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.
