a number of subcooled boiling experiments in vertical channels were analyzed using a thermal-hydraulic component code, CUPID. The prediction of the void fraction distribution using the CUPID code agreed well with experimental data at high-pressure conditions; whereas at low-pressure conditions, the predicted void fraction deviated considerably from measured ones. Sensitivity tests were performed on the submodels for major parameters in the heat partitioning model to find the optimized sets of empirical correlations suitable for low-pressure subcooled flow boiling. The effect of the K-factor on the void fraction distribution was also evaluated.

• Journal of Korean Biological Nursing Science
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• v.21 no.3
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• pp.169-177
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• 2019

Purpose: The purpose of this paper was to identify blood pressure, interdialytic weight gain, thirst and intradialytic discomfort in subjects after applying individual low-sodium dialysis fluid (1,2,3 mEq/L) to hemodialysis patients for 12 weeks. Methods: This study was a non-equivalent pre-post design. For 12 weeks, dialysate concentration was maintained at 1 mEq/L or 2 mEq/L or 3 mEq/L based on average sodium concentration of each individual, and the difference was compared after applying individually. Results: Change in blood pressure significantly decreased in the group where in pre-hemodialysis systolic pressure decreased the gradient of sodium concentration in serum sodium and dialysis solution by 2mEq/L. Interdialytic weight gain, and thirst showed significant decrease in all three groups. But in all three groups, intradialytic discomfort among dialysis showed no significant changes. Conclusion: Although application of low sodium dialysis fluid showed no change in intradialytic discomfort, lowered blood pressure, thirst, and interdialytic weight gain, which could be used for individual showing increased interdialytic weight gain and increased blood pressure. There is need for continued study on this.

• Wind and Structures
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• v.21 no.1
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• pp.1-23
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• 2015

Wind tunnel testing of a low-rise building with openings (holes) of different sizes and shapes on a roof corner is conducted to measure the internal and external pressures from the building model. Detailed analysis of the testing data is carried out to investigate the characteristics of the internal and external pressures of the building with different openings' configurations. Superimposition of the internal and external pressures makes the emergence of positive net pressures on the roof. The internal pressures demonstrate an overall uniform distribution. The probability density function (PDF) of the internal pressures is close to the Gaussian distribution. Compared with the PDF of the external pressures, the non-Gaussian characteristics of the net pressures weakened. The internal pressures exhibit strong correlation in frequency domain. There appear two humps in the spectra of the internal pressures, which correspond to the Helmholtz frequency and vortex shedding frequency, respectively. But, the peak for the vortex shedding frequency is offset for the net pressures. Furthermore, the internal pressure characteristics indirectly reflect that the length of the front edge enhances the development of the conical vortices.The objective of this study aims to further understanding of the characteristics of internal, external and net pressures for low-rise buildings in an effort to reduce wind damages to residential buildings.

• Journal of the Korean Society for Railway
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• v.13 no.5
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• pp.516-520
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• 2010

Parametric study has been conducted to calculate the capacity of vacuum pump system that will be used to maintain the pressure of the tube structure under atmosphere level. Recently many railroad researchers pay attention to the tube train system as one of the super high speed transportation system. To achieve the super high speed, the inside of tube system should be maintained at low pressure level. In the low pressure environment, it is well known that air resistance of train is drastically decreased. Vacuum pump system will be used to make low pressure state for tube structure, exhaust the leakage air and supplement additional vacuum pumping. As results of these studies, we get the lump capacity of vacuum pump for various parameters. These results can be applied to analyze the effects of the reduction of air resistance.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.393-400
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• 2013

The air supply system has a significant effect on the efficiency of polymer electrolyte membrane fuel cell (PEMFC) systems. The performance and efficiency of automotive PEMFC systems are greatly influenced by their air supply system configurations. This study deals with the system simulation of automotive PEMFC systems using MATLAB/Simulink framework. In this study, a low-pressure operating PEMFC system adopting blower sub-module (turbo-blower) is modeled to investigate the effects of stack operating temperature and air stoichiometry on the parasitic power and efficiency of automotive PEMFC systems. In addition, the PEMFC net system efficiency and parasitic power of air supply system are mainly compared for the two types (low-pressure operating and high-pressure operating) of automotive PEMFC systems under the same net power conditions. It is suggested that the obtained results from this system approach can be applied for establishing the novel operating strategies for FC vehicles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.610-620
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• 1999

Recently, numerous modifications of low Reynolds number $k-{\epsilon}$ model have boon carried out with the aid of DNS data. However, the previous models made in this way are too intricate to be used practically. To overcome this shortcoming, a new low Reynolds number $k-{\epsilon}$ model has boon developed by considering the distribution of turbulent properties near the wall. This study proposes the revised a turbulence model for prediction of turbulent flow with adverse pressure gradient and separation. Nondimensional distance $y^+$ in damping functions is changed to $y^*$ and some terms modeled for one dimensional flow in $\epsilon$ equations are expanded into two or three dimensional form. Predicted results by the revised model show an acceptable agreement with DNS data and experimental results. However, for a turbulent flow with severe adverse pressure gradient, an additive term reflecting an adverse pressure gradient effect will have to be considered.