Modelling and measurements of heat transfer in charcoal from pyrolysis of large wood particles

The pyrolysis rate limiting heat transfer properties of charcoal from large wood particles are studied by comparing experiments and simulations of transient heat conduction in large charcoal samples. The interior temperatures in cylindrical charcoal samples of 20 +/- 2 mm radius were measured during heating from room temperature to 700 degrees C in an inert atmosphere. Simulations are performed for two cases of constant material properties and for two cases of temperature dependent specific heat and/or effective thermal conductivity. The material properties of charcoal used in the simulations are found in literature related to modelling of wood pyrolysis. The simulations show that a constant thermal diffusivity of approximately 0.7 mm(2)/s agrees better with measured data than the assumption of temperature dependent material properties. Constant material properties are preferred due to simplicity, although the correct interpretation is that the increase in specific heat and effective thermal conductivity with temperature cancel each other. (C) 2000 Elsevier Science Ltd. All rights reserved.