Phase split in parallel vertical channels in presence of a variable depth protrusion header

• Experimental study of air–water phase distribution in parallel vertical channels.
• Comparison between different protrusion configurations and reference (no fitting).
• Minimum protrusion depth (0.5 D) useful for improving the phase.
• Best distribution figure of merits measured with variable depth protrusions.

The air and water flow distribution are experimentally studied in a test section simulating a heat exchanger composed by a round header and 16 parallel upward channels. The effects of the tube protrusion depth as well as the gas and liquid superficial velocities are investigated and the results are compared with previous data. A new fitting solution to be inserted in the header has been developed based on previous findings by the Authors. The fitting geometry belongs to the family of the protruding pipes but the protruding depth has been varied along the header in order to cope with expected liquid and gas mass flow rates in the parallel channels. The flow at the header inlet is intermittent and annular and water and air have been employed as two phase mixture. The new header fitting demonstrated to yield meaningful improvements in phase distribution in terms of either dimensionless liquid and gas flow ratios or standard deviation of phase flow ratio (the overall performance parameter STD2 here presented decreased by 64%) when compared to the previous configurations.