• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.103-110
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• 2012

The flow field, fuel-air mixing, and behaviors of turbulent flames have been investigated using the large eddy simulation (LES) numerical technique in a premixed swirl combustor equipped with EV double cone burners. Recirculation zones are generated by the swirl burner, and lean premixed flames are formed within a distance of 0.2 m from the tip of the burner. NOx emission of 0.46 ppm is predicted at 1 atm and an air/fuel ratio of 38.7. However, most of the CO generated in a flame front continues to be oxidized as it moves toward the exit, and CO emission of 5.45 ppm is predicted at the exit. The NOx emission can be reduced by decreasing the pressure and air/fuel ratio. The characteristics of NOx emission have been investigated through RANS simulations for various fuel injection types, and it is found thereby that five-lance-hole injection produces the lowest NOx emission rate.

• Journal of Korean Biological Nursing Science
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• v.3 no.1
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• pp.41-52
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• 2001

This study was undertaken to investigate the effects of n-6(corn oil) & n-3(fish oil) fatty acids on infarction size and the cerebral activities of antioxidant enzyme in rat focal brain ischemia model. Weaning Sprague-Dawley rats were fed with either corn oil supplemented diet(COD, 14% corn oil) or fish oil supplemented diet(FOD, 14% menhaden oil) for 6 weeks. The right middle cerebral artery was occluded for 2 hours with a silicon rubber coated nylon surgical thread. After 24 hours of recirculation, the rats were sacrificed and brain sections were photographed using CCD camera after staining with 2, 3, 5-triphenyltetrazolium chloride for 60 minutes in room temperature. The infarcted area was measured and the volume of infarction was calculated. Catalase(CAT), superoxide dismutase(SOD) activities, and fatty acid composition in the brain were also measured. The total and corrected infarction volumes were not significantly different between FOD and COD group. The docosagexaenoic acid(DHA) and DHA content/arachidonic acid(AA) ratio of the cerebral cortex, an index of defense against lipid oxidation, were significantly increased in FOD group compared to those of COD group(p<0.05). In the left cortex(non-infarction side) as well as the right cortex(infarction side) of FOD group, CAT and Cu/Zn SOD activities were higher than those of the COD group(p<0.05). However, CAT and Cu/Zn SOD activities were not significantly different between the left cortex(non-infarction side) and the right cortex(infarction side) of both FOD and COD group. GPx activities were also not significantly different between two groups. Our results demonstrate that the brain infarction size in FOD and COD were not significantly different. However, cerebral lipid composition and antioxidant enzyme activities in FOD and COD group were different. Fish oil, a source of n-3 polyunsaturated fatty acid(PUFA) and corn oil, that of n-6(PUFA) may have a protective effect against oxidative stress induced via different mechanisms.

• Clean Technology
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• v.29 no.3
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• pp.185-192
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• 2023

This study was conducted to obtain basic process simulation data before conducting pyrolysis experiments for the development of a thermochemical conversion system by recirculation of heat carrier and gases thereby. In this study, polypropylene (PP) was used as a pyrolysis sample material as an alternative to waste plastics, and fluid sand was used as a heat transfer medium in the system. Manganese (Mn) was chosen as the catalyst for the pyrolysis experiment, and the catalyst pyrolysis was performed by impregnating it in the sand. The basic properties of PP were analyzed using a thermogravimetric analyzer (TGA), and liquid oil was generated through catalytic pyrolysis under a nitrogen atmosphere at 600℃. The carbon number distribution of the generated liquid oil was confirmed by GC/MS analysis. In this study, the effects of the presence and the amount of Mn loading on the yield of liquid oil and the distribution of hydrocarbons in the oil were investigated. When Mn/sand was used, the residue decreased and the oil yield increased compared to pyrolysis using sand alone. In addition, as the Mn loading increased, the ratio of C₆~C₉ range gasoline in the liquid oil gradually increased, and the distribution of diesel and heavy oil with more carbon atoms than C₁₀ in the oil decreased. In conclusion, it was found that using Mn as a catalyst and changing the amount of Mn could increase the yield of liquid oil and increase the gasoline ratio in the product.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.343-350
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• 2012

