Behavior of steam-condensate countercurrent two-phase flow in a vertical pipe

Steam-condensate countercurrent two-phase flow was studied in a vertical steam pipe with a cooling pipe. The lower plenum pressure and distribution of coolant temperature in axial direction were measured. The plenum pressure increases as the steam velocity increases, and attains a maximum when condensed water started to overflow from the top of pipe. For a further increase of steam velocity, the plenum pressure begins to decrease and shows periodic oscillation in the case of low flow rate of coolant. During overflow of the condensate, no steam emission was observed from the pipe. The heat balance indicates the existence of a region in which the condensate might stay as a single phase.