THE THERMAL-CONDUCTIVITY AND POROUS STRUCTURE OF CHAR PARTICLES

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.