• Title, Summary, Keyword: stirring number

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The Chaotic Stirring in a Shallow Rectangular Tank (얕은 직사각형 통내의 혼돈적 교반)

  • 서용권;문종춘
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.2
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    • pp.380-388
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    • 1994
  • Study on the chaotic stirring has been performed numerically and experimentally for a shallow rectangular tank accompanying a vortex shedding. The model is composed of a rectangular tank with a vertical plate with a length half the width of the tank. The tank is subject to a horizontal sinusoidal oscillation. The chaotic stirring was analysed by Poincare sections, unstable manifolds and Lyapunov exponents. As Reynolds number is increased the stirring effect is decreased due to the growth of a regular regions near the lower surface of the tank. In the other hand decrease of Reynolds number gives a weaker vortex shedding resulting in the poorer stirring effect. It was also found that the Lyapunov exponent is the highest at the dimensionless period of 1.3-1.5, which seems to be the best condition for the efficient stirring. The experimental visualization for the deformation of materials exhibits the striation pattern similar to the unstable manifold obtained numerically.

A numerical study on a chaotic stirring in a model for a single screw extruder (압출용 스크류 모델에서의 혼돈적 교반)

  • Seo,Yong-Gwon;Kim,Yong-Gyun;Mun, Jong-Chun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.12
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    • pp.1615-1623
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    • 1997
  • Numerical study on the chaotic stirring of the screw extruder model proposed has been performed. The velocity field was used in obtaining the trajectories of passive particles for studying the stirring effect of the screw extruder. Two nonlinear dynamical tools, that are Poincare sections and Lyapunov exponents, were used in analysing the stirring effect. The Poincare sections and the Lyapunov exponents show that the stirring effect is most satisfactory, when n(the number of flights in a section) is 1, for the case a (aspect ratio ; flight height divided by the spacing between flights) being O.1. It is also required to set n=3, or 5 at a= 0.2, 0.3 for a uniform stirring.

Physical Modeling of Process Parameters for Aluminum-Foam Generation (물리적 모델링을 이용한 알루미늄 발포공정 영향 인자 해석)

  • 옥성민;문영훈
    • Transactions of Materials Processing
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    • v.10 no.7
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    • pp.558-564
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    • 2001
  • An experimental modeling is applied to investigate the formation of forms in molten aluminum By using a specially designed equipment, the effect of process variables, such as the shape of stirrer, stirring velocity and fluid viscosity, on the formation of foams were studied in the glycerine added water. Bubbles formed in water had various diameter from 1 to 10 mm and the number of bubbles was 0 to 20/$cm^2$. It turned out that among various variables the stirring velocity and fluid viscosity played important roles on the formation of bubbles. The results obtained from the model experiment were preyed to be convincible also in the real aluminum foam.

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Investigation of Reinforced Distribution in Fabrication Process of Metal Matrix Composites by Combined Stirring Process (복합교반법에 의한 금속복합재료의 제조공정에 따른 강화재의 분산성 검토)

  • 이동건;강충길
    • Composites Research
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    • v.14 no.5
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    • pp.1-11
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    • 2001
  • The particulates reinforced metal matrix composites(PMMC) have a number of interesting mechanical properties. including high strength and good resistance to wear at high temperature and low thermal expansion. The equipment structure to obtain the homogeneous distribution in composites are proposed for the continuous pouring of reinforcement at the desired temperature. The particulates reinforced metal matrix composites(A357/SiCp) were fabricated by the process of the combined stirring method with the various fabrication process. The combined stirring method to niform distribution of particle is consisted of two stirring force both electro-magnetic stirring generated from induction heating and mechanical stirring with graphite stirrer. PMMC billets were fabricated with the volume fractions ranged from 0% to 20% and particle sizes ranged from 14${\mu}{\textrm}{m}$ to 25${\mu}{\textrm}{m}$. It is important to cont the size of primary $\alpha$-Al solid particles because it could become the cause of the particle pushing or capture phenomena from the fact that secondary dendrite arm spacing size depends on the cooling rate during the solidification in hypoeutectic Al-Si alloy. Therefore, the effect of primary $\alpha$-Al on the reinforcement distribution in matrix alloys has been investigated. The microstructure of PMMC fabracated with various volume fractions(0%, 10%, and 20%) and particle size were observed.

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Preparation of Monodisperse Poly(Acrylic acid) with a Water-Soluble Initiator by Solution Polymerization in Aqueous Phase (수용액 내에서 수용성개시제를 이용한 단분산성 폴리아크릴산의 용액중합)

  • Park, Moonsoo;Kim, Yeji
    • Elastomers and Composites
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    • v.49 no.3
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    • pp.232-238
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    • 2014
  • Solution polymerization was conducted with water-soluble acrylic acid (AA) as a monomer and potassium persulfate (KPS) as an initiator at a selected temperature between $60^{\circ}C$ and $90^{\circ}C$ with water as a reaction medium. When the ratio between AA and water was reduced or initiator concentration increased, molecular weights decreased. An increase in the reaction temperature produced lower molecular weights. The polydispersity index was close to 1.5 in most of the reactions. An increase in the stirring speed up to 400 rpm led to a progressive increase in molecular weights. When the stirring speed reached 800 rpm, however, we found that both the number and weight average molecular weights decreased. The glass transition temperature was nearly independent of moelcular weights and determined to be between $113^{\circ}C$ and $116^{\circ}C$.

