[01] Sana Ben Mariem, National Research Institute for Rural Engineering, Water and Forestry (INRGREF), University of Carthage, Ariana, Tunisia. [02] Slah Ben Mabrouk, Research and Technology Centre of Energy, Borj Cedria, (C.R.T.En.), University of Carthage, Hammam-Life, Tunisia.

In this study, numerical model for heat and mass transfer of granular products in a fixed-bed tunnel dryer was developed. A system of four differential equations constitutes the model structure. The obtained system of non-linear partial differential equations was numerically solved by a finite difference method. A computer code in FORTRAN language was written for the numerical solution of the problem. The drying process was simulated under real operating conditions based on a thin layer model and experimental drying kinetics. The numerical code allows establishing the profiles of temperature, absolute humidity, moisture content and drying front propagation of tomatoes slices spread out in a tunnel dryer of 10 m length, during the drying process. The obtained results were simulated for several operating conditions, the temperature and velocity of the drying air varied from 30°C to 70°C and 1m/s to 5m/s, respectively. The profile showed an evolution in temperature around an asymptotic limit which is the temperature of the drying air. Drying is manifested by the drying front propagation from the upstream flow to the downstream one. This drying front has clearly appeared after a blowing time for 4 hours. An abrupt increase of product temperature is followed. The drying time is shorter when the temperature is high, which is explained by the increase in the potential exchange between the air and the product. The model was validated by comparing experimental values of tomatoes in a thin layer with numerical simulations.

Tunnel Dryer, Moisture Content, Mathematical Model, Numerical Simulation, Tomatoes

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