Up-flow boiling of R1234yf in aluminum multi-port extruded tubes

The characteristics of local heat transfer and pressure drop were experimentally investigated for the vertical up-flow boiling of refrigerant R1234yf in two types of aluminum multi-port extruded tubes. One with 16 channels with a cross-section of 0.91 × 0.21 mm (tube A), and one with 40 channels with a cross-section of 0.34 × 0.21 mm (tube B). At an evaporating temperature of 15 °C, the local heat transfer coefficient and pressure drop for the heat flux range of 3-16 kW/m2, and mass flux range of 60-240 kg/m2 s were measured. The heat transfer coefficient decreased nearly linearly with increasing vapor quality in both tubes. As the vapor quality increased, the dry patch areas became larger in these rectangular channels, which degraded the heat transfer performance significantly. Compared with the multi-port extruded tube (tube C), with 16 channels with a cross-section of 0.9 × 0.9 mm, at a mass flux of 60 kg/m2 s, tube C demonstrated better heat transfer performance than tubes A and B. When the mass flux increased to 120 kg/m2 s, the dry-out was alleviated in tubes A and B, and better performance was observed for low vapor quality regions, while in high vapor quality regions the dry patches reoccupied the heat transfer area, thereby resulting in worse heat transfer performance in tubes A and B. The pressure drop and heat transfer coefficient was not effectively predicted by the existing correlations.