• Title/Summary/Keyword: Transient mixing

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Numerical Simulation of Steel Mixing during Sequential Casting of Dissimilar Grades in the Continuous Caster (연속주조시 강종 혼합에 관한 수치해석적 연구)

  • Cho, M.J.;Kim, I.C.;Kim, S.J.;Park, H.;Lee, S.S.
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.436-443
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    • 2001
  • In order to investigate the mixing of dissimilar grades during the arbitrary grade transition in bloom caster, a computational model has been developed. The model is fully transient and consists of two sub models, which account for mixing in the bloom tundish, mixing in the strand. The developed model was verified using concentration histories measured on 1 : 1 scale bloom tundish water model. The result of numerical model showed good agreement with the experimental results of water model. By using this numerical model, the mixing of dissimilar grades in bloom caster has been simulated. As that result, the characteristics of the steel mixing in the bloom tundish and strand was showed and the amount of the intermixed grade bloom was predicted.

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TRANSIENT SIMULATION OF SOLID PARTICLE DISTRIBUTION WITH BAFFLES DESIGN PARAMETERS IN A STIRRED TANK (배플 형상에 따른 교반기 내부 고체입자 분포의 비정상상태 해석)

  • Kim, Chi-Gyeom;Won, Chan-Shik;Hur, Nahm-Keon
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.171-175
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    • 2008
  • In the present study, a numerical simulations are investigated in a stirred solid/liquid system by using Eulerian multi-phase model. The transient flow field of liquid phase and distribution of solid particles are predicted in stirred tanks consisting of 4-pitched paddles impeller and baffles. The effects of number and width of baffles on the mixing time and the quality of solid suspension in a stirred tank are presented numerically. The result shows that the mixing time decreases as the width and number of baffles increase.

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NUPEC BFBT SUBCHANNEL VOID DISTRIBUTION ANALYSIS USING THE MATRA AND MARS CODES

  • Hwang, Dae-Hyun;Jeong, Jae-Jun;Chung, Bub-Dong
    • Nuclear Engineering and Technology
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    • v.41 no.3
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    • pp.295-306
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    • 2009
  • The subchannel grade void distributions in the NUPEC (Nuclear Power Engineering Corporation) BFBT (BWR Full-Size Fine-Mesh Bundle Tests) facility were evaluated with the subchannel analysis code MATRA and the system code MARS. Fifteen test series from five different test bundles were selected for an analysis of the steady-state subchannel void distributions. Two transient cases, a turbine trip without a bypass as a typical power transient and a re-circulation pump trip as a flow transient, were also chosen for this analysis. It was found that the steady-state void distributions calculated by both the MATRA and MARS codes coincided well with the measured data in the range of thermodynamic qualities from 5% to 25%. The results of the transient calculations were also similar and were highly feasible. However, the computational aspects of the two codes were clearly different.

The Fuel Spray Structure of High Pressure Gasoline Injector in a Constant Volume Chamber (정적챔버내의 고압 가솔린 인젝터의 연료분무구조)

  • 귄의용;조남효
    • Transactions of the Korean Society of Automotive Engineers
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    • v.8 no.4
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    • pp.10-17
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    • 2000
  • This work presents an investigation of aerodynamic characteristics of fuel spray injected from a high pressure hollow cone swirl injector into a constant volume chamber. Laser tomography visualization was used to interrogate the fuel and air mixing characteristics and the effect of chamber pressure and temperature increase was analyzed, Preliminary results on spray development showed that mixing effect tends to increase with the increase of injection pressure and chamber gas pressure yielding a decrease of spray penetration and an attenuation of well-defined vortex structure. Topological analysis of the spray structure has been performed to initiate the understanding of mixing and vaporization process. For the present experimental conditions fuel injection pressure and chamber gas pressure appear as the dominant factors which govern the transient mixing characteristics. Moreover spray atmixation characteristics are improved by increasing chamber gas temperature.

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The Mixing Ratio Effect of Insert Metal Powder and Insert Brazing Powder on Microstructure of the Region Brazed on DS Ni Base Super Alloy (일방향응고 Ni기 초내열합금 천이액상화산접합부의 미세조직에 미치는 모재와 삽입금속 분말 혼합비의 영향)

  • Ye Chang-Ho;Lee Bong-Keun;Song Woo-Young;Oh In-Seok;Kang Chung-Yun
    • Journal of Welding and Joining
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    • v.23 no.6
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    • pp.99-105
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    • 2005
  • The mixing ratio effect of the GTD-111(base metal) powder and the GNI-3 (Ni-l4Cr-9.5Co-3.5Al-2.5B) powder on TLP(Transient Liquid Phase) bonding phenomena and mechanism was investigated. At the mixing ratio of the base metal powder under $50wt\%$, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solid phases in the bonded interlayer grew epitaxially from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The number of grain boundaries farmed at the bonded interlayer corresponded with those of base metal. At the mixing ratio above $60wt\%$, the base metal powder melted only at the surface of the powder and the amount of the base metal dissolution was also less at the initial time. Nuclear of solids firmed not only from the base metal near the bonded interlayer but also from the remained base metal powder in the bonded interlayer. Finally, the polycrystal in the bonded interlayer was formed when the isothermal solidification finished. When the isothermal solidification was finished, the contents of the elements in the boned interlayer were approximately equal to those of the base metal. Cr-W borides and Cr-W-Ta-Ti borides formed in the base metal near the bonded interlayer. And these borides decreased with the increasing of holding time.

