A two-phase flow regime of a gas and a liquid in a vertical pipe or tube characterized by a continuous gas core with a wall film of liquid. The flow regime occurs at high gas velocities compared with the liquid. There is often a simultaneous flow of the liquid phase entrained in the gas as a fine dispersion of droplets. In horizontal pipes, the effect of gravity causes the film to become thicker on the bottom of the pipe. As the gas velocity is increased, the film becomes more uniform around the circumference. See multiphase.