HYDRODYNAMIC CAVITATION
How cavitation forms
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Hydrodynamic cavitation is a process of vaporisation, bubble generation and bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in local pressure. Cavitation will only occur if the local pressure declines below the saturated saturated vapor pressure of the liquid. Bubble generated will collapse with subsequent recovery above the vapor pressure.
Hydrodynamic cavitation can be produced by passing a liquid through a constricted channel at a specific flow velocity or by mechanical rotation of an object through a liquid. Based on the geometry of the system, the combination of pressure and kinetic energy create the hydrodynamic cavitation cavern downstream of the local constriction generating high energy cavitation bubbles. Different cavitation types can be generated by liquid flow initial steady cavitation, developed cavitation or supercavitation
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Venturi hydrodynamic cavitation
Rotational hydrodynamic cavitation
The process of bubble generation, and the subsequent growth and collapse of the cavitation bubbles, may result in very high energy densities and in very high local temperatures and local pressures at the surface of the bubbles for a very short time. The global liquid medium temperature of the liquid, however, remains at ambient conditions.
The application of hydrodynamic cavitation
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When uncontrolled, cavitation is damaging for the equipment. The cavitation phenomenon can be controlled to enhance the performance of high-speed marine vessels and projectiles, as well as in material processing technologies, in medicine. Controlled cavitation can be used to enhance chemical reactions which results in either the intensification of the chemical reaction or may even result in the propagation of certain reactions not possible under otherwise ambient conditions. Due to free radicals generation in the process hydrodynamic cavitation or in destruction of polutatnts. Hydrodynamic cavitation can also improve some industrial processes. For instance, cavitated corn slurry shows higher yields in ethanol production compared to uncavitated corn slurry in dry milling facilities. This is also used in the mineralization of bio-refractory compounds which otherwise would need extremely high temperature and pressure conditions.
Efficient killing of bacteria with hydrodynamic cavitation
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We have used hydrodynamic cavitation to destroy Gram positive and Gram negative bacteria such as E. coli, L. pneumophila, B. subtilis. The larges effect was observed with supercavitation. With the use of rotational cavitation the number of passes of liquid over cavitatator has been significantly reduced. Recently it has been shown that small scale hydrodynamic cavitators can be very efficient in destroying viruses.
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