• Analytical Science and Technology
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• v.6 no.2
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• pp.207-215
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• 1993

$Si_3N_4$ powders were mixed with sintering additives($3Y_2O_3{\cdot}5Al_2O_3$, YAG) by coprecipitation method. Mixing homogeneity, sintered and mechanical properties of coprecipitation-mixed powder compacts were compared with those of mechanically-mixed ones. SIMS-analysis for composition on the surface and in the matrix of prepared powder mixtures showed that the added YAG exists mainly on the $Si_3N_4$ powder surfaces in a form of coating. From this result it could be concluded that coprecipitation method is superior to mechanical mixing in the mixing homogeneity. This mixing homogeneity can accompany an improvement in sintered density, microstructure and consequently the mechanical properties of sintered bodys.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.256-261
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• 1998

Uranium silicide는 우수한 조사안정성을 가지는 유망한 연구로용 저농축 분산형 핵연료 소재이나 상대적으로 낮은 uranium 함량으로 인해 고출력에 필요한 8~9g-U/㎤ 정도의 uranium 충진 밀도를 얻기 위해서는 Al기지내에 uranium silicide 핵연료 입자의 부피분율을 높여주는 것이 필요하다 핵연료 입자의 부피분율을 높이기 위하여는 핵연료봉의 Al 기지내에 핵연료 입자가 균일하게 분포되어야 한다. 균질한 핵연료 심재를 제조하기 위해서는 핵연료 입자와 알루미늄과의 균일한 혼합이 중요하며 이러한 혼합체내의 분말에 대한 균질도를 정확히 평가하는 방법의 개발이 필요하다. 본 연구에서는 혼합분말의 충진시 겉보기 밀도 측정을 통한 조성의 표준편차를 구하는 방법과 X-ray image 분석법을 새로운 균질도 평가방법으로 제시하였다. 구형의 U$_3$Si분말과 Al분말의 혼합시 drum 회전법의 경우에는 밀도차에 의한 segregation이 발생되고 있으나, Spex mill 혼합법의 경우에는 균질도가 향상되었다. 45-150$\mu\textrm{m}$의 분말크기 분포를 갖는 구형 U$_3$Si의 경우가 작은 입자들이 큰 입자들 사이를 효과적으로 채울 수 있기 때문으로 균일한 분포를 갖는 것으로 생각되며, 밀도차가 큰 U$_3$Si의 경우는 밀도차가 작은 구형 Cu-Sn 혼합체에 비해 균질도가 저하됨을 확인하였다. 겉보기 밀도 측정에 의한 균질도 측정평가와 X-ray image 분석법과의 관계에서는 같은 경향성을 찾을 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.814-822
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• 2012

To improve the flow and mixing characteristics of marine SCR system, two different mixer including up-down and swirl type mixer were considered. The purpose of this study is to analyse turbulence intensity and uniformity index in detail and to improve the performance of SCR with respect to the mixer structure. The results showed that, the concentration uniformity index is improved by about 5% with the utilization of both mixers in the front of catalyst part. Although the RMS value and relative turbulence intensity increased after the up-down type mixer, it could observed that the value of two parameters decreased with the flow proceeding forward to the downstream. For the case of swirl type mixer, the decrease of RMS value and relative turbulence intensity were relatively smaller than that of up-down type mixer, and uniform distribution of relative turbulence intensity was observed. As a results, it could be concluded that the mixing effects and the distance of the two kinds of mixer were different.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.23-23
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• 1999

후류손실을 가지는 혼합 전단층에 대하여 밀도변화가 없는 유동 및 밀도변화가 있는 유동의 선형 불안정성 해석을 수행하였다. 기본 유동의 속도장 및 밀도장은 tanh 함수를 사용하였으며, Gaussian 형태의 해석적 함수를 사용하여 두 유동을 분리시키는 평판 바로 다음에 존재하는 후류 손실 유동을 포함시켰다. 공간적 선형 불안정성 해석을 수행하여 불안정성 모드의 성장률과 파장속도를 주파수의 함수로서 구하였다. 해석 결과로부터 후류 손실을 가지는 혼합층은 sinuous 모드와 varicose 모드의 두 개의 불안정성 모드를 가짐을 알았다. 밀도가 균일한 경우에는 varicose 모드보다 sinuous 모드가 지배적이다. 밀도가 균일한 경우에는 varicose 모드보다 sinuous 모드가 지배적이다. 밀도구배가 존재하나 빠른 자유유동의 밀도가 높은 경우에는 밀도가 균일한 경우와 마찬가지로 sinuous 모드가 지배적인 모드가 된다. 그러나 느린 자유 유동의 밀도가 높은 경우에는 밀도장의 두께가 속도장의 두께보다 상대적으로 얇아지면 varicose 모드가 sinuous 모드보다 더욱 불안정하여질 수 있다. varicose 모드와 sinuous 모드의 성장률이 비슷한 밀도장의 두께에서는 두 불안정성 모드가 주파수 변화에 따라 분지 되어지는 경향을 보인다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.429-434
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• 2016

Among various De-NOx technologies, Urea-based Selective Catalytic Reduction (SCR) systems are known to be the most effective in marine diesel applications. The spraying and mixing behavior of the urea-water solution has a decisive effect on the system's net efficiency. Therefore, in this study, the spray behavior and ammonia uniformity with and without a static mixer were analyzed by CFD in order to optimize the SCR system. The results showed that the static mixer significantly affected the uniformity of velocity and ammonia concentration. Static mixers may be especially suited for marine SCR systems with space constraints.

