• 제목/요약/키워드: mixing problem

검색결과 376건 처리시간 0.024초

농도분산에 근거한 혼합지수 사용의 문제 (On the Problem of Using Mixing Index Based on the Concentration Dispersion)

  • 서용권
    • 대한기계학회논문집B
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    • 제30권8호
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    • pp.796-805
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    • 2006
  • In this study, the problem of using the mixing index as a measure of the mixing performance for a certain flow field has been discussed. The flow model subjected to this study is the two-dimensional unsteady lid-driven cavity flow. The transport equation for the concentration within the cavity was solved by using the finite volume method where the convective terms are discretized with the central difference scheme. It was shown that both the concentration dispersion and the mixing index depend highly on the initial distribution of the concentration, and therefore the mixing index obtained from the concentration dispersion equation loses its universal applicability.

기연가스의 혼합이 상호작용을 하는 예혼합화염의 소화특성에 미치는 영향에 관한 연구 (Effect of burnt gas mixing on the extinction of interacting flames premixed)

  • 임홍근;정석호
    • 오토저널
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    • 제11권3호
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    • pp.37-48
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    • 1989
  • The effects of burnt gas mixing, which can be caused by turbulent eddy mixing, on the interaction and extinction characteristics of premixed flames are analyzed using large activation energy asymptotics adopting counterflow as a model problem. The results show that the burnt gas mixing, preferential diffusion and heat loss affect the fuel consumption rate, flame temperature and the oxidizer concentration at the flame which influence the flame behavior and the extinction characteristics.

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지오폴리머 기반 순환골재 혼입율에 따른 친환경성 인조석재의 특성 (Properties of Eco-friendly Artificial Stone according to the mixing ratio of Geopolymer-based recycled Aggregate)

  • 경석현;최병철;강연우;이상수
    • 한국건축시공학회:학술대회논문집
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    • 한국건축시공학회 2020년도 봄 학술논문 발표대회
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    • pp.126-127
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    • 2020
  • Recently, as interest in environmental issues increases, minimizing carbon dioxide generated during cement manufacturing is a problem to be solved. In order to solve such a problem, it is required to use an industrial by-product of recycled aggregate, blast furnace slag, and circulating fluidized bed boiler fly ash to replace it on the basis of geopolymer(=cementless). This study examines the characteristics of eco-friendly artificial stone according to the mixing ratio of geopolymer-based recycled aggregate. As a result of the experiment, when the addition rate of the alkali stimulant was 15% and the mixing ratio of the circulating aggregate was 70%, the flexural strength and compressive strength were the highest. Density and water absorption decreased as density of circulating aggregates increased and water absorption increased. However, when the mixing ratio of the circulating aggregate exceeded 70%, the flexural strength and compressive strength decreased. Therefore, in order to obtain strengths meeting the KS standards, the mixing ratio of recycled aggregate was set to 70%, and artificial stone was manufactured using industrial by-products.

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Replicating the chemical composition of the binder for restoration of historic mortars as an optimization problem

  • Miriello, D.;Lezzerini, M.;Chiaravalloti, F.;Bloise, A.;Apollaro, C.;Crisci, G.M.
    • Computers and Concrete
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    • 제12권4호
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    • pp.553-563
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    • 2013
  • The present study aims to show how the problem of reproducing, as closely as possible, binders of historic mortars by mixing raw materials which are commercially available, can be formulated as a linear optimization problem. The study points out that by mixing five standard raw materials (end-members) it is possible to obtain mortar binders with the almost same chemical compositions of those determined on the historic and archaeological mortar samples studied in some recent scientific papers. An advanced function of the Microsoft Excel spreadsheet, the Solver add-in, was used for the calculation of the right amount of each raw material to be mixed for producing the new binders. This approach could be useful to provide an optimal solution in the process of restoration of ancient monuments, where it is necessary to replace the historic mortars with new highly compatible repair mortars.

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

  • 김용대;맹주성
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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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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Effect of Mixing Method on Mechanical Properties of Fiber Reinforced Concrete

  • Kim, Hyun Wook;Lee, Chang Joon
    • 한국건축시공학회지
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    • 제15권3호
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    • pp.351-357
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    • 2015
  • Fiber reinforced concrete (FRC) has been successfully used to enhance the flexural toughness of concrete. As fibers are randomly oriented in FRC, they sometimes produce clumps that reduce the mechanical performance, and a properly chosen mixing protocol can be a way to minimize this problem. In this research, the effects of mixing method on the mechanical properties of FRC were investigated. The compressive strength, flexural strength, and flexural toughness were measured using three different mixing methods. It was shown from the results that the compressive strength and peak flexural load were not affected by changes in mixing method. However, in terms of flexural toughness, the changes in mixing method clearly affected the flexural toughness of FRC. The truck-mixed FRC outperformed two pan-mixed FRCs.

CFD를 이용한 가향 탱크 내부 유동에 관한 연구 (A Study on Internal Flow of Mixing Tank by CFD)

  • 정한주;조성일;양진철
    • 한국연초학회지
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    • 제32권2호
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    • pp.63-69
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    • 2010
  • In the chemical, mineral and electronics, mechanically stirred tanks are widely used for complex liquid mixing processes. The paper present results from a computational fluid dynamics (CFD) model for the mixing tank in casing process. We used CFD software, FLUENT(Fluent, Inc, Lebanon, NH, version 6.2). A species transport model was used to model the problem. The flow patterns in a mixing tank, 1.6 m in diameter and 2.0 m in height, were studied using CFD. Numerical analysis results show that improved mixing tank was reduced low speed flow region and turbulent region in internal flow of mixing tank.

