Thermal System Modeling for Lunar and Martian Surface Regenerative Fuel Cell Systems

The Advanced Exploration Systems (AES) Advanced Modular Power Systems (AMPS) Project is investigating different power systems for various lunar and Martian mission concepts. The AMPS Fuel Cell (FC) team has created two system-level models to evaluate the performance of regenerative fuel cell (RFC) systems employing different fuel cell chemistries. Proton Exchange Membrane fuel cells PEMFCs contain a polymer electrolyte membrane that separates the hydrogen and oxygen cavities and conducts hydrogen cations (protons) across the cell. Solid Oxide fuel cells (SOFCs) operate at high temperatures, using a zirconia-based solid ceramic electrolyte to conduct oxygen anions across the cell. The purpose of the modeling effort is to down select one fuel cell chemistry for a more detailed design effort. Figures of merit include the system mass, volume, round trip efficiency, and electrolyzer charge power required. PEMFCs operate at around 60 degrees Celsius versus SOFCs which operate at temperatures greater than 700 degrees Celsius. Due to the drastically different operating temperatures of the two chemistries the thermal control systems (TCS) differ. The PEM TCS is less complex and is characterized by a single pump cooling loop that uses deionized water coolant and rejects heat generated by the system to the environment via a radiator. The solid oxide TCS has its own unique challenges including the requirement to reject high quality heat and to condense the steam produced in the reaction. This paper discusses the modeling of thermal control systems for an extraterrestrial RFC that utilizes either a PEM or solid oxide fuel cell

Solid Oxide Fuel Cell Modeling

This paper discusses the modeling of a solid oxide fuel cell using both lumped and distributed modeling approaches. In particular, the focus of this paper is on the development of a computationally efficient lumped-parameter model for real-time emulation and control. The performance of this model is compared with a detailed distributed model and experimental results. The fundamental relations that govern a fuel cell operation are utilized in both approaches. However, the partial pressure of the species (fuel, air, and water) in the distributed model is assumed to vary through the length of the fuel cell. The lumped model approach uses the partial pressure of the species at the exit point of the fuel cell. The partial pressure of the species is represented by an equivalent RC circuit in the lumped model

Space power systems technology

Reported here is a series of studies which examine several potential catalysts and electrodes for some fuel cell systems, some materials for space applications, and mathematical modeling and performance predictions for some solid oxide fuel cells and electrolyzers. The fuel cell systems have a potential for terrestrial applications in addition to solar energy conversion in space applications. Catalysts and electrodes for phosphoric acid fuel cell systems and for polymer electrolyte membrane (PEM) fuel cell and electrolyzer systems were examined

Solid oxide fuel cell microstructure and performance modeling

The fundamental operation of Solid Oxide Fuel Cells (SOFCs) relies on the liberation of electrons at reaction sites within porous electrodes. These reaction sites, or triple-phase boundary (TPB) points, must be percolated to allow for reactants and products to flow to and from these sites. Due to the fact that electrochemical reactions in composite electrodes are dependent on the presence of TPB sites, a direct link exists between SOFC electrode microstructures and electrochemical performance. Recently, the development of advanced tomography and imaging techniques has allowed for this link to be better understood and quantified. This thesis presents the development of a novel effective conductivity model (ResNet) for 3D composite, anisotropic microstructures in the context of Ni-YSZ electrode characterization. The ResNet model is first used to derive the effective conductivity of simple structures, conductivities of which can be found in the literature. Good agreement was found in this initial study. The model is then used to compute the effective conductivities of more complex synthetic microstructures, comparing model outputs to those given by COMSOL Multiphysics, a commercial modeling platform. It was found that for a sufficiently high resolution, both models converge to the same results. Varying the discretization resolution allowed for an optimum discretization resolution to be determined, based on the mean particle size used for fabrication. The introduction of Volume Elements into the ResNet model is then presented, and the optimum aggregation resolution is extracted from a set of simulations. This allowed for the analysis of a real SOFC anode microstructure to be carried out, and underlined the importance of selecting a microstructure sample of a size that can be considered representative of the entire electrode. After a series of simulations on synthetically generated microstructures, several microstructural parameters are varied to carry out a sensitivity analysis on the effective conductivities and current densities of the microstructures. This analysis yielded an optimum ratio of 7 particles per structure length for microstructure size representativeness. Using the parameters derived from the studies presented in this thesis, the effective conductivities of two experimental Ni/10ScSZ anodes are extracted using the ResNet model and compared to their experimentally determined values. Excellent agreement was obtained, validating the ResNet model and associated work. In a final instance, it was shown that using the ResNet model in the electronic phase in conjunction with the VOF model developed by Golbert et al. does not yield a noticeable difference in current density output when compared to results obtained without using the ResNet. When applied to the ionic phase however, using the ResNet model in conjunction with the VOF model is found to predict as much as 50% lower computed area current densities than when the volume fraction average model is used.Open Acces

Thermodynamic modeling of La2O3-SrO-Mn2O3-Cr2O3 for solid oxide fuel cell applications

The thermodynamic La-Sr-Mn-Cr-O oxide database is obtained as an extension of thermodynamic descriptions of oxide subsystems using the calculation of phase diagrams approach. Concepts of the thermodynamic modeling of solid oxide phases are discussed. Gibbs energy functions of SrCrO4, Sr2.67Cr2O8, Sr2CrO4, and SrCr2O4 are presented, and thermodynamic model parameters of La-Sr-Mn-Chromite perovskite are given. Experimental solid solubilities and nonstoichiometries in La1−x Sr x CrO3−δ and LaMn1−x Cr x O3−δ are reproduced by the model. The presented oxide database can be used for applied computational thermodynamics of traditional lanthanum manganite cathode with Cr-impurities. It represents the fundament for extensions to higher orders, aiming on thermodynamic calculations in noble symmetric solid oxide fuel cell

