Sangseok Yu

A Dynamic Model of PEMFC System for the Simulation of Residential Power Generation

A proton exchange membrane fuel cell (PEMFC) system of residential power generator (RPG) has a different operating strategy from the PEMFC system of transportation application because of its environmental difference. In this study, a dynamic simulation model of the PEMFC system is introduced, which has a model for a turbo blower, a membrane humidifier, two cooling circuits, and a PEMFC stack. The thermal efficiency of the PEMFC system for the RPG is very high because it supplies the electricity and hot water to the house. This study is designed to study the dynamic response of individual components during the dynamic change of current density. In particular, since the operation of the turbo blower is very sensitive at low current density the parasitic power consumption of the blower is significant. Additionally, the system performance and the operating strategy are also presented.

Flow Uniformity of Catalytic Burner for Off-Gas Combustion of Molten Carbonate Fuel Cell

A catalytic combustor is a device to burn out the fuel by surface combustion that is used for the combustion of anode off-gas of molten carbonate fuel cell. By employing the catalytic combustor, the purified exhaust gas is able to be recirculated into the cathode channel for CO2 supply to improve thermal efficiency. The design of catalytic combustor depends on many parameters but the flow uniformity is particularly important during the emergency shut-down of fuel cell stack. Right before the temperature control of catalytic combustor is not yet activated, the catalytic combustor should burn out more than two times of rated amount of fuel flow rate. At the over-loaded condition, assurance of flow uniformity at the inlet of catalytic combustor can reduce the damage of catalytic burner caused by local hot zone. In this study, the flow uniformity of the catalytic combustor is investigated in two steps such as preliminary step with model combustor and main analysis step with practical 250 kW catalytic combustor. The 0.5 kW and 5 kW class combustors are applied for preliminary step. In preliminary step, the model combustor is used to determine supporting matters for the flow uniformity. Inlet direction of mixing chamber below the catalytic combustor is also examined in the preliminary step. In the main analysis step, flow uniformity of scale-up combustor has been examined with selected supporting matter and inlet direction into mixing chamber. Geometric and operating parameters are investigated. In particular, the flow rate at off-design operating condition has been examined.Copyright

Mass and Heat Transfer Analysis of Membrane Humidifier with a Simple Lumped Mass Model

The performance of proton exchange membrane fuel cell (PEMFC) is seriously changed by the humidification condition which is intrinsic characteristics of the PEMFC. Typically, the humidification of fuel cell is carried out with internal or external humidifier. A membrane humidifier is applied to the external humidification of residential power generation fuel cell due to its convenience and high performance. In this study, a simple static model is constructed to understand the physical phenomena of the membrane humidifier in terms of geometric parameters and operating parameters. The model utilizes the concept of shell and tube heat exchanger but the model is also able to estimate the mass transport through the membrane. Model is constructed with FORTRAN under Matlab/Simulink O environment to keep consistency with other  components model which we already developed. Results shows that the humidity of wet gas and membrane thickness are critical parameters to improve the performance of the humidifier

Dynamic Modeling of Cooling System Thermal Management for Automotive PEMFC Application

The typical operating temperature of an automotive fuel cell is lower than that of an internal combustion engine, which necessitates a refined strategy for thermal management. In particular, the performance of the cooling module has to be higher for a fuel cell system because the temperature difference between the fuel cell and the surrounding is lower than in the case of the internal combustion engine. Even though the cooling system of an automotive fuel cell determines the operating temperature and temperature distribution of the fuel cell, it has attracted little research attention. This study presents the mathematical model of a cooling system for an automotive fuel cell system using Matlab/Simulink Ⓡ . In particular, a radiator model is developed for design optimization from the development stage to the operating stage for an automotive fuel cell. The cooling system model comprises a fan, pump, and radiator. The pump and fan model have an empirical relation, and the dynamics of the pump and fan are only explained by motor dynamics. The basic design study was conducted, and the geometric setup of the radiator was investigated. When the control logic was applied, the pump senses the coolant inlet temperature and the fan senses the coolant out temperature. Additionally, the cooling module is integrated with the fuel cell system model so that the performance of the cooling module can be investigated under realistic operating conditions.

Experimental Study of Steam Reforming Assisted by Catalytic Combustion in Concentric Annular Reactor

In this paper, the heat-transfer characteristics of steam reforming in an annular reactor are presented. Heat is supplied by the catalytic combustion of syn-gas. The thermal behaviors of exothermic and endothermic reactions in a directly coupled concentric-tube packed-bed reactor were investigated experimentally. The gas mixture supplied for catalytic combustion consisted of the off-gas emitted from MCFC anode. Methane in steam at a suitable S/C (steam-to-carbon) ratio was used in the reforming reactions. On the basis of the experimental results, a simple simulation was performed to predict the temperature profile required in the reforming side of the reactor to achieve optimum hydrogen yield. The results of this study may be utilized as reference data in future studies for further development of coupled reactors.

Analysis of neural networks with time-delays using the Lambert W function

Neural networks have been used in various areas. In the implementation of the networks, time-delays and uncertainty are present, and induce complex behaviors. In this paper, stability and robust stability of neural networks considering time-delays and parametric uncertainty is investigated. For stability analysis, the dominant characteristic roots are obtained by using an approach based on the Lambert W function. The Lambert W function has already embedded in various commercial software packages (e.g., Matlab, Maple, and Mathematica). In a way similar to non-delay systems, stability is determined with the locations of the characteristic roots in the complex plane. Conditions for oscillation and robust stability are also given in term of the Lambert W function. Numerical examples are provided and the results are compared to existing approaches (e.g., bifurcation method) and discussed.

