Study of aqueous foams evolution by means of X-ray radioscopy

This paper aims to show the applicability of time-resolved X-ray imaging (X-ray radioscopy) to the study of evolving density profiles and bubble structure in aqueous foam columns. Two different experimental configurations have been tested with different purposes. The macro-mode configuration allowed a precise determination of the liquid fraction profile in the foam column in a rather large cylindrical container (h = 120 mm Ø = 68 mm). The spatial resolution in the height direction was approximately 50 μm with a total number of 2230 pixels lines. Time resolution for this configuration was in the range of 2 s. Alternatively, the micro-mode configuration (7 μm pixel size) permitted a sharp visualization of the individual bubbles contained in a thin -3 mm- rectangular prism container with higher time resolutions 600 ms. Information about the liquid fraction profile and its evolution has been also calculated under this configuration. Foam columns produced from different beer styles have been used as testing specimens. Liquid fraction profiles permitted to analyse precisely the foam stability and the foam–liquid interface with a combined accuracy and spatial resolution not obtained before. Bubble degeneration events have also been sharply visualized with X-rays by using time resolutions in the limit of the technique.