Abstract

An experimental study using an ultrasonic transducer, submerged into the fluids (water-lubricant-refrigerant), is utilised to produce cavitation bubbles. Images are focused on two critical areas: the lower surface of the horn and across the boundary of the sample. The sample consists of a chromium ball mounted on a Bakelite base and implemented on the bottom of the experimental tank. The results revealed that the lubricant bubbles have a similar behaviour to those produced in water. Refrigerant bubbles have a peculiar performance, especially across the boundary wall where they sustain a continuous oscillatory movement without regularly collapsing. The damage produced by the refrigerant bubbles is smaller than that observed within water and oil lubricant. On the contrary, lubricant bubbles exert a much higher micro-jet impact pressure. A lubrication thickness layer developed across the boundary is observed to provide a cushion, absorbing the jet impact during the implosion of a bubble. Thus the micro-jet impact pressure can significantly be decreased. A thorough investigation of the dynamic behaviour of the bubbles and their cavitation mechanisms is conducted using each of the three liquids respectively.