A parallel cellular automata Lattice Boltzmann Method for convection-driven solidification

This article presents a novel coupling of numerical techniques that enable three-dimensional convection-driven microstructure simulations to be con- ducted on practical time scales appropriate for small-size components or experiments. On the microstructure side, the cellular automata method is efficient for relatively large-scale simulations, while the lattice Boltzmann method provides one of the fastest transient computational fluid dynamics solvers. Both of these methods have been parallelized and coupled in a single code, allowing resolution of large-scale convection-driven solidification problems. The numerical model is validated against benchmark cases, extended to capture solute plumes in directional solidification and finally used to model alloy solidification of an entire differentially heated cavity capturing both microstructural and meso-/macroscale phenomena

Status and market opportunities of solid oxide fuel cells based cogeneration systems

The most sustainable technology for conversion of natural gas into electricity and heat in the low to medium power levels, is a Solid Oxide Fuel Cell (SOFC) based Combined Heat and Power (CHP) unit. Electrical efficiencies of up to 60 % and total efficiencies of more than 90 % down to electrical powers of only 1 kW, makes these systems attractive for applications in varying power classes. The range between 10 and 50 kWel is especially promising for competition with conventional CHP units and the electrical grid. Different system layouts options exist to meet the technical requirements of specific applications as well as the cost targets for a early market entry. Main distinguishing features are the method of processing natural gas into a hydrogen-rich reformate (i.e. partial oxidation vs. steam reforming) and the cell stack technology used. As a result, electrical efficiencies, system complexity, and costs vary. Applied to cogeneration, the overall efficiency has the ma in impact on the profitability of the CHP unit, provided there is existence of a sufficient heat demand. Electrical efficiencies are dominated by power to heat ratios or the utilization factor, this means the number of operation hours needs to be increased. The calculation of CHP cost saving potentials is impeded strongly by application dependent parameters like profiles of heat and electricity demand as well as local gas and electricity prices. For Germany, payback periods can be calculated since typical load profiles of single and multi-family homes are available. Here, the choice of SOFC system layout depends on the economic viability of electricity feed-in to the grid. If funding is available, high electrical efficiencies are clearly favored. This is also valid for applications where only domestic hot water heating is required. Small base load power generators are profitable provided that the system cost targets can be met. Larger SOFC system in a power range of >100 kWel face a strong compe

Design, Construction, and Testing of a Gasifier-Specific Solid Oxide Fuel Cell System

This paper describes the steps involved in the design, construction, and testing of a gasifier-specific solid oxide fuel cell (SOFC) system. The design choices are based on reported thermodynamic simulation results for the entire gasifier- gas cleanup-SOFC system. The constructed SOFC system is tested and the measured parameters are compared with those given by a system simulation. Furthermore, a detailed exergy analysis is performed to determine the components responsible for poor efficiency. It is concluded that the SOFC system demonstrates reasonable agreement with the simulated results. Furthermore, based on the exergy results, the components causing major irreversible performance losses are identified