• Journal of Korean Society of Water and Wastewater
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• v.24 no.5
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• pp.629-639
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• 2010

To evaluate the performance of high rate coagulation system(HRCS) for CSOs treatment, fundamental function of lab scale HRCS has been tested by using the Jar tester and lab scale HRCS. The optimum pH dose by Streaming Current value was found in the range of 5.3~6.0 in Fe(III), and in the range of 5.8~6.6 in Al(III) and the optimum chemical dose were 0.44mM of $Al_2(SO_4)_3$ and 0.93mM of $FeCl_3$. The removal efficiencies at optimum $Al_2(SO_4)_3$ dose were 75%($TCOD_{Cr}$), 97%(TP), 95%(SS) and 96%(turbidity), respectively. And the removal efficiency of particles with less than $5{\mu}m$ of diameter was 70% and that of particles with higher than $5{\mu}m$ of diameter was 90%. The optimum alum dose in lab scale HRCS was 150mg/L, and the treatment efficiency was the best with addition of 1.0mg/L polymer. The effect of Micro sand addition was not clear, because the depth of the sediment tank in lab scale HRCS was not long enough. But the HRT of this lab scale HRCS was able to be shorten less then 7 minutes by adding the micro sand. The surface loading rates with respect to using different chemicals were 0.43m/h with alum only, 5.78m/h with alum and polymer and 6.22m/h with alum, polymer and micro sand. As a result, HRCS using coagulant, polymer and micro sand developed in this study was evaluated to be very effective for CSOs treatment.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.389-398
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• 2002

The mixed mode problem (I and II) of a peny-shaped interface cracks in remote tension loading on a bi-material cylinder is studied using finite element method. The energy release rates for the tip of the crack in the interface were calibrated for several different moduli combinations and crack ratios using the modified crack closure integral technique and J-integral method, with numerical results obtained from a commercial finite element program. Numerical results show that non-dimensional value of$\sqrt{G_{II}E^*}/\sqrt[p]{\pi a}$ increases as the crack size or moduli ratio increases. Meanwhile, non-dimensional value of$\sqrt{G_{I}E^*}/\sqrt[p]{\pi a}$ decreases as the moduli ratio increases, but above the moduli ratio of 3 its value decreases then increases again as the crack size increases. Reliability of the numerical analysis in this study was acquired with comparison to an analytical solution for the peny-shaped interface crack in an infinite medium.

• Advanced Composite Materials
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• v.17 no.2
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• pp.157-166
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• 2008

In this study, multiwalled carbon nanotubes (MWCNTs) were compounded with the poly($\varepsilon$-caprolactone) (PCL) matrix at the solution state using chloroform. For homogeneous dispersion of MWCNTs in polymer matrix, oxygen-containing groups were introduced on the surface of MWCNTs. The mechanical properties of the PCL/MWCNTs composites were effectively increased due to the incorporation of MWCNTs. The composites were characterized using scanning electron microscopy in order to obtain information on the dispersion of MWCNT in the polymeric matrix. In case of 1.2 wt% of MWCNTs in the matrix, strength and modulus of the composite increased by 12.1% and 164.3%, respectively. In addition, the dispersion of MWCNTs in the PCL matrix resulted in substantial decrease of the electrical resistivity of the composites as the MWCNTs loading was increased from 0 to 2.0 wt%. Furthermore, thermal stability of the PCL and PCL/MWCNTs-COOH composites were investigated using the data acquired from the thermogravimetric analysis. The detailed kinetics of the thermal degradation of the composites was investigated by analyzing their thermal behavior at different heating rates in a nitrogen atmosphere. Activation energy of thermal degradation was determined by using the equations proposed by Kissinger and Flynn-Wall-Ozawa. The apparent activation energy of PCL/MWCNTs-COOH composite was considerably higher than that of neat PCL.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.4
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• pp.454-459
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• 2011

In this study, the recovery rate of Tedlar bag (T) sampler was investigated in comparison to polyester aluminum bag (P) sampler. To derive the comparative data sets for the relative performance between different samplers, a series of calibration experiments were performed by using 1 ppb standard of four offensive reduced sulfur compounds (RSC) odorants ($H_2S$, $CH_3SH$, DMS, and DMDS) along with $SO_2$ and $CS_2$. All the analysis was made by gas chromatography/pulsed flame photometric detector (GC/PFPD) combined with air server/thermal desorber (AS/TD). The measurement data were obtained by loading gaseous standards (1 ppb) at 3 injection volumes (250, 500 and 1,000 mL) at three intervals (0, 24 and 72 hrs). The recovery rates (RR) of P sampler were computed against the slope values of T sampler. According to our analysis, P sampler exhibits slightly enhanced loss relative to T, especially with light RSCs ($H_2S$ and $CH_3SH$). At day 0, RR for the two were 88 and 85%, respectively. Such reduction proceeded rather rapidly in the case of $H_2S$ through time. However, P sampler was more stable to store $SO_2$ unlike others. Despite slightly reduced recovery, P sampler appears as a good replacement of T sampler.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.10
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• pp.694-701
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• 2012

