• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.4
• /
• pp.377-385
• /
• 2013

To identify the effects of an outflow area on pool boiling heat transfer in a vertical annulus, three different flow restrictors were studied experimentally. For the test, a heated tube of smooth stainless steel and water at atmospheric pressure were used. Both annuli with open and closed bottoms were considered. To validate the effects of the outflow area on the heat transfer, the results of the annulus with the restrictor were compared with the data for the plain annulus without the restrictor. The reduction of the outflow area ultimately results in a decrease in the heat transfer. As the outflow area is very small, a slight increase in heat transfer is also observed. The major cause of this tendency is explained as the difference in the intensity of liquid agitation cause by the movement of coalesced bubbles. It is identified that the convective flow, pulsating flow, and evaporative mechanism are considered as the important mechanisms.

• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.1
• /
• pp.87-93
• /
• 2004

Recently, with the development of bio-technology the interests in the micro-fluidic devices for analysis in the fields of biology and medical science have been steadily increasing. Although polymer is considered as one of the best materials for micro-fluidic devices. glass or silicon molds fabricated by photo-lithographic technique have been commonly used. However, it is generally perceived that the conventional photolithographic technique has the limitation for fabricating micro-channels for micro-fluidic devices. In this work, the possibility of fabrication of micro-fluidic channels on PDMS by using the mechano-chemical process and the effect of surface states on the fluid flow were investigated. Experimental results revealed that PDMS mold fabricated by the mechano-chemical process could be used effectively to replicate micro-fluidic channels with high reproducibility and dimensional accuracy. It was also found that the fluid flow generation and flow speed were largely affected by the hydrophilicity and the surface roughness of the micro-channel surfaces.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.9
• /
• pp.1219-1226
• /
• 2001

Pressure drops were measured for the flow boiling process within horizontal rectangular channels. The gap between the upper and the lower plates of each channel ranges from 0.4 to 2mm while the channel width being fixed to 20mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200kg/㎡s and the channel walls were uniformly heated up to 15kW/㎡. The quality range covers from 0.15 to 0.75. The present experimental conditions coincide with the operating conditions of compact heat exchangers in which the liquid and gas flows are laminar and turbulent. The measured results were well represented by the two-phase frictional multiplier of Lee (2001) which has been developed for air-water two-phase flows within the deviation of $\pm$20%.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.245-253
• /
• 2010

The present study shows some results of developing evaporative heat exchangers with mini-channels. Heat exchangers with three different water paths were manufactured and tested to compare performances of cooling and pressure drop. Among the three types of heat exchangers, Type 2 with full-etching was proved to be the best in the cooling performances for considered operating conditions, and thus it is recommended to adopt Type 2 for its simplicity of production and outstanding performance. However, Type 1 was shown to be better when it is operated at a high air inlet temperature condition. The developed evaporative heat exchanger will be installed in Environmental Control Systems(ECSs) for aerial vehicles, and it can be used effectively in case an ECS is not only limited in its weight and volume but also required to absorb heats without supplying water (or a coolant) for a certain period of time.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.2
• /
• pp.114-121
• /
• 2013

In order to estimate the efficiency of an evaporative heat exchanger having mini channel, the equations to calculate heat exchanger properties, those are air temperatures and water temperatures etc, are derived from the governing equations based on the Navier-Stokes equation, even though there are several assumptions to make problem simplify. There are three heat transfer zones at the mini channel heat exchanger depending on the water condition. So, there are three governing equations and solutions to calculate the properties. As the results of this study, the equations to calculate a saturation point and a dry point are derived to evaluate an evaporative heat exchanger having micro channel. It is supposed to predict and evaluate the performance of a mini channel heat exchanger with evaporation of liquid.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1998.05a
• /
• pp.173-176
• /
• 1998

FCC (Fluid Catalystic Cracking) 장치는 중질유의 원유와 잔사유로부터 가솔린과 heating oil. 디젤연료 제조 등에 사용되고 있다. 이 장치는 50년 동안 fine-powder 유동화에 중요하게 응용되고 있으며, 현재 세계적으로 약 350여 개의 장치가 조업되고 있다. FCC 장치에서 미세한 분해촉매는 촉매에 의한 중질유의 분해가 일어나는 상승관 (riser)과 촉매의 재생이 일어나는 재생반응기(regenerator) 사이에서 높은 속도로 순환되고 있다. (중략)

• Proceedings of the Korean Society of Rheology Conference
• /
• 2006.06a
• /
• pp.57-60
• /
• 2006

• Proceedings of the KIEE Conference
• /
• 2004.07c
• /
• pp.2093-2095
• /
• 2004

본 논문은 압전소자를 구동장치로 사용한 마이크로 펌프의 제작과 실험에 관한 논문이다. 마이크로 펌프의 상부기판은 polydimethyl siloxane(PDMS)을 소재로 미세유로에 상시 닫힌 밸브가 일체화된 구조로 제작되었고, 하부기판은 polymethyl methacrylate(PMMA)를 소재로 3개의 압전 디스크가 구동기로 부착되었다. 최종적으로 상, 하부 기판은 액상 PUMS로 접합하여 제작했다. 구동기의 입력신호는 6상으로 구형파를 인가하여 연동구동하며 주파수와 전압을 가변하면서 유량을 측정하였다. 구동 주파수가 0.167 Hz이고 전압이 20 V일 때, 마이크로펌프의 1회 토출량은 104 nl이고, 유량은 1.04${\mu}{\el}$/min이다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.12
• /
• pp.1784-1792
• /
• 2001

Numerical analysis on a parallel flow heat exchanger(PFHE) is performed using 2 dimensional turbulent porous modeling. This modeling can consider three-dimensional configuration of passage (flat tube with micro-channels), and the stability and accuracy of numerical results are improved. The geometrical parameters(e.g., the position of separators, inlet/outlet, and porosity of passages of a PFHE) are varied in order to examine the flow and thermal characteristics and flow distribution of the single phase multiple passages system. The flow non-uniformities along the paths of the PFHE are observed to evaluate the thermal performance of the heat exchanger. The location of inlet affects the heat transfer, and the location of outlet affects the pressure drop. The porosity with the optimum thermal performance is around 0.53.

• Proceedings of the KIEE Conference
• /
• 2000.11c
• /
• pp.583-585
• /
• 2000

This study reports the fluidic handling method using hydrophobic patterns inside PDMS microchannels. In order to obtain hydrophobic patterns, we pattern fluorcarbon(FC) film surfaces by lift-off process. FC films are deposited by spin coating method and plasma polymerization method. Hydrophobic surfaces are used as the barriers to control fluid flow. Injected liquid is spontaneously filled up inside PDMS-microchannels by the capillary action. Liquid flow stops when it meets hydrophobic regions which can be the barrier against fluid flow. Then, again, when liquid is pressurized externally, liquid can move toward another hydrophilic region by external air pressure. Contact angle analyses are performed on fluorocarbon films to estimate the wettability of film surfaces.