Visualisation et quantification de la séparation de l’écoulement diphasique liquide-vapeur dans un collecteur vertical à faible qualité d'entrée

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 (η_l, η_v). Two-phase flow characteristics inside the header are analyzed for better understanding of separation efficiencies η_l and η_v. 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.