A Systematic Parametric Study of Porous Media Combustion-Based Thermophotovoltaic Energy Conversion

Thermophotovoltaic (TPV) systems represent an indirect, and potentially highly efficient means to convert primary energy into electricity. TPV devices can be designed to be portable since they are able to provide high power density using a variety of heat sources, such as hydrocarbon fuel, solar, nuclear and waste heat. Moreover, efficiencies over 60% can (theoretically) be achieved, which makes this technology quite attractive for military, space, and other remote electrical generation applications. Since TPV systems require high driving temperatures, one of the major technical challenges is reducing waste heat. For hydrocarbon fuel-drive TPV systems, a large portion of the input energy (primarily the chemical energy of the fuel) is typically lost through convection in the flue gases. This can be overcome, to some extent, by using porous media combustion (PMC) which is characterized by intense heat exchange from the combustion gases to the solid media, enabling higher temperatures at outer (actively radiating) surface of the solid matrix. If designed well, the porous media matrix surface can be effectively used as the emitter for the TPV system. In this study, a systematic analysis of this type of innovative system is presented, which includes the full, coupled governing equations of a PMC-TPV system. To help identify feasible systems for future development, this study investigates, in detail, how the porosity, the emitter and (or) filter optical performance and the PV cell type affect the performance of both the PMC and the TPV. The PMC-TPV system is modelled by solving the heat transfer governing equations using finite difference programmed in Fortran90, and by using the ideal two-band-model for TPV. The results indicate that using porous media increases the temperature of the solid media and hence (ultimately) delivers a higher fraction of the primary energy to the PV cells, leading to higher overall efficiency. In combination with re-cycling and use of the heat carried by the combustion gases, this innovative PMC-TPV concept could significantly increase the overall performance as compared to previously reported TPV studies