Improvement of the internal reforming of metal-supported SOFC at low temperatures

Automotive Solid oxide fuel cells (SOFCs) require improvements in mechanical robustness, power generation at low temperatures, and system compactness. To address these issues, we attempt to improve the internal reformation of metal-supported SOFCs (MS-SOFCs) via catalyst infiltration. After introducing nickel/gadolinium-doped ceria (Ni/GDC) nanoparticles, power densities of 1.16 Wcm⁻² with hydrogen (3%H₂O) and 0.85 Wcm⁻² with methane (Steam-to-Carbon ratio, S/C = 1.0) are obtained at 600 °C, 0.7 V. This is the highest performance achieved in previous studies on MS-SOFCs. Internal reforming with various hydrocarbon is also demonstrated. In particular 0.64 Wcm⁻² at 600 °C, 0.7 V is obtained when the fuel is iso-octane. We develop a numerical model to separately analyze reforming and electrochemical reaction. Catalyst infiltration dramatically increases the number of active sites for steam reforming. In addition, ruthenium/gadolinium-doped ceria (Ru/GDC) should be suitable as a catalyst metal at low temperatures because of the lower activation energy of steam reforming.     

Estimation of Groundwater Aquifer Formation-strength Parameters from Geophysical Well Logs: The Southwestern Coastal Area of Yun-Lin,Taiwan

Abstract

The purpose of this study is to estimate groundwater aquifer formation-strength parameters including shear modulus, bulk modulus, Poisson's ratio, and Young's modulus by using geophysical well logs. A new dispersed-shale index equation was developed by using the natural gamma-ray log and the compensated formation density log to solve a confusing problem of the compaction factor setting in the calculation of sonic porosity for an unconsolidated groundwater aquifer. A useful Poisson's ratio estimation method was employed to estimate groundwater aquifer formation-strength parameters when shear-wave transit time data is lacking in groundwater wells. Hydrogeologic parameters are characterized in estimating formation-strength parameters. Five wells in the southwestern coastal area of Yun-Lin, Taiwan, were logged, and four shallow aquifers were identified from log-derived hydrogeologic characteristics less than 200 m in depth. The formation-strength parameters for aquifers between 310 and 500 m in depth were calculated in two wells because complete formation density and compressional-wave transit time data were available. The results of the aquifer's formation-strength parameters demonstrate that both shear modulus, ranging from 0.15 to 0.42 * 10⁶ psi, and Young's modulus, ranging from 0.40 to 1.07 * 10⁶ psi, increase with depth, whereas bulk compressibility, ranging from 1.2 to 2.6 * 10^?6 psi^?1, decreases with increasing depth.     

A novel constitutive stress-strain law for compressive deformation of the gas diffusion layer

Substantial compressive deformation occurs in the gas diffusion layer (GDL) under the pressure applied during the fuel cell assembly. The GDL deformation has a direct impact on the efficiency and performance of the fuel cell since it leads to the alteration of the GDL microstructure and porosity. This makes the accurate characterization of the GDL compressive behavior crucial for analyzing the fuel cell performance and its optimal design. In this paper, analytical, experimental, and numerical methods have been employed to comprehensively study the constitutive law of the GDL under compression. Starting from the recently developed stress-density relations, the constitutive stress-strain equations are derived for the GDL and the relation between the stress-density and stress-strain laws are revealed. Experimental compression tests have been performed on GDL samples and the capability of the proposed constitutive law in capturing the real behavior of the material has been proved. It has been observed that the simplifying assumption of constant zero Poisson's ratio in the through-plane direction made in many previous studies cannot accurately represent the GDL material behavior and a modification is proposed. The developed constitutive law has been successfully implemented in a finite element model of the GDL-bipolar plate assembly in the fuel cell structure and the variations of the GDL porosity, density, and through-plane Young's modulus and Poisson's ratio have been investigated for different vertical displacements of the bipolar plate.     

