Applications involving foams in industrial processes are widespread. Often the development of foam is a desired outcome. Foams are used in enhanced oil recovery and drilling operations, in the production of cosmetics, and in the development of new insulation and construction materials. However, in applications such as glass melting and fining or fermentation processes, foam layers act as barriers to heat and mass transfer, and the presence of foam is undesirable. Due to their widespread use and importance, techniques for characterizing foams are of interest. Previously, diffusing-wave spectroscopy has been used to investigate the time evolution and the rheological properties of foams. This paper will describe the use of diffusing-wave spectroscopy to characterize the layer thickness, scattering coefficient, and asymmetry parameter of a foam layer. A model of the propagation of radiation from a steady source and from a sinusoidally modulated source through a non-absorbing foam layer is developed. Relationships between layer thickness, scattering coefficient, asymmetry parameter and the phase shift of the reflected radiative flux are derived based on this model. Model predictions reveal an experimentally viable technique for characterizing industrial foams. To the best of the authors’ knowledge, the determination these properties has been heretofore elusive, and the results presented here describe for the first time a non-intrusive method for determining foam properties.

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