An advanced numerical model for energy conversion and crack growth predictions in Solid Oxide Fuel Cell units

Ghassemi

Env Prog and Sustain Energy

2020

Converting chemical energy into electricity is done by an electrochemical device known as a fuel cell. Thermal stress is caused by high operating temperature, between 700 and 1,000 C, of solid oxide fuel cell (SOFC). Thermal stress is the main cause of crack initiation and crack propagation. This phenomenon may cause gas leakage, structure instability and cease operation of the SOFC before its lifetime. The aim of this study is to present a method that predicts the initiation of cracks in an anisotropic porous planar SOFC. The coupled governing nonlinear differential equations are solved numerically as for heat transfer, fluid flow, mass transfer, mass continuity, and momentum. An in-house computer code which is based on computational fluid dynamics, computational structural mechanics and extended finite element method is utilized and developed. This code, according to Darcy and Navier-Stokes thermofluid model, determines the temperature and stress distribution. The results show that the highest thermal stress occurs at the upper corners of cathode and at the lower corners of the anode. The maximum temperature occurs at the middle of the electrolyte cathode and electrolyte anode, while the maximum pressure occurs at the middle of the upper and lower section of the anode and cathode. In addition, the thickness of the cathode electrode at the left side is increased by 1.5%. Finally, the crack initiation occurs at the left side between the upper and lower corners of the cathode.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical study of detecting crack initiation in a planar solid oxide fuel cell

Ghassemi

Env Prog and Sustain Energy

2020

“…The simulations in this study use boundary conditions: gas flow is assumed laminar, incompresible ideal gas. The gas velocity inlet is 1 ms -1 and 2 ms -1 [12], constant temperature of heating wall is 800⁰C, simulation is done under steady state conditions. Verify the results of computing based on convergence criteria and flux report.…”

Section: Simulation Resultsmentioning

confidence: 99%

Analysis of the Effect of Anode Porosity on Temperature Distribution on Planar Radial Type SOFC

2018

Solid Oxide Fuel Cell (SOFC) is an electrochemical equipment that converts gas into electricity directly. The waste products resulting from SOFC are water vapor and heat when using hydrogen gas. The electrode of the SOFC is the anode, electrolyte and cathode. The performance of SOFC is influenced porosity of the electrode. This study explained the relationship between porosity of the anode and temperature distribution using computational fluid dynamics modeling approach (CFD). In this study, CFD modeling was done by using Fluent software. The geometry model of computational modeling is a planar radial-type SOFC. The assumptions of some boundary conditions used from the study of literature and the object of study. The standard deviation and the different of temperature of the anode-electrolyte surface used to analyse the result. Non-homogenous temperature distribution rise if the anode porosity and gas flow rate is increasing. This indicates the gradient of temperature is bigger in the higher porosity, which may cause thermal stress and degrades the materials of electrode.

“…Since SOFC operates at high temperatures, the mechanical failure stimulated by thermal stress is serious . Researchers usually used numerical methods to examine the thermal stress characteristics of different SOFC structures, including single channel units, single cell and cell stack. Xu et al evaluated the stress distribution under different interconnect‐electrode contact area through a single channel model and they found that a larger contact area can effectively reduce the first principle stress close to the corner of interconnect‐cathode contact region at the fuel inlet.…”

Section: Introductionmentioning

confidence: 99%

Effect of interface morphology on the residual stress distribution in solid oxide fuel cell

Cao

et al. 2020

Int J Energy Res

Summary Solid oxide fuel cell directly and efficiently converts chemical energy to electrical energy. However, the necessity for high operating temperatures can result in mechanical failure. Fuel cell is a multilayer system and its stress distribution is greatly affected by the interface morphology. In this work, cosine interfaces with different amplitudes are used to approximate the fluctuation of actual interface. The effects of interface morphology on stress state, energy release rate of crack and creep behavior have been investigated. The results show that if the interface is planar, the residual normal stress component is zero on the interface, while the nonplanarity of interface can cause the normal stress Sn and shear stress St on the interface. When the amplitude is relatively small, the max values of Sn and St on the interfaces vary linearly with increasing amplitudes in both anode and cathode. Above a certain value, nonlinearity of the interface becomes important. Max tensile Sn always occurs at the peak of convex interface, but the position of max compressive Sn varies. Max shear stress is prone to occur at 1/4 of the wavelength at small amplitude and moves towards 1/2 of the wavelength when the amplitude increases. Fracture mechanics analysis shows that the surface crack possibly penetrates into the anode function layer and then is constrained by the stiff electrolyte. On the other hand, the horizontal crack likely penetrates into the electrolyte layer when the interface is not planar. Creep analysis shows that 11 800 hours of continuous operation at high temperature cannot remove stress undulation introduced by nor‐planar interface but can make max value of Sn and St decrease around 30%.