| The solid oxide fuel cell is one of the most promising means for direct conversion of chemical to electrical energy and with its high temperature waste heat there are multiple cogeneration applications. The problem is that no models have been created that accurately scale up results from a single cell to a stack module and finally to a system configuration. Another problem is that all present single cell models at some point use data obtained by reverse curve fitting empirical performance results. These issues lead to the motivation for this research.; To further unite these different modeling levels, three models were created for the tubular solid oxide geometry, each representing a different stage of development. The first model was an integrated electrochemical and thermal model of a single solid oxide fuel cell tube. This model accurately predicted the power and current density of a single cell under multiple design parameters. This model allowed for the use of natural gas, and not simply hydrogen, as the fuel and determined the probability of carbon formation under the operating conditions imposed by the use of a normal hydrocarbon fuel. The results from this model agreed well with field data from a 3 kW test module run at Osaka Gas in Japan.; The next level of modeling performed simulated the performance of a power module, or 'stack'. To date, no researcher has generated any true stack models. This model not only shows that single cell results cannot be multiplied linearly to produce stack results, but it also addresses the issues of off-design performance. Whether a cell becomes open or shorts the circuit, a decrease in power will result which is a conclusion that is not easily determined from a single cell model.; The final stage of modeling was the prediction of solid oxide fuel cell performance in a power system configuration. Building on the results generated from the single cell and stack models, performance curves were developed for a solid oxide fuel cell power module. These performance curves address issues such as power output, exhaust stream temperatures, and exhaust stream compositions. By utilizing these curves, a design engineer can now determine the effects of placing a solid oxide fuel cell power module in an overall power system. |