Preparation of Monodisperse Poly(Methacrylic acid) with a Water-Soluble Initiator by Solution Polymerization in the Aqueous Phase (수용액 내에서 수용성개시제를 이용한 단분산성 폴리메타크릴산의 용액중합)

  • Moon, Jiyeon;Chung, Kyungho;Park, Moonsoo
    • Elastomers and Composites
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    • v.48 no.4
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    • pp.294-299
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    • 2013
  • Solution polymerization was conducted with water-soluble methacrylic acid (MAA) as a monomer and potassium persulfate (KPS) as an initiator at a selected temperature between $70^{\circ}C$ and $90^{\circ}C$. When the ratio between MAA and water was reduced or initiator concentration increased, molecular weights decreased. Molecular weights of poly(methacrylic acid) (PMAA) showed nearly no dependence on reaction temperature. The Weissenberg effect was observed in most polymerization reactions, while its effect weakened at $90^{\circ}C$. The polydispersity index was less than 1.5 in most of the reactions. An increase in the stirring speed produced PMAAs with increasing molecular weights. When the stirring speed reached 800 rpm, we retrieved a monodisperse PMAA with both the number and weight average molecular weights of 791,000 g/mol. The glass transition temperature was found to be $162^{\circ}C$.

Characteristics of Friction Stir Lap Welded A5052 with Probe Length (프루브 길이에 따른 A5052 겹치기 마찰교반접합 특성)

  • Ko, Young-Bong;Kang, Chae-Won;Choi, Jun-Woong;Park, Kyeung-Chae
    • Journal of the Korean institute of surface engineering
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    • v.42 no.6
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    • pp.294-300
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    • 2009
  • The Friction Stir Welding (FSW) has mainly been used for making butt joints in Al alloys. The development of Friction Stir Lap Welding (FSLW) would expand the number of applications. In this study, for effective application on thin aluminum alloy lap joint, non-heat treatment A5052 alloys were joined by FSLW with the length of probe 2.3 mm and 3.0 mm. Investigating the characteristics of joint area showed the results were as below ; When the length of probe was 2.3 mm, good joint area was formed at all welding condition except for 600 rpm-700 mm/min. In the case of 3.0 mm probe length, there was formed good joint area without defects at 1500 rpm-100 mm/min. The width of joint area, position and size of defects were very important factors for FSLW, due to heat input and stirring intensity.

Numerical Study for Mixing Characteristics of an Oscillating Micro-stirrer (미소진동교반기의 혼합특성에 대한 수치적 연구)

  • Kim, Yong-Dae;Maeng, Joo-Sung
    • 유체기계공업학회:학술대회논문집
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    • pp.309-312
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    • 2006
  • Effective mixing is an important problem in microfluidics for chemical and biomechanical applications. In this study, the influences of the Reynolds number and the oscillating frequency on mixing characteristics of micro-stirrer are studied in a microchannel with single stirrer. The influence of fluid inertial effects in an active mixer is first discussed. It is found that the stirring effects by stirrer oscillation are promptly attenuated at low Reynolds number, which makes greatly difficult the rapid mixing. As the inertial effects are increased, the chaotic advection is generated and then developed. The mixing phase is finally developed some mushroom shaped structure. And the mixing efficiency is also studied as a function of the oscillating frequency. We found that the mixing efficiency does not always increase with higher oscillating frequency of stirrer. Consequently, we found the functional relation between the optimal frequency of a stirrer and the Reynolds number.

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Characteristics of Friction Stir Lap Weldment according to Joining Parameter in 5052 Aluminium Alloy (5052 알루미늄 합금에서 접합변수에 따른 겹치기 마찰교반접합부의 특성)

  • Ko, Young-Bong;Park, Kyeung-Chae
    • Journal of the Korean institute of surface engineering
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    • v.45 no.5
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    • pp.181-187
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    • 2012
  • The Friction Stir Welding (FSW) has mainly been used for making butt joints in Al alloys. The development of Friction Stir Lap Welding (FSLW) would expand the number of applications. In this study, microstructures and mechanical properties of FSLW in A5052 alloy were investigated under varying rotating speed and probe length. Investigating the characteristics as FSLWed conditions were as below ; Failure Maximum load by shear fracture was increased proportional to the width of joint area, which was increased by input heat, stirring intensity in the case of 2.3 mm probe length. Tensile fracture occurred, and maximum load was determined due to side worm hole of joint area and softening of microstructure in the case of 3.0 mm probe length. In the case of 3.7 mm probe length, material hook and bottom worm hole were appeared at the end interface of joint area. The most sound FSLW condition with no defects was 3.0 mm probe length and 1500 rpm-100 mm/min. No defects were showed in 1500 rpm-100 mm/min and 1800 rpm-100 mm/min, but Vickers microhardness distribution in TMAZ/HAZ which was fracture zone was lower in 1800 rpm-100 mm/min than in 1500 rpm-100 mm/min. In this condition highest tensile strength, 215 MPa (allowable rate 78% of joint efficient) was obtained.

A CFD STUDY ON THE SOLIDS SUSPENSION IN POLYMERIZATION REACTORS (CFD를 이용한 고분자 반응기내 입자 부유에 관한 연구)

  • Cha Hyo Sook;Song Hyun-Seob;Han Sang Phil
    • 한국전산유체공학회:학술대회논문집
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    • pp.31-34
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    • 2005
  • This article has investigated the spatial distribution of the solid particles in polymerization reactors using CFD analysis (FLUENT v. 6.2.1). The suspension of the solids in stirred reactors is affected by a number of parameters including particle diameter, vessel shape, impeller size, impeller speed, and rotating direction of stirrer. The degree of solids suspension in the vessel was quantified with a statistical average value, ${\sigma}^2$. The best stirring conditions were determined based on ${\sigma}^2$, which was found to depend on the vessel bottom shape.

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