Ultrasonic spectral analysis of cavitation bubbles in vegetable oils.

Abstract

Ultrasound-induced cavitation in vegetable oils can be used to control the crystallization and resulting texture of food products such as shortenings. Cavitation in oils has not been explored as extensively as in aqueous systems, however. To more fully understand cavitation in vegetable oils, high-intensity ultrasound (HIU) and broadband 1.0-MHz transducers were used to generate and measure cavitation in soybean oil experimentally. To interpret the results, multipole-based models were used to simulate ultrasonic scattering from the cavitation bubbles in the 0.4–4.0 MHz range. Ultrasonic reflection spectra, transmission spectra, and velocities were simulated for spherical bubble clouds centered between two transducers. The size, concentration, and random configuration of the bubbles in the clouds were varied to find diagnostic features to correlate with experimental data. The models indicated that the configuration of the bubbles have unexpectedly large effects on the ultrasonic spectra even at dilute concentrations (0.2–5.0%). The simulated spectra additionally showed low-frequency (<2 MHz) and high-frequency (>2 MHz) features that correlated with bubble concentration and bubble size, respectively. The experimental results included spectral features that may be associated with turbulence in the oil and the persistence of low-frequency backscatter after stopping the HIU, indicating a slow decay in bubble concentration.