cavitation (ultrasound)

2 .3 .1 Introduction of Ultrasound

Ultrasound is simply sound pitched above human hearing . Ultrasound is the part of the sonic spectrum which ranges from about 20 kHz to 10 MHz and can be roughly subdivided in three main regions (A ) low frequency high power ultrasound (20-100 kHz (B ) high frequency , medium power ultrasound (100 kHz-1 MHz (C ) and high frequency , low power ultrasound (1-10 MHz . The frequency level is inversely proportional to the power output . High power , low frequency ultrasound does alter the state of the medium and is the type of [banner_entry_middle]

ultrasound typically used for sonochmical applications . Table A shows the application of ultrasound (1

2 .3 .2 Theory

The chemical effects due to the cavitation have been explained by the two theories , which exist as Hot-spot theory (2 , and the Electrical theory (3 4 . The drastic conditions , which are created due to the cavitation collapse , have been experimentally shown by the Hot-spot theory . It has also been explained in the theory that these changes occur inside the medium , which takes an extremely short time and requires 2000-5000K of temperature , and up to 1800 atm of pressure inside the cavity that collapses , as mentioned previously in our discussion

Under certain conditions , the emission of light is considered as a remarkable event , which occurs during the collapse of the cavitation These certain conditions are usually known as sono-luminescence Furthermore , a couple of strong physical effects are caused by the collapse outside the air bubbles in the liquid , resulting in the shock waves , shear forces , and jet waves . A postulation regarding the electrical charge has been given in the Electrical theory . The surface of a cavitation bubble has been shown as the place of creation of the electrical charge , which results in the formation of massive electrical field gradients . These bubbles are found to be across the bubble that may result in the breakage of the bond upon the collapse of the cavity

2 .3 .4 Acoustic cavitation

An interface of acoustic waves with the substance at a molecular or atomic stage does not result in the chemical consequences of high-intensity ultrasound . Instead , primary mechanism for sono-chemical effects is provided by the acoustic cavitation , that is , the cycle of the formation , development , and collapsing process of the bubbles (13 in the liquids that are irradiated with the high-intensity ultrasound as mentioned above

The phenomenon of acoustic cavitation is the origin of sono-chemical effects in the liquids . A sinusoidal pressure variation is imposed by the ultrasonic waves that travel through a solution in the liquid , which results in the compression of liquid molecules by the overcoming process of the intermolecular forces indirectly . For instance , the compression of the liquid molecules will take place in the ultrasonic frequency of 20 kHz obscuring each second . Therefore , the observations show varied results regarding the distance among the molecules , which occurs due to the oscillation of the molecules around their mean positions . However the molecular structural intact is not supported and hold by the intra-molecular… [banner_entry_footer]