Correlations for the equilibrium moisture content of solids

Water adsorption and desorption isotherms at various temperatures have been generated for a variety of particulate materials (ion exchange resin, silica gel, wheat and cellulose materials). Most of the data were obtained with the SPS Equilibrium Moisture Content rig, using a dynamic equilibration method. Equilibration over saturated salt solutions at 20 degree C (static method) was also used for some of the data. Seven semi-empirical correlations, available in the literature, and one developed by SPS have been used to relate the equilibrium moisture content of the material to the relative humidity and temperature of the air. These equations enable the equilibrium moisture content to be predicted under various conditions of relative humidity and temperature from a small number of tests. For each of the six materials tested at least one of the correlations gave a good fit. However, there was no correlation which predicted the equilibrium moisture content well for every one of the six materials.