The main purpose of this study is to evaluate of backwash system of hydrodynamic separator filter (HSF) with solar powered submerged pumps. It consists of a photovoltaic solar array, control electronics, battery, and two submersible pump powered by a 12 voltage DC motor. The laboratory scale study on treatable potential of micro particles using backwash HSF that was a combined with perlite filter cartridge and backwash nozzles. Since it was not easy to use actual storm water in the scaled-down hydraulic model investigations, it was necessary to reproduce ranges of particle sizes with synthetic materials. The synthesized storm runoff was made with water and addition of particles; ion exchange resin partices, silica gel particles, and commercial area manhole sediment particles. HSF was made of acryl resin with 250 mm of diameter filter chamber and overall height of 800 mm. Four case test were performed with different backwashing conditions and determined the SS removal efficiency with various surface loading rates. The operated range of surface loading rate was about 308~$1,250m^3/m^2/day$. It was found that SS removal efficiency of HSF using two submersible pumps improved by about 18% compared with HSF without backwash. Nonpoint control devices with solar water pumping systems would be useful for backwashing the filter in areas with not suppling electricity and reduce filter media exchange cost.

• Elastomers and Composites
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• v.39 no.2
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• pp.131-141
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• 2004

The recycling of waste XLPE(crosslinked polyethylene), which is a major source of scraps from high voltage power transmission cables, has been discussed. The waste XLPE scraps were ground into fine powder with various sizes from less than $100{\mu}m$ up to about $1000{\mu}m$ using two types of tailor-made pulverizers. The compounds were prepared in a modular intermeshing co-rotating twin screw extruder at various conditions such as different compositions, types and powder sizes of waste XLPE, screw configurations and various polymer matrices (LDPE, HDPE, PP, PS). The mechanical and rheological properties and the fracture surface or the compounds were investigated. It was found that an improved impact strength was obtained from the compound with white XLPE powder pulverized from the scraps without outer/inner semi-conductive layers. Generally, the impact strength increases with the content of XLPE but decreases with the size of XLPE. Especially for LDPE, the extrusion was possible up to 80 wt% loading of XLPE. Also, the impact strength increases with the number of kneading disc blocks in the given screw configurations. The melt viscosity of the compounds increases with increasing XLPE loading. However, the higher shear thinning behavior of the compounds at common shear rates implies proper processibility of the compounds. In addition, the impact strength for other polymer matrices used increases with XLPE and it is noticeable that the impact strength of PS/XLPE (80/20 wt%) compound was improved twice that of pure PS.

• Structural Engineering and Mechanics
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• v.55 no.4
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• pp.857-869
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• 2015

The aluminum 7075-T6 is known as an alloy widely used in aircraft structural applications, which does not exhibit strain rate sensitivity during dynamic compressive tests. Despite mechanical importance of the material, there is not enough attention to determine appropriate sample dimensions such as a sample diameter relative to the device bar diameter and sample length to diameter (L/D) ratio for dynamic tests and how these two parameters can change mechanical behaviors of the sample under dynamic loading condition. In this study, various samples which have different diameters of 31.8, 25.4, 15.9, and 9.5 mm and sample L/D ratios of 2.0, 1.5, 1.0, 0.5, and 0.25 were tested using Split Hopkinson Pressure Bar (SHPB), as this testing device is proper to characterize mechanical behaviors of solid materials at high strain rates. The mechanical behavior of this alloy was examined under ${\sim}200-5,500s^{-1}$ dynamic strain rate. Aluminum samples of 2.0, 1.5 and 1.0 of L/D ratios were well fitted into the stress-strain curve, Madison and Green's diagram, regardless of the sample diameters. Also, the 0.5 and 0.25 L/D ratio samples having the diameter of 31.8 and 25.4 mm followed the stress-strain curve. As results, larger samples (31.8 and 25.4 mm) in diameters followed the stress-strain curve regardless of the L/D ratios, whereas the 0.5 and 0.25 L/D ratios of small diameter sample (15.9 and 9.5 mm) did not follow the stress-strain diagram but significantly deviate from the diagram. Our results indicate that the L/D ratio is important determinant in stress-strain responses under the SHPB test when the sample diameter is small relative to the test bar diameter (31.8 mm), but when sample diameter is close to the bar diameter, L/D ratio does not significantly affect the stress-strain responses. This suggests that the areal mismatch (non-contact area of the testing bar) between the sample and the bar can misrepresent mechanical behaviors of the aluminum 7075-T6 at the dynamic loading condition.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.1
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• pp.13-23
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• 2014

