Modelling of drying kinetics during non-isothermal convective drying of passion fruit seeds

A model to identify the effective diffusivity and to predict the dr ying kinetics during non-isothermal convective drying of yellow passion fruit (Passiflora edulis Sims f. flavicarpa Degener) seeds was formulated and validated. The governing equations for coupled mass and heat transfer phenomena were expressed in a generalized coordinate system in order to obtain a one-dimensional model suitable for the non-regular geometry of the seeds. Solid shrinkage, moisture and temperature-dependent transport properties, convection heat and mass transfer at the seed surface and symmetrical distribution of moisture content and temperature inside the material were considered. To identify the moisture effective diffusivity, model estimations were fitted to data from drying experiments carried out at air temperatures of 40, 50, and 60°C and at air velocities of 0.6 and 1.4 m·s-1. The air velocity promoted a lower effect than the air temperature on drying rate, suggesting the internal resistance to mass transfer controlled the water diffusion. The proposed model could contribute to understand the diffusion mechanisms in the material, offering an alternative approach to study the convective drying of non-regular particles due to it requires a simpler solving process and a shorter calculation time than some multidimensional approaches. © 2016 Japan Society for Food Engineering.