Visualization and quantification of separation of liquid-vapor two-phase flow in a vertical header at low inlet quality

This paper presents the experimental study of separation of two-phase flow in a vertical header of microchannel heat exchanger based on quantified visualization using fast camera. A prototype unit, representing the real condenser has an inlet in the center of the header. Downstream of the intermediate header are two branches: lower for liquid and upper vapor flow. The header for experiment provides full visual access. R-134a is used as the fluid and mass flux through the inlet microchannels is controlled at 54 kg m−2 s−1-193 kg m−2 s−1. The results indicate that within the range of lower inlet quality (5-25%), good separation in that header can happen at low mass flux up to 90 kg m−2 s−1. Results are presented in function of liquid and vapor separation efficiencies (ηl, ηv). Two-phase flow characteristics inside the header are analyzed for better understanding of separation efficiencies ηl and ηv. The efficiency deteriorates dramatically when liquid reaches the vapor exit, with increasing inlet flow rate and/or quality. Better two-phase separation can be achieved by reducing the liquid upward momentum or the vapor, and decreasing liquid and vapor interaction.