Specific heat and thermal conductivity of softwood bark and softwood char particles

Very few data exist regarding the thermal properties of softwood bark and therein derived softwood chars. This work describes the measurement of specific heat and particle thermal conductivity of softwood (SW), softwood bark (SB) and therein derived softwood char (SC). Differential scanning calorimetery (DSC) was used to measure the specific heat. At 313 K, the measured specific heat was found to be 1172, 1364 and 768 J kg⁻¹ K⁻¹ for SW, SB and SC, respectively. The specific heat of SW and SB increased linearly from 1172 to 1726 and 1364 to 1777 J kg⁻¹ K⁻¹, respectively, with an increase in temperature from 313 to 413 K. With an increase in temperature from 313 to 713 K, the specific heat of SC doubled from 768 to 1506 J kg⁻¹ K⁻¹ and followed a polynomial relationship with temperature. A modified Fitch apparatus was constructed, calibrated and used for measurement of particle conductivity of SW, SB and SC. The particle thermal conductivity of SB was found to be twice that of SC, i.e. 0.2050 and 0.0946 W m⁻¹ K⁻¹, respectively, at 310 K. The particle thermal conductivity of SW, SB and SC followed a linear increase with temperature.     

Predicting the effective thermal conductivity of polydispersed beds of softwood bark and softwood char

In this paper, the effective thermal conductivity (ETC) of softwood bark and softwood char particle beds which are highly polydispersed has been studied theoretically and experimentally. Use of the linear packing theory and unit cell model of heat conduction enabled to express ETC of polydisperded beds as a function of particle size distribution. Each of the softwood bark and softwood char samples were sieved into seven fractions. The initial porosity and binary packing size ratio of the particles have been characterized as a function of mean sieve size. ETC of polydispersed beds of bark and char has been predicted as a function of particle size distribution. Model predictions were in good agreement with the experimental measurements. The proposed approach can be used to predict the ETC of any size distribution of softwood bark and softwood char beds without measuring the in situ bed porosity.