Kilsung Kwon

Evaluation of reciprocating electromagnetic air pumping for portable PEMFC

In this paper, we present a proton exchange membrane fuel cell (PEMFC) integrated with an electromagnetic (EM) air pump. The EM air pump provides the PEMFC with air by reciprocating motions of the permanent magnet attached to a flexible membrane. We performed a parametric study to decide the optimal dimensions of the reciprocating EM air pump. The effects of various operating parameters on the EM air pump were investigated with the root-mean-square (RMS) flow rate and current. A core with a higher relative permeability shows better performance. The RMS current linearly increases with the applied voltage and shows no dependence on the frequency. The RMS flow rate also increases with the voltage. The RMS flow rate per power consumption is highest at the frequency around 20 Hz and decreases as the applied voltage increases. When the reciprocating EM air pump was used to supply air to the portable PEMFC, it was found that the power density of the PEMFC increases with the applied voltage and shows the highest performance at the frequency of 10 Hz. We compared the performance of the PEMFC between the flow meter and the EM air pump used as an air supplier. About 81% of the output power using the flow meter was obtained when the EM air pump is operated at the applied voltage of 5 V. The parasitic power ratio reaches at its minimum value about 0.1 with an EM applied voltage of 0.25V.

Air Pumps for Polymer Electrolyte Membrane Fuel Cells

초록: 본 논문은 고분자전해질막 연료전지의 공기 공급을 위해 전기침투현상에 기반을 둔 공기 공급 방법을 제안하고 이를 실험적으로 평가하였다. 작동 유체의 구동을 위해서 전기침투펌프를 낮은 주파수의 교류 전기장에서 사용하였다. 작동 유체는 유연한 막에 의해 막 밀봉하였고, 막의 움직임에 의해 연료전지 내로 공기를 공급하였다. 본 연구에서는 전기침투현상 기반 공기펌프를 사용하여 연료전지의 공기 공급을 성공적으로 설명하였다. 펌프의 출력은 연료전지에서 생성되는 출력을 초과하였지만, 본 논문에서는 펌프의 출력 당 연료전지의 출력비를 줄이기 위한 몇 가지 방법들에 대해 설명하였다. Abstract: We propose an electroosmosis-based air delivery scheme for polymer electrolyte fuel cells and experimentally investigate its feasibility. An electroosmotic pump under a low-frequency AC electric field is used to displace initially a volume of pump working liquids. This working liquid is then pumped into a space enclosed by a flexible membrane and the movement of the membrane delivers air to a fuel cell. We successfully demonstrated the operation of a forced-convection fuel cell using this technique. In this preliminary study, however, the power consumption of the pump exceeds the power generated by the fuel cell. We conclude this paper with a discussion of several ways to reduce the pump-to-fuel cell power ratio.

Nanofluidic reverse electrodialysis platform using controlled assembly of nanoparticles for high power energy generation

This paper presents a novel microplatform for high power energy generation based on reverse electrodialysis. The effective cation-selective membrane for power generations is realized between two microfluidic channels using geometrically controlled in situ self-assembled nanoparticles with cost-effective and simple way. Nano-interstices between the assembled nanoparticles have a role as the collective three-dimensional nanochannel networks and they can increase the generated power, significantly. The proposed system can contributes to supply power sources to miniaturized devices and be also used to studies and investigate nanoscale electrokinetics by changing sizes, materials, and shape of the assembled nanoparticles, or geometry control of microchannel.

Comparison of spacer-less and spacer-filled reverse electrodialysis

Reverse electrodialysis (RED) is a renewable energy technology used to recover dissipated chemical energy in river estuaries globally. This technology has recently attracted significant attention owing to its great reliability and scalability. In this study, we propose the use of a spacer-less RED (i.e., a system in which a woven mesh is excluded from the flow channel). The performance of spacer-less RED, including its gross power density, internal resistance, and hydraulic loss, is compared with that of the spacer-filled RED, in relation to the variation in the inlet flow rate. The mixing enhancement is more important than the spacer shadow effect when considering power generation. The spacer-filled RED has uniform internal resistance over the whole range of flow rates, while the spacer-less RED shows a dramatic decrease in resistance with the increasing flow rate. The hydraulic loss is much lower in the spacer-less RED. The maximal net power, accordingly, is generated at the flow rate of 3 ml/min (for s...

