Research into ultrasoic and hydrodinamic cavitation phenomena in a hydraulic system

Abstract

The article describes the course of the ultrasonic cavitation in a hydraulic tank and the hydrodynamic cavitation in a gear pump. The course of those phenomena was confirmed in experimental tests carried out with the use of a tank and a pump made of transparent plastics. It has been proved that the oscillator-cavitation system made according to the original project is useful to induce the phenomenon of ultrasonic cavitation. It has also been shown that the PIV visualization method, consisting in a special system of illuminating transparent objects and recording the flow through those objects with a fast camera, is useful for the studying of the cavitation phenomena. A visible interaction between the ultrasonic and the hydrodynamic cavitation was observed. The induction of ultrasonic cavitation in the tank causes degassing of the oil, and the degassed oil supplying the pump reduces the hydrodynamic cavitation in its internal channels and clearances. This is an example of beneficial effects of the ultrasonic cavitation on the operation of a pump and a hydraulic system. The presented work is an example of effective co-operation between the communities of Wroclaw University of Science and Technology and Igor Sikorsky Kiyv Politechnic Institute, National Technical University of Ukraine.

Some problems of modeling the liquid cavitation degassing. I. Acoustic cavitation.

“…Present in ordinary water, they act as catalysts for corrosion processes Cavitation degassing methods are aimed specifically at removing bubbles containing free gas from a liquid. The effectiveness of the method increases when degassing supersaturated liquids in which the content of gas exceeds the threshold of its solubility at a given pressure and ambient temperature in accordance with Henry's law [3][4][5]. If for some reason the equilibrium is disturbed and the liquid becomes supersaturated, excess gas from the solution quickly moves into the bubbles due to the developed phase contact surface.…”

“…, small bubbles can exist for as long as desired, performing weak pulsations at the field frequency ac f . If the level of acoustic pressure cr ac p p  , these bubbles expand and collapse sharply within several periods of field oscillation, initiating characteristic dynamic effects -erosion of solid surfaces [4,5,13]., sonoluminescence, etc. [9,10,13,15,16].…”

“…Another important problem is the fact that a structured bubble cluster is formed at the surface of the ultrasonic transducer, which poorly transmits sound waves, which worsens the acoustic behavior of the liquid and leads to the formation of chaotically changing bubble structures in it [5,9,[12][13][14][15][16].…”