EXPERIMENTAL ESTIMATION OF EFFECTIVE TRANSPORT-COEFFICIENTS IN FREEZE-DRYING FOR SIMULATION AND OPTIMIZATION PURPOSES

In this work a quasi-steady-state analysis is used to describe the evo lution of the sublimation front temperature in freeze-drying of a food model (aqueous solution of Tylose, 3%). From the water loss data obta ined in a freeze-drying experiment, in which the upper dried surface t emperature and that of the frozen zone of the food model are controlle d to a certain heating strategy, several values of the transport coeff icients in the dried layer are calculated under different operational conditions (i.e. chamber pressure and average product temperature). Th ese values are correlated by non linear regression and expressions for the effective thermal conductivity and water vapour diffusivity in th e dried layer of the material are obtained. These correlations can be used to simulate freeze drying and obtain the best operational strateg y; that is, the one which maximizes drying rate throughout the process .