Estimation of the diffusivities and mass transfer coefficients for pears dried under different methods.

Traditionally, in Portugal pears of the variety S. Bartolomeu are dried through an open-air sun exposure. However, this method of drying has some disadvantages, among which not being able to fully guarantee the necessary quality and sanitary standards for commercialization. Hence, the development of alternative drying methods to replace the traditional drying is of great importance nowadays, and the knowledge of the transfer phenomena happening during drying helps to understand these processes. The present work aimed at determining the mass transfer properties of pears for air drying performed in three drying systems: solar stove with forced air convection (STFC), solar stove with natural air convection (STNC) and drying tunnel with hot air from a solar collector (DT). The methodology used to determine the mass transfer properties was a diffusion model, which accounted for shrinkage. The values of the diffusion and mass transfer coefficients for the drying in the three systems were estimated, and from them was possible to conclude that the values of D e in the STNC and DT systems are similar to each other, whereas the STFC system gives a lower value of diffusivity, indicating that in this system the internal moisture transfer is less efficient. As to h m , the system that presents the higher values is STNC, demonstrating a higher efficiency of surface mass transfer