A lab-scale Anaerobic Baffled Reactor (ABR) was applied to treat a primary sludge taken from a municipal wastewater treatment plant. In this experiment, acidogenic reaction was promoted by operating the ABR with short hydraulic retention time (HRT) to produce sufficient volatile fatty acids (VFA) instead of production of methane. The performance of ABR on the VFA production and total solids reduction was observed with different operating conditions with 2, 4, 6, and 8 days of HRT. Corresponding organic loading rates were 6.7, 3.4, 2.2, and $1.6kgCOD_{cr}/m^3{\cdot}day$. As HRT increased the removal rate of TCOD was also increased (82.5, 84.2, 96.9, and 95.9 % in average for HRT of 2, 4, 6, and 8 days, respectively) because the settlement of solids was enhanced in the baffle by the decrease of upflow velocity. At HRT of 2 days the average concentration of VFA in the effluent was measured at $1,306{\pm}552$ mgCOD/L corresponding to 107 % increment as compared to the VFA concentration in the influent. However, as HRT increased VFA concentraiotn was decreased to $143{\pm}552$ mgCOD/L at HRT of 8 days. The reduction rates of total solids were 12.2, 26.5, 24.8, and 43.0 % for HRT of 2, 4, 6, and 8 days. As HRT increased the hydrolysis of organic particulate matters in the reactor was enhanced due to the increasing of solids retention time in the baffle zone with low upflow velocity in long HRT condition. Consequently, we found that a primary sludge became a good source of VFA production by the application of ABR process with HRT less than 4 days and the 12-26 % of total solids reduction was expected at these conditions.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.4
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• pp.381-390
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• 2017

In Korea, commercial nuclear power plants and research reactors have on-site storage systems for the spent nuclear fuel, but it is difficult to expand the facilities used for the storage systems. If decommissioning of nuclear power plants starts, an amount of high level radioactive waste will be generated. In this study, a radiological impact assessment of the railroad transport of high level radioactive waste was carried out considering radiation workers and the public, using the developed transport container as the transport package. The dose rates for workers and the public during the transport period were estimated, considering anticipated transport scenarios, and the results compared with the regulatory limit. A sensitivity analysis was also carried out by considering the different release ratios of the radioactive materials in the high level radioactive waste, and different distances between the transport container and workers during loading and unloading phases and while attaching another freight car. For all the anticipated transport scenarios, the radiological impacts for workers and the public met the regulatory limits.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.4
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• pp.3600-3610
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• 1974

Experimental work of batch-type dryer was conducted to develop its optimurm operating conditions by analyzing the major factors which affect the drying performance. A laboratory batch-type dryer was constructed and tested for various levels of heated-air rates, and depths of grain deposit. Tong-il rice variety having the initial moisture content of approximaely 23 per cent in wet basis was used for the experiment. The criteria selected for establishing the optimum operating condition were the drying performance rate, the thermal efficiency, and the operational cost of the dryer. The results of the study are summarized as follows: 1. The performance rate of dryer for a specific operating condition was defined as total amount of material dried per hour when the moisture content of grains in the upperlayer reaches to 16 per cent in wet basis. The optimum operating conditions as viewed in the rate of drying performance could be justified by functional realtionship between the depth of grain deposit and air flow rate. In other words, there was a definite depth of grain deposit for a given air-rate which make the dryer performance maximum. The optimum grain depth for the batch-type dryer with 3.3㎡ loading area and with the attached axial fan was about 35cm. 2. The thermal efficiency for the dryer was evaluated by the ratio of the latent heat required to evaporate the grain moisture to the heat input required to raise the ambient air-temperature to 40 degree centigrade. The optimum operating condition as viewed in term of thermal efficiency analyzed was that grater depth and lower air flow-rate may be desirable. This condition is contracted with the optimum condition as viewed by the dryer performance rate. 3. The annual operating cost of batch-type dryer was analyzed for different annual hour of use and for different operation condition. The optimum condition as viewed in terms of operating cost was almost identical to one as viewed in terms of dryer performance rate. Therefore, the most economical use of batch-type dryer for the same annual operating hours can be obtained when the dryer operated in the condition of maximum dryer performance rate. Increasing the annual operating hour may be desirable to cut down the dryer operation cost, since the annual hour of dryer use is much sensitive to the operating cost than any peractical conditions of dryer operation. 4. The most desirable operational condition as justified by combining all the criteria, dryer performance rate, thermal efficiency and annual operating cost, could be concluded to operate the dryer in the condition of maximum performance rate. The condition in general is identical to the lowest operation cost for a given annual operating hour.