Ultrasonic Induced Nucleation

Freezing and crystallization are linked in that both processes involve initial nucleation followed by crystallization. Sonication is thought to enhance both the nucleation rate and rate of crystal growth in a saturated or supercooled medium by producing a large number of nucleation sites in the medium throughout the ultrasonic exposure. Two main theories which explained the mechanism of nucleation are Hickling theory and molecular segregation theory. Among two theories Hickling is most commonly cited. According to this theory, violent collapses of cavitation bubbles produced by power ultrasound can generate very high localized pressure in a very short time. Such collapse generates high degrees of super cooling and favors instantaneous ice nucleation. According to this theory, nucleation is expected to occur immediately after the collapse of cavitation bubbles. Molecular segregation is another theory proposed to explain the power ultrasound induced nucleation in the crystallization process of different solutions. According to this theory; the pressure gradient around the cavitation bubbles produced by power ultrasound can act as the driving force for nucleation. This pressure gradient can result in a …show more content…
One very important area related to freezing in the food industry is the formation of ice crystals during the freezing of water present in the food material. The problems related to conventional freezing reported by I.P. Lakshmisha et al. (2008) and T. Norton et al. (2009) like non-uniform crystal development, destruction of food material structure and loss in sensory food quality have given rise to use some innovative technologies such as air blast, plate contact, fluidized-bed freezing, immersion freezing, cryogenic freezing, high-pressure freezing and their combinations are the most common methods used in the