• 한국물환경학회지
• /
• 제34권2호
• /
• pp.226-233
• /
• 2018

Small-scale wastewater discharge facilities account for 98% of all workplaces, but in the generation and emission of major pollutants, they account for 27.5 % and 23.5 %, respectively. Since the proportion of the emission load of the small-scale workplace is not large, the national environmental policy has been established mainly around large-scale wastewater discharge facilities. However, in the case of specific hazardous substances in water, the amount of the discharge load of the small-scale wastewater discharge facility was 2.4 times higher than that of the generation load. Certain types of specific hazardous substances in water, which have a higher discharge load than large-scale wastewater discharge facilities, account for 24 ~ 32 %. There are also cases in which the discharge load from a small-scale discharge facility is more than four times higher, depending on the specific kind of water pollutant. As a result of inspections, the violation rate of the small-scale wastewater discharge facility among the total violations by facilities is 93.9 ~ 97.5 %. As a result, the ecotoxicity value of small-scale wastewater discharge facilities was high in most industries, and there was a fluctuation in the measured value. This indicates that the ecological integrity of the water system can be largely influenced by small-scale wastewater discharge facilities. Therefore, it is necessary to expand the environmental management of small-scale wastewater discharge facilities, and in some cases, the effect of the improvement in quality may be more significant than in the management of large-scale wastewater discharge facilities.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3003-3008
• /
• 2007

Critical nozzle has been frequently employed to measure the flow rate of various gases, but hydrogen gas, especially being at high-pressure condition, was not nearly dealt with the critical nozzle due to treatment danger. According to a few experimental data obtained recently, it was reported that the discharge coefficient of hydrogen gas through the critical nozzle exceeds unity in a specific range of Reynolds number. No detailed explanation on such an unreasonable value was made, but it was vaguely inferred as real gas effects. For the purpose of practical use of high-pressure hydrogen gas, systematic research is required to clarify the critical nozzle flow of high-pressure hydrogen gas. In the present study, a computational fluid dynamics(CFD) method has been applied to predict the critical nozzle flow of high-pressure hydrogen gas. Redlich-Kwong equation of state that take account for the forces and volume of molecules of hydrogen gas were incorporated into the axisymmetric, compressible Navier-Stokes equations. A fully implicit finite volume scheme was used to numerically solve the governing equations. The computational results were validated with some experimental data available. The results show that the coefficient of discharge coefficient is mainly influenced by the compressibility factor and the specific heat ratio, which appear more remarkable as the inlet total pressure of hydrogen gas increases.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
• /
• pp.227-230
• /
• 2006

The method of mass flow rate measurement using a critical nozzle is well established in the flow satisfying ideal gas law. However, in the case of measuring high-pressure gas flow, the current method shows invalid discharge coefficient because the flow does not follow ideal gas law. Therefore an appropriate equation of state considering real gas effects should be applied into the method. The present computational study has been performed to give an understanding of the physics of a critical nozzle flow for high-pressure hydrogen gas and find a way for the exact mass flow prediction. The two-dimensional, axisymmetric, compressible Navier-Stokes equations are computed using a fully implicit finite volume method. The real gas effects are considered in the calculation of discharge coefficient as well as in the computation. The computational results are compared with the previous experimental data and predict well the measured mass flow rates. It has been found that the discharge coefficient for high-pressure hydrogen gas can be corrected properly adopting the real gas effects.

• Carbon letters
• /
• 제15권4호
• /
• pp.277-281
• /
• 2014

A series of high capacity soft carbons with different phosphorus contents were successfully prepared by carbonizing petroleum cokes treated with hypophosphorous acid at $900^{\circ}C$. The effect of phosphorus content on the electrochemical performance of the soft carbons was extensively investigated. The P-doped soft carbons exhibited greatly enhanced discharge capacities and outstanding rate capabilities with increasing phosphorus content. In addition, the influence of temperature on the electrochemical behaviors of the soft carbons was investigated in a wide temperature range of $25^{\circ}C$ to $50^{\circ}C$. Surprisingly, the electrochemical properties of the pristine and P-doped soft carbons were highly sensitive to the operating temperature, unlike conventional graphite. The pristine and P-doped soft carbons exhibited significantly high discharge capacities of 470 and 522 mAh/g, respectively, at a high temperature of $50^{\circ}C$.

• Bulletin of the Korean Chemical Society
• /
• 제34권9호
• /
• pp.2573-2576
• /
• 2013

Rate capability and cyclability of $LiMn_2O_4$ should be improved in order to use it as a cathode material of lithium-ion batteries for hybrid-electric-vehicles (HEV). To enhance the rate capability and cyclability of $LiMn_2O_4$, it was coated with $MnV_2O_6$ by a sol-gel method. A $V_2O_5$ sol was prepared by a melt-quenching method and the $LiMn_2O_4$ coated with the sol was heat-treated to obtain the $MnV_2O_6$ coating layer. Crystal structure and morphology of the samples were examined by X-ray diffraction, SEM and TEM. The electrochemical performances, including cyclability at $60^{\circ}C$, and rate capability of the bare and the coated $LiMn_2O_4$ were measured and compared. Overall, $MnV_2O_6$ coating on $LiMn_2O_4$ improves the cyclability at high temperature and rate capability at room temperature at the cost of discharge capacity. The improvement in cyclability at high temperature and the enhanced rate capability is believed to come from the reduced contact between the electrode, and electrolyte and higher electric conductivity of the coating layer. However, a dramatic decrease in discharge capacity would make it impractical to increase the coating amount above 3 wt %.

