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Thermal stress assessment inside steam reactor to prevent future damage is necessary due to the high temperatures of the hot gases used for endothermic reactions. This study combined solid mechanics equations, mass, energy, and fluid flow to develop a model could describe the thermal stress and deformation inside hydrocarbon-steam reactors. The model results were validated and compared to experimental results over a range of operating temperatures with an error of less than 2%. The results show that the temperature of the inlet gas in the reactor bed decreases in the early stages of the reactor, then increases later causing simultaneous gas velocity increase proportional with the temperature. The study shows that both hot gases temperature and gas velocity could control endothermic reactions rates. Where, at T = 900 K of inlet hot gases, full propane consumption is achieved at the reformer outlet and the velocity could reach twice that of the inlet. Furthermore, at a certain temperature, the non-uniform thermal stress distribution within the steam-propane reformer unit can cause deflections, which lead to cracks. [Display omitted] • The thermal stress inside steam reactors was described by a novel model. • The study combined solid mechanics equations with mass, energy, and fluid flow. • Inlet gas velocity inside reactor increase proportionally coincide with temperature. • Both temperature and velocity of hot gases can affect endothermic reactions. • In a certain temperature range, thermal stress causes cracks inside a reactor. [ABSTRACT FROM AUTHOR]

Mechanical degradation is often studied in single-cell proton exchange membrane (PEM) fuel cell stack models in assembly process. This however, can increase substantially when moving from assembly process to operation conditions; and also from single-cell to multiple cells. In this study, PEM fuel cell stacks consisting of 1, 3, and 5 cells with an active area of 25 cm² per cell have been simulated in operation mode. Three dimensional non-isothermal solid mechanics-CFD model of a PEM fuel cell stack, integrating the real full scale geometry of all components have been used to study the influence of the number of cells on the stress distribution in a running PEM fuel cell stack. Simulation of a running multi cells stack was successful and has not been previously seen in literatures work. The results showed that the center of the electrode tends to un-displacement. This un-displacement area increases by increasing the clamping torque. The deformations in the stack components during operation were about ten times higher than during assembly process. During assembly process, the increasing in the number of cells increases the total displacement distribution. These status were different during operation, the increasing in the number of cells enhances the uniformity of the total displacement. Increasing the number of cells enhances the uniformity of the mechanical state. The better contact pressure homogeneity was obtained with the greater number of cells and leads to the lower contact resistance. In general, the results showed lower stresses values with lower distributions and more homogeneous and uniformity in the stack that consisting of multi cells. [ABSTRACT FROM AUTHOR]

This paper investigates mechanical and thermal stresses that arise in the exhaust valve due to its operating with and without thermal coating layer (ceramic) on face exhaust valve. Three dimensional models of an exhaust valve four cylinders, four stroke, and direct injection diesel engine have been presented. The governing equations were discretized using a finite-volume method (FVM) and solved using multi-physics COMSOL® package Version 5. The engine's exhaust valve crown is coated with various materials in different thermal conductivity such as (Gd2Zr2O7), over a 150µm thickness of bond coat. The maximum thickness of coating is about 300 µm. Results indicate that after creating a coating layer exhaust valve the temperature distribution, temperature gradients distribution, von-Mises stress distribution and displacement distribution are decreased. [ABSTRACT FROM AUTHOR]

A three-dimensional, multi-phase, non-isothermal computational fluid dynamics model of a proton exchange membrane fuel cell has been used and developed to investigate the hygro and thermal stresses in polymer membrane, which developed during the cell operation due to the changes of temperature and relative humidity. The behaviour of the membrane during operation of a unit cell has been studied and investigated under real cell operating conditions. The results show that the non-uniform distribution of stresses, caused by the temperature gradient in the cell, induces localized bending stresses, which can contribute to delaminating between the membrane and the gas diffusion layers. These stresses in the membrane may explain the occurrence of cracks and pinholes in the membrane under steady-state loading during regular cell operation. The results show that the maximum displacements in membrane for the low, intermediate and high load conditions were 2.58, 2.66, and 2.78 µ m respectively. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive three-dimensional, multi-phase, non-isothermal model of a Proton Exchange Membrane (PEM) fuel cell that incorporates significant physical processes and key parameters affecting the fuel cell performance. The model construction involves equations derivation, boundary conditions setting, and solution algorithm flow chart. Equations in gas flow channels, gas diffusion layers (GDLs), catalyst layers (CLs), and membrane as well as equations governing cell potential and hygro-thermal stresses are described. The algorithm flow chart starts from input of the desired cell current density, initialization, iteration of the equations solution, and finalizations by calculating the cell potential. In order to analyze performance, water and thermal distribution, and mechanical related failure in the cell, the equations are solved using a computational fluid dynamic (CFD) code. Performance analysis includes a performance curve which plots the cell potential (Volt) against nominal current density (A/cm²) as well as losses. Velocity vectors of gas and liquid water, liquid water saturation, and water content profile are calculated. Thermal distribution is then calculated together with hygro-thermal stresses and deformation. The CFD model was executed under boundary conditions of 20°C room temperature, 35% relative humidity, and 1 MPA pressure on the lower surface. Parameters values of membrane electrode assembly (MEA) and other base conditions are selected. A cell with dimension of 1 mm x 1 mm x 50 mm is used as the object of analysis. The nominal current density of 1.4 A/cm² is given as the input of the CFD calculation. The results show that the model represents well the performance curve obtained through experiment. Moreover, it can be concluded that the model can help in understanding complex process in the cell which is hard to be studied experimentally, and also provides computer aided tool for design and optimization of PEM fuel cells to realize higher power density and lower cost. [ABSTRACT FROM AUTHOR]