Elastic properties of Sr- and Mg-doped lanthanum gallate at elevated temperature

The elastic moduli, i.e., Young’s modulus, shear modulus and Poisson’s ratio, of a sintered La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ bulk have been experimentally determined in the temperature range from room temperature to 1373 K using a resonance technique. Anomalous elastic properties were observed over a wide temperature range from 473 to 1173 K. In the results for internal friction and in X-ray diffraction measurements at elevated temperature, two varieties of structural changes were seen in La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ in the examined temperature range. The results agreed with the findings of a previous crystallographic study of the same composition system by Slater et al. In addition, the temperature range in which a successive structural change occurred in La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ was the same as that exhibiting the anomalous elastic properties. Taking all the results together, it can be inferred that the successive structural change in the significant temperature range is responsible for the elastic property anomaly of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ.     

Elastic properties of perovskite-type hydride NaMgH3 for hydrogen storage

Mechanical properties of NaMgH₃ were investigated using the norm-conserving pseudopotentials and plane waves (PP–PW) within the general gradient approximation (GGA) in the frame of density functional theory (DFT). The elastic constants of NaMgH₃ were calculated for the first time. The NaMgH₃ compound is found to be mechanically stable at ambient pressure. The linear bulk modulus and the bulk modulus along crystallographic axes of single crystals have been derived using elastic constants. The calculated linear bulk moduli are found to be in good agreement with the theoretical value reported in the literature. Shear and Young's moduli as well as Poisson's ratio for ideal polycrystalline NaMgH₃ are also calculated. According to the obtained results, NaMgH₃ can be classified as brittle material. The shear anisotropic factors and the elastic anisotropy are also discussed. A Debye temperature of 648 K was also determined using theoretical elastic constants.     

Modeling and analysis of a model solid oxide fuel cell running on low calorific value coal gases

Solid oxide fuel cell (SOFC) is a device that produces electricity directly from oxidizing a fuel. Some of the advantages are operating at high temperatures and converting various hydrocarbon fuels directly into electricity. This study investigates the parameters that influence the cell characteristics of a cathode-supported SOFC (CSSOFC) model. Numerical modeling has been performed utilizing low calorific value coal gases, generator gas, and water gas by deriving an SOFC model based on finite element method (FEM). The effects of fuel compositions, temperature, pressure, and porosity on the performance of the developed SOFC have been examined using COMSOL software. These effects are presented by polarization and power curves. A mathematical model has been developed to determine the performance of a CSSOFC with low calorific value coal gases that were obtained from Turkey/Turk coal. It is predicted that the performance of CSSOFC is higher than that of the electrolyte-supported SOFC (ES-SOFC) for all studied fuels. Besides this, the cost of the cathode supporting materials for high-performance CSSOFC is low. The performance of SOFC using water gas is higher than that of the generator gas. This being maybe the hydrogen content of the water gas is higher compared with the generator gas. Therefore, the result confirmed that low calorific value coal gases could be used in SOFCs as a source of fuel. Moreover, the power of the CSSOFC increases as the pressure, temperature, and hydrogen content increase.     

Axisymmetric and One-Dimensional Thermoelastic Fields of Radially Graded Bodies

In this paper, both Young's modulus and Poisson's ratio along with thermal expansion coefficient are allowed to vary across the radius in a solid ring and a curved beam. Effects of non-constant Poisson's ratio on the thermoelastic field in these graded axisymmetric and one-dimensional problems are studied. A governing differential equation in terms of stress function is obtained for general axisymmetric and one-dimensional problems. Two linearly independent solutions in terms of hypergeometric functions are then attained to calculate the stresses and the strains. Using Green's function method, a form of a solution for the stress functions in terms of integral equations for a curved beam and a solid ring are obtained. Specifically, closed form solutions for the stress functions, when Young's modulus and Poisson's ratio are expressed as power law functions across the radius, are calculated. The results show that the effect of varying Poisson's ratio upon the thermal stresses is considerable for the solid ring. In addition, a non-constant Poisson's ratio has significant influences on the thermal strain field in solid rings. The effect of varying Poisson's ratio upon the thermal stresses is negligible for the curved beam. However, non-constant Poisson's ratios have substantial effects on the thermal strain field in curved beams. Finally, the effects of varying Poisson's ratio on the thermal stresses in thick solid rings and curved beams are also investigated.     

