• Korean Chemical Engineering Research
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• 제55권6호
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• pp.822-829
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• 2017

하수처리장에서의 총 인 저감을 위한 방안으로 완속교반/침전 섬유여과시스템을 적용하여 하수 방류수와 반류수를 제어하는 방법에 대해 비교 검토하였다. 물질수지를 통해 인의 최종 농도를 강화된 기준치인 0.2 mg/L로 낮추기 위해서는 약 92.4 kg T-P/day를 제거해야 되는 것으로 분석되었으며, 이를 위한 총 인 제거효율은 하수 방류수는 96%, 반류수(탈수여액)은 69.2% 이상이 되어야 한다. 총 인 제거 목표치를 달성하기 위한 시스템 운영비용을 검토하였으며, 하수방류수를 처리하는 것보다 유량은 적으나 고농도의 인을 함유한 반류수를 처리하는 것이 약품비용은 약 1/2.4, 전력비용은 약 1/120 정도로 절감되는 것으로 나타났다. 한편 반류수 처리를 위해 개발시스템인 완속교반/침전 섬유여과시스템과 일반적인 응집침전시스템을 적용하는 경우에 대한 경제성을 검토하였으며, 완속교반/침전 섬유여과시스템이 일반적인 응집침전시스템에 비해 설치면적이 약 1/7로 작고 약품소요량 및 전력비를 포함한 연간운전비용은 약 1/1.7 소요되어 개발시스템이 보다 경제성이 있는 것으로 평가되었다.

• 한국해양학회지
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• 제27권2호
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• pp.154-163
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• 1992

박테리아의 개체수와 생산량의 분포률, 그리고 하구 혼합 (estuarine mixing)이 이들 분포에 미치는 영향을 조사하기 위해, 1990년 10월부터 1991년 8월까지 만경강 및 동진강 하구의 유광대에서 박테리아의 개체수, 생산량, 수온 및 염분도를 3번 조사 하였다. 제한된 조사에도 불구하고 조사기간에 나타난 박테리아의 개체수와 생산량은 넓은 범위의 값을 보였다. 각각 0.4-5.8$\times$10/SUP 9/ 1/SUP -1/와 0.1-22.2 ug C /SUP -1/ d/SUP -1/이었다. 이는 박테리아의 성장이, 하구에서 매우 유동적임을 나타냈다. 흥미롭게도 박테리아의 개체수는 대부분의 수임이 얕은 정점의 표면 아래에서 증가하 였으나, 박테리아의 생산량은 뚜렷이 감소하였다. 이러한 현상은 하구 혼합에 의해서 설명될 수 있을 것으로 판단되며, mixing diagrams의 분석은 하구 혼합이 박테리아 개 체수와 생산량을 conservative하게 혼합하기도 하나, 박테리아 개체수를 증가시키며, 생산량을 감소시키는 작용을 하였으며를 보여주었다. 이것은 하구 혼합의 역할이 박테 리아의 개체수와 생산량의 분포에 따라서 하구에서의 생지화학적 순환에 있어서 중요 함을 제시하였다.

• 대기
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• 제34권3호
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• pp.283-304
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• 2024

This study analyzed the variability and correlation between ground-level air pollutant concentrations and the atmospheric mixing layer height using data from four types of air pollutants (PM_2.5, PM₁₀, NO₂, and O₃) collected at AirKorea monitoring stations nationwide over a five-year period (2018~2022), and aerosol backscatter data observed by the Vaisala CL31 to derive atmospheric mixing layer heights. The five-year trends and variability of ground-level air pollutant concentrations under seasonal and hourly conditions were examined, as well as the seasonal distribution and diurnal variation of the atmospheric mixing layer height. Five correlation coefficient methodologies were applied to analyze the correlations between ground-level air pollutants and atmospheric mixing layer height under various seasonal and hourly conditions, confirming the dilution effect of the atmospheric mixing layer height. The results showed that PM_2.5, PM₁₀, and NO₂ generally had negative correlations with the atmospheric mixing layer height, while O₃ showed a strong positive correlation up to an altitude of 1,200~1,500 meters, and a negative correlation beyond that altitude. It was also shown that a single high concentration event (e.g., PM₁₀) can alter the overall correlation. The correlation can also vary depending on the characteristics of the correlation coefficient methodology, highlighting the importance of applying the appropriate methodology for each case during the analysis process.

