CFD study of the flow pattern in an ultrasonic horn reactor: Introducing a realistic vibrating boundary condition

Abstract

Recently, great attention has been paid to predict the acoustic streaming field distribution inside the sonoreactors, induced by high-power ultrasonic wave generator. The focus of this paper is to model an ultrasonic vibrating horn and study the induced flow pattern with a newly developed moving boundary condition. The numerical simulation utilizes the modified cavitation model along with the "mixture" model for turbulent flow (RNG, k-ε), and a moving boundary condition with an oscillating parabolic-logarithmic profile, applied to the horn tip. This moving-boundary provides the situation in which the center of the horn tip vibrates stronger than that of the peripheral regions. The velocity field obtained by computational fluid dynamic was in a reasonably good agreement with the PIV results. The moving boundary model is more accurate since it better approximates the movement of the horn tip in the ultrasonic assisted process. From an optimizing point of view, the model with the new moving boundary is more suitable than the conventional models for design purposes because the displacement magnitude of the horn tip is the only fitting parameter. After developing and validating the numerical model, the model was utilized to predict various quantities such as cavitation zone, pressure field and stream function that are not experimentally feasible to measure.

Characterisation of flow behaviour and velocity induced by ultrasound using particle image velocimetry (PIV): Effect of fluid rheology, acoustic intensity and transducer tip size

“…Specifically, CFD has been employed to assess both the fluid dynamics and mixing behaviours of ultrasonic processors [11,[19][20][21][22][23][24][25], and additionally the associated thermal effects of ultrasound in liquid media, due to the chaotic implosion of ultrasonic cavitations [21,26,27]. Xu and co-authors used a numerical approach to simulate velocity distribution of flow from a 490 kHz ultrasonic transducer in water [20].…”

“…Although significant research has been conducted on the flow behaviour resulting from ultrasound using CFD [11,21], there has been limited research conducted in direct measurement through experimentation of these phenomena. To the authors' knowledge, there are only a few research articles detailing the use of experimentation to assess flow behaviours from ultrasound using either particle image velocimetry (PIV) [25,28,29], laser Doppler anemometry (LDA) [14] or streak photography techniques [30]. PIV is an optical method which relies on tracking the trajectory of tracer particles for the instantaneous measurement of velocity and other associated properties of fluids in motion (i.e., shear rate or rate of energy dissipation) [31,32].…”

“…These results indicate the presence of deadzones adjacent to the conical sound beam, but are not fully discussed. Additionally, Rahimi and co-authors used PIV as a validation method of CFD results [25]. From their results, the development of conical flow structures were observed emanating from the tip of the transducer of 20 kHz ultrasonic processor, with a diameter of 40 mm.…”

A PDE-Based Data Reconciliation Approach for Systems with Variations of Parameters

“…Due to some advances in the computational techniques, the partial differential equation (PDE) can be developed to describe the system behaviour within the computational domain. The PDE-based model can be used to predict the values of some variables such as temperature, concentration and so on [9][10][11][12][13][14] at different positions within the system. Haghshenasfard and Hooman [15] used the PDE to predict the rate of asphaltene deposition from crude oil.…”

Ultrasonic Cavitation Structures in a Conical Vessel

“…They also describe a method to adjust the depth of the sonotrode tip (node or antinode) inside the liquid. Rahimi et al [10] and Klíma et al [11] proposed the optimization of the sonoreactor geometry based on a numerical simulation of local ultrasonic intensity and its qualitative comparison with experimental results. Both groups predicted an acoustic streaming field distribution inside the sonoreactor, with the 10th International Symposium on Cavitation -CAV2018 Baltimore, Maryland, USA, May 14 -16, 2018 CAV18-05214 first group studying the induced flow pattern with a moving boundary condition, and the second paying attention to the intensity distribution of the ultrasonic energy, driving frequency, dip size of the sonotrode tip, proposing a "horn up" optimized at 20 kHz.…”