• Journal of the Korean Society for Precision Engineering
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• v.25 no.10
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• pp.144-149
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• 2008

Configuration of filling imbalance which is originated from imbalanced share rate of melt on runner is changed by runner layout, runner shape, material property, injection pressure, injection speed, melt temperature and mold temperature. In this paper, we conducted a study of runner layout and shape that are main factors of filling imbalance. Other factors such as the sharp corner effect and the groove corner effect are recently released were also considered. The results of study are showed that filling rate of between inside and outside cavity was influenced on shape of runner. Especially, this study suggests a new runner system for filling balance by adapting the two effects of unary branch type runner at multi cavity mold and theoretical investigated flow in the sharp corner type runner.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.706-709
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• 2005

Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed in multi-cavity injection mold. These filling imbalances are results from non-symmetrical shear rate distribution within melt as it flows through the runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during the injection molding processing. This paper presents a solution of these filling imbalances by using runner core pin which creates a symmetrical shear distribution within runner and the effects on filling imbalance when modifying a shape of runner core pin. As a result of using runner core pin, a remarkable improvement in reducing filling imbalance was confirmed. In addition we investigated how filling imbalances were affected by shape of runner core pin.

• The KSFM Journal of Fluid Machinery
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• v.11 no.4
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• pp.45-51
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• 2008

The purpose of this study is to examine the effect of nozzle shape on the performance and internal flow of a cross-flow hydro turbine. CFD analysis for three kinds of nozzle shape is conducted to simulate the effect of nozzle shape. The results reveal that relatively narrow nozzle width is effective to increase the turbine efficiency and output power. Almost output power is achieved at Stage 1. Therefore, optimum design of the nozzle shape is necessary to improve the turbine performance. Recirculation flow in the runner passage decreases the turbine efficiency and output power because the flow make hydraulic loss and collision loss in the region. Air should be put into the runner passage and the recirculating flow should be suppressed by the air layer in the runner.

• Design & Manufacturing
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• v.6 no.1
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• pp.52-57
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• 2012

Aspect of filling imbalance that is originated from imbalanced share rate in runner is changed by material property, runner layout that are factors of changing viscosity and by injection pressure, injection speed, melt temperature and mold temperature that are injection conditions. In this paper, we made a study of runner system that is one of factor of filling imbalance and Sharp Conner Effect and Groove Corner Effect that are recently released. The study are showed that filling rate of between inside and outside cavity was influenced on shape of runner. Also, we suggested runner system for filling imbalance by adapting the two effects at multi cavity of unary branch type and theoretical investigated flow in the Shrap Conner runner type.

• Design & Manufacturing
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• v.2 no.5
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• pp.16-20
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• 2008

Almost all injection molds have multi-cavity runner system for mass production, which are designed with geometrically balanced runner system in order to accomplish filling balance between cavity to cavity during processing; However, even though geometrically balanced runner is used, filling imbalances have been observed. In these day, the CAE has been used widely in injection molding. However, CAE with fusion mesh can't indicate such as jetting, flow mark and filling imbalance in multi cavity mold. In this study, we investigated the filling imbalance according to runner shapes by CAE analysis. As a result in CAE, in case of binary branch runner system, filling imbalance was indicated between cavity to cavity, but the flow pattern of each cavity uniformed in unary branch runner system.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.5
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• pp.698-706
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• 2008

Performance improvement of Small hydro turbine is a very important subject to solve in the stage of introduction and development of the turbine. Cross-flow hydro turbine should be also studied more in detail for the turbine performance in order to extend the sites of application. In order to improve the turbine performance, the effect of the turbine shape on the turbine performance should be examined. Therefore, the effect of runner blade number on the turbine performance is investigated by use of a commercial CFD code. The results show that runner blade number gives remarkable effect on the efficiency and output power of the turbine. Pressure on the surface of the runner blade changes considerably by the blade number at Stage 1, but relatively small change of velocity distribution occurs in the flow passage.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.191.2-191.2
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• 2010

