Micrometric Ripples in a Capillary Tube, the Effect of Microgravity

The oscillatory motion of a fluid carrying micron-sized particles inside a capillary tube is investigated experimentally in standard gravity condition. It is found that initially uniformly distributed particles can segregate and accumulate to form regularly spaced micron-sized particle clusters. The wavelength of the micro clusters is compared to data for macro-scale sand-ripple patterns and found to obey the same universal scaling as these. A physical and dimensional analysis is performed that confirms the universality of the experimentally observed scaling. The effect of gravity can therefore be discussed on the basis of this universal scaling.