Predictive Models for the Convective Drying Kinetics of Pinus spp. Energy Wood Chips

The phenomena of capillarity, dipole–dipole attractions, and hydrogen bonding make the application of mass transfer models to predict the drying rate by air convection in wood chips imprecise. So, the modification of these models by tailoring their equations is required. This study aims to adapt theoretical mass transfer models to improve the prediction of drying time for Pinus spp. chips subjected to a known hot air stream with known velocity, temperature, and relative humidity. An experimental device was constructed to control the variables, where the air stream passes vertically through a cylinder filled with wood chips. The tested air velocities ranged between 7 and 10 m/s, with relative humidity between 10 and 30% and temperatures between 40 and 70 °C with 3 and 6 cm chip columns. It was demonstrated that the drying rate of chips in a convective process with air is not constant but rather decreases over time, and that the critical moisture content is above 42%. Factors such as the height of the chips pile influence the predictive equations for the drying rate. The average relative drying rate ranged between 0.063 and 0.040 g of water s−1 kg of dry chip−1 in both heights; meanwhile, the average absolute drying rate was between 0.0031 and 0.0032 g of water s−1. Modifications of the models have been developed that adjust theoretical values with experimental values, resulting in an r2 value of 0.80.