Localized Convection Through Laser-Induced Cavitation
Authors:Darren Banks, Molly Daniels
Mentor:Guillermo Aguilar, Professor of Mechanical Engineering , University of California, Riverside
Using high-power lasers focused into a liquid, cavitation can be induced. This cavitation bubble agitates the surrounding liquid strongly, with the potential to greatly increase local convective cooling. This technique would be beneficial for adjusting the temperature of a very small region. For example, suppose a particular core in a multi-core CPU is overheating. With current air- and liquid-cooled heat sinks, cooling is applied evenly across the whole chip surface. These techniques cannot efficiently cool the ‘hot-spots’ due to asymmetric chip design. With cavitation increasing local convection in the liquid, these hot spots can be dealt with easily. Cavitation is the process by which forces acting on a liquid cause a rapid disturbance within the liquid. In this experiment, a green laser producing a 5 nanosecond pulse is focused into a cuvette filled with water. The water breaks down into a plasma, which then causes explosive boiling around the focal point. The resulting bubble grows very rapidly until the plasma’s energy is depleted, at which point it collapses equally quickly. Using a high-speed video camera, the bubble’s size can be measured over its very short duration. The goal of this project is to perfect the optical and fluid conditions that lead to cavitation, and then to demonstrate that local heat transfer can be increased by inducing a cavitation bubble nearby. Currently we are exploring the phenomena that accompany the cavitation bubbles, namely, an acoustic shockwave emitted when the bubble collapses, and secondary bubbles that form after the primary one has disappeared. Also underway is the development of a fast-response temperature sensor so that the thermal effects of cavitation can be observed.