Ultrasonication involves high frequency sound waves above human hearing capacity i.e. above 20 kHz.
Unlike electromagnetic waves, they are mechanical waves, which pass through solid, gas and liquid media.
These waves propagate by rarefactions and compression.
These expansions cause negative pressure in the liquid.
If the pressure exceeds the tensile strength of the liquid then formation of vapor bubbles occurs.
These vapor bubbles undergo implosive collapse in strong ultrasound fields which is known as cavitation.
The implosion of cavitation bubbles generates macroturbulence,high-velocityinter-particlecollisions,andperturbation in micro-porous particles of the biomass.
Cavitation near liquid– solid interfaces directs a fast moving stream of liquid through the cavity at the surface. Impingement by these micro-jets results in surface peeling, erosion, and particle break down facilitating the release of bioactive compounds from the biological matrix .
Ultrasound can be employed as a pre-treatment before drying to improve the drying kinetics and to reduce the energy costs involved in the unit operation.
This study investigated the use of ultrasound as a pre-treatment prior to hot air convective drying of seaweed. The influence of ultrasound power on drying kinetics, water gain, solid loss and changes in color of seaweed were examined. The combined process of ultrasound and air-drying was optimized and various mathematical models were applied to the drying kinetics.