Laminar bubbly flow in an open capillary channel in microgravity

The effect of the gas flow rate on the shape of the free surface is analysed from image processing. The local curvature of the free surface can be related to the local wall friction taking into account the entrance effects in the channel. The wall shear stress is found to be increased in two-phase flow by comparison to single-phase flow. The mean bubble velocities averaged over the channel cross section are also measured by image processing. They are directly proportional to the mixture velocity. The bubble size increases along the channel due to coalescence. The bubble size evolution is well predicted by the coalescence model previously developed by the authors.