EFFECTIVE SPECIFIC HEAT OF WOOD BRIQUETTES.

The effective specific heat of wood briquettes was determined by using a mathematical model developed for bulk pellets/briquettes and by measurements made in parallel and perpendicularly to the briquettes axis in the range of moisture contents below and above equilibrium moisture content. The mathematical model was based on the assumption that bulk pellets/briquettes are a porous system, consisting of solid particles and gas, with effective thermal properties. The model applied to the briquettes with the moisture content above the equilibrium moisture content is different to that applied to the briquettes with the moisture content below equilibrium moisture content, since alongside with wood fiber swelling, the magnitude and the number in the voids between chips increases. That is why, the briquettes density decreased in this moisture content range. New equations are proposed for this moisture content range considering a larger wood cell lumen that includes the chips interspaces. Experiments were performed at the temperature of briquettes ranging from 19 to 24°C and the average moisture content from 0 to 22.7%, dry basis. When increasing the moisture content above equilibrium moisture content, the briquettes expanded due to fiber swelling, but also due to the increase in the magnitude and number of chips interspaces. Both swelling and increase in briquettes voids influenced the effective specific heat. [ABSTRACT FROM AUTHOR]