Numerical and Experimental Analysis of Micro Gas Turbine Heat Transfer Effect

* Dept. of Mechanical Engineering, Pohang Univ of Science and Technology., ** Dept. of Mechanical Engineering, Sogang Univ.,*** School of Elec. Eng. and Comp. Sci., Kyungpook Nat’l Univ. (Received June 23, 2014 ; Revised October 23, 2014 ; Accepted December 9, 2014)Key Words: Micro Gas Turbine(초소형 가스 터빈), Heat Transfer(열전달), CFD(전산유체역학)초록: 본 연구에서는 MEMS기술을 적용한 2W급 초소형 가스터빈엔진의 개발과 실제 연소 환경에서의 발전 가능성을 해석적, 실험적으로 입증하였다. 초소형 가스터빈엔진은 터보차저, 연소기, 발전기로 이루어져 있다. 터보차저는 각각 직경 10mm와 9mm의 MEMS 공정 압축기와 터빈으로 구성되어 있으며 발전코일 또한 MEMS공정으로 설계되었다. 제작된 압축기와 터빈은 정밀 기계 가공된 축과 공기 베어링으로 지지되고 회전하며, 회전축 끝단에 영구자석을 설치하여 발전을 하게 된다. 공기 베어링과 압축기를 통한 냉각 효과를 해석하여 연소기에서 발생한 열을 충분히 차단할 수 있는 것으로 분석되었고, 이를 실험을 통해 검증하였다.Abstract: In this study, a 2-W micro-gas turbine engine was designed using micro-electro-mechanical systems (MEMS) technology, and analytical and experimental investigations of its potential under actual combustion conditions were performed. An ultra-micro-gas turbine contains a turbo-charger, combustor, and generator. A compressor, turbine blade, and generator coil were manufactured using MEMS technology. The shaft was supported by a precision computer numerical control machined air bearing, and a permanent magnet was attached to the end of the shaft for generation. An analysis found that the cooling effect of the air bearing and compressor was sufficient to cover the combustor heat, which was verified in an actual experiment.

Numerical Study of Hydrogen/Air Combustion in Combustion Chamber of Ultra Micro Gas Turbine by Change of Flow Rate and Equivalence Ratio

In this study, we performed a numerical study of hydrogen/air combustion in the combustion chamber of an ultra micro gas turbine. The supply flow rate and equivalence ratio are used as variables, and the commercial computational fluid dynamic program (STAR-CCM) is used for the numerical study of the combustion. The flow rate significantly affects the flame position, flame temperature, and pressure ratio between the inlet and the outlet. The flame position is close to the outlet in the combustion chamber, and the flame temperature and pressure ratio monotonously increases with the supply flow rate. The change in the equivalence ratio does not affect the flame position. The maximum flame temperature occurs under stoichiometric conditions.

Porous Glass Electroosmotic Pumps Reduced Bubble Generation Using Reversible Redox Solutions

This paper presents the performance of a porous glass electroosmotic pump using an iodide/triiodide aqueous solution. The porous glass electroosmotic pump is characterized in terms of the flow rate and voltage. The flow rate and voltage increases linearly with current. A point where the voltage significantly increases is observed owing to an excess in redox capacity. The transition time monotonously decreases with current. The normalized flow rate (flow rate per membrane surface area) is used to compare previous results with results obtained in this study. The normalized flow rate of porous glass frits is three times higher than that of Nafion 117.

Development of Porous Silicon Electro-osmotic Pumps for High Flow Rate Per Current Flow Delivery of Organic Solvents

Two types of electro-osmotic pumps were prepared: with anodized and DRIE porous silicon. The pump performance was characterized for both types in terms of flow rate and flow rate per current using organic solvents. Both types of electro-osmotic pumps showed a better performance compared to porous glass electro-osmotic pumps. The DRIE porous silicon electro-osmotic pump especially demonstrated an excellent flow rate and flow rate per current performance. The DRIE porous silicon electro-osmotic pump is expected to help in the development of electro-osmotic pumps and micropumps in general due to the recently widespread availability of DRIE processes.

Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Particle Tracking Velocimetry

We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation—whose meaning is comparable to turbulent intensity—and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number.

Non-equilibrium electrokinetic micro/nano fluidic mixer with spatially controlled self-assembled nanoparticle networks

This paper reports an active micromixer which utilizes vortex generation due to non-equilibrium electrokinetics near the geometrically controlled in situ self-assembled nanoparticles. The large interfacing area where the possible vortices are created can be realized, because nano-interstices between these assembled nanoparticles have a role as the collective three-dimensional nanochannel networks. We investigate the variation of mixing performance by changing the size of the nanoparticles. Moreover, we achieve shorter mixing time and mixing length as compared to conventional silicon based nanochannels.