Eur. Phys. J. E (2017) 40: 73
https://doi.org/10.1140/epje/i2017-11562-0

Regular Article

Investigating the origin of acoustic attenuation in liquid foams

¹ Sorbonne Universités, UPMC Univ Paris 06, CNRS (UMR 7190), Institut Jean Le Rond d’Alembert, Paris, France
² Laboratoire Matière et Systèmes Complexes, Université Paris-Diderot, Sorbonne Paris Cité, CNRS (UMR 7057), Paris, France
³ Sorbonne Universités, UPMC Univ Paris 06, CNRS (UMR 7057), Laboratoire Matière et Systèmes Complexes, Paris, France

^* e-mail: juliette.pierre@upmc.fr
^** e-mail: valentin.leroy@univ-paris-diderot.fr

Received: 1 June 2017
Accepted: 3 August 2017
Published online: 22 August 2017

Abstract

Liquid foams are known to be highly efficient to absorb acoustic waves but the origin of the sound dissipation remains unknown. In this paper, we present low frequency (0.5-4kHz) experimental results measured with an impedance tube and we confront the recorded attenuations with a simple model that considers the foam as a concentrate bubbly liquid. In order to identify the influence of the different parameters constituting the foams we probe samples with different gases, and various liquid fractions and bubble size distributions. We demonstrate that the intrinsic acoustic attenuation in the liquid foam is due to both thermal and viscous losses. The physical mechanism of the viscous term is not elucidated but the microscopic effective viscosity evidenced here can be described by a phenomenological law scaling with the bubble size and the gas density. In our experimental configuration a third dissipation term occurs. It comes from the viscous friction on the wall of the impedance tube and it is well described by the Kirchhoff law considering the macroscopic effective viscosity classically measured in rheology experiments.