CFD ANALYSIS FOR THERMAL MIXING CHARACTERISTICS OF A FLOW MIXING HEADER ASSEMBLY OF SMART (SMART 유동혼합헤더집합체 열혼합 특성 해석)

  • Kim, Y.I.;Bae, Y.M.;Chung, Y.J.;Kim, K.K.
    • Journal of computational fluids engineering
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    • v.20 no.1
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    • pp.84-91
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    • 2015
  • SMART adopts, very unique facility, an FMHA to enhance the thermal and flow mixing capability in abnormal conditions of some steam generators or reactor coolant pumps. The FMHA is important for enhancing thermal mixing of the core inlet flow during a transient and even during accidents, and thus it is essential that the thermal mixing characteristics of flow of the FMHA be understood. Investigations for the mixing characteristics of the FMHA had been performed by using experimental and CFD methods in KAERI. In this study, the temperature distribution at the core inlet region is investigated for several abnormal conditions of steam generators using the commercial code, FLUENT 12. Simulations are carried out with two kinds of FMHA shapes, different mesh resolutions, turbulence models, and steam generator conditions. The CFD results show that the temperature deviation at the core inlet reduces greatly for all turbulence models and steam generator conditions tested here, and the effect of mesh refinement on the temperature distribution at the core inlet is negligible. Even though the uniformity of FMHA outlet hole flow increases the thermal mixing, the temperature deviation at the core inlet is within an acceptable range. We numerically confirmed that the FMHA applied in SMART has an excellent mixing capability and all simulation cases tested here satisfies the design requirement for FMHA thermal mixing capability.

A PARAMETRIC SENSITIVITY STUDY OF GDI SPRAY CHARACTERISTICS USING A 3-D TRANSIENT MODEL

  • Comer, M.A.;Bowen, P.J.;Sapsford, S.M.;Kwon, S.I.
    • International Journal of Automotive Technology
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    • v.5 no.3
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    • pp.145-153
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    • 2004
  • Potential fuel economy improvements and environmental legislation have renewed interest in Gasoline Direct Injection (GDI) engines. Computational models of fuel injection and mixing processes pre-ignition are being developed for engine optimisation. These highly transient thermofluid models require verification against temporally and spatially resolved data-sets. The authors have previously established the capability of PDA to provide suitable temporally and spatially resolved spray characteristics such as mean droplet size, velocity components and qualitative mass distribution. This paper utilises this data-set to assess the predictive capability of a numerical model for GDI spray prediction. After a brief description of the two-phase model and discretisation sensitivity, the influence of initial spray conditions is discussed. A minimum of 5 initial global spray characteristics are required to model the downstream spray characteristics adequately under isothermal, atmospheric conditions. Verification of predicted transient spray characteristics such as the hollow-cone, cone collapse, head vortex, stratification and penetration are discussed, and further improvements to modelling GDI sprays proposed.

A Study on the Vibration Characteristics by the Change of Impact Load Direction in the Collecting Plates of Electrostatic Precipitator (충결하중의 방향에 따른 정전집진기 집진판의 진동 특성 연구)

  • 나종문;이기백;양장식
    • Journal of KSNVE
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    • v.5 no.2
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    • pp.247-256
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    • 1995
  • In this paper, double exposure holographic interferometry using ruby pulse laser is formed in order to investigate the propagation of transient waves. The vibration characteristics according to the change of impact load direction, i.e., impacted in the shear direction and in the normal direction are analyzed. It was observed that the macroscopic trends of transient wave generation and propagation in the assembly of precipitator plates were almost similar regardless of the change of impact load direction. But the propagation and mixing of transient wave was advanced relatively slowly when impacted in the normal direction.

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Unsteady Transient Flowfield in an Integrated Rocket Ramjet Engine (램제트 엔진의 비정상 천이 유동에 관한 연구)

  • H.K. Sung;Vigor Yang
    • Journal of the Korean Society of Propulsion Engineers
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    • v.4 no.1
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    • pp.74-92
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    • 2000
  • A numerical analysis has been conducted to study the transient flowfield during the transition from the booster to sustainer phase in an integrated rocket ramjet (IRR) propulsion system. Emphasis is placed on the unsteady inlet aerodynamics, fuel/air mixing in an entire ramjet engine during the flow transient phase. The computational geometry consists of the entire IRR engine, including the inlet, the combustion chamber, and the exhaust nozzle. Turbulence closure is achieved using a low-Reynolds-number two-equation model. The governing equations are solved numerically by means of a finite-volume, preconditioned flux-differencing scheme over a wide range of Mach umber. Various important physical processes are investigated systemically, including terminal shock train.

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Analysis of Fuel/Coolant Mixing in Steam Explosion (증기 폭발시 용융 핵연료/냉각수 혼합에 대한 해석)

  • Lee, Tae-Ho;Jo, Seong-Youn;Park, Goon-Cherl
    • Nuclear Engineering and Technology
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    • v.25 no.2
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    • pp.215-221
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    • 1993
  • A required initial condition for a steam explosion to occur following core meltdown accidents of a nuclear power plant is the formation of a coarse mixture of molten fuel and water. The extent of a premixing is the measure of efficiency of steam explosion that may follow. A simple one-dimensional, transient model and the flooding criteria have been applied to evaluate the fuel/coolant mixing limit. Also, both instant breakup and dynamic breakup models for the mixing process have been separately used here and compared each other. The results indicate that fuel temperature, ambient pressure, mixing diameter, water depth, and pouring diameter are the important parameters affecting the mixing behavior.

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