Aerodynamic and aeroacoustic performance of airfoils with morphing structures

Aerodynamic and aeroacoustic performance of airfoils fitted with morphing trailing edges are investigated using a coupled structure/fluid/noise model. The control of the flow over the surface of an airfoil using shape optimization techniques can significantly improve the load distribution along the chord and span lengths whilst minimising noise generation. In this study, a NACA 63‐418 airfoil is fitted with a morphing flap and various morphing profiles are considered with two features that distinguish them from conventional flaps: they are conformal and do not rely on conventional internal mechanisms. A novel design of a morphing flap using a zero Poisson's ratio honeycomb core with tailored bending stiffness is developed and investigated using the finite element model. Whilst tailoring the bending stiffness along the chord of the flap yields large flap deflections, it also enables profile tailoring of the deformed structure which is shown to significantly affect airfoil noise generation. The aeroacoustic behaviour of the airfoil is studied using a semi‐empirical airfoil noise prediction model. Results show that the morphing flap can effectively reduce the airfoil trailing edge noise over a wide range of flow speeds and angles of attack. It is also shown that appropriate morphing profile tailoring improves the effect of morphing trailing edge on the aerodynamic and aeroacoustic performance of the airfoil. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of alumina on the curvature, Young's modulus, thermal expansion coefficient and residual stress of planar solid oxide fuel cells

Planar solid oxide fuel cells (SOFCs) are composites consisting of porous and dense functional layers as electrodes and electrolytes, respectively. Because of the thermo-elastic mismatch between the individual layers, residual stresses develop during manufacturing and cause unconstrained cells to warp. The addition of alumina decreases the thermal expansion coefficient (TEC) of the NiO and yttria-stabilized zirconia (YSZ) anode-support material. Correspondingly, the lower TECs have flattened the half cells during fabrication. In addition, the residual stress at room temperature (RT) for samples with more than 4 wt% alumina is only 20% of the residual stress of the samples without alumina, at approximately 100 MPa. The effects of Al₂O₃ on the curvature, Young's modulus, TEC and residual stress of the SOFC with (NiO-YSZ)_1−x(Al₂O₃)_x (x = 1-5 wt%) anode support are discussed in this work.     

Semi-exact solution of elastic non-uniform thickness and density rotating disks by homotopy perturbation and Adomian's decomposition methods. Part I: Elastic solution

In this work, two powerful analytical methods, namely homotopy perturbation method (HPM) and Adomian's decomposition method (ADM), are introduced to obtain distributions of stresses and displacements in rotating annular elastic disks with uniform and variable thicknesses and densities. The results obtained by these methods are then compared with the verified variational iteration method (VIM) solution. He's homotopy perturbation method which does not require a “small parameter” has been used and a homotopy with an imbedding parameter p ∈ [0,1] is constructed. The method takes the full advantage of the traditional perturbation methods and the homotopy techniques and yields a very rapid convergence of the solution. Adomian's decomposition method is an iterative method which provides analytical approximate solutions in the form of an infinite power series for nonlinear equations without linearization, perturbation or discretization. Variational iteration method, on the other hand, is based on the incorporation of a general Lagrange multiplier in the construction of correction functional for the equation. This study demonstrates the ability of the methods for the solution of those complicated rotating disk cases with either no or difficult to find fairly exact solutions without the need to use commercial finite element analysis software. The comparison among these methods shows that although the numerical results are almost the same, HPM is much easier, more convenient and efficient than ADM and VIM.     

Semi-exact solution of non-uniform thickness and density rotating disks. Part II: Elastic strain hardening solution

Analytical solutions for the elastic–plastic stress distribution in rotating annular disks with uniform and variable thicknesses and densities are obtained under plane stress assumption. The solution employs a technique called the homotopy perturbation method. A numerical solution of the governing differential equation is also presented based on the Runge–Kutta's method for both elastic and plastic regimes. The analysis is based on Tresca's yield criterion, its associated flow rule and linear strain hardening. The results of the two methods are compared and generally show good agreement. It is shown that, depending on the boundary conditions used, the plastic core may contain one, two or three different plastic regions governed by different mathematical forms of the yield criterion. Four different stages of elastic–plastic deformation occur. The expansion of these plastic regions with increasing angular velocity is obtained together with the distributions of stress and displacement.