• Particle and aerosol research
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• v.13 no.1
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• pp.1-10
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• 2017

Accurate prediction of size, shape and velocity of a bubble rising through a liquid pool is very important for predicting the particulate removal efficiency in pool scrubbing, for designing engineering safety features to prepare for severe accidents in nuclear power plants, and for predicting the emission of fission products from MCCI (molten core-concrete interaction) process during severe accidents. In this review article, previous studies on the determination of the size, shape and rising velocity of a bubble in liquid are reviewed. Various theoretical and parameterization formulas calculating the bubble size, shape and velocity from physical properties of liquid and gas flowrate are compared. Recent studies tend to suggest simple parameterizations that can easily determine the bubble shape and rising velocity without iteration, whereas iteration has to be performed to determine the bubble shape and velocity in old theories. The recent parameterizations show good agreement with measured data obtained from experiments conducted using different liquid materials with very diverse physical properties, proving themselves to be very useful tools for researchers in related fields.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.66-70
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• 2001

The combustion characteristics have been investigated to develop the low $NO_{x}$ gas turbine combustor. The lean premixed combustion technology was applied to reduce the $NO_{x}$ emission. Also, the conventional combustor was designed and tested for the baseline of low $NO_{x}$ combustor performance. The test was conducted at the condition of high temperature and ambient pressure. The combustion air which has the temperature of 500K were supplied to the combustor through the air preheater. The temperature and emissions of $NO_{x}$ and CO were measured at the exit of combustor. The premixing chamber can be operated very lean condition of equivalence ratio around 0.35. The $NO_{x}$ was decreased with decreasing the equivalence ration. The CO was decreased with decreasing the equivalence ratio, but the CO was increased with decreasing the equivalence ratio below 0.45. But, at the very lean condition of equivalence ratio below 0.35 both NOx and CO were increased because of the flame unstability. The $NO_{x}$ was decreased slightly and CO was increased with increasing inlet air flowrate. This results can be used to determine the size of combustor. The low $NO_{x}$ combustor has lower values of $NO_{x}$ and CO compared with conventional one. Consequently the performance of combustor shows the possibility of the application to the gas turbine system.

• Journal of Environmental Science International
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• v.27 no.1
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• pp.39-45
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• 2018

In this study, the International Maritime Organization (IMO)'s guideline MEPC. 277 (64) was developed and evaluated for the removal efficiency of T-N in a SBR and MBR combined process. This combined process of resized equipment based on large capacity water treatment device for a protection of marine aquatic life. In this experiment, T-N concentration of influent and effluent was measured through with the artificial wastewater. The SBR reactor operation time was varied according to the C : N : P ratios so that different conditions for mixing and aeration period in mins (90 : 60, 80 : 40, 70 : 50) and two C: N: P ratios (10 : 5 : 3, 10 : 3 : 1) were used. During experiment in the reactor's aeration and anoxic tank DO concentrations were 3 mg/L and 0.2 mg/L respectively. Furthermore, in the reactor MLSS concentration was 2000 mg/L and flowrate was 2 L/hr. Experiment results showed that C : N : P, 10 : 3 : 1 ratio with 90 mins mixing and 60 mins aeration maximized removal efficiency at 97.3% T-N as compared to other conditions. The application of the SBR and MBR combined process showed efficient results.

• Particle and aerosol research
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• v.7 no.3
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• pp.79-85
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• 2011

Porous $TiO_2-SiO_2$ particles were synthesized by co-assembly of nanoparticles of $TiO_2$ and $SiO_2$ in evaporating aerosol droplets. Poly styrene latex (PSL) particles were employed as a template of porous particles. Flowrate of dispersion gas, weight ratio of $TiO_2/SiO_2$ and $SiO_2$ concentration in the precursor, and PSL size were chosen as process variables. The morphology, crystal structure, chemical bonding, and pore size distribution were analyzed by FE-SEM, XRD, FT-IR, BET. The morphology of porous $TiO_2-SiO_2$ particles was spherical and the average particle size range were from 1 to $10{\mu}m$. The particles were composed of meso and macro pores. The average particle diameter and pore volume of the as prepared particles were dependant on process variables. It was found that UV-Vis absorption of the porous particles was comparable with pure $TiO_2$ nanoparticles even though $TiO_2/SiO_2$ ratio is low in the porous particles.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.3
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• pp.245-253
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• 2001

Mixing zone characteristics of the wastewater effluents discharged from Sokcho ocean outfall have been investigated using an outfall mixing zone model which was developed on the basis of Huang et al.'s(1996) analysis method. The model was applied to Sokcho ocean outfall case and was used to simulate the concentration distribution of wastewater effluents using winter season's data, ie. daily effluent flowrate, ocean current and density stratification data which were measure for two months in the outfall area. Hourly concentration distribution of outfall effluent discharges was calculated and they were averaged for the period of 15 days which covers the ambient flow variability of the neap and the spring tidal currents. The results show that near-field dilution was relatively high with the minimum dilution of 130 for the winter season. The mixing zone was extended to the coastal beach area rather than offshore because of major direction of coastal currents. This may cause a deteriorating impact on coastal water quality, especially to the adjacent swimming beach area.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.7
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• pp.750-757
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• 2005

