Abstract
Atmospheric freeze drying consists of a convective drying process using air at a temperature below the
freezing point of the processed product, and with a very low relative humidity content. This paper focuses
on the use of a simple one-dimensional model considering moving boundary vapor diffusion to describe
the ultrasonic assisted atmospheric freeze-drying of foodstuffs. The case study is the drying of apple
cubes (8.8 mm) at different air velocities (1, 2, 4 and 6 m/s), temperatures (5, 10 and 15 C), without
and with (25, 50 and 75 W) power ultrasound application. By fitting the proposed diffusion model to the
experimental drying kinetics, the effective diffusivity of water vapor in the dried product was estimated.
The model was successfully validated by drying apple samples of different size and geometry (cubes and
cylinders). Finally, a 23 factorial design of experiments revealed that the most relevant operating parameter
affecting the drying time was the applied ultrasound power level.