• 한국수소및신에너지학회논문집
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• 제20권4호
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• pp.265-273
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• 2009

Proton Exchange Membrane Fuel Cell (PEMFC) has low operating temperature and high efficiency. And PEMFC consists of many components as bipolar plate, gas diffusion layer, membrane etc.. Flow-field in bipolar plate roles path for transporting reactants to membrane. Therefore a design of flow-field has an effect on PEMFC's performance. In this study, Computational Fluid Dynamics (CFD) simulations were performed for comparing mixed multiple serpentine (MMS) flow-field and multiple serpentine (MS) flow-field. And we studied an effect according to change mixing region design in MMS flow-field. Finally the applicability of results is verified by performing CFD simulation about fixed MMS flow-field which is combined good designs.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.972-977
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• 2017

고체 추진기관의 불량 발생 요인 중 가장 큰 부분을 차지하고 있는 추진제 기공 및 크랙은 추진제의 점도와 물성이 큰 영향을 미친다. 본 연구는 혼합형 고체 추진제의 한 종류인 나이트레이트 폴리이서(Nitrate Ester Polyester; NEPE)계열의 추진제에서 주로 사용되는 RDX의 입도 및 혼합 함량에 따른 추진제 점도, 기계적 물성 및 연소특성 변화를 관찰하였다. RDX 입도와 혼합 함량에 따라 미경화 추진제의 경시적 점도가 크게 변화가 되었으며, 이에 따른 추진제 물성 또한 변화가 있었다. 추진제의 낮은 점도와 안정된 기계적 물성을 동시에 고려할 때, RDX의 입도 및 혼합 함량은 NEPE계 추진제의 주요 인자로 확인할 수 있다.

• Journal of Biosystems Engineering
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• 제28권5호
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• pp.411-420
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• 2003

Physical and cultural properties were investigated on the rice-seed pellets made by the pelleting machine(Yu, 2003) as the changes with mixing ratios of soil to rice seed of 6 : 1, 7 : 1, and 8 : I, and rotating speeds of forming rolls of 7, 10, and 13 rpm. Average weight, average diameter, and average sphericity of the pellets were 1.70 g, 12.0 ㎜, and 99.1 ％, respectively. Average number of seeds per pellet was more than 3, and almost all pellets had more than 3 seeds in the cases of mixing ratios of 6 : 1, and 7 : 1 at the forming rolls' speed of 7 rpm. Gradual drying was needed because rapid drying caused cracks on surface of the pellets. Compression strength of the pellets dried in shady room was in the range of 132 ∼ 152 N, which was enough for handling. Comparing with the previous pellets(Park, 2002), average number of seeds per pellet, ratio of pellets including more than 3 seeds, and compression strength increased due to the effects of pressure feed of pellet materials, and improvements of the forming rolls. Emergence ratio of the pellets made at the mixing ratio of 6 : 1 and the forming rolls' speed of 7 rpm, was 100 % on dry paddy and was 97 % on flooded paddy surface. Good growth characteristics, and yield except number of seedling stand and ratio of missing plant were shown in planting of the pellets made at the mixing ratio of 7 : 1 and the forming rolls' speed of 7 rpm on flooded paddy surface field. Considering the cultural results, the mixing ratio of 6 : 1, and the forming rolls' speed of 7 rpm seems to be optimum operating condition for the improved pelleting machine.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2004년도 추계학술대회
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• pp.153-158
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• 2004

