Thin-film profile around long bubbles in square microchannels measured by chromatic interference method

To study the thin lubrication film around long bubbles with length-to-radius aspect ratio more than 10 in square capillaries, a chromatic interference method was developed. Three-dimensional profile of the lubrication film was acquired from moving long bubbles with the length-to-radius aspect ratio up to 500. The dynamics and profiles of the film were found to be dependent of the dimension-less downstream distance x of the long bubble. For 1 << x << Ca-1, the film has a thickness of order Ca-2/3 at the center and order Ca 1 at the sides, while for x similar to Ca-1, the film at the sides thins to order Ca-4/3, which matches well with the existing theoretical results. Published by AIP Publishing.