Counter pressure on ventilation of different types of wood chip and chunkwood

The pressure resistance to airflow during ventilation was measured for different types of wood chips and chunk and one type of wood pellet made from sawdust. The influence of the air velocity and particle size was determined and the results described by a mathematical equation. The measured pressure resistance correlated very well with the size distribution of the different chip and chunk types. The lowest pressure resistance was found in a 100 mm long chunk produced with a Sasmo chunker from Sitka spruce whole trees at only 14 Pam−1 at an airflow rate of 0.1 ms−1. The highest resistances were found in 35 mm long chip produced with a Sasmo chipper from Norway spruce logging residue, and for long-pole Contorta pine chip produced with a TP 960 chipper. These measured 61 and 68 Pam−1, respectively, at an air flow rate of 0.1 ms−1. If the chip is stored, the pressure resistance during ventilation will increase considerably. Drying of the chip will only reduce the pressure resistance slightly. The pressure resistance to airflow was a factor of 6–60 lower for the wood chip tested than for agricultural crops like rape seed and grain.