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Analytical Investigation of Water Transport
Sukkee Um,Kwan-Soo Lee,Hye-Mi Jung 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
Comprehensive analytical models focusing on the anode water loss, the cathode flooding, water equilibrium, and water management strategy are developed for polymer electrolyte fuel cells. Analytical solutions presented in this study are compared with two-dimensional computational results and shows a good agreement in predicting those critical characteristics of water. General features of water concentration profile as a function of membrane thickness and current density are presented to illustrate the net effect of the back-diffusion of water from the cathode to anode and the water production by the cathode catalytic reaction on water transport over a fuel cell domain. As one of practical applications, the required humidity level of feed streams for full saturation at the channel outlets are investigated as a function of the physical operating condition. These analytical models can provide good understanding on the characteristic water.
Effect of Baffle Pattern Applied to Cathode Parallel Channel on PEMFC Performance
Jonghyun Son,Sukkee Um,Young Beom Kim 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.11 No.1
Many efforts have been made to improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). One approach has been the enhancement of the mass transport property by applying various channel designs and modifying them. Of those channels, the parallel channel as applied in PEMFCs has a low pressure drop and poor mass transfer property. To improve the mass transfer, a baffle that forces the reactant flow into the gas diffusion layer (GDL) from the channel can be installed in the parallel channel. In this study, various parallel channels designed with different baffle patterns and the effect was assessed by the PEMFC performance. All the baffle patterns analyzed in this study improved the performance of the PEMFC. However, depending on the baffle pattern, the reactant transfer and the current density of the PEMFC were affected differently. The staggered baffle pattern showed the best PEMFC performance among the analyzed models; when the staggered pattern was located near the outlet and the gap between the staggered baffles was wide, the PEMFC performance was further improved and the pressure drop of the cathode flow field was also lower than with the other baffle patterns.
Jonghyo Lee,Namkwon Lee,Sukkee Um 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.8
A three-dimensional thermofluidic model was developed for simulating fluid flow and heat transfer in interior permanent magnet synchronous motors (IPMSMs) with internal air circulation for effective thermal management. Protrusion-shaped flow inducers were introduced to facilitate the internal air circulation through rotor ventilation holes, increasing convection and preventing temperature rises in primary motor components. The numerical model agreed well with the experimental data. Subsequently, various geometrical design variables of the protrusion were selected to determine the thermofluidic characteristics of the electric motor associated with local temperature distributions for critical motor components. The protrusion increased the mass flow into the ventilation holes; accordingly, the maximal rotor temperature was inversely proportional to the protrusion design. Additionally, a thin airgap between the stator and rotor affected the radial heat transfer rate by forming additional thermal resistance layers. This flow was modeled using the Taylor-Couette paradigm, with the relative error under 1 %.
리튬이온 전지의 내압변화 원인과 안전변의 작동압 피로 시험
김용삼(Yongsam Kim),엄석기(Sukkee Um) 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
Inner pressure of Li-ion battery is easily changed by temperature, battery SOC %, storage time and side reaction. Gas evolution by side reaction is main factor for inner pressure increase but the mechanism was not clearly defined. So inner pressure of Li-ion battery was directly measured during cycling and storage. Through this measurement it was found that maximum cell inner pressure came from high temperature storage by side reaction. General Li-ion battery has a vent of safety device for gas exhausting. It was predicted that vent is very weak for repeated inner pressure change because vent material is aluminum and vent is very thin. So vent fatigue test was done for operation reliability during life. The degradation of vent operation pressure by repeated inner pressure change was fount but it was not critical to vent operation.
Jung, Hye-Mi,Um, Sukkee American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.12
<P>This paper presents an experimental comparative study involving the characterization of the thermo-electrical and structural properties of graphene-based vanadium oxide (graphene-VOx) composite thin films on insulating and conducting surfaces (i.e., fused quartz and acrylic resin-impregnated graphite) produced by a sol-gel process via dipping-pyrolysis. A combination of FE-SEM and XPS analyses revealed that the graphene-VOx composite thin films (coated onto fused quartz) exhibiting the microstructure of 2-graded nanowire arrays with a diameter of 40-80 nm were composed of graphene, a few residual oxygen-containing functional groups (i.e., C-O and C=O), and the VO2 Magn?li phase. The temperature-dependent electrical resistance measured on the as-deposited thin films clearly demonstrated that the graphene-VOx composite nanowire arrays thermally grown on fused quartz act as a semiconductor switch, with a transition temperature of 64.7 degrees C in the temperature range of -20 degrees C to 140 degrees C, resulting from the contributions of graphene and graphene oxides. In contrast, the graphene-VOx composite thin films deposited onto acrylic resin-impregnated graphite exhibit a superlinear semiconducting property of extremely low electrical resistance with negative temperature coefficients (i.e., approximately four orders of magnitude lower than that of the fused quartz), despite the similar microstructural and morphological characteristics. This difference is attributed to the synergistic effects of the paramagnetic metal feature of the tightly stacked nanowire arrays consisting of hexagonal V2O3 on the intrinsic electrical properties of the acrylic resin-impregnated graphite substrate, as revealed by FE-SEM, EDX, AFM, and XRD measurements. Although the thermo-sensitive electrical properties of the graphene-VOx composite thin films are very substrate specific, the applicability of graphene sheets can be considerably effective in the formation of highly planar arrays of VOx nanowires to enhance carrier transport.</P>
열 사상법을 이용한 유도 기동형 동기 전동기의 비정상 3차원 열해석
김치원(Chiwon Kim),엄석기(Sukkee Um) 한국자동차공학회 2012 한국자동차공학회 학술대회 및 전시회 Vol.2012 No.11
This paper describes thermal modeling of a line start permanent magnet (LSPM) motor using a computational flow dynamics method. First, 2-dimensional electromagnetic design is carried out in order to comprehend heat losses at winding, stator, rotor and cage. New coupling method called Heat mapping method (HMM) will be introduced which converts 2-D information of electromagnetic domain to 3-D information of thermal domain. Transient thermal analysis under rated operating conditions is performed to identify the load saturation time and temperatures in the LSPM motor. Experimental results are collected under the same operating conditions and computational results are verified against the experimental data. Finally, thermal path analysis at a steady-state is conducted to figure out the direction and magnitude of heat flux in the LSPM motor. These results can be useful to design effective cooling systems of electrical motors.