Modelling of acoustic pressure waves in bubbly liquids with application to sonochemical reactors

Abstract

This thesis investigates the acoustic wave propagation in bubbly liquids as part of the SONO project supported by the FP7 European Commission programme, which is aimed at developing a pilot sonochemical plant in order to produce antibacterial medical textile fabrics by coating of the textile with ZnO or CuO nanoparticles. The findings of this research are anticipated to aid the design procedures and also to provide better understanding of the micro scale physical and chemical events.

Propagation of acoustic pressure waves in a bubbly liquid is modelled by using Helmholtz equation in this thesis. Computational models are developed based on meshless approaches, i.e. radial basis integral equation (RBIE) and local boundary integral equation (LBIE) methods. A major part of the research focuses on improving the efficiency and the accuracy of the developed methods. For this purpose, numerical tests are carried out with several example problems in order to cross-verify the applicability of the methods. As a result of these tests, the optimal parameters which should be used to minimize the numerical error are suggested. Further, strategies are proposed in order to handle the thin inclusions, such as textile fabric, in the domain.

The wave propagation in bubbly liquids involves coupled effects of the sound field and bubble population field, such as dissipation of the acoustic energy by bubble oscillations. The problem is therefore non-homogeneous due to presence of bubbles and nonlinear due to coupled effects. The governing equations, derived from linearized or nonlinear theories, can be found in the literature. Examples of both linear and nonlinear wave propagation are solved in this study. Results related to a 3D sonoreactor including textile fabric are also presented. Effects of bubble size distribution and bubble volume fraction on the acoustic wave propagation are discussed in the example problems.

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