• 한국입자에어로졸학회지
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• 제9권2호
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• pp.69-78
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• 2013

In this study, the atmospheric aerosol concentration measured at different relative humidity levels was analyzed. Using an optical particle counter, PM10 and PM2.5 concentration as well as particle size distribution were measured and the relation between these size resolved data and relative humidity was studied. The results showed that mass concentration increases as relative humidity increases. The comparison between PM1, PM2.5 and PM10 showed that the fine particles grow more than coarse particles as relative humidity increases. The results also showed that PM10-2.5 and relative humidity do not show close correlation, which means that the mass increase of PM10 at high relative humidity is mainly due to the growth of PM2.5.

• Asian Journal of Atmospheric Environment
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• 제10권4호
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• pp.226-231
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• 2016

In order to remove fog often causes various troubles in our daily lives, the novel defog blower equipped the roller brush made of recycled horse's mane hair was developed. This work presents the overview of new defog devices and the experimental data obtained at two different kinds of defogging experiments. In the model experiment carried out at the enclosed cleanroom ($W5.9m{\times}L5.1m{\times}H2.4m$) targeted a vinyl house, fog was dissipated in less than 30 seconds in case with wind entrainment and two minutes 45 seconds in case without wind entrainment after running of the newly designed defog blower. When the demisting blower was run in a duct, it has an excellent mist sweeping qualities as well as a great removal effect for the background particles (89.5% and 65.4% scavenging rates for fine and coarse particles, respectively). It can be therefore said that the mist eliminator presented in this paper is ideal for use in the sealing space like a vinyl house and the industrial sites where required to remove both harmful mist and particle.

• 한국정밀공학회지
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• 제18권9호
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• pp.165-170
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• 2001

In normal grinding abrasive particles of a grinding wheel rotate on planes parallel to the direction of workpiece fred. which may induce continued scratch lines on ground surface as the workpiece feeds. Instead in helical scan grinding the planes make an angle, called a helical angle, with the feeding direction. Thus scratch lines produced by abrasive particles per one revolution are discontinued which implies that the generation of scratch lines are suppressed by the helical scan grinding. In this study some experimental works have been done on the helical scan grinding of glass to find the effects of grinding conditions on the surface roughness and estimate the optimal grinding conditions. The helical angle, fred rate, material removal rate and the wheel speed are taken as factors for three kinds of grinding wheels i.e., coarse(#140 mesh), medium(#400) and fine(#800) diamond wheels. The experiments are scheduled by Taguchi technique and ANOVA has been carried out for the interpretation of the results. As a result of this study effects of the factors are verified quantitatively showing that the major factors are changed according to the wheel's mesh size and the helical angle is one of the influencing factors on the surface quality.

• 자원리싸이클링
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• 제7권2호
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• pp.23-30
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• 1998

제철소의 고로에서 발생하는 슬러지로부터 산화철 및 탄소분과 같은 유용 성분을 회수하여 리싸이클링하기 위하여 슬러지의 물리화학적 특성과 습식 사이클론을 이용한 분급특성을 조사형T다. 슬러지 입자의 크기에 따른 성분의 부존 상태를 조사한 결과, 탄소는 graphite 상으로 주로 굵은 입자에, 아연은 zinc sulfide로서 주로 미세한 입자에 분포하였다. 그러나 슬러지 중에 hematite 및 magnetite 상으로 존재하는 철분은 입경에 따른 편석이 없었다. 내경 75mm인 습식 사이클론에서 적정한 조건으로 고로슬러지를 분급하면 저아연 슬러지의 회수율과 탈아연율이 각 67.9~73.6% 및 72.7~86.8% 수준에 도달하였다.

• Geomechanics and Engineering
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• 제19권3호
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• pp.229-240
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• 2019

The physical models are useful to understand the soil behaviour. Hence, these tools allow validating analytical theories and numerical data. This paper addresses the design, construction and implementation of a physical model able to simulate the soil liquefaction under different cyclic actions. The model was instrumented with a piezoelectric actuator and a set of transducers to measure the porewater pressures, displacements and accelerations of the system. The soil liquefaction was assessed in three different grain size particles of a natural sand by applying a sinusoidal signal, which incorporated three amplitudes and the fundamental frequencies of three different earthquakes occurred in Colombia. In addition, such frequencies were scaled in a micro shaking table device for 1, 50 and 80 g. Tests allowed identifying the liquefaction susceptibility at various frequency and displacement amplitude combinations. Experimental evidence validated that the liquefaction susceptibility is higher in the fine-grained sands than coarse-grained sands, and showed that the acceleration of the actuator controls the phenomena trigging in the model instead of the displacement amplitude.

