• Journal of the Korean Society of Propulsion Engineers
• /
• v.23 no.5
• /
• pp.1-9
• /
• 2019

Infrared signal and exhaust gas temperature distribution with bypass ratio were measured using a micro turbojet engine. Micro turbojet engine was modified to simulate the turbofan engine behaviour. Core flow was simulated using the jet flow of the micro turbojet engine, and high-pressure air was supplied to its external duct to simulate bypass flow. The effects of bypass ratios (0.5, 1.0, and 1.4) were examined. The experimental results indicate that the infrared signal decreases as the bypass ratio increases. And also gas temperature decreases with bypass ratios. Additionally, Schlieren visualization of the exhaust gas plume was conducted. From the exhaust gas temperature distribution and Schlieren images, the structure of jet plume with various bypass ratios was understood.

• Journal of the KSME
• /
• v.53 no.5
• /
• pp.35-40
• /
• 2013

이 글에서는 최근 많은 연구가 수행되는 자연모사 기법 중 식물모사 기법을 소개하고자 한다. 식물의 유동 원리 및 중요성, 식물 유동원리를 이용한 식물모사 마이크로 디바이스의 설계, 식물의 진화혼적 최적화의 공학적 접근에 대해 논한다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.4
• /
• pp.349-354
• /
• 2010

Fuel cells have attracted enormous interest as new power sources because the cells can be used to solve the problem of environmental pollution as well as the natural-resource exhaustion problem. In this study, hydrogen-gas flow in microchannels of different shapes was numerically analyzed to improve the efficiency of a microfuel cell. Flow characteristics in six microchannels of different shapes but under identical boundary conditions were simulated. The analysis result shows that the flow characteristics such as velocity, uniformity, and flow rate, greatly depend upon the channel shape. This implies that the efficiency of microfuel cell can be expected to be increased by adopting the optimal configuration of channel shape for hydrogen-gas flow. The experimental results show that power density of a PEMFC with a microflow channel is higher than that of a PEMFC without a microflow channel; however, a durable catalyst is required in MEA.

• Journal of the Korean Society of Visualization
• /
• v.1 no.2
• /
• pp.47-51
• /
• 2003

Microfluidic chips such as lab-on-a-chip (LOC) include micro-channels for sample delivery, mixing, reaction, and separation. Pressure driven flow or electro-osmotic flow (EOF) has been usually employed to deliver bio-samples. Having some advantages of easy control, the flow characteristics of EOF in microchannels should be fully understood to effectively control the electro-osmotic pump for bio-sam-pie delivery. In this study, a micro PIV system with an epifluorescence inverted microscope and a cooled CCD was used to measure velocity fields of EOF in a glass microchannel and a PDMS microchannel. The EOF velocity fields were changed with respect to electric charge of seeding particles and microchannel materials used. The EOF has nearly uniform velocity distribution inside the microchannel when pressure gradient effect is negligible. The mean streamwise velocity is nearly proportional to the applied electric field. Glass microchannels give better repeatability in PIV results, compared with PDMS microchannels which are easy to fabricate and more suitable for PIV experiments.

• Journal of the KSME
• /
• v.44 no.10
• /
• pp.50-56
• /
• 2004

이 글에서 먼저 microfluidics에 관련된 유동제어 기술을 먼저 살펴보고 microfluidic와 nanofluidics의 차이점을 살펴본 후 nanofluidic에 대해 다루기로 한다.

• Journal of the KSME
• /
• v.42 no.4
• /
• pp.42-45
• /
• 2002

이 글에서는 카오스의 이론적인 관점에서 성공적이라 할 수 있는 3차원 유동의 적용 예 중에서 산업적으로 관심의 대상이 될 수 있는 파이프 유동에서의 혼합증진, 혼합탱크 내의 혼합증진, 단축압출기에서의 혼합증진, 그리고 마이크로 채널 유동에서의 혼합증진 등 네 가지 유동에 대해 소개하도록 한다.

• Journal of the Korea Convergence Society
• /
• v.9 no.10
• /
• pp.237-242
• /
• 2018

A micromixer is a component of a lab-on-a-chip or microfluidic device that mixes two or more chemicals together(convergence). The purpose of this study is to assess the performance of passive micromixer of various shapes. Six shapes of micromixers were compared and three dimensional modeling was carried out to have the same hydraulic diameter. The commercial code, ANSYS Fluent, was used to simulate the internal mixing flow. A numerical analysis method is described in detail in this paper. The performance of the micromixer was compared with the mixing index and pressure drop. Consequently, the CDM-8T shape showed reasonable mixing performance and relatively low pressure drop.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.04a
• /
• pp.25-29
• /
• 2007

Minimization of conventional propulsion device has been studied for altitude control of micro satellite. We studied micro nozzle performance and found higher significant loss for a micro nozzle with smaller nozzle throat diameter. To overcome this loss, we proposed thermal transpiration based micro propulsion system. This new system has no moving parts and can control flow by temperature gradient, and this can be an option for potential new micro propulsion system.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.6
• /
• pp.383-389
• /
• 2016

Based on a surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool-boiling Critical Heat Flux (CHF). The microcavity structures could prevent liquid flow by the capillary pressure effect. In addition, the microchannel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow was clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through an analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related to the gravitational pressure head and capillary pressure effect.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.11a
• /
• pp.76-79
• /
• 2007

From the previous researches about flow characteristic of micro-nozzle， we found that viscosity and back pressure induced heavy losses in micro nozzle. To overcome thess losses, we began to study new conceptual micro propulsion system that is thermal transpiration based micro propulsion system. It has no moving parts and can pump the gaseous propellant by temperature gradient only (cold to hot). Most of previous research on thermal transpiration is in its early stage and mainly studied for application to small vacuum facility or gas chromatography in ambient condition using nanoporous material like aerogel. In this study, we focus on basic research of propulsion system based on thermal transpiration using polyimide material in vacuum conditions.