EVALUATION AND CONTROL OF EQUILIBRIUM MOI STURE CONTENTS IN POWDERY MATERIALS

The physical meaning of equilibrium moisture contents in powdery mater ials at a certain humidity (30-90%) is discussed and the capability of moisture control in powder is examined. Wet powdery materials just be fore entering drying processes after some wet processes usually contai n much or less soluble impurities (mostly salts). Such impurities will . be concentrated in drying processes, and they cover particle surface s or are contained in liquid bridges formed between particles. Our for mer analysis and experimental results for liquid bridges formed betwee n two spherical particles, in which the liquid bridges contain a certa in amount of soluble impurities, have been applied to evaluate the moi sture contents in powdery materials. It was found from the analysis th at the moisture contents in powder could be predicted from the amount of soluble impurities contained in the powder and the surrounding humi dities. This suggests that the moisture contents in the powder which i s equilibrated by surrounding air in high humidity can be controlled b y the soluble impurity concentration in wet powder being fed to drying processes.