• Weed & Turfgrass Science
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• v.6 no.1
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• pp.67-76
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• 2017

The study was initiated to evaluate the effects of overseeding warm-season grass (Zoysia japonica Steud.) with cool-season grasses (CSG) on turfgrass density, uniformity and tiller appearance and to determine turfgrass species and seeding rate applicable for a practical use. Treatments were comprised of Kentucky bluegrass (KB, Poa pratensis L.), perennial ryegrass (PR, Lolium perenne L.), tall fescue (TF, Festuca arundinacea Schreb.) and their mixtures. Overall turfgrass density and uniformity were much better with the overseeded treatments over the control. In early stage after overseeding, the greater the PR in treatments, the greater the turfgrass density and uniformity. But the higher the KB, the lower the density and uniformity. From the middle-stage evaluation, however, we observed the opposite results as compared with early-stage findings. Accordingly, the KB was highest in turfgrass density and uniformity, while the PR lowest. In regards of mixtures, both turfgrass density and uniformity were better with increased KB and decreased PR in overseeding rates. As for a medium-quality mixtures of Korean lawngrass with CSG, it would be the best choice to apply with KB at $50g\;m^{-2}$ and equal combination of KB, PR and TF by 1/3 in mixing at $75g\;m^{-2}$ in terms of sustainable density and uniformity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.74-79
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• 2021

This study examined the mixing efficiency of exhaust gas and urea according to the mixer shape in the SCR system. For the experiment, an SCR simulation system was manufactured, and a uniformity detector was attached to the catalyst location to measure the uniformity. The experiment was conducted by setting the exhaust-gas flow rate, temperature, mixer type, and catalyst distance as variables. The experimental results confirmed the swirl angle analysis, urea number distribution, and uniformity. The swirl angle experiment of Models A and B confirmed that the swirl angle of Model A was formed approximately 7 to 8 degrees higher over the entire RPM range. When there was no mixer in the SCR system, the urea and water were concentrated to one side. Mixer Model A showed an even distribution overall, and Model B showed a slightly concentrated tendency at the beginning but then showed a stable distribution of urea. The mixing efficiency of 90%, which was the uniformity target, could be satisfied in Model A and Model B. In particular, Model A showed excellent results that satisfied 90% efficiency at 10 cm of the catalyst position.

• Asian Journal of Turfgrass Science
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• v.17 no.4
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• pp.129-146
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• 2003

Research was initiated to compare establishment vigor, uniformity, rooting potential and turf quality in sods of cool-season grasses (CSG). Several turfgrasses grown under pure sand soil were tested. Establishment vigor, uniformity, rooting potential and turf quality were evaluated in the study. Turfgrass entries were comprised of three blends from Kentucky bluegrass (KB, Poa pratensis L.), perennial ryegrass (PR, Lolium perenne L.), and tall fescue (TF, Festuca arundinacea Schreb.), respectively and three mixtures among them. Differences by treatments were significantly observed in establishment vigor, uniformity, rooting potential and turf quality. Early establishment vigor was mainly influenced by germination speed, being fastest with PR, intermediate with TF and slowest with KB. In a late stage of growth, however, it was affected more by growth habit, resulting in highest with KB and slowest with TF. There were considerable variations in sod uniformity among turfgrasses. Best uniformity among monostand sods was associated with KB, while poorest one with TF. PR sod produced intermediate uniformity between KB and TF. The uniformity of polystand sods of CSG mixtures was inferior to that of monostands of KB, PR and TF, due to characteristics of mixtures comprised of a variety of color, density, texture and growth habit. The greatest potential of sod rooting was found with PR and the poorest with KB. Intermediate potential between PR and KB was associated with TF. In CSG mixtures, it was variable, depending on turfgrass mixing rates. Generally, the higher the PR in mixtures, the greater the sod rooting potential. At the time of sod harvest, however, turfgrass quality of KB was superior to that of PR. because of its characteristics of uniform surface, high density and good mowing quality. These results suggest that a careful expertise based on turf quality as well as sod characteristics like establishment vigor, uniformity and rooting potential be strongly required for the success of golf course or athletic field in establishment.

• Journal of the Korean Data and Information Science Society
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• v.26 no.2
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• pp.313-322
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• 2015

A mixture distribution of a discrete uniform or degenerated distribution and two binomial distribution is proposed and a method of obtaining the maximum likelihood estimates of the parameters is provided. For the proposed model simulation studies were conducted to see performance of the maximum likelihood estimates and a mixture of a degenerated distribution and two binomial distributions was applied to fit a lecture evaluation data to show a good result.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1995.11a
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• pp.56-61
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• 1995

균일한 속도를 갖는 주유동장에 연료를 분사하였을때 분사된 연료가 주유동장의 공기와 혼합되는 정도를 정량적으로 설명하기 위하여 실험과 수치 계산을 실시하였다. 본 연구에서는 혼합 진전 정도를 나타내기 위하여 혼합진전변수(mixing progress variable)를 도입하여 유동조건에 따라 혼합 정도를 정량적으로 비교하였다. 주유동 속도가 일정할때 분사 속도를 증가시키면 연료가 주유동장의 공기와 혼합이 촉진됨을 알 수 있었다.