The objective of this study is an understanding of the effect of inlet flow angle on the output power performance of a Francis hydraulic turbine, An optimum induced angle at the inlet of the turbine is one of the most important design parameters to have the best performance of the turbine at a given operating condition, In general. rotating speed of the turbine is varied with the change of water mass flowrate in a volute, The induced angle of the inlet water should be properly adjusted to the operating condition to have maximum energy conversion efficiency of the turbine, In this study. a numerical simulation was conducted to have detail understanding of the flow phenomenon in the flow path and output power of the model Francis turbine. The indicated power produced by the model turbine at a given operating condition was found numerically and compared to the brake power of the turbine measured by experiment at KIER. From comparison of two results, turbine efficiency or energy conversion efficiency of the model turbine was estimated. From the study, it was found that the rotating power of the turbine linearly increased with the rotating speed. It means that the higher volume flow rate supplied. the bigger torque on the turbine shaft generated. The maximum brake efficiency of the turbine is around 46$\%$ at 35 degree of induced angle. The difference between numerical and experimental output of the model turbine is defined as mechanical efficiency. The maximum mechanical efficiency of the turbine is around 93$\%$ at 25$\∼$30 degree of induced angle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.437-442
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• 2013

In recent times, surface texturing methods have been widely applied to reduce friction and improve the reliability of machine components such as parallel thrust bearings, mechanical face seals, and piston rings. In this study, a numerical analysis is carried out to investigate the effect of uniformly spaced hemispherical dimples on the lubrication characteristics of a slider bearing using a commercial computational fluid dynamics (CFD) code, FLUENT. The pressure distributions, load capacity, leakage flowrate, and friction force are strongly affected by the dimple diameter and the number of dimples. In particular, the load capacity and friction force decrease linearly with the dimple density whereas the leakage increases. These results can be used for designing the optimum dimple characteristics in order to improve the lubrication performance of slider bearings, for which further studies are required.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.259-266
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• 1990

Leaks at the piston seal and the by-pass port of a small volume prover have relatively large influence on the proving accuracy in comparison with a conventional ball prover. The pulse interpolator, which is to increase the discrimination, is affected by the characteristic of the flowmeter signal. In this study, a small volume prover of the double cylinder type was designed in order to study the pulse interpolation error as well as the leak error. The basic volume of the prover determined by a water draw method was about 9.68L. Experimental results revealed that interpolation data attained by the repeated piston pass for turbine meters at a fixed flowrate may be treated effectively by applying a statistical method. It was possible to limit the pulse interpolation error less than .+-. 0.02% at the 95% confidence level. However, in the case of the bulk meter, if failed to achieve the required repeatability level because of the pulse characteristics. The basic volume change appeared to be independent of the piston velocity within the .+-. 0.05% of tolerance.

• Journal of Plant Biotechnology
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• v.31 no.4
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• pp.307-312
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• 2004

The bioreactor system for the large-scale plant tissue culture was developed to control the pH concentration and DO (dissolved oxygen), and air flowrate. The system controlling the proper air flow rate for each bulblet growth stage and monitoring the contamination of bioreactor using the pH change was controled by computer program. For the uniform bulblet distribution in bioreactor, the proper air flow rate was 300 cc/min at the beginning of bulblet culture, 400 cc/min after 20 days, 500 cc/min after 40 days, 600 cc/min after 60days, and 700 cc/min after 80 days. It was possible to maintain the pH concentration within 5.5$\pm$0.5 during the culture by control system of bioreactor.

• Journal of Environmental Science International
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• v.22 no.12
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• pp.1643-1650
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• 2013

This study investigated water quality of effluents and stream from the sewage treatment plants located at Gumi Complex 4, Gumi, and Wonpyeong in Gumi. Downstream region was found to increase the concentration of nutrients for sewage treatment plant effluent. Both phosphorus and nitrogen were accounted most as soluble form. In particular, the high ratio of dissolved effluent of sewage treatment plants were investigated. In the streams, Phosphorus concentration was high during rainy season and nitrogen concentration was high in the dry season. Sewage treatment plant effluent was relatively less microbial activity and nutrient concentrations were higher in the winter. TN/TP ratio was the highest in the upstream region and the lowest in the sewage treatment plant effluent. The effect of the nutrient matter from a discharge of a sewage treatment plant on rivers varied depending on the size of the river and the treatment plant. However, the influence of the concentration was greater than that of flowrate. Sewage treatment plant effluent loads phosphorus, nitrogen accounted for 8% and 6% respectively at the point N3 of the Nakdong river.