• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1162-1167
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• 2006

Because the mixing efficiency is influenced remarkably by varying the geometrical configurations, the study of flow characteristics inside the agitator is very important. The draught tube in the agitator makes intermixing between the screw and tube by interrupting radial flow, and the helical screw agitator with a draught tube (HSA) is proved more efficient to mix than the others. Consequently, the shapes of helical screw and number of pitches are the main parameters for improving the performance of HSA. In this study, numerical analyses were carried out, using a commercial CFD code, Fluent, to obtain the velocity and pressure distributions under steady, laminar flow and no-slip condition. Results are graphically depicted with various parameters.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.317-323
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• 2008

In the current study, A model for the flow analysis of fresh and highly flowable concrete has been developed using a particle method, the moving particle semi-implicit (MPS) method. The phenomena on the flow of concrete has been considered as a visco-plastic flow problem, and the basic governing equation of concrete particle dynamics has been based on the Navier-Stokes equation in Lagrangian form and the conservation of mass. In order to formulate a visco-plastic flow constitutive law of fresh concrete, concrete is modeled as a highly viscous material in the state of non-flow and as a visco-plastic material in the state of flow after reaching the yield stress of fresh concrete. A flow test of fresh concrete in the L-box was simulated and the predicted flow was well matched with the experimental result. The developed method was well showed the flow motion of concrete particles because it was formulated to be based on the motion of visco-plastic fluid dynamics.

• KSBB Journal
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• v.9 no.1
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• pp.85-90
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• 1994

The Gellan-type polysaccharide produced by Pseudomonas elodea(ATCC 31461) is one of the new heteropolysaccharides, having useful properties as gelling, suspending, stabilizing, emulsifying and binding agents in aqueous systems. Medium compositions for growth stage and production stage are improved. The problems of low cell concentration and poor productivity in highly viscous fermentation were attributed to inadequate mixing accompanied by insufficient oxygen transfer. During continuous culture, cell growth and polysaccharide production were greatly affected by the apparent viscosity, and they showed oscillation behavior, i.e. as the product concentration increases, cell concentration decreases. With improved culture conditions, the productivity of continuous culture increased up to 0.6g/$\ell$/hr(6-fold that of batch culture ) at dilution rate, D=$0.14hr^{-1}$.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.1-7
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• 2002

Flow mechanism of contractive and dilative motion is numerically investigated to obtain a propulsive force in highly viscous fluid, which is the simulation of the propulsion in micro-organisms. The computing code for the analysis of complicated motions is developed with cell-centered unstructured grid scheme. The developed code is validated by the well-known problems of cavity flow and oscillating wall. The validated code is applied to the contractive and dilative motion in narrow tube. The computed results are compared with nodal points scheme. By the present results, it is found that propulsive force can be obtained by the contractive and dilative motion through simulation with the developed code.

• KSBB Journal
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• v.11 no.3
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• pp.340-346
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• 1996

Variations of rheological properties of culture broth during the production of biopolymer by an alkali tolerant Bacillus sp. were investigated. Correlations among the rheological characteristics of culture broth, cell growth and biopolymer production were examined. Rheology of the culture broth changed in the course of fermentation. The culture broth showed a non-Newtonian flow behavior, as the viscosity and pseudoplasticsity increased during the cultivation. The rheological parameters such as flow index, consistency index, yield stress and apparent viscosity during the cultivation were not influenced by the cell growth, but significantly related to the biopolymer synthesis. Changes in the rheological parameters of the broth were affected not only by the biopolymer concentration, but also by the progress of fermentation. Some rheological parameters showed maximum values just before the completion of biopolymer production and substrate consumption. Hence, it was shown that the rheological characteristics of the culture broth could be used as a good indicator for the detection of the progress or completion of fermentation.