Simulation of the spatial distribution of the acoustic pressure in sonochemical reactors with numerical methods: A review

Highlights

• Last 15 years on the simulation of the acoustic field inside sonoreactors by numerical methods are briefly summarised.

• Pros and cons of the different models reviewed in the manuscript are explained.

• Recent works on novel topics (vibration of the reactor walls, nonlinear phenomena) are illustrated.

• Challenges that must be addressed in the next years are also briefly discussed.

Abstract

Numerical methods for the calculation of the acoustic field inside sonoreactors have rapidly emerged in the last 15 years. This paper summarizes some of the most important works on this topic presented in the past, along with the diverse numerical works that have been published since then, reviewing the state of the art from a qualitative point of view. In this sense, we illustrate and discuss some of the models recently developed by the scientific community to deal with some of the complex events that take place in a sonochemical reactor such as the vibration of the reactor walls and the nonlinear phenomena inherent to the presence of ultrasonic cavitation. In addition, we point out some of the upcoming challenges that must be addressed in order to develop a reliable tool for the proper designing of efficient sonoreactors and the scale-up of sonochemical processes.

Introduction

Sonochemistry [1] is the area of high-energy chemistry which studies chemical reactions and processes involving acoustic cavitation formed by the application of an ultrasonic field in a frequency range which commonly varies between 20 kHz and 10 MHz. It allows chemists to increase the conversion, improve the yield, initiate and change the reaction pathways in all sorts of biological, chemical or electrochemical processes [2], becoming a prominently used technique in a wide variety of research areas, including: (i) material science [3] (ii) synthetic chemistry [4], [5], (iii) water remediation [6], [7], (iv) biotechnological applications [8], (v) electrochemical processes [9], (vi) food technology [10], and (vii) spent nuclear fuel reprocessing [11], among others. The versatility of the use of ultrasound in chemistry permits its combination with other technologies such as photocatalysis [12] or microwaves [13], proving the enormous potential of Sonochemistry.

Despite this extensive research at laboratory scale, a limited number of applications have been industrially scaled-up due to two main reasons: (i) the lack of expertise in diverse areas such as ultrasonics or sonochemical engineering, and (ii) the lack of proper reactor designing strategies. Related to this, Sutkar and Gogate have stated that understanding the cavitational activity and its distribution would yield efficiently designed sonochemical reactors and systems [14], and for this purpose, theoretical analysis of the cavitational activity distribution with proper experimental validation could be used for the optimization of sonochemical processes taking into account building materials, geometry of the reactor and working frequency of the sonochemical system. A correct understanding of the acoustic field structure inside a sonochemical reactor is therefore needed to proceed with its optimization and scale-up in order to design efficient large scale reactors [15].

The numerical simulation of the spatial distribution of the acoustic pressure inside sonochemical reactors has widely emerged in the last 15 years to shed new light on this issue, and quite a few groups around the world have tried to model the acoustic field inside sonoreactors with the aim of predicting the cavitation events within the reactor. To our knowledge, the most recent review on this topic found in the literature was published more than 10 years ago [16], and no exhaustive literature revisions are usually found in most of the papers that deal with the simulation of the acoustic field in a sonoreactor. Therefore, the goal of the present paper is to introduce numerical methods for the development of sonochemical reactors to a wider audience of scientists by summarizing the continuous development of numerical methods employed by the scientific community from the late 1990s until now. In this paper, basic methodologies and results from many works are briefly commented, pointing out the strong and weak points in the most representative cases from a qualitative point of view. And new trends and future challenges on the problem are also discussed.