CavLab is a research laboratory dedicated to a fundamental understanding of acoustic cavitation, refinement of its medical and industrial applications.
Cavitation refers to the formation of bubbles, usually in a liquid host medium – you could technically say that champagne ‘cavitates’ when the cork is popped – of course most people just use the word ‘fizz’. A boiling kettle also represents a ‘cavitating system’ – in this case, the elevated temperature is responsible for generating vapour bubbles within the liquid hot water, which rise to the surface under the action of buoyancy.
Cavitation is a phenomenon that also occurs when a liquid is subjected to a negative pressure (i.e. when it’s stretched). This is a common occurrence in pumps, and around ships’ propellers, for example. You know that knocking sound when you turn a tap on sharply? That’s cavitation occurring in the water backed up along the pipe, as the pressure is released when the tap is opened.
Acoustic cavitation refers to the formation of bubbles, specifically in a host medium exposed to ultrasound, of sufficient intensity. Ultrasound, in essence, is a pressure wave, consisting of a series of high (squashing) and low (stretching) pressure phases. The low pressure phases are responsible for drawing dissolved gas out of solution, and hey, presto! We have acoustic cavitation.
Bubbles are generally thought of as delicate and fragile, ‘floaty’ or ‘foamy’. Acoustic cavitation is anything but! The pressure fluctuations of the ultrasound that first generate the bubbles, will then drive those bubbles to do some pretty amazing things.
Core temperatures in acoustically driven bubbles can reach in excess of 10,000 degree C, at 1000’s of atmospheres of pressure. A bubble can collapse asymmetrically to form a high-speed liquid jet, flowing at more that 100 m/s. Acoustic cavitation is known to etch through hard metallic surfaces.
These bubbles are not to be messed with! We think they are fascinating, and potentially very useful….
At CavLab, we’re trying to figure how cavitation works, and ways to meaningfully and actively control it. Our favourite toy is an ultra-high speed camera, capable of imaging up to 10 million frames per second! We use this device to directly observe cavitation activity, which as you may have guessed, occurs extremely quickly!