• 한국방재학회 논문집
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• 제6권3호
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• pp.47-56
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• 2006

기후변화와 관련한 한반도 배경대기의 에어러솔에 대한 특성 연구는 관측된 입자 수농도와 대기 복사 관측 자료를 바탕으로 에어러솔의 물리적, 화학적 및 광학적 특성에 대하여 분석하였다. 에어러솔의 물리적 특성 연구는 2001년부터 2003년까지 제주도 고산관측소에 설치된 광학입자계수기(Optical Particle Counter, OPC)로 $0.3{\sim}25{\mu}m$직경의 에어러솔을 8개 구간으로 나누어 관측하여 분석하였다. 그 결과 황사의 발생률이 높은 봄철에 조대 입자($2.2{\mu}m$이상)의 수농도가 다른 계절보다 높게 나타났다. 기상요소 (상대습도, 풍속, 풍향, 시정 등)와 입자 수농도의 상관관계 분석에 의하면 $0.3{\sim}0.5{\mu}m$ 크기 구간에서는 상관성이 없는 것으로 나타났으며 $0.5{\sim}2.23{\mu}m$ 구간에서는 에어러솔 수농도와 상대습도가 서로 양의 상관관계를 가지는 것으로 나타났다. 풍속과의 상관성에서 작은 입자들은 풍속이 강해질수록 감소하는 패턴으로 분석되었으며 겨울철에는 조대입자 수농도가 높은 풍속에 증가하는 것으로 나타났다. 그리고 시정거리는 $0.5{\sim}1{\mu}m$ 크기 정도의 에어러솔 수 농도와 밀접한 관련이 있는 것으로 나타났으며 에어러솔 수 농도가 증가할수록 시정거리는 감소하는 경향을 보였다.

• 한국지구과학회지
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• 제21권3호
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• pp.276-286
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• 2000

서남극 남쉐틀랜드 군도 킹조지 섬 마리안 소만에서 중력시추기로 얻은 길이 2.3 m의 시추퇴적물은 홀로세 동안 이 지역에서 일어났던 빙해양 퇴적작용의 특성을 보여준다. 층준 115 cm를 기준으로 상부층과 하부층으로 나뉘어진다. 하부층은 조립질 물질이 우세하며 상부는 리드마이트와 괴상(塊狀) 니질(泥質) 층이 우세하다. 상부층에서 우세한 조립물질은 보통 빙하로 운반된 물질과 이미 존재하던 빙퇴석으로 구성되는 바, 세립물질은 융빙수, 빙하,바람으로 공급된 육성기원 쇄설물이 대부분이며 생물기원물질도 상당량 혼재되었다. 세립물질 내에 포함된 조립물질은 유빙운반물질로 해석된다. 깊이 105cm의 아래부분은 질소 총량, 탄소 총량, 유기물 총량이 적은 반면 유황 총량과 탄산칼슘 총량은 많다. 유기물 총량과 질소총량 사이의 비(C/N ratio)는 대체로 큰 변화가 없다. 현재의 마리안소만 동쪽 빙벽은 리드마이트와 빙퇴석의 산출시기를 고려할 때 지금부터 8,300년 전에는 1.6km 서쪽에 위치했던 것으로 보인다. 마리안소만의 퇴적물은 7,970${\pm}$70년 전 빙벽이 시추심 위치에서 후퇴하면서 세립물질과 유빙운반물질이 우세해졌다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.328-331
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• 2007

It was carried out to evaluate microstructure and mechanical properties of friction stir welded(FSW) on magnesium alloys. Two types magnesium alloy was used in this work, AZ31 wrought and AZ91 cast magnesium alloy. Microstructure near the weld zone showed general weld structures such as stir zone(SZ), thermo-mechanically affected zone(TMAZ) and heat affected zone(HAZ). In the AZ91 alloy, the SZ had a fine grain size and $\beta$ phase particles which were well distributed in matrix. It was characterized to redistribute by partial or full re-solution of the $\beta$ phase which is coarse in base metal during FSW processing. The hardness of the SZ slightly increase than the base metal in AZ31 Mg alloy.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.466-472
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• 1988

Pneumatic transportation systems are operated most economically, if the transportation velocity is somewhat greater than the limit velocity. Therefore it is very important to find out this limit velocity. That is well known for coarse and fine particles, but not yet for long ribbon type material. In this study a formula for the mass ratio of transported material to air in limit load point is derived for ribbon type material from the pneumatic transportation theory and the model theory. A relationship for estimating the limit velocity is also found out through experiments. The possibility of the generalization of this formula, which is obtained from a given pneumatic transportation system, should be estimated through further systematic studies.

• Computers and Concrete
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• 제26권6호
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• pp.505-513
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• 2020

Grading of aggregate influences significantly almost all of the concrete performances. The purpose of this paper is to propose practicable equations that express the optimized total aggregate gradation, by weight or by number of particles in a concrete mix. The principle is based on the fractal feature of the grading of combined aggregate in a solid skeleton of concrete. Therefore, equations are derived based on the so-called fractal dimension of the grain size distribution of aggregates. Obtained model was then applied in such a way a correlation between some properties of the dry concrete mix and the fractal dimension of the aggregate gradation has been built. This demonstrates that the parameter fractal dimension is an efficacious tool to establish a unified model to study the solid phase of concrete in order to design aggregate gradation to meet certain requirements or even to predict some characteristics of the dry concrete mixture.