Thermal Effects in Ultrasonic Cavitation of Ionic Liquids

Ionic liquids have favorable properties for sonochemistry applications in which the high temperatures and pressures achieved by cavitation bubbles are important drivers of chemical processes. A model was developed to simulate ultrasonic cavitation in ionic liquids. The model uses the finite element method (FEM) and accounts for spatial variations in pressure and temperature in the interior and exterior of the bubble. This model provides insight into heat transfer across the bubble surface and thermal penetration into the liquid. Parametric studies are presented for sonochemistry applications involving ionic liquids as a solvent, examining a range of realistic ionic liquid properties to determine their effect on temperature and pressure inside the bubble and in the surrounding liquid. Results are presented for parametric variations including viscosity, thermal conductivity, and acoustic frequency. An additional study examines thermal penetration into the surrounding ionic liquid during bubble collapse. Among the most significant findings are that liquid viscosity and acoustic frequency have a strong effect on altering bulk and surface temperatures and pressures of the bubble. In all cases, the amount of thermal penetration into the exterior liquid is very small. Overall, the results suggest the prospect of tuning ionic liquid properties for specific applications.