A planar solid oxide fuel cell (PSOFC) is studied in its application in a high-temperature stationary power plant. Even though PSOFCs with external reformers are designed for application from the distributed power source to the central power plant, such PSOFCs may sacrifice more system efficiency than internally reformed SOFCs. In this study, modeling of the PSOFC with an external reformer was developed to analyze the feasibility of thermal energy utilization for the external reformer. The PSOFC system model includes the stack, reformer, burner, heat exchanger, blower, pump, PID controller, 3-way valve, reactor, mixer, and steam separator. The model was developed under the Matlab/Simulink environment with Thermolib$^{(R)}$ modules. The model was used to study the system performance according to its configuration. Three configurations of the SOFC system were selected for the comparison of the system performance. The system configuration considered the cathode recirculation, thermal sources for the external reformer, heat-up of operating gases, and condensate anode off-gas for the enhancement of the fuel concentration. The simulation results show that the magnitude of the electric efficiency of the PSOFC system for Case 2 is 12.13% higher than that for Case 1 (reference case), and the thermal efficiency of the PSOFC system for Case 3 is 76.12%, which is the highest of all the cases investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.8
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• pp.665-670
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• 2014

Because reducing atmospheric pollution is becoming a serious issue, studies are actively focusing on exhaust gas reduction. This study was conducted to determine the emission characteristics when applying an EGR system, the main approach used for NOx reduction, to an off-road mechanical diesel engine. For the application of the EGR system, the emission characteristics in consideration of the engine conditions were analyzed. The optimum EGR ratio for NOx emission reduction was determined by applying variable EGR conditions for each engine speed condition. Considering the above process, the emission characteristics of the modified EGR condition are compared with those of other conditions (non-EGR and existing EGR condition) in the NRTC mode. Consequently, NOx emission was reduced by around 42 compared with the non-EGR condition when using the modified EGR map.

• Journal of Ocean Engineering and Technology
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• v.10 no.3
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• pp.138-152
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• 1996

Many studies of heat transfer on the swirling flow or unswirled flow in a abrupt pipe expansion are widely carried out. The mechanism is not fully found evidently due to the instabilities of flow in a sudden change of the shape and appearance of turbulent shear layers in a recirculation region and secondary vortex near the corner. The purpose of this study is to obtain data through an experimental study of the swirling flow and heat transfer downstream of an abrupt expansion in a circular pipe with uniform heat flux. Experiments were carried out for the turbulent flow nd heat transfer downstream of an abrupt circular pipe expansion. The uniform heat flux condition was imposed to the downstream of the abrupt expansion by using an electrically heated pipe. Experimental data are presented for local heat transfer rates and local axial velocities in the tube downstream of an abrupt 3:1 & 2:1 expansion. Air was used as the working fluid in the upstream tube, the Reynolds number was varied from 60, 00 to 120, 000 and the swirl number range (based on the swirl chamber geometry, i.e. L/d ratio) in which the experiments were conducted were L/d=0, 8 and 16. Axial velocity increased rapidly at r/R=0.35 in the abrupt concentric expansion turbulent flow through the test tube in unswirled flow. It showed that with increasing axial distance the highest axial velocities move toward the tube wall in the case of the swirling flow abrupt expansion. A uniform wall heat flux boundary condition was employed, which resulted in wall-to-bulk temperatures ranging from 24.deg. C to 71.deg. C. In swirling flow, the wall temperature showed a greater increase at L/d=16 than any other L/d. The bulk temperature showed a minimum value at the pipe inlet, it also exhibited a linear increase with axial distance along the pipe. As swirl intensity increased, the location of peak Nu numbers was observed to shift from 4 to 1 step heights downstream of the expansion. This upstream movement of the maximum Nusselt number was accompanied by an increase in its magnitude from 2.2 to 8.8 times larger than fully developed tube flow values.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.2
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• pp.675-680
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• 2010

