Speed of Sound in Bubbly Liquids

Chengjian Wu, Cody Youmans, and Kaiwen Zhang

University of Minnesota

Methods of Experimental Physics Spring 2012

Abstract

The acoustic property of a liquid will dramatically changes when a small amount of gas is added in it. A simple mathematical model, Wood's equation, predicts the relationship between the speed of sound in such a liquid in the low frequency limit and the void fraction (the volume fraction of the gas phase). In this experiment, we verified Wood's equation by investigating the speed of sound in a bubbly liquid contained in a half-meter long waveguide. Our Measurements of the resonance frequencies of the sound using a hydrophone and a simple electronic circuit determined the speed of sound within the liquid at different volume fractions ranged from 0.2% to 3.4%. In order to demonstrate this effect in an audible and pleasing way, an amplified loudspeaker system is also used to broadcast the signal.