30F-8 |
Mathematical modeling of transport phenomena during immersion freezing process of foods |
S. E. ZORRILLA, Instituto de Desarrollo Tecnológico para la Industria Química, Universidad Nacional del Litoral - CONICET, Güemes 3450, (3000) Santa Fe, Argentina and A. C. Rubiolo. Immersion chilling and freezing of foods (ICF) in aqueous solutions has recognized advantages such as shorter processing times or higher final food quality compared to other freezing techniques. However, one of the major disadvantages is the uncontrolled uptake of solutes. Mathematical modeling may help to predict temperature and concentration profiles and to have a better understanding and control of the process. Our objectives were to develop a mathematical formulation to represent the transport phenomena involved in the ICF process, solve the model, and validate the results obtained. When a solid food is immersed in a concentrated aqueous solution (e.g. 23% w/w NaCl) at a low temperature (e.g. -15°C), the freezing process starts with a simultaneous mass transfer (solute gain and water loss). The following assumptions were considered: heat conduction in the solid food, negligible heat of generation, thermal properties depending on temperature, uniform initial temperature, third type boundary conditions, mass diffusion in the solid food, no chemical reaction, constant diffusion coefficient, uniform initial concentration, and first type boundary conditions. The enthalpy formulation was used to avoid the phase-change problem during freezing. The control-volume approach simplified the numerical formulation for finite solids. Heat and mass transfer relationship was established through the dependence of the initial freezing point (Tf) with the aqueous solute concentration. Moreover, the thermal properties and enthalpy depend on Tf. When a node reached temperature Tf, solute concentration did not change further on. The predicted temperature and concentration profiles were similar to those reported in literature. The formulation was easily generalized for the regular geometries. This work contributes with a simple model for predicting heat and mass transfer phenomena during ICF process and may help in future studies such as sensitivity analysis or optimization, and to study new alternatives where the solute uptake is desired.
Session 30F, Food Engineering: Transport processes and kinetics
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