Collaborative Research: Probing Cavitation Inception in Dielectric Liquids with Sub-Nanosecond Precision

Princeton University, Princeton NJ

Investigators

Abstract

Cavitation is the formation of bubbles (or cavities) in liquids due to decreased pressure. Accurate determination of the critical conditions of cavitation is of fundamental interests to many technological fields such as fluid machinery design and targeted drug delivery. So far, the experimental results of cavitation threshold pressures have not been consistent. One prominent factor is that the existing techniques cannot reliably capture the very early stage of cavitation inception. Recent works have shown that nanoscale cavities can form in dielectric liquids due to negative pressure generated by nanosecond-pulsed electric fields. Since this process can be synchronized and controlled electrically (which is not the case for existing methods), it hints at a novel technique to “pinpoint” cavitation inception with sub-nanosecond precision in time and therefore enable a more accurate determination of cavitation thresholds. This research project will explore the potential of the proposed method and use it to measure the cavitation thresholds of water and other liquids, which would be very valuable for the validation of cavitation theories and models. This interdisciplinary research will have substantial educational outputs, with an emphasis on innovative approaches to STEM enrichment for underrepresented minority students. The PIs will develop and deliver new learning modules on topics related to the research, such as electrical discharges and fluid mechanics in everyday life. The objective of this project is to experimentally characterize the initial stages of electrostrictive cavitation in simple dielectric liquids as well as liquids with dispersed particles and theoretically elucidate underlying physical processes at the sub-ns timescale. As relevant theoretical analyses have been limited to oversimplified scenarios and experimental evidence is rare and far from systematic, the approach to accomplish the objective is through synergistic use of diagnostic measurements at different developmental stages and numerical modeling of the actual experimental scenarios. The research plan has two specific aims: (1) detection of cavitation initiation in liquids under ultra-short pulsed electric fields; and (2) examination of the effects of the dispersed phase in liquids on cavitation. Optical diagnostics including Schlieren/shadowgraph, Rayleigh scattering, and speckle imaging, combined with electrical and material characterization measurements, will be used to probe early-stage cavitation in various dielectric liquids, with and without dispersed particles, under different electrode geometries. For simple liquids such as water, the experimental data will be compared with the results from systematic numerical simulations to determine the critical conditions of cavitation initiation. For two-phase dispersions, the correlations between the experimental conditions and optical diagnostic results will be established, which will provide the information for the analysis and modeling of electrostrictive cavitation near dispersed particles, and by doing so, deepen the understanding of the physical processes involved. The expected outcomes of the research will include the determination of critical parameters for cavitation initiation in various liquids and a delineation of the physical picture of the subsequent developments of cavitation and the effects of the dispersed phase. This project will bridge the knowledge gap of cavitation initiation at sub-nanosecond timescale and be instrumental in advancing the technologies related to cavitation as well as nanosecond/sub-nanosecond plasma discharge in liquids. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.