Durability is one of the most critical remaining issues impeding successful commercialization of broad PEM fuel cell transportation energy applications. Automotive fuel cells are likely to operate with neat hydrogen under load-following or load-levelled modes and be expected to withstand variations in environmental conditions, particularly in the context of temperature and atmospheric composition. In addition, they are also required to survive over the course of their expected operational lifetimes i.e., around 5,500 hrs, while undergoing as many as 30,000 startup/shutdown cycles. The damage mechanisms in a PEM fuel cell are accelerated by mechanical stresses arising during fuel cell assembly (bolt assembling), and the stresses arise during fuel cell running, because it consists of the materials with different thermal expansion and swelling coefficients. Therefore, in order to acquire a complete understanding of the damage mechanisms in the membrane, mechanical response under steady-state hygro-thermal stresses should be studied under real cell operating conditions and in real cell geometry (three-dimensional). In this work, full three-dimensional, non-isothermal computational fluid dynamics model of a PEM fuel cell has been developed to simulate the stresses inside the PEM fuel cell, which are occurring during fuel cell assembly (bolt assembling), and the stresses arise during fuel cell running due to the changes of temperature and relative humidity. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model. In addition, the temperature and humidity dependent material properties are utilize in the simulation for the membrane. The model is shown to be able to understand the many interacting, complex electrochemical, transport phenomena, and stresses distribution that have limited experimental data. This model is used to study and analyse the effect of operating parameters on the mechanical behaviour of PEM. The analysis helped identifying critical parameters and shed insight into the physical mechanisms leading to a fuel cell durability for vehicular applications. [ABSTRACT FROM AUTHOR]

Damage mechanisms in a proton exchange membrane fuel cell are accelerated by mechanical stresses arising during fuel cell assembly (bolt assembling), and the stresses arise during fuel cell running, because it consists of the materials with different thermal expansion and swelling coefficients. Therefore, in order to acquire a complete understanding of the mechanical behaviour of the catalyst layers during regular cell operation, mechanical response under steady-state hygro-thermal stresses should be studied under real cell operating conditions and in real cell geometry (three-dimensional). In this work, full three-dimensional, non-isothermal computational fluid dynamics model of a PEM fuel cell has been developed to investigate the behaviour of the cathode and anode catalyst layers during the cell operation. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model. In addition, the temperature and humidity dependent material properties are utilize in the simulation for the membrane. The model is shown to be able to understand the many interacting, complex electrochemical, transport phenomena, and deformation that have limited experimental data. [ABSTRACT FROM AUTHOR]

Damage mechanisms in a proton exchange membrane (PEM) fuel cell are accelerated by mechanical stresses arising during fuel cell assembly (bolt assembling), and the stresses arise during fuel cell running, because it consists of the materials with different thermal expansion and swelling coefficients. Therefore, in order to acquire a complete understanding of the damage mechanisms in the membrane and gas diffusion layers, mechanical response under steady-state hygro-thermal stresses should be studied under real cell operating conditions and in real cell geometry (three-dimensional). In this work, full three-dimensional, non-isothermal computational fluid dynamics model of a PEM fuel cell has been developed to simulate the hygro and thermal stresses in PEM fuel cell, which are occurring during the cell operation due to the changes of temperature and relative humidity. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model. The mechanical behaviour of the membrane, catalyst layers, and gas diffusion layers during the operation of a unit cell has been studied and investigated. The model is shown to be able to understand the many interacting, complex electrochemical, transport phenomena, and stresses distribution that have limited experimental data. The results show that the non-uniform distribution of stresses, caused by the temperature gradient in the cell, induces localized bending stresses, which can contribute to delaminating between the membrane and the gas diffusion layers. These results may explain the occurrence of cracks and pinholes in the membrane during regular cell operation. This model is used to study the effect of operating, design, and material parameters on fuel cell hygro-thermal stresses in polymer membrane, catalyst layers, and gas diffusion layers. Detailed analyses of the fuel cell durability under various operating conditions have been conducted and examined. The analysis helped identifying critical parameters and shed insight into the physical mechanisms leading to a fuel cell durability under various operating conditions. Optimization study of a PEM fuel cell durability has been performed. To achieve long cell life, the results show that the cell must be operate at lower cell operating temperature, higher cell operating pressure, higher stoichiometric flow ratio, and must have higher GDL porosity, higher GDL thermal conductivity, higher membrane thermal conductivity, narrower gases channels, thicker gas diffusion layers, and thinner membrane. In these optimum conditions, the maximum deformation (displacement) reduction by about 50% than the base case operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: A three-dimensional, multi-phase, non-isothermal computational fluid dynamics model of a proton exchange membrane fuel cell has been developed and used to investigate the displacement, deformation, and stresses inside the whole cell, which developed during the cell operation due to the changes of temperature and relative humidity. The behaviour of the fuel cell during operation has been studied and investigated under real cell operating conditions. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model for a complete cell with both the membrane-electrode-assembly and the gas distribution flow channels. The results show that the non-uniform distribution of stresses, caused by the temperature gradient in the cell, induces localized bending stresses, which can contribute to delaminating between the membrane and the gas diffusion layers. The non-uniform distribution of stresses can also contribute to delaminating between the gas diffusion layers and the channels, especially in the cathode side. These stresses may explain the occurrence of cracks and pinholes in the fuel cells components under steady-state loading during regular cell operation, especially in the high loading conditions. [Copyright &y& Elsevier]