Ultrasound-assisted bleaching: Mathematical and 3D computational fluid dynamics simulation of ultrasound parameters on microbubble formation and cavitation structures.

The implementation of ultrasound-assisted bleaching (UAB) is gaining interest in commercial oil refining, as an alternative to the current bleaching procedure (BP), because this technique has several advantages compared to the conventional BP. The mathematical and 3D computational fluid dynamics (CFD) simulation of the influence of ultrasound power, frequency and temperature for predicting microbubble formation and heat transfer in the ultrasonic treatment of soybean oil was assessed in order to optimize the UAB process. The fluctuation frequency and wave speed showed opposite effects on system response to the imposed pressure pulse. As the bubble radius shrinks to zero (after bubble explosion), its internal pressure increases, showing a maximum pressure of 136, 180 and 188 kPa for fluid temperatures of 35, 50 and 65 °C, respectively. On the other hand, as the pressure applied was increased from 1.5 to 2.5 bar, the collapse radius increased more than 10 times for f = 25 kHz. In addition to the magnitude of the applied pressure, the oscillation frequency and temperature had a minor effect on the collapse radius. In general, the temperature showed a direct influence on bubble growth for an oscillation frequency of 55 kHz, although it was also observed that the bubble collapse radius tended to maximize at mid-range temperatures (around 50 °C). Finally, increasing the magnitude of cavitation pressure resulted in the enhancement of the collapse temperature. • Ultrasound assisted bleaching (UAB) offers numerous advantages vs current bleaching • The 3D multiphase CFD simulation + bubbles dynamics modelling performed • Microbubbles formation and heat transfer under various UAB conditions investigated • Enhanced colour reduction with increasing amplitude and decreasing frequency • The internal pressure of the bubbles increased as they shrink towards zero radius [ABSTRACT FROM AUTHOR]