• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.18-22
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• 2011

This paper presents the transient performance analysis of a micro-hydro Pelton turbine for the osmotic power generation using the commercially available computational fluid dynamics (CFD) code, ANSYS CFX. The detailed flow field in the micro Pelton turbine with a single-jet is investigated by the CFD code adopted in the present study. Predicted characteristic curves agree fairly well with measured data for a prototype Pelton turbine over the normal operating conditions. The computational analysis method presented herein can be effectively applied to the hydraulic design optimization process of general purpose Pelton turbine runners.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.46-52
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• 2004

The Magnetorheological fluid has the properties that its viscosity has drastic changed under some magnetic fields therefore, Magnetorheological fluids has been used fur micro polishing of the micro part(for example, a spherical surface in a micro lens). The polishing process may appears as follows. A part rotating on the spindle is brought into contact with an Magnetorheological finishing(MRF) fluids which is set in motion by the moving wall. In the region where the part and the MRF fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. Resonable calculated and experimental magnitudes of the material removal rate for glass polishing lends support the validity of the approach.

• Journal of Mechanical Science and Technology
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• v.14 no.6
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• pp.690-698
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• 2000

The laminar boundary layer flow and heat transfer of anisotropic fluids in the vicinity of a wedge have been examined with constant surface temperature. The similarity variables found by Falkner and Skan are employed to reduce the stream wise-dependence in the coupled nonlinear boundary layer equations. The numerical solutions are presented using the fourth-order Runge - Kutta method and the distribution of velocity, micro-rotation, shear and couple stresses and temperature across the boundary layer are plotted. These results are also compared with the corresponding flow problems for Newtonian fluid over wedges. It is found that for a constant wedge angle, the skin friction coefficient is lower for micropolar fluid, as compared to Newtonian fluid. For the case of the constant material parameter K, however, the magnitude of velocity for anisotropic fluid is greater than that of Newtonian fluid. The numerical results also show that for a constant wedge angle with a given Prandtl number, Pr = I, the effect of increasing values of K results in increasing thermal boundary layer thickness for anisotropic fluid, as compared with Newtonian fluid. For the case of the constant material parameter K, however, the heat transfer rate for anisotropic fluid is lower than that of Newtonian fluid.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1865-1868
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• 2003

This paper provides a new method for hybrid machining, particularly suited to micro fabrication applications such as micro point, micro line, micro structure, micro partition and so on. Developed micro fabrication process by electrical discharge machining (EDM) and electrical discharge deposition (EDD) with metal powder (Ti, Fe) has been studied to build TiC or FeC structure. Titanium powder or iron powder is supplied from working fluid (kerosene or de-ionized water with powder) and adheres on a workpiece by the heat and electric power caused by the electrical discharge. The use of a tool electrode is expected to keep powder concentration high in the gap between a workpiece and a tool electrode and to accrete powder material on the workpiece. The deposition is tried under various electrical conditions (workpiece. tool electrode, working fluid, discharge current, voltage and powder etc.). On the other hand. using electrical discharge machining (EDM) with the same tool electrode, it can be used as a removal process (cutting) by electro erosion at the same time. Therefore. this new method can do a hybrid machining to build up and down a structure with the workpiece.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.301-304
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• 2006

This paper presents a review of the important recent literature available in the area of micro-channel flow analysis and mixing. The topics covered include the physics of flows in micro-channels and integrated simulation of micro-channel flows. Also the flow control models and electro-kinetically driven micro-channel flows are explained. A comparison of various mixing principles in micro-channels are provided in sufficient detail.

• The KSFM Journal of Fluid Machinery
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• v.9 no.3 s.36
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• pp.36-43
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• 2006

Recently, micro hydropower and it's useful utilization are taking a growing interest as a countermeasure of global worming by carbon dioxide and exhaustion of fossil fuel. The purpose of this study is to investigate the possibility of extracting micro hydropower wasted by a valve in water supply system using micro cross-flow hydraulic turbine. In order to fulfill the functions of controlling flow rate and pressure in substitute for the valve, air and water are supplied into an air suction hole which is installed on the side wall of micro cross-flow hydraulic turbine. The results show that in case of supplying a lot of air into the air suction hole, about 50% of flow rate and relatively high value of loss coefficient are controlled by the turbine. Moreover, including high possibility of applying the micro cross-flow turbine to water supply system, extended application of the turbine to the water discharge system of drainage and irrigation canal.

