Modeling And Analysis Of Coupled Thermo-chemo-mechanical Problems In Chemically Active Solids At High Temperature

Clean energy technology will play an important role in the development of energy in future.In order to optimize the structural design and predict the durability of clean energy devices better,it is necessary to conduct theoretical models of related materials.These models should accurately describe the complex processes in materials,including mass transfer,heat transfer and chemical reactions,which are caused by thermal,chemical and mechanical loads.Taking the chemical-electrical energy conversion technology as an example,in lithium batteries and fuel cells,chemical reaction and mass diffusion may cause considerable stress and strain.Conversely,stress can also influence the processes of chemical reaction and mass diffusion.Studying the interaction between thermal,chemical and mechanical processes may not only expand the current theoretical knowledge,but also promote the development of industry,thus it has both scientific and engineering value.Based on thermodynamics of irreversible process with internal variables,chemometrics and reaction kinetics.,the present research formulate and calculate two thermo-chemo-mechanical problems in chemically active materials at high temperature.To study the stress caused by the oxidation of nickle particles in single cell of anode-supported planar solid oxide fuel cell,a specialized model with idealized parameter for chemically active solid plate is established.This model considers the influences of chemical reaction heat and non-linear heat transfer on physical fields.The steady state solution of the reaction-diffusion process between fuel gas and oxygen ions in porous Ni-YSZ anode is obtained,further the corresponding stress distribution in four-edge-fixed plate is calculated.In addition,the high temperature thermo-chemo-mechanical problem of the oxygen defects in non-stoichiometric compound ceramics was studied.The stress and oxygen defect equilibrium state are quantitatively related by stress-dependent chemical affinity and chemical kinetics equation.As an example,the equilibrium of oxygen defects in lanthanum strontium cobalt ferrite is calculated numerically.The results show that the effect of stress on the oxygen defect equilibrium is limited,which is due to a small chemical expansion coefficient.Based on the oxygen defect model,we formulate and calculate an axisymmetric fully coupled reaction-diffusion-mechanical problem.The coupling of stress with material diffusion and surface chemical reactions are considered in calculation.The effects of mechanical constraints,temperature and surface reaction rate on the coupled thermo-chemo-mechanical process are discussed by simulation.