해양에 방류되는 오폐수의 흐름형태 즉 흔합특성을 제어하고 설계하기 위해 다양한 연구가 진행되고 있다. 최근 들어 선진국을 중심으로 바람직한 수질관리를 목표로 법적혼합역과 관련한 수질기준을 정하여 오염무의 방류로 인한 해양수질환경의 오염을 최소화하고자 하는 노력이 진행되고 있다. 본 논문에서는 이러한 근역 및 원역에서의 법적혼합역을 CORMIX 모델로 구현하고 법적혼합역의 필요성을 강조하며 이를 효율적으로 규제하기 위한 방안을 모색하고자 하였다. 이는 보다 개선된 방류수 모델링을 제안하고 나아가 효율적인 해양방류관 설계뿐 아니라 건전한 항만의 설계 및 개발에 기여할 것이다.

• 산업경영시스템학회지
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• 제4권5호
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• pp.1-10
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• 1981

The purpose of this study is to cut down cost of production and improve the productivity of industry through quality improvement of castings and reduction of defectives by applying the experimental design to the foundry sand mixing operation done at molding department in the foundry. Among the related foundry sand mixing factors which have an effect on casting the experiment of which factors have a dominant effect on quality improvement was performed between two different levels by means of "$2^n$ type orthogonal array." The results cail be summarized as follows ; (1) The optimum conditions per each foundry sand mixing between two different levels proved to be such as $A_2$(used sand) : 24 unit (172.8kg), $B_2$(unused sand ) : 2 unit (15.0kg), $C_2$(binder) : 2.5 unit (4.4kg). $D_2$(addition agent) : 1 unit(1.4kg) and $F_1$(moisture) : 7.4%(14.6kg). (2) As a result of the application of experimental design, the fraction defective during the foundry sand mixing operation turned out to be reduced front 6.6% to 2.04%. (3) For the purpose of cost-down, It was found that the optimum level decision of foundry sand mixing for various castings is required to be made by means of experimental design.al design.

• 한국전산유체공학회지
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• 제11권3호
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• pp.46-51
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• 2006

This paper presents the numerical results of fluid flow and mixing in a microfluidic device for electro-osmotic flow (EOF) with an trapezoidal electrode array on the bottom wall (ETZEA). Differently from previous EOF in a channel which only transports fluid in colloidal system. ETZEA can also be utilized to mix a target liquid with a reagent. In this study we propose a method of controlling fluid flow and mixing enhancement. To obtain the flow and mixing characteristics, numerical computations are performed by using a commercial code, CFX-10, and a self-made code LBM-D. It was found that the flow near the trapezoidal electrode in the ETZEA is of 3-D complex flows due to the zeta potential difference between the trapezoidal electrode and channel walls, and as a consequence the hetrogeneous zeta potential on the electrodes plays an important role in mixing the liquid.

• 한국환경과학회지
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• 제15권9호
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• pp.897-905
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• 2006

This study has been conducted to investigate biodegradation characteristics and optimum mixing ratio for co-digestion with thermophilic acid-fermented food waste and sewage sludge using batch anaerobic digester. As the basis operating conditions for anaerobic digestion, the reaction temperature was controlled $35{\pm}1^{\circ}C$ and stirrer was set 70rpm. Thermophilic acid-fermented food waste and sewage sludge were mixed at the ratio of 10:0, 7:3, 5:5, 3:7, 0:10 and 5;5(food waste : sewage sludge) as the influent substrates. In results of co-digestion according to mixing ratio of thermophilic fermented food wastes and sewage sludge in batch mesophilic anaerobic digestion reactor, $385mL\;CH_4/g\;VS_{added}$ of methane production rate at 1:1 mixing ratio was more than that of any other mixing ratios. Compared with $293mL\;CH_4/g\;VS_{added}$ of methane production rate at 1:1 mixing ratio of food wastes and sewage sludge, pretreatment of food wastes by thermophilic acid fermentation was more effective in co-digestion with sewage sludge.