• 기술사
• /
• 제18권3호
• /
• pp.28-35
• /
• 1985

As the paper industry consumes much water in process and discharge wastewater containing suspended solid and COD(chemical oxygen demand), relevant law against this discharge has been set up to limit the total containment of COD in discharge. This study has been carried out to improve the treatment method for the soluble COD in wastewater produced during the process of paste-board production, which is made of semichemical pulp and waste paper. Applicated methods are, O$_2$AS : O$_2$ activated sludge process DAS : Deep well activated sludge process SAS : standard activated sludge process and proper combination of DAS and SAS 1) As a result of this experiment, we get the following conclusion between in COD sludge loading "X" and COD removable rate in the process of treating waste-water. COD removable rate(％)=(0.778+0.0146/X)${\times}$100(％)……(7) 2) In case that the COD sludge loading is high, it has been cleared out that the COD removable rate shall become low due to unknown unsoluble substances contained in the process. Meanwhile, to increase the efficiency rate of treatment, it is thought to be necessary, to provide long-time contacts with activated sludge. 3) Once the COD of original waste-water and the target COD of treated water are decided, COD sludge loading is obtained from equation(7), and capacity of aeration tank in the effective systems such as O$_2$AS, DAS, to bet the required COD removable rate can be decided. Therefore the choice among SAS, O$_2$AS, DAS methods is made in consideration of required COD removable rate and allowable installation area. 4) In the sedimentation tank with sludge bulking, it is possible to increase the COD removable rate by 3～7％ but still there exist many obstacles to manage this operation.

• Asian-Australasian Journal of Animal Sciences
• /
• 제9권1호
• /
• pp.57-61
• /
• 1996

Four castrated Corriedale sheep were used in an experiment to observe the changes in insulin, growth hormone and cortisol in blood plasma following a prolonged infusion of a high rate of somatostatin (SRIF). The animals wee infused with either saline, 25 or $50{\mu}g/kg/h$ of SRIF for 3 hours. Blood samples wee taken every 20 minutes until 1 hour following the end of the SRIF infusion. Both SRIF infusion levels suppressed the release of insulin into plasma to approximately 3.5 mU/l. The SRIF infusions reduced the concentration of growth hormone to barely detectable levels. Following the withdrawal of SRIF there was a massive release of growth hormone. The plasma concentration of growth hormone reached 60 ng/ml within 20 minutes, the length of the growth hormone discharge was in excess of 1 hour. The extent of the discharge of growth hormone following the SRIF infusions was greater than that suppressed by the infusion. The SRIF apparently caused an increase in the plasma concentration of cortisol at the end of the infusion and following is withdrawal. This is possibly associated with some change in the metabolic rate associated with the suppression of insulin or glucagons release. The present experiment demonstrates that a high rate of SRIF infusion can not completely inhibit the release of insulin into the plasma.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
• /
• pp.259-264
• /
• 2000

The functions of the plug valve are the control of flow rate as well closing and opening pipe lines. Analyses on the flow characteristics in plug valve port are required to improve the performance and safety at severe operating conditions such as high-pressure and high-temperature. In this study, numerical analyses are carried out with varying the opening rate (fraction of the full open to close) of the valve and the shapes of valve Uk: straight, convex, concave and mixed shapes. The parameters influencing the flow characteristics in the valve are the discharge coefficient( $C_v$) and the resistance coefficient( K). Therefore, the distributions of static pressure, velocity vector and stream lines are investigated, and $C_v$ and K are calculated in each opening rate and shape. In case of full open, the static pressure passed through the valve port has almost been recovered. However, in case of other opening rates, the pressure does not permanently regained due to pressure drop leading to loss. This phenomenon in each shape of the valve shows the different behaviors. Calculation results show that the mixed shape has the best flow attribute.

• Journal of Electrochemical Science and Technology
• /
• 제14권2호
• /
• pp.139-144
• /
• 2023

In this study, carbon-coated porous nanofibers were prepared via electrospinning and the performance of Li[Ni_0.93Co_0.07]O₂ (NC) synthesized by electrospinning (E-NC) and co-precipitation (C-NC) was compared. E-NC had a discharge capacity of 206 mAh g^-1 at 0.1C (17 mA/g), which is 10% higher than that of C-NC (189.2 mAh g^-1). E-NC shows a high-rate performance of 118.32 mAh g^-1 (61.7%) at 5C (850 mA/g), which is 50% higher than that of C-NC (78.22 mAh g^-1 = 45.7%). Charge transfer of the carbon-coated porous nanofiber E-NC decreased by 35% compared to C-NC after 20 cycles as observed using electrochemical impedance spectroscopy. The results of this study show that the nanofiber structure with carbon coating shortens the Li-ion diffusion path, improves electrical conductivity, resulting in excellent rate performance.

• 대한기계학회논문집B
• /
• 제30권2호
• /
• pp.170-176
• /
• 2006

A spark discharge aerosol generator using air as a carrier gas has successfully been applied to silver nanoparticle production. The spark discharge between two silver electrodes, which was periodically obtained by discharging the capacitor, produced sufficient high temperatures to evaporate a small fraction of the silver electrodes. The silver vapor was subsequently supersaturated by rapid cooling and condensed to silver nanoparticles by nucleation and condensation. The morphology of the generated particles observed by transmission electron microscope was spherical. The element composition of the nanoparticles was silver, which was determined by energy dispersive X-ray spectroscopy. The crystal phase of the particles spark-generated under air atmosphere was composed of silver and silver oxides phase, which was determined by Xray diffraction analysis. While the nanoparticles generated under nitrogen atmosphere had only silver phase. This XRD data indicates that some fraction of the evaporated silver vapor could be oxidized in air atmosphere by the reaction with oxygen. A stable operation of the spark discharge generator has been achieved. The size and concentration of the particles can be easily controlled by altering the repetition frequency, capacitance, gap distance and flow rate of the spark discharge system.