• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.1
• /
• pp.89-95
• /
• 2012

In this paper, microchannels for the flow control of two fluids with different volumes have been designed, fabricated, and verified. The dimensions of the inlets were determined based on the Stokes equation in order to realize that the flow of the two fluids meet at the same time, and to maintain a certain configuration when the flows passed through each inlet channel. The designed microchannels were confirmed using computational fluid dynamics simulation for the incompressible, Newtonian, and transient flows. In addition, a microfluidic system containing the designed microchannels was fabricated by soft lithography, and the pressure-driven flows of the two fluids were characterized by microfluidic experiments.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.1
• /
• pp.77-82
• /
• 2010

Our study aims to understand the flow of liquid in an open-top rectangular microchannel that can be used in micro total analysis systems ($\mu$-TAS) because it has advantages in terms of light transmission and energy efficiency. We measured the liquid velocity using particle tracking technique and conducted a simulation with computational fluid dynamics by altering the area of channel cross section and channel length for the capillary-driven flow in the open-top rectangular microchannel. When liquid water drops to an entrance of the fabricated microchannel with a height of 20 μm and a width of 20 ${\mu}m$, it flows along the microchannel by only capillary force. In the wetting behavior of the liquid, important parameters of this flow are channel size, contact angle and liquid properties such as surface tension and viscosity, which are used to control the flow of liquid in the microchannel.

• 한국가시화정보학회:학술대회논문집
• /
• 2007.11a
• /
• pp.66-70
• /
• 2007

현재 많은 연구들이 작은 크기에 여러 공정을 집적시킬 수 있는 장점을 가진 마이크로 장치의 개발과 활용에 집중되고 었다. 마이크로 장치에서 가장 중요한 것은 미세 유동의 효율적인 제어이다. 본 연구에서는 마이크로 장치에 직접 적용 가능한 표면 개질 된 마이크로 채널의 유동에 대하여 고려하였다. 표면 개질(surface treatment)은 물리적, 화학적인 작용을 통해서 채널 내부 표면의 습윤성을 변화시켜 유동을 제어하는 방법이다. 친수성(glass)을 가지는 마이크로 채널 내부의 일부를 소수성(teflon)으로 개질 후, 고속카메라를 이용하여 채널 내부를 흐르는 유체의 유동 경계면 변화를 분석하였다. 또한 유동 해석을 위한 상용 코드(CFD-ACE)를 이용하여 유동에 대한 수치 해석을 진행하여 가시화된 실험 결과와 비교 분석하였다. 실험 결과와 수치 해석 결과를 통해, 친수성과 소수성 표면 배열에 따른 일시적인 유동 변화를 관찰하였다. 본 연구 결과를 통해 마이크로 채널 유동의 최적화 상태를 찾을 수 있으며, 보다 용이한 미세 유동 제어가 가능하다.

• Journal of Power System Engineering
• /
• v.13 no.2
• /
• pp.18-29
• /
• 2009

미세유동에 대한 폭발적인 관심에 의해 이 분야의 연구는 다양한 측면에서 이루어지고 있다. 본 연구는 사각 미세채널에서의 슬립유동에 관한 연구 중 아직 제대로 이루어져 있지 않은 마찰특성에 관한 종횡비의 영향에 초점을 맞추어 3차원 수치해석을 행하였다. 그 결과 종횡비가 1.0 일 때 상하 벽면 및 좌우측 벽면에서의 전단음력은 동일하나, 종횡비가 감소함에 따라 전단응력은 상하 벽면과 좌우측 벽면이 상이한 강도로 증가함을 보였다. 또한 Knudsen 수의 증가에 따라서는 전단응력이 감소함을 알 수 있었다. 따라서 벽면에서의 전단응력은 종횡비를 증가시키거나 혹은 Knudsen 수를 증가시키면 감소시킬 수 있으며, 마찰계수(fRe)도 종횡비를 증가시키거나 혹은 Knudsen 수를 증가시키면 감소됨을 밝혔다.

