• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.6 s.237
• /
• pp.747-754
• /
• 2005

Because the liquid-vapor interfacial shear stress affects seriously the liquid flow and the maximum heat transport rate of the grooved wick heat pipe, an accurate modeling for the pressure drop characteristics of the liquid flow is required. A novel method for calculating the liquid pressure drop and the velocity profile of an open channel flow in a microchannel with an arbitrary cross-section is suggested and validated by experiments. An experimental apparatus for the Poiseuille number of the liquid flow in open rectangular microchannels with the hydraulic diameters of 0.40mm, 0.43mm, 0.48mm is used in order to reproduce real situations in the grooved wick heat pipe. Analytic results from the suggested method are compared with the experimental data and they are in a close agreement with each other.

• Korean Journal of Optics and Photonics
• /
• v.17 no.5
• /
• pp.437-446
• /
• 2006

A fabrication method fur high-aspect-ratio microchannels in stainless steel using laser-assisted thermochemical wet etching is reported in this paper. The fabrication of deep microchannels with an aspect ratio over ten is realized by applying a multiple etching process with an optimization of process conditions. The cross-sectional profile of the microchannels can be adjusted between rectangular and triangular shapes by properly controlling laser power and etchant concentration. Excellent dimensional uniformity is achieved among the channels with little heat-affected area. Microchannels with a width ranging from 15 to $50{\mu}m$ can be fabricated with an aspect ratio of ten and a pitch of 150 m or smaller. The effects of process variables such as laser power, scan speed, and etchant concentration on the fabrication results, including etch width, depth, and cross-sectional profile are closely examined.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.8
• /
• pp.823-829
• /
• 2014

In the present study, simple models were proposed to predict the capillary-driven flow length in a surfactant-added poly(dimethylsiloxane) (PDMS) rectangular microchannel. Owing to the hydrophobic nature of PDMS, it is difficult to transport water in a conventional PDMS microchannel by means of the capillary force alone. To overcome this problem, microchannels with a hydrophilic surface were fabricated using surfactant-added PDMS. By measuring the contact angle change on the surfactant-added PDMS surface, the behavior was investigated to establish a simple model. In order to predict the filling length induced by the capillary force, the Washburn equation was modified in the present study. From the investigation, it was found that the initial rate-of-change of the contact angle affected the filling length. Simple models were developed for three representative cases, and these can be useful tools in designing microfluidic manufacturing techniques including MIcroMolding In Capillaries (MIMIC).

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.274.2-274.2
• /
• 2013

We described a simple and efficient fabrication method for generating microfluidic channels with a circular-cross sectional geometry by exploiting the reflow phenomenon of a thick positive photoresist. Initial rectangular shaped positive photoresist micropatterns on a silicon wafer, which were fabricated by a conventional photolithography process, were converted into a half-circular shape by tuning the temperature to around $105^{\circ}C$. Through optimization of the reflow conditions, we could obtain a perfect circular micropattern of the positive photoresist, and control the diameter in a range from 100 to 400 ${\mu}m$. The resultant convex half-circular photoresist was used as a template for fabricating a concave polydimethylsiloxane (PDMS) through a replica molding process, and a circular PDMS microchannel was produced by bonding two half-circular PDMS layers. A variety of channel dimensions and patterns can be easily prepared, including straight, S-curve, X-, Y-, and T-shapes to mimic an in vivo vascular network. To inform an endothelial cell layer, we cultured primary human umbilical vein endothelial cells (HUVECs) inside circular PDMS microchannels, and demonstrated successful cell adhesion, proliferation, and alignment along the channel.

• Clean Technology
• /
• v.13 no.3
• /
• pp.195-200
• /
• 2007

This study investigated the flow rate changes of the heterogeneous rectangular microchannels which have different hydrophilic property on the bottom surface. The heterogeneous rectangular microchannel has three native PDMS (poly-dimethyl siloxane) surfaces which were patterned by the soft lithography. PDMS bottom surface was treated by the argon plasma and coated by the allyl alcohol (99%). The channel length was 10, 20 and 30 mm and the channel width was 100, 200 and $300\;{\mu}m$, respectively. Several external voltages were applied to make the fluid flow by the electroosmosis in the microchannel. For the same electric field strength and hydrophilicity of the bottom surface, the flow rate is almost same. This result is matched to the theoretical expectation and confirms that the experimental system is reliable. With increasing the channel width, the flow rate increased for the same hydrophilicity of the bottom surface. The flow rate of the microchannel of higher hydrophilicity was larger than that of the microchannel of lower hydrophilicity. This result implies that the hydrophilicity change of the bottom surface could be applied to control the flow rate in the microchannel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.4
• /
• pp.285-290
• /
• 2007

This study has been numerically conducted to investigate the removal efficiency of Volatile Organic Compound (VOC) in photocatalytic micro-reactor. This study has placed emphasis on the improvements of the working condition of photocatalytic micro-reactor. The micro-reactor consists of 19 microchannels with a rectangular cross-section. For the validation of the current numerical study, a computation has been carried out to simulate an existing experimental study on the cylindrical reactor, which has shown a good agreement. The degradation characteristics with different inlet concentrations and velocities have been obtained. The current results can be used for the design of advanced photocatalytic micro-reactor.

• Korea-Australia Rheology Journal
• /
• v.17 no.4
• /
• pp.207-215
• /
• 2005

We present a finite difference solution for electrokinetic flow in rectangular microchannels encompassing Navier's fluid slip phenomena. The externally applied body force originated from between the nonlinear Poisson-Boltzmann field around the channel wall and the flow-induced electric field is employed in the equation of motion. The basic principle of net current conservation is applied in the ion transport. The effects of the slip length and the long-range repulsion upon the velocity profile are examined in conjunction with the friction factor. It is evident that the fluid slip counteracts the effect by the electric double layer and induces a larger flow rate. Particle streak imaging by fluorescent microscope and the data processing method developed ourselves are applied to straight channel designed to allow for flow visualization of dilute latex colloids underlying the condition of simple fluid. The reliability of the velocity profile determined by the flow imaging is justified by comparing with the finite difference solution. We recognized the behavior of fluid slip in velocity profiles at the hydrophobic surface of polydimethylsiloxane wall, from which the slip length was evaluated for different conditions.