Two Phase Flow 

    A single gas bubble moving under the influence of gravitational, inertial, viscous and interfacial forces, relative to another fluid contained in a vertical cylindrical tube. The bubble is axisymmetric bullet shaped, with a thin film of water (flowing downwards) between air bubble and hydrophilic wall of the column . However, in the case of hydrophobic column the wall, being non-wetting in nature, has less affinity for water and the air bubble touches the column wall. Since the bubble displaces water while rising, the water flows past the air bubble in downward direction through a narrow stream.