  The role of surface tension and wettability in the dynamics of air-liquid
interfaces during immiscible fluid displacement flows in capillary tube driven
by pressure has been investigated. The contact angle and capillary number drive
the force wetting processes which is controlled by the balance between the
capillary and the viscous lubrication forces. The dynamic wetting condition
with the critical capillary number is studied analytically and validated
experimentally, which demonstrates that the critical capillary number is
associated with the contact angle, slip length and capillary radius.
