Modelling and simulation of pear drying R.P.F. Guine ´ a, * , A.E. Rodrigues b , M.M. Figueiredo c a Food Engineering Department, ESAV, Polytechnic Institute of Viseu, Quinta da Alagoa, Estrada de Nelas, 3500-606 Viseu, Portugal b LSRE – Chemical Engineering Department, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal c Chemical Engineering Department, University of Coimbra, Po ´ lo II, Pinhal de Marrocos, 3030-290 Coimbra, Portugal To the memory of Professor Jose ´ Almiro Castro Abstract In the present work a diffusion based model was adopted to represent the drying behaviour of pears in a continuous convective drier, taking into consideration the variation of the properties of the pears along drying. The program developed simulated a significant number of situations resultant from the variation of some of the oper- ating conditions. The temperatures tested were 30, 40 and 50 °C, the air velocities were 0.5, 1.0 and 1.5 m/s, and the relative humidity of the drying air was 40%, 50% and 60%. From the situations analyzed, and considering the specifications required for the final product, it was concluded that the drying should be carried out at 40 °C, with a drying air velocity of 1.5 m/s and containing 60% RH. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Drying; Shrinkage; Pear; Diffusion; Fick’s law; Modelling; Simulation 1. Introduction The operation of drying has been widely used to preserve food products, and fruits in particular, since the reduction of their water content to certain levels inhibits microbial growth and enzymatic modifications. Addi- tionally, food drying presents other advantages like avoiding the need of using expensive cooling systems for preservation, or facilitating transport and storage due to the reduction in size. On the other hand, it allows the diversification of available food products, with different flavours and textures [8,4]. Fruits like grapes, figs, plums, apricots and peaches have been dried over centuries, and represent an impor- tant portion of the worldwide food trade. However, more recently some other fruits have also been dried, like apples, mango, pawpaw, pineapple banana or pears. In Portugal, pears have been traditionally dried at direct open-air sun exposure, by a complex process involving many different stages: peeling, first drying on open fields (5–8 days), barrelling at shadow (2–3 days), pressing and, finally, second drying also on open fields 0096-3003/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.amc.2007.02.121 * Corresponding author. E-mail address: raquelguine@esav.ipv.pt (R.P.F. Guine ´). Applied Mathematics and Computation 192 (2007) 69–77 www.elsevier.com/locate/amc