Temperature distribution profiles inside biomass under dielectric breakdown conditions

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Under the effect of a sufficiently strong electric field, all materials suffer from a form of breakdown, which involves the flow of current through them. Although wood is sometimes utilized as an electrical insulator, it is also subject to breakdown when exposed to high electric fields. In general, dielectric breakdown is considered a negative effect for electrically insulating materials since it implies the loss of insulating properties of the material. However, the high temperatures generated inside the material can be used as an efficient way to induce the thermo-chemical decomposition of biomass with the purpose of sustainable energy generation. A mathematical model of the dynamics of temperature and electric field inside a small piece of biomass is developed to study temperature distribution and thermal instability growth under thermal dielectric breakdown conditions. A two-dimensional model is implemented for different electric field strengths with biomass dielectric properties obtained from the literature. Temperature, current and electric potential distributions have been analyzed and reported for several cases. The temperature development over time has also been analyzed and reported. The results show that higher voltages lead to almost instantaneous thermal breakdown. Similar results are obtained for AC voltage when the frequency is decreased. These conditions are desired for efficient gasification of biomass.