This study was investigated to complement nitrogen removal of low concentration influent municipal sewage. The following are the results of the effect of Internal Recircularion and Step Feed rates on Treatment efficiency at a BOD low concentration influent municipal sewage. Up to 90.0% of BOD, 87.8% of COD, 71.0% of T-N, 75.3% of T-P were removed on average at a low concentration influent. Whereas BOD and T-P were removed without any relations to Step Feed rates, T-N was influenced. Nitrogen removal efficiencies in 80% of Step Feed rates was 65%, which was caused by the lack of Carbon Source for denitrification. Nitrogen removal efficiency in 40% of Step Feed rates was 58%, which means it was not removed but dischared. Consequently, the efficiency was 73%, 80%, and 78% in 70%, 60% and 50% of Step Feed rates, which was concluded as the best range of Step Feed rates. Nitrogen removal efficiency increased under the condition of Internal Recircularion. At over 150% of Internal Recircularion rate, the efficiencies were not affected any more. It is believed that lots of Recircularion caused inflow of DO to anoxic tank. Therefore, the most appropriate Internal Recircularion rate can be concluded as 50~150%.

• Journal of the Korea Organic Resources Recycling Association
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• v.23 no.2
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• pp.28-35
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• 2015

In this study, the experiment was carried out to produce methane by applying Semi-Continuous Leachate Recirculation Anaerobic Digestion System fed with source separated food waste from school cafeteria. There were two systems and each system consisted of a bioreactor and a liquid tank. Each bioreactor had a screen near the bottom of the reactor. 2.5L of separated liquid was transferred to the liquid tank for 30min each day by using a tubing pump and the liquid from the liquid tank was pumped to the bioreactor at the upper of the bioreactor as soon as the transfer was ended. Through this circulation, the liquid having high concentration of VFAs was supplied to the top of bioreactor. At the beginning of the experiment, food waste/inoculum anaerobic sludge volume ratio was 2:8 that is 9g VS/L of OLR(Organic Loading Rate). Feeding was conducted every two weeks. Experimental results showed that the contents of moisture, combustible matter, ash were 65.91%, 32.73%, and 1.36%, respectively. Two different food waste loading were studied. The average organic loading rates were 3.51g VS/d for System A and 3.86g VS/d for System B, respectively. The average produced methane based on food waste fed to bioreactor were observed as $6.30m^3CH_4/kgVS{\cdot}d$ for system A and $4.94m^3CH_4/kgVS{\cdot}d$ for System B, respectively.

• Korean Journal of Environmental Biology
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• v.37 no.2
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• pp.129-135
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• 2019

Juvenile Paralichthys olivaceus (mean weight 685.3±36.7 g) were raised in different and closed recirculating bio-floc system (control, bio-ball, and shelter) for 7 months. The water environment such as water temperature, dissolved oxygen, salinity, pH, and alkalinity according to the difference of closed recirculating system remained stable during the rearing period. No significant changes were observed in dissolved inorganic nitrogen such as ammonia, nitrite, and nitrate were observed in different closed recirculation system. The final weights according to the difference of closed recirculating were 1,524 g (control), 1,674 g (bio-ball), and 1,630 g (shelter). The survival rate was higher than 98%, and the final FCRs (Feed coefficient ratio) were 1.2, 1.1, and 1.2. The results of this study indicated high growth and survival rate in all systems.

• Journal of Wetlands Research
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• v.20 no.2
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• pp.145-154
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• 2018

In this study, three pilot-scale wetland systems were built for treating stormwater runoff from asphalt road. Each of the system consists of a settling tank and a vertical flow wetland packed with 25%, 50%, and 75% woodchip as treatment media. According to the analysis of the distributions of particle size, it was found that solids ranging in size $0.52-30{\mu}m$ were predominant in the stormwater runoff. After 24-hours settling, those coarser than $20{\mu}m$ were significantly detained. Further retention, especially for the finer-sized fraction, occurred in the wetland through internal recirculation during the dry day periods. As a primary media of the wetland, woodchip showed a high filtration and attachment capacity for the particulates in pre-settled stormwater, whereas overall amount of solids in the wetland effluent increased due to the detachment of woody elements from the media. This was observed mainly during the initial 75 days of operation, and the size and detachment rate were found to be strongly related with the woodchip packing ratio. The mechanism involving woody particle detachment was modeled as a first-order form. In addition, water quality factors and operational parameters affecting the detachment were analyzed and discussed.