Natural wind drying of willow stems

The process of natural wind drying of willow (Salix viminalis) stems in large piles was investigated. A simple drying model was developed for stems. Large-scale drying experiments were conducted and drying data were statistically analysed. Whether drying in a pile of willow stems was uniform was investigated. After harvest (between November and April), during storage until August the average pile moisture content was reduced from about 1.0 to between 0.2 and 0.3 kg (water) kg−1 (DM), which approximates to the equilibrium moisture content. Moisture diffusion within a willow stem is a long-term process which is governed by the relative air humidity and ambient temperature. Evaporation of moisture at the outside of a willow stem is a short-term process which is governed by rainfall, wind and global radiation. Within a single willow stem, during the summer the moisture content becomes more or less uniform. In a pile of willow stems, drying is uniform, except for the top of the pile which forms only a small part of the pile. Covering the pile is not necessary. The good results of natural drying of willow stems indicate that storage of willow stems in large piles is an efficient low cost drying method.