The conventional method to assess turbine performance is its model testing which becomes costly and time consuming for several design alternatives in design optimization. Computational fluid dynamics (CFD) has become a cost effective tool for predicting detailed flow information in turbine space to enable the selection of best design. In the present paper, Francis turbine of commercial small hydropower plants which is under 70kw is investigated. Solutions are investigated with respect to the hydraulic characteristics against an outward angle of guide vane, the number of guide vane and head (inlet velocity). By suitable modification of the runner shape, low pressure zone on the leading edge can be reduced. If the entire runner is to be optimized in this manner, flow simulation tests have to be carried out on a series of different geometrical shape.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.392-399
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• 2009

The paper concerns the description of the step by step development process of the new fixed blade runner called "Mixer" suitable for the uprating of the Francis turbines units installed at the older low head hydropower plants. In the paper the details of hydraulic and mechanical design are presented. Since the rotational speed of the new runner is significantly higher then the rotational speed of the original Francis one, the direct coupling of the turbine to the generator can be applied. The maximum efficiency at prescribed operational point was reached by the geometry optimization of two most important components. In the first step the optimization of the draft tube geometry was carried out. The condition for the draft tube geometry optimization was to design the new geometry of the draft tube within the original bad draft tube shape without any extensive civil works. The runner blade geometry optimization was carried out on the runner coupled with the draft tube domain. The blade geometry of the runner was optimized using automatic direct search optimization procedure. The method used for the objective function minimum search is a kind of the Nelder-Mead simplex method. The objective function concerns efficiency, required net head and cavitation features. After successful hydraulic design the modal and stress analysis was carried out on the prototype scale runner. The static pressure distribution from flow simulation was used as a load condition. The modal analysis in air and in water was carried out and the results were compared. The final runner was manufactured in model scale and it is going to be tested in hydraulic laboratory. Since the turbine with the fixed blade runner does not allow double regulation like in case of full Kaplan turbine, it can be profitably used mainly at power plants with smaller changes of operational conditions or in case with more units installed. The advantages are simple manufacturing, installation and therefore lower expenses and short delivery time for turbine uprating.

• Transactions of Materials Processing
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• v.18 no.2
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• pp.122-127
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• 2009

The injection mold with multi-cavity is essential for mass production of plastic products. Multi-cavity molds are designed to geometrically balanced runner system to uniformly fill to each cavity. However, despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed in injection molding. To solve these problems, many studies such as Melt Flipper, RC Pin, and others have been presented. The results of these studies have been an effect on filling balances in multi-cavity molds. But, those have had a limitation that additional insert parts must have existed in the mold. In this study, a new runner system is suggested for filling balance between cavity to cavity using "Melt-Buffer" with simple change of runner shape. A series of simulation to confirm feasibility of Melt-Buffer's effects was conducted using injection molding CAE program. Also, a series of injection molding experiment was conducted using plastic materials such as ABS and PP. As results of this study, feasibilities of filling balances by Melt-Buffer were confirmed.

• Journal of KSNVE
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• v.8 no.6
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• pp.1062-1068
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• 1998

This paper describes the vibration characteristics of a high head pump-turbine runner. with nine blades and an outer diameter of 4.410 mm. of the pumped storage power plant. Mode shapes and natural frequencies were obtained by means of both the finite element analysis and modal testing. both in air and in water. The natural frequencies in air were calculated using the finite element method by ANSYS software. In order to confirm calculation results. the natural frequencies and mode shapes of the runner were measured using a hydraulic exciter both in air and in water. Natural frequencies of the pump-turbine runner were found at 174. 310 Hz in air, and at 107. 184 Hz in water. The first mode shape is flat plate mode with two nodal diameter and the second one is also flat plate mode with three nodal diameter. It can be shown that the natural frequencies of the pump-turbine runner in water is reduced approximately 40 ％ due to additional mass effect. Natural frequencies in air predicted by ANSYS software are in good agreement with test results.