Basic Analysis of Heat and Mass Transfer Characteristics of Tubular Membrane Humidifier for Proton Exchange Membrane Fuel Cell

The proton exchange membrane (PEM) fuel cell system is critically dependent on the humidity, which should be properly maintained over the entire operating range. A membrane humidifier is used for the water management in the PEMFC because of the membrane humidifiers reliable performance and zero parasitic power loss. In the PEMFC system, the membrane humidifier is required to provide appropriate humidity for the design point of the fuel cell. Although the performance of the fuel cell depends on the performance of the humidifier, few studies have provided a systematic analysis of the humidifier. We carry out an experimental analysis of the membrane humidifier using a vapor condensation bottle. The dry air pressure, water flow temperature, and air flow rate were chosen as the operating parameters. The results show that the time constant for the dynamic response of the membrane humidifier is relatively short, but additional analysis should be carried out.

A System Simulation Model of Proton Exchange Membrane Fuel Cell for Residential Power Generation for Thermal Management Study

초록:이온교환막연료전지는전세계적인에너지고갈문제와온실효과에대한대응책의하나이다.특히,이온교환막연료전지는전기화학반응에의해전기를생산함과동시에열을발생하기때문에가정용으로적용하기에적당하다.가정용연료전지의열관리목적은연료전지가최적조건에서운전할수있도록적절히온도를제어해주는것으로, 본연구에서는부하변화시가정용연료전지시스템의응답특성과열관리특성을알아보기위한해석모델을개발하였다. 열관리해석모델은연료전지의온도를조절하기위한펌프와열교환기로구성된1차측,주택에온수를공급하기위한탱크와펌프계통의2차측으로구성되었다.부하를순차적으로증가시킬때와감소시킬때를구분하여열관리계통의응답특성을확인하였다.결과적으로탱크의초기승온에많은시간이소요되기때문에부하를다단으로오랜시간동안서서히증가시키면서시스템응답특성을확인하였다.또한,본연구에서는가정용연료전지의부하변화시의열관리특성을고려한운전전략에대해서도조사하였다.Abstract:APEMFC(protonexchangemembranefuelcell)isagoodcandidateforresidentialpowergenerationto be coped with the shortage of fossil fuel and green house gas emission. The attractive benefit of thePEMFC is to produce electric power as well as hot water for home usage. The thermal management ofPEMFC for RPG is to utilize the heat of PEMFC so that the PEMFC can be operated at its optimalefficiency.Inthisstudy,thermalmanagementsystemofPEMFCstackismodeledtounderstandthedynamicresponse during load change. The thermal management system of PEMFC for RPGFC is composed of twocoolingcircuits,oneforcontrolingthefuelcelltemperatureandtheotherforheatingupthewaterforhomeusage. The different operating strategy is applied for each cooling circuit considering the duty of those twocircuits. Even though the capacity of PEMFC system (1kW) is enough to supply hot domestic water forresidence, heat-up of reservior takes some hours. Therefore, in this study, time schedule of the simulationreflects the heat-up process. Dynamic responses and operating strategies of the PEMFC system areinvestigatedduringloadchanges.

One-dimensional Numerical Analysis of the Effect of Seawater Feed Rate on Multi-effect Solar Stills

In a multi-effect solar distiller, a feeding rate of seawater to each effect should be decreased as the effect number is increased. In previous studies, the feed rate of seawater was not reduced evenly between the effects, which is unreasonable, since the thermal energy input of each effect decreases by the same amount. In this work, numerical analysis was carried out in order to elucidate this discrepancy. The results showed that the amount of distillates produced was almost the same for both evenly and unevenly reduced flow rates between the effects. Optimum feed rates of seawater with various energy inputs from exhaust gas heat exchanger were also obtained. The results showed that the optimum feed rate of the first effect increased linearly or reached a steady state depending on the heat flux. 이 논문은 대한기계학회 창립 주년 기념 70 학술대회 제주 발표논문임 (2015. 11. 10-14., ICC ) . Corresponding Author, bzoo77@kimm.re.kr 2016 The Korean Society of Mechanical Engineers C 임병주 유상석 박창대 정경열 · · · 478 b 베이진 해수 : c 대류 : d 전도 : e 증발 및 응축 : g 배기가스 : i 효용단의 순서 : in 입구 : out 출구 : pi 번째 평판 : i r 복사 : wi 번째 윅 : i

Numerical Analysis of Steam-methane Reforming Reaction for Hydrogen Generation using Catalytic Combustion

A steam reformer is a chemical reactor to produce high purity hydrogen from fossil fuel. In the steam reformer, since endothermic steam reforming is heated by exothermic combustion of fossil fuel, the heat transfer between two reaction zones dominates conversion of fossil fuel to hydrogen. Steam Reforming is complex chemical reaction, mass and heat transfer due to the exothermic methane/air combustion reaction and the endothermic steam reforming reaction. Typically, a steam reformer employs burner to supply appropriate heat for endothermic steam reforming reaction which reduces system efficiency. In this study, the heat of steam reforming reaction is provided by anode-off gas combustion of stationary fuel cell. This paper presents a optimization of heat transfer effect and average temperature of cross-section using two-dimensional models of a coaxial cylindrical reactor, and analysis three-dimensional models of a coaxial cylindrical steam reformer with chemical reaction. Numerical analysis needs to dominant chemical reaction that are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming(DSR) reaction. The major parameters of analysis are temperature, fuel conversion and heat flux in the coaxial reactor.