Simulation of food drying: FEM analysis and experimental validation Stefano Curcio * , Maria Aversa, Vincenza Calabro ` , Gabriele Iorio Department of Engineering Modeling, University of Calabria, Ponte P. Bucci – Cubo 39/c, 87030 Rende, CS, Italy Received 26 October 2007; received in revised form 11 January 2008; accepted 14 January 2008 Available online 31 January 2008 Abstract The aim of the present work is the formulation of a theoretical model describing the simultaneous transfer of momentum, heat and mass occurring in a convective drier where hot dry air flows under turbulent conditions around a food sample. The proposed model does not rely on the specification of interfacial heat and mass transfer coefficients and, therefore, represents a general tool capable of describ- ing the behavior of real driers over a wide range of process and fluid-dynamic conditions. The system of non-linear unsteady-state partial differential equations modeling the behavior of a cylindrical-shaped vegetable sample in a drier, has been solved by using finite elements method. It has been observed that air characteristics influence drying performance only when external resistance to mass transfer is the rate controlling step. An experimental study was undertaken which shows very good agreement between model predictions and exper- imental results. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Food drying; Transport phenomena; Finite elements method; Process modeling 1. Introduction When warm dry air flows around a cold moist food sam- ple, simultaneous heat and mass (water) transfer occurs, leading to, both, a decrease in food water content and an increase in its temperature. The above effects enhance food preservation, since microbial spoilage is generally pro- moted by low temperature and high moisture content. Heat and mass transfer rates depend on both temperature and concentration differences, but also on the air velocity field which strongly influences the transfer rate at food–air inter- faces and, therefore, has to be properly evaluated. An exhaustive analysis of all the complex transport phenom- ena involved in drying process has often been regarded as being too onerous and time consuming for practical pur- poses. For this reason, many simplified approaches have been proposed, and are widely used by industrial drier designers (Mujumdar Arun, 2006). These approaches are based either on simplifying hypotheses, which may not be applicable in practice, or on the use of semi-empirical cor- relations for estimating the heat and water fluxes at food– air interfaces (Saravacos and Maroulis, 2001). Herna `ndez et al. (2000) assumed fruit drying as an iso- thermal process occurring at a fixed air temperature; this simplification restricted the analysis to mass transfer only. Wu and Irudayaraj (1996) experimentally verified that drying is an isothermal process only if Biot number is very low. When Biot number is significantly greater than unity, the internal transport resistances are not negligible. Wang and Brennan (1995) developed a one-dimensional model for the simultaneous heat and mass transfer within potato slices. The hypothesis of one-dimensional transport was experimentally verified in the same study and also adopted by other authors (Kalbasi and Mehraban, 2000; Rovedo et al., 1995; Migliori et al., 2005). In a recent paper, Datta (2007 Part I) showed the different approaches that have to be used to model heat and mass transfer in food drying process. In some cases, the size of the pores as well as vapor generation within the sample have to be taken into consideration, whereas in some others cases, they can be 0260-8774/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2008.01.016 * Corresponding author. Tel.: +39 0984 496 711/670/703/709; fax: +39 0984 496671. E-mail addresses: stefano.curcio@unical.it (S. Curcio), maria.aversa @unical.it (M. Aversa), vincenza.calabro@unical.it (V. Calabro `), gabriele. iorio@unical.it (G. Iorio). www.elsevier.com/locate/jfoodeng Available online at www.sciencedirect.com Journal of Food Engineering 87 (2008) 541–553