Modelling approach for analysis of moisture transport in diatomaceous earth pellets

Gradual moisture loss from spherical porous pellets is a prerequisite to induce entomopathogenic nematodes into a partial state of anhydrobiosis and for extending their shelf-life under non-controlled storage conditions. The aim of this work was to analyse the moisture loss in diatomaceous earth pellets through a mathematical model based on the molecular diffusion into a spherical porous structure. A natural and a forced convection scenarios were studied. For the experiments, pellets of 5 mm in radius with an initial moisture content of 1.0 (kg H₂O/kg dry matter) were stored at 23 °C and 96% relative humidity. The moisture loss represents a drying process in two-stages and a crack formation in the pellet was observed, causing a moisture re-absorption phenomenon between 5 and 8 days; this event could originate an increase of the macro-porosity and the capillary pressure. The theoretical prediction showed a better accuracy for natural convection. The deviation in the case of forced convection is explained by the crack formation, which was not considered in the model.