CAVITATION (Latin cavitas deepening, a cavity) — process of education in a nappe of cavities (cavitational bubbles) filled with mix of fluid steams with the gases dissolved in it as a result of local pressure decline to nek-ry (critical) value. If pressure decline is caused by emergence in a fluid flow of big local speeds, To. call hydrodynamic if acoustic vibrations — acoustic.
The phenomenon To. it is widely used for disintegration of fabrics and cells, for allocation from animal and plant cells of enzymes, hormones and other biologically active agents. To. can take place in body tissues at ultrasonic cutting and welding of metal, and also at physiotherapeutic use of ultrasound with the intensity exceeding 1 W-cm 2 . The phenomenon To. it is observed at destruction of underlying fabric structures by the focused bunch of ultrasound (see. Ultrasonic therapy ).
In the pure and decontaminated liquid K. it is complicated since for a gap such, liquid needs to put big negative pressure. Theoretical durability of water on a gap is equal apprx. 1500 kg/cm 2 . Real liquids are less strong that is connected with existence in them of so-called cavitational germs (i.e. motes, microvials of gas, ions, hydrophobic areas of macromolecules etc.). At pressure decline below critical the formed cavities are filled with vapors or gases dissolved in liquid, quickly increase in volume and turn into big cavitational bubbles. Having got to a zone of supertension, they are quickly reduced in volume (slam) that is followed by sharp temperature increase of the gas which is in a bubble. To. physical is followed various. - the chemical phenomena — a luminescence, shockwaves, an erosion of a surface of solids, and also emergence or acceleration of chemical reactions, which in absence To. or proceed with small speeds, or are not observed at all.
Hydrodynamic To., as a rule, negatively influences operation of hydraulic machines, ship rowing screws, turbines, pumps, etc. It is supposed that it can take place in a flow of blood, significantly different from usual currents of liquid as moving blood is put into system of elastic pipes and tests periodic pulsations. To. in blood can lead to injury of heart valves and walls of arteries, stimulating development of atherosclerosis. At the sharp movements in hyperinflate sites of fabric or liquid there can be stable gas germs which at decrease in barometric pressure (rise on height, emersion from depth) increase in sizes, turn into gas bubbles and lead to development compressed-air disease (see). However this phenomenon differs from To., since. To. means not only vesiculation, but also their bystry reduction with the accompanying manifestations (temperature increase, shockwaves, a luminescence etc.).
Acoustic To. arises at action on liquid of a sound, intensity to-rogo surpasses threshold value. The size of a threshold depends on the content In liquid of cavitational germs and can change over a wide range depending on hydrostatic pressure, the frequency of acoustic vibrations, duration of influence, volume of liquid, and also from properties of the liquid — viscosity, pressure of the sating vapors, ability to dissolve gases etc. As parameters of the sound causing acoustic To., it is rather easy to regulate, it finds more and more broad application in many industries for creation of new technological processes and improvement of old. In the majority practical application ultrasound (see) it is based on
K. K. effect in fabrics can be followed by destruction of separate cells or emergence of the intracellular microflows displacing organellas of cells, a luminescence in visible and ultra-violet areas, a cut it can be localized both in a cell, and out of it. In cells at the same time there can be a formation of reactive particles which, reacting with biomacromolecules of cellular membranes and cellular contents, are capable to lead to profound and irreversible changes of intensity and nature of the exchange and other processes proceeding in cells.
Bibliography: Pirsol I. Cavitation, the lane with English, M., 1975, bibliogr.; El-p and N of e r I. E. Biofizika of ultrasound, M., 1973; Lele P. P., Senapati N. a. Hsu W. L. Mechanisms of tissue — ultrasonud interaction, in book: Ultrasonics in med., ed. by M. de Vlieger a. o., p. 345, Amsterdam, 1974, bibliogr.
V. B. Akopyan.