Coupled Transport Effects in Solid Oxide Fuel Cell Modeling

With its outstanding performance characteristics, the SOFC represents a promising technology for integration into the current energy supply system. For cell development and optimization, a reliable quantitative description of the transport mechanisms and the resulting losses are relevant. The local transport processes are calculated by a 1D model based on the non-equilibrium thermodynamics (NET). The focus of this study is the mass transport in the gas diffusion layers (GDL), which was described as simplified by Fick’s law in a previously developed model. This is first replaced by the Dusty-Gas model (DGM) and then by the thermal diffusion (Soret effect) approach. The validation of the model was performed by measuring U, j-characteristics resulting in a maximum deviation of experimental to simulated cell voltage to up to 0.93%. It is shown that, under the prevailing temperature, gradients the Soret effect can be neglected, but the extension to the DGM has to be considered. The temperature and heat flow curves illustrate the relevance of the Peltier effects. At T = 1123.15 K and j = 8000 A/m2, 64.44% of the total losses occur in the electrolyte. The exergetic efficiency for this operating point is 0.42. Since lower entropy production rates can be assumed in the GDL, the primary need is to investigate alternative electrolyte materials. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

A Process Based Cost Model for Multi-Layer Ceramic Manufacturing of Solid Oxide Fuel Cells

Planar Solid Oxide Fuel Cell manufacturing can be considered in the pilot plant stage with efforts driving towards large volume manufacturing. The science of the solid oxide fuel cell is advancing rapidly to expand the knowledge base and use of material combinations and layer forming methods for the unit cell. Few of the many processing methods, over 15, reported in literature for layer formation are used today in high volume manufacturing. It is difficult to establish future market demand and cost levels needed to plan a course of action today. The need to select amongst different designs, materials and processes will require a tool to aid in these decisions. A modeling tool is presented to robustly compare the various process combinations and manufacturing variable to make solid oxide fuel cells in order to identify key trends prior to making strategic investment decisions. The ability to accurately forecast investment requirements and manufacturing cost for a given high volume manufacturing (HVM) process based on expected volume is critical for strategic decisions, product placement and investor communications. This paper describes the use of an updated process based cost model that permits the comparison of manufacturing cost data for various process combinations, production volumes, and electrolyte layer thickness tolerances. The effect of process yield is addressed. Processing methods discussed include tape casting, screen printing and sputtering

A Process Based Cost Model for Multi-Layer Ceramic Manufacturing of Solid Oxide Fuel Cells

Planar Solid Oxide Fuel Cell manufacturing can be considered in the pilot plant stage with efforts driving towards large volume manufacturing. The science of the solid oxide fuel cell is advancing rapidly to expand the knowledge base and use of material combinations and layer forming methods for the unit cell. Few of the many processing methods, over 15, reported in literature for layer formation are used today in high volume manufacturing. It is difficult to establish future market demand and cost levels needed to plan a course of action today. The need to select amongst different designs, materials and processes will require a tool to aid in these decisions. A modeling tool is presented to robustly compare the various process combinations and manufacturing variable to make solid oxide fuel cells in order to identify key trends prior to making strategic investment decisions. The ability to accurately forecast investment requirements and manufacturing cost for a given high volume manufacturing (HVM) process based on expected volume is critical for strategic decisions, product placement and investor communications. This paper describes the use of an updated process based cost model that permits the comparison of manufacturing cost data for various process combinations, production volumes, and electrolyte layer thickness tolerances. The effect of process yield is addressed. Processing methods discussed include tape casting, screen printing and sputtering

A New Inverter for Improved Fuel Cell Performance in Grid-Tied Application

The interconnection of a solid oxide fuel cell (SOFC) with the power conditioning units vis-à-vis a DC/DC converter and a DC/AC inverter for interfacing with the utility grid is presented. Fuel cells operate at low voltages and hence need to be boosted and inverted in order to be connected to the grid. The fuel cell and the DC/DC converter modeling are briefly explained. The methodology and the controller design for the control of power flow from the fuel cell to the utility grid are discussed. Power characteristics of the DC/AC inverter are compared with the characteristics of the DC/DC converter and the fuel cell. Fuel cells have slow response time which prevents it from grid-tie applications. Simulations validate the improvement in the response when the power conditioning unit is connected

Energy and exergy analysis of fuel cells: a review

In this paper, the fundamental overview of theoretical and practical aspects of thermodynamics analysis for mainly used fuel cells (FCs) are presented. The FC converts the chemical energy of fuel (normally hydrogen) directly into electrical energy resulting heat and liquid water as a waste products. In first part, governing equation of mass, energy, entropy and exergy are presented according to first law of thermodynamics (FLT) and second law of thermodynamics (SLT), more specifically energy and exergy analysis are covered for fuel cell system. Basic criteria of energy and exergy analysis of flowing and non-flowing system, energy and exergy efficiencies, analysis procedure and models of reference environment are discussed in detail. In the second part, electrochemical reactions and thermodynamics modeling of proton exchange membrane or polymer electrolyte membrane fuel cell (PEMFC), solid oxide fuel cell (SOFC), and molten carbonate fuel cell (MCFC) are presented