Axial acoustic field along a solid-liquid fluidized bed under power ultrasound

Abstract

This work investigates the ultrasound propagation within a liquid-solid fluidized bed. The acoustic mapping of the reactor is achieved by means of a hydrophone. A spectral analysis is carried out on the measured signals to quantify the cavitation activity. The effects of several parameters on the spectral power distribution is appraised including emitted ultrasound power, liquid superficial velocity and solid holdup. Results show that increasing US power promotes a higher energy transfer from the driving frequency toward the broad-band noisewhich is the signature of transient cavitationand yields a stronger acoustic shielding. The presence of a flow opposite to the acoustic streaming may affect the sonoreactor behavior by sweeping the cavitation bubbles away from the ultrasonic horn. Finally the presence of millimeter sized particles significantly increases wave attenuation, presumably due to viscous losses on the one hand, and through the contribution of their surface defects to bubble nucleation on the other hand. Moreover, the influence of the solid holdup appears to depend upon the particle material (glass or polyamide).

Effect of ultrasonic pretreatment monitored by real‐time online technologies on dried preparation time and yield during extraction process of okra pectin

“…The oscillating bubble emits an acoustic cavitation noise that is shown by the frequency spectra, 43 and the spectral analysis is carried out on measured signals to quantify the cavitation activity 46 . The stronger the ultrasonic field intensity, the greater the signal power peak that exists, with a stronger emission signal; the contribution of signal noise increased from less than 40% at 60 W to about 95% at 200 W, showing a higher cavitation level 46 . The material morphology was also changed due to the ultrasonic disturbance 47 …”

Microstructure and Formation Mechanism of Ultrasound-Assisted Transient Liquid Phase Bonded Magnesium Alloys with Ni Interlayer

“…It can be seen that L3 was wider than L4. This is mainly because the ultrasonic horn was placed on the L3 side of the BM and the ultrasonic wave had the characteristic that it can be attenuated in solid and liquid phase [28,29,30]. The L3 zone received USV that transferred across the solid BM while the L4 zone received USV that transferred across the solid BM, liquids in L3, and solid Ni interlayer, which meant that more energy from the USV is dissipated in the L3 zone than the L4 zone.…”

Acoustic characterization of cavitation intensity: A review

“…Chao Li et al [74] proposed that the integration of broadband noise spectrum can also be used to characterize the hydrodynamic cavitation intensity. Since then, various researchers [42] , [59] , [60] , [75] , [76] , [77] , [78] , [79] , [80] used cavitation noise to characterize cavitation intensity through different specific strategies, as shown in Table 1 , especially in the field of biomedical engineering, the PCD [81] , [82] , [83] and its upgraded method PCM (passive cavitation mapping) [84] , [85] , [86] , [87] have almost become conventional methods.…”

“… I. Tzanakis et al [76] The cavitation intensity was measured in liquid aluminum using a high temperature cavitation meter calibrated by National Physical Laboratory; Integration of cavitation noise over frequency spectrum was used to character the cavitation intensity (more details of the noise spectrum analysis were not mentioned in the paper, readers might be referred to the paper [80] ); There was an optimal power setting, in which bubble structure and amplitude reach physical equilibrium and the cavitation intensity reaches the maximum. V. Grosjean, et al [77] Axial sound field was measured by a hydrophone; spectrum analysis of the measured signals was made to quantify the cavitation intensity; The total power was obtained by integrating the spectrum up to 150 kHz, and the power of broadband noise is derived by subtracting the power of peaks from the total; Increasing ultrasonic power promoted transient cavitation and stronger sound shielding. Liu et al [78] Cavitation intensity distribution in gaseous liquid was measured via a hydrophone; The total energy was obtained by numerical integration of the noise spectrum over whole frequency domain, the power spectrum integral with a frequency range of f 0 ± 2.5 kHz was used to represent the linear partial energy, the cavitation effect is approximately expressed by the difference between total energy and line energy; Reducing the gas content to a certain extent could evidently promote the cavitation effect, while the gas content reached a certain value, continuing to reduce the gas content slightly weaken the cavitation effect.…”