The Basics of Cavitationi- Physics of cavitationCavitation is a general fluid mechanics phenomenon which can occur whenever aliquid used in a machine inducing pressure and velocity fluctuations in the fluid (e.g.Pumps, turbines, propellers, bearings, even the heart and knee joints).When cavitation occurs the liquid changes its phase into vapour at certain flow regionwhere local pressure is very low due to the high local velocities (e.g. propeller tips).There are two types of vaporization:1. The first is the well-known process of vaporization by increasing temperature(boiling)2. Vaporization under nearly constant temperature due to reduced pressure (i.e. coldboiling) as in the case of cavitation.The cold boiling process and hence cavitation depends on the purity of water. If watercontains a significant amount of dissolved air, then as the pressure decreases the aircomes out of the solution and forms cavities in which the pressure will be greater thanthe “vapour pressure”. This effect applies also when there are no visible bubbles.Submicroscopic gas bubbles can provide suitable nuclei for cavitation purposes.Hence cavitation can either be “vaporous” or “gaseous” perhaps, a combination ofboth.When cavities are formed in fluid, this violates the homogeneous character of theliquid resulting in practical problems.

(cavitation)

Cavitation is a physical phenomenonassociated with three aspects: formation, growth andcollapse of bubbles within the body of a liquid due tothe variations of local static pressure. However it isreferred to as the collapse and release of energy. Thebubbles form and grow in the regions of low pressure,and after collapse in the regions of high pressure.

(cavitation Theory)

(cavitation reactor)

Cavitation results in conditions of very high local temperatures and pressures at the same time releasing free radicals which intensifies many chemical reactions.

Bubble collapse during cavitation serves as an e_ective means of concentrating the di_use energy of sound: compression of a gas generates heat. When the compression of bubbles occurs during cavitation, heating is more rapid than thermal transport, creating a shortlived localized hot spot. There is a nearly universal consensus that this hot spot is the source of homogeneous sonochemistry. Rayleigh's early descriptions of a mathematical model for the collapse of cavities in incompressible liquids predicted enormous local temperatures and pressures (Rayleigh 1917). (acoustic cavitatin)