난류연소 유동장에서의 확률밀도함수 전달방정식을 이용한 난류혼합 모델링 (Modeling of Turbulent Molecular Mixing by the PDF Balance Method for Turbulent Reactive Flows)

  • 문희장
    • 한국연소학회지
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    • 제2권1호
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    • pp.39-51
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    • 1997
  • A review of probability density function(PDF) methodology and direct numerical simulation for the purpose of modeling turbulent combustion are presented in this study where particular attention is focused on the modeling problem of turbulent molecular mixing term appearing in PDF transport equation. Existing mixing models results were compared to those evaluated by direct numerical simulation in a turbulent premixed medium with finite rate chemistry in which the initial scalar field is composed of pockets of partially burnt gases to simulate autoignition. Two traditional mixing models, the least mean square estimations(LMSE) and Curl#s model are examined to see their prediction capability as well as their modeling approach. Test calculations report that the stochastically based Curl#s approach, though qualitatively demonstrates some unphysical behaviors, predicts scalar evolutions which are found to be in good agreement with statistical data of direct numerical simulation.

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도시 하수의 해양방류 및 근역혼합특성 분석 (Analyses of Ocean Discharges Municipal Water and its Near-Field Mixing Characteristics)

  • 김강만;김지연;이중우
    • 한국항해항만학회:학술대회논문집
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    • 한국항해항만학회 1999년도 추계학술대회논문집
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    • pp.243-252
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    • 1999
  • Recently several research groups using CORMIX, approved by EPA, have been working on the hydrodynamic mixing processes due to the ocean discharges. It provides a useful tool for analyzing near field mixing characteristics through the outfall system. This paper applies CORMIX 1 & 2 to the Pusan Jungang Effluent Outfall System, which is planned to be in the Gamchun harbour and will be completed in 2011. This model output shows the trajectoral variation of dilution and concentration for three cases of outfall system. Dilution differences have been simulated and found the highest dilution condition under the different displacement of outfall system. On the basis of these outputs it will be proposed the optimum outfall system type and location. This approach might contribute on protecting the serious water quality problem due to the ocean discharge.

서해 연안지역 천부지하수의 수리지구화학 : 연안 대수층의 해수 혼입에 관한 연구 (Hydrogeochemistry of shallow groundwaters in western coastal area of Korea : A study on seawater mixing in coastal aquifers)

  • 박세창;윤성택;채기탁;이상규
    • 한국지하수토양환경학회지:지하수토양환경
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    • 제7권1호
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    • pp.63-77
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    • 2002
  • Salinization is an important environmental problem encountered in coastal aquifers. In order to evaluate the salinization problem in the western coastal area of Korea, we have performed a regional hydrochemical study on shallow well groundwaters (N=229) collected within 10 km away from the coastline. The concentrations of analyzed solutes are very wide in range, suggesting that the hydrochemistry is controlled by several processes such as water-rock interaction, seawater mixing, and anthropogenic contamination. Based on the graphical interpretation of cumulative frequency curves for some hydrochemical parameters (esp., $Cl^{-}$ and ${NO_3}^-$), the collected water samples were grouped into two major populations (1) a background population whose chemistry is predominantly affected by water-rock interaction, and (2) an anomalous population which records the potential influences by either seawater mixing or anthropogenic pollution. The threshold values obtained are 34.7 mg/l for $Cl^{-}$ and 37.2 mg/l for ${NO_3}^-$, Using these two constituents, groundwaters were further grouped into four water types as follows (the numbers in parenthesis indicate the percentage of each type water) : (1) type 1 waters (38%) that are relatively poor in $Cl^{-}$ and ${NO_3}^-$, which may represent their relatively little contamination due to seawater mixing and anthropogenic pollution; (2) type 2 waters (21%) which are enriched in $Cl^{-}$, Indicating the considerable influence by seawater mixing; (3) ${NO_3}^-$-rich, type 3 waters (11%) which record significant anthropogenic pollution; and (4) type 4 waters (30%) enriched in both $Cl^{-}$ and ${NO_3}^-$, reflecting the effects of both seawater mixing and anthropogenic contamination. The results of the water type classification correspond well with the grouping on a Piper's diagram. On a Br x $10^4$versus Cl molar ratio diagram, most of type 2 waters are also plotted along or near the seawater mixing line. The discriminant analysis of hydrochemical data also shows that the classification of waters into four types are so realistic to adequately reflect the major process(es) proposed for the hydrochemical evolution of each water type. As a tool for evaluating the degree of seawater mixing, we propose a parameter called 'Seawater Mixing Index (S.M.I.)’ which is based on the concentrations of Na, Mg, Cl, and $SO_4$. All the type 1 and 3 waters have the S.M.I. values smaller than one, while type 2 and type 4 waters mostly have the values greater than 1. In the western coastal area of Korea, more than 21% of shallow groundwaters appear to be more or less affected by salinization process.