• Journal of Internet of Things and Convergence
• /
• v.9 no.3
• /
• pp.93-98
• /
• 2023

In this paper, an artificial neural network based on simulated annealing was constructed. The mapping relationship between the parameters of micro-scaled flow channels electrochemical machining and the channel shape was established by training the samples. The depth and width of micro-scaled flow channels electrochemical machining on stainless steel surface were predicted, and the flow channels experiment was carried out with pulse power supply in NaNO3 solution to verify the established network model. The results show that the depth and width of the channel predicted by the simulated annealing artificial neural network with "4-7-2" structure are very close to the experimental values, and the error is less than 5.3%. The predicted and experimental data show that the etching degree in the process of channels electrochemical machining is closely related to voltage and current density. When the voltage is less than 5V, a "small island" is formed in the channel; When the voltage is greater than 40V, the lateral etching of the channel is relatively large, and the "dam" between the channels disappears. When the voltage is 25V, the machining morphology of the channel is the best.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.25 no.3
• /
• pp.113-126
• /
• 2021

In order to develop active cooling systems for a hypersonic cruise vehicle, a series of studies need to be preceded on regenerative cooling technologies by using endothermic reaction of liquid hydrocarbon aviation fuels. Among them, it is essential to scrutinize fluid flow/heat transfer/endothermic pyrolysis characteristics of supercritical hydrocarbons in a micro-channel, as well as to acquire thermophysical properties of hydrocarbon fuels in a wide range of temperature and pressure conditions. This study, therefore, reviewed those technologies and analyzed major findings in related research areas which have been carried out worldwide for the development of efficient operational regenerative cooling systems of a hypersonic flight vehicle.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.4
• /
• pp.385-390
• /
• 2011

In this study, we developed a micromixer based on the non-equilibrium electrokinetics at the junction of a microchannel and nanochannel. Two fluid streams were mixed by an electro-osmotic flow and a vortex flow created as a result of the non-equilibrium electrokinetics at the junction of the microchannel and nanochannel. Initially, the microchannel was fabricated using Polydimethylsiloxane (PDMS) by the general soft lithography process and the nanochannel was created at a specific position on the microchannel by applying a high voltage. To evaluate the mixing performance of the micromixer, fluorescent distribution was analyzed by using the fluorescent dye, Rhodamine B. About 90% mixing was achieved with this novel micromixer, and this micromixer can be used in microsystems for biochemical sample analysis.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.5
• /
• pp.644-654
• /
• 2003

An analytical solution for a vertically stratified viscous flow in a microchannel with a rectangular cross-section is constructed, assuming fully developed laminar flow where the interfaces between the fluid layers are flat. Although the solution is for n-layer flow, restricted results to symmetrical three-layer flow are presented to investigate the effects of the viscosity and thickness ratios of the fluid layers and the aspect ratio of the microchannel on the flow field. Relations between the flow rate and thickness ratios of the fluid layers with varying viscosity distributions are found, considering the cross -sectional velocity profiles which vary noticeably with the three parameters and differ significantly from the velocity profiles of the flow between infinite parallel plates. Interfacial instability induced by the viscosity stratification in the microchannel is discussed referring to previous studies on the instability analysis for plane multilayer flow. Exact solution derived in the present study can be used for examining a diffusion process and three -dimensional stability analysis. More works are needed to formulate the equations including the effects of interfacial' tension between immiscible liquids and surface wettability which are important in microscale transport phenomena.

• Journal of the Korean Society of Visualization
• /
• v.2 no.2
• /
• pp.66-72
• /
• 2004

The heat transfer and pressure drop characteristics of $CO_{2}$ are substantially different from those for CFC and HCFC refrigerants. In addition, geometric effects on two-phase flow patterns of $CO_{2}$ are also very significant in many respects. Therefore, two-phase flow patterns of $CO_{2}$ in a narrow rectangular channel or a small diameter tube whose gap size or hydraulic diameter is less than 2 mm are very important to understand heat transfer characteristics and to develop an appropriate heat transfer correlation. In the present study, the evaporation process of $CO_{2}$ in a narrow rectangular channel is visualized at various test conditions, and then the effects of operating conditions are analyzed.

• Proceedings of the SAREK Conference
• /
• 2008.11a
• /
• pp.269-274
• /
• 2008

The present study has been studied on a thermal and flow characteristic of the microchannel waterblock with flow distributions in each channels. Results of a numerical analysis using the CFX-11 are compared with results of an experiment. Numerical analysis and experiment are conducted under a heat transfer rate of 150W, inlet temperature of $20^{\circ}C$ and mass flow rates of $0.7{\sim}2.0\;kg$/min. Base temperature and pressure drop are investigated with standard deviations of mass flow rates in each channels of samples at 0.7 kg/min.