Two different methods are considered for the determination of the ther
mal conductivity of small particles (50-300 mu m) of char. Both method
s are based on imposing a temperature gradient on a suspended particle
. In the first, the thermal conductivity is obtained from measuring th
e photophoretic force induced by laser radiation on a suspended partic
le. Three patterns of behavior of the thermal conductivity during burn
ing were observed: (a) a significant decrease of the thermal conductiv
ity at low conversions, (b) a moderate change at intermediate conversi
ons, and (c) a rise at high conversions. The observed changes of therm
al conductivity are used to gain insights into the evolution of the po
rous structure during oxidation. The second method is based on a compa
rison of the shrinkage under oxidation in regime I of evenly heated pa
rticles with those that are unevenly heated. The method also supports
previous models and observations of shrinkage of highly porous chars i
n regime I. The two methods agree well for the thermal conductivity of
highly porous chars. (C) 1998 by The Combustion Institute.