Experimental investigation on up-flow boiling of R1234yf in aluminum multi-port extruded tubes

The characteristics of local heat transfer and pressure drop were investigated experimentally for the vertical up-flow boiling of refrigerant R1234yf in two types of aluminum multi-port extruded tubes having 16 channels with a crosssection of 0.91 × 0.21 mm (tube A) and 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 heat flux ranging from 316 kW/m and mass flux ranging from 60-240 kg/ms were measured. The heat transfer coefficient almost linearly decreased with increasing vapor quality in both tubes. As the vapor quality increased, the dry patch area became lager in these rectangular channels, which deteriorated the heat transfer performance significantly. Compared with the multi-port extruded tube (tube C) having 16 channels with a cross-section of 0.9 × 0.9 mm, at a mass flux of 60 kg/ms, tube C demonstrated better heat transfer performance than tubes A and B. When the mass flux increased to 120 kg/ms, 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 patch reoccupied the heat transfer area, thereby resulting in worse heat transfer performance in tubes A and B. The pressure drop was not effectively predicted by any of the three correlations investigated.