Drying of carrots in a fluidized bed. I. Effects of drying conditions and modelling

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70degreesC and 160degreesC, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75degreesC. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D-e) was determined by a correlation based on the air velocity (nu), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X-0). Loss of carotenes is minimized when dehydration is carried out at about 130degreesC with a drying time below 12 min.