The magnitude of the effects of ultrasound depends on the process
variables, such as air temperature, air velocity, mass load density,
applied acoustic energy or the raw material processed. The air
velocity has been found to be one of the most important variables
involved in power ultrasound assisted air drying (Cárcel et al.,
2007a; García-Pérez et al., 2007). From experimental measurements,
Riera et al. (2011) found that the increase of the air velocity
produced the reduction of the sound pressure level in the drying
chamber. As a consequence, the energy available for the samples
at high air velocities could not be enough to affect the mass transfer
process.