• Wind and Structures
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• v.19 no.2
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• pp.199-217
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• 2014

Reported experimental and computational fluid dynamic (CFD) studies have demonstrated significant power augmentation of diffuser shrouded horizontal axis micro wind turbine compared to bare turbine. These studies also found the degree of augmentation is strongly dependent on the shape and geometry of the diffuser such as length and expansion angle. However study flow field over the rotor blades in shrouded turbine has not received much attention. In this paper, CFD simulations of an experimental diffuser shrouded micro wind turbine have been carried out with the aim to understand the mechanisms underpinning the power augmentation phenomenon. The simulations provide insight of the flow field over the blades of bare wind turbine and of shrouded one elucidating the augmentation mechanisms. From the analysis, sub-atmospheric back pressure leading to velocity augmentation at the inlet of diffuser and lowering the static pressure on blade suction sides have been identified as th dominant mechanisms driving the power augmentation. And effective augmentation was achieved for ${\lambda}$ above certain value. For the case turbine it is ${\lambda}$ greater than ${\approx}2$.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.45-68
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• 2009

An aim of the study is to develop an efficient numerical simulation technique that can handle the two-scale analysis of fluid permeation filters fabricated by the partial sintering technique of small spherical ceramics. A solid-fluid mixture homogenization method is introduced to predict the mechanical characters such as rigidity and permeability of the porous ceramic filters from the micro-scale geometry and configuration of partially-sintered particles. An extended finite element (X-FE) discretization technique based on the enriched interpolations of respective characteristic functions at fluid-solid interfaces is proposed for the non-interface-fitted mesh solution of the micro-scale analysis that needs non-slip condition at the interface between solid and fluid phases of the unit cell. The homogenization and localization performances of the proposed method are shown in a typical two-dimensional benchmark problem whose model has a hole in center. Three-dimensional applications to the body-centered cubic (BCC) and face-centered cubic (FCC) unit cell models are also shown in the paper. The 3D application is prepared toward the computer-aided optimal design of ceramic filters. The accuracy and stability of the X-FEM based method are comparable to those of the standard interface-fitted FEM, and are superior to those of the voxel type FEM that is often used in such complex micro geometry cases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.682-687
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• 2004

Y-junction microchannels are widely used as a flew mixer. Fluids are entered from two branch channels and merged together at a combined channel. In this study, we suggest a simple method to create the fluid digitization using flow instability phenomena. Two immiscible liquids (water/oil) are infused continuously to each Y-junction inlets. Because of the differences in fluid and flow properties at the interface, oil droplet is formed automatically followed by flow instability. In order to clarify the hydrodynamic aspects involved in oil droplet formation, a quantitative flow visualization study has performed. Highly resolved velocity vector fields are obtained by a micro-PIV technique, so that detail flow structures around the droplet are illustrated. In this study, fluorescent particles were mixed with water only for visualization of oil droplet and velocity field measurement in water flow.

• The KSFM Journal of Fluid Machinery
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• v.18 no.4
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• pp.22-29
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• 2015

In this study, an in-house program to predict steady state operation of micro gas turbines is constructed using MATLAB. The program consists of two parts: design and off-design simulations. The program is fully modular in its structure, and performance of each component (compressor, combustor, turbine, recuperative heat exchanger and pipe elements) is calculated in a separate calculation module using mass and energy balances as well as models for off-design characteristics. The off-design modules of compressor and turbine use performance maps, which are program inputs. The off-design operation of a micro gas turbine under development was predicted by the program. The prediction results were compared with those by commercial software, and the validity of the in-house program was confirmed.