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Experiment And Numerical Simulation For Planar Anode-supported Solid Oxide Fuel Cell

Posted on:2006-09-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:G T TangFull Text:PDF
GTID:1102360155963257Subject:Thermal Engineering
Abstract/Summary:PDF Full Text Request
Today human beings are confronted with the great challenge for the realization of economy and social sustainable development under the restriction of finite resources and environment protection with strict demand, especially for the energy problem. It is of deep economic and social benefit to develop solid oxide fuel cell (SOFC) for Chinese sustainable development and socialism modernization construction with China characteristic. It will play an important role in country security and national defense strategy because it adapts to the demand of security, multipolarization and long-term demand of energy supply. In many aspects planar anode-supported SOFC has priority over other types of SOFC, therefore it has been necessary result to develop next generation SOFC.The first step of cell assembly preparation is the preparation of solid solution powder. In the paper two methods of preparation procedure of nano-scale powder have been made detailed discussion. The uniform and ultrafine nanoparticles Ce0.8Y0.2O1.9 with average crystal particle size of 5-8 nm have been synthesized in a reverse microemulsion solution containing water, CTAB, cyclohexane and immediate-length alcohol. The effect of different factors on ultimate products has been investigated, including cosurfactants, different molar rate between water and surfactants, concentrations of the solute, aging time, ammonia concentrations and so on. Transmission electron microscopy (TEM) was utilized to characterize the shape and size of the obtained nanoparticle products. The results show that there has little effect on the nanoparticle products for some factors such as cosurfactants, different ω0 and aging time. However, there are some factors which can change the crystal size of nanosized solid solution Ce0.8Y0.2O1.9 , including the solution concentration and ammonia concentration. Nanoscale solid solution power Sm0.15Gd0.05Ce0.8O1.9 was synthesized by several coupling routes of sol gel and low temperature self-propagating combustion including citric acid-nitrate, glycine-nitrate and EDTA chelation-nitrate processes. The phase identification and morphology were investigated by X-ray diffraction(XRD), transmission electron microscopy (TEM) and laser Raman spectroscopy (LRS), respectively. A combined analysis of XRD and LRS can give precise information on the structure and phase purity of Sm0.15Gd0.05Ce0.8O1.9 solid solutions. The samples synthesized by these methods are high purity doped ceria solid solution and have good crystal shape and bad dispersity. The results showed that several effecting factors on the average size of ultrafine powder are species and characterization of organic chelates, the rate of organic chelates and total cation ions,the temperature at which the solid solutions formed.It has been developed for the preparation of intermediate-temperature solid oxide fuel cell key materials, PEN (postive/electrolyte/negative) and its sintering technology. Ni-Gdo.2Ceo.801.9 porous anode has been made by dry pressure shape method. The electrolyte nano-scale Gdo.2Ceo.8O19 powder has reached the status of compactness at the temperature 1400°C by comparing different sintering temperature. Otherwise the better cathode membrane has been fabricated. The chemical compatibility between Lao.6Sro.4Coo.2Feo.8O3.6-^/ Gdo.2Ceo.8O19 has better result under the temperature of 1200°C.Three-dimensional mathematical model of planar anode-supported solid oxide fuel cell(SOFC) has been developed in this paper under the consideration of gas flow, charge transfer and electrochemical dynamics. The performance of single cell is investigated from the gas concentration distribution, potential distribution and concentration overpotential by numerical simulation. The results show that the cell potential along fuel flow change little when low fuel concentration area does not appear. The concentration overpotential is higher at high fuel utilization or high current density. The small fluctuation of concentration for reactants results in bigger concentration overpotential change when they are in the area of low concentration. The change of geometry structure has little effect on homogeneous distribution of the reactants at the interface of electrolyte and anode in the direction perpendicular to fuel flow, but it has some impact on concentration overpotential. The concentration overpotential becomes higher with the increasing of anode thickness. On the other hand, the concentration overpotential decreases when the pore structure parameter e /1 of the anode increases.The reasons that produce thermal stress have been comprehensively analyzed. Thermal stress of planar anode-supported SOFC and the factors that affect the SOFC stack temperature field have been discussed from the point of view of structural mechanics and mass and heat transfer. The results show that reducing the working and manufacturing temperature of stack is an effective route to make thermal stress change within the acceptable range. The design map to select membrane geometries resistant to buckling and fracture has been put forward by analyzing the PEN tensile and compressive stress. The gas high-speed flow makes the gas concentration and current density in the stack more uniform, therefore achieving uniform temperature field. Otherwise it is for co-flow fuel cell channel to more effectively reduce the temperature difference in the stack than for counter-flow. There is a detailed analysisto physically make the temperature difference lessened and possible schemes have been brought forward.Lastly a dynamic model for anode-supported intermediate-temperature solid oxide fuel cell (IT-SOFC) was developed for simulating the transient operation of stack with Matlab. The transient voltage and power responses to a load change including step response. It provides the basis for the construction of dynamic model of combined circulation between SOFC and microturbine and ac grid-connection.
Keywords/Search Tags:solid oxide fuel cell, nano-scale ceria solid solution, PEN(positive-electrolyte-negative), thermal stress, concentration overpotentials, dynamic modeling
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