A simple model to predict the mass and heat transfer during the combined osmotic-microwave drying of fruits

J.R. ARBALLO; L.A. CAMPAÑONE; R.H. MASCHERONI

Atenas

Congreso; ICEF 11; 2011

Universidad Técnica de Atenas

The heat and mass transfer during the combined process of osmotic dehydration and microwave drying of fruits was studied theoretically and experimentally through modeling and numerical simulation. With the aim to describe the transport phenomena involved during the combined dehydration process, the mass and energy microscopic balances were raised. For the first step, osmotic dehydration, it was used the Spiazzi and Mascheroni osmotic-diffusive model, which is based on the mass transfer through cellular membranes and the multicomponent diffusion across intercellular spaces. On the other hand, for microwave drying, the energy and mass balances were solved, using moisture and temperature dependent properties; inner heat generation due to transformation of the electromagnetic energy was accounted for by using the approximation of Lambert?s law. In this second step, two successive stages were considered: material heating followed by liquid evaporation. The obtained balances constitute a system of nonlinear differential equations highly coupled that were solved applying numerical methods. The solution obtained from osmotic dehydration simulation was incorporated as initial values for the simulation of microwave drying. The numerical methods were coded in Matlab® 7.2 (Mathworks, Natick, MA). The model validation was carried out in pears, fresh and osmodehydrated during 2 hours in sucrose osmotic solutions of 20, 40 or 60ºBrix and then irradiated in a microwave oven of 500W during 4 minutes. The mathematical model was successfully evaluated, allowing the prediction of temperature and moisture profiles during the combined process of osmotic-microwave drying in a wide range of operating conditions.