R410A flow boiling in horizontal annular channels of enhanced tubes, part I: Pressure drop

Pressure drop during flow boiling of R410A was experimentally investigated at a saturation temperature of 279 K over a mass flux range of 50–80 kg/(m²s) and a vapor quality range of 0.2–0.8. The inner tubes with the same outside diameter of 19 mm contain a smooth tube and three enhanced tubes: a micro-porous (No. 1) tube, a ring-shaped finned (No. 2) tube, and an independent small-bosses surface (No. 3) tube. It was observed that the pressure drop in single-phase and flow boiling conditions increased with the increase of the mass flux, and the ring-shaped finned tube showed the highest pressure drop (more than 1.35 times and 1.31 times that of the smooth tube, respectively) due to the effect of the ring-shaped fins. The pressure drop in the micro-porous tube and the smooth tube increased with the increase of outlet vapor quality in the range of the mass fluxes tested. Results from correlation analysis showed that two existing correlations can be implemented to predict the frictional pressure drop in a smooth tube within a deviation of ± 10%. Improved correlations to predict pressure drop in the enhanced tubes were presented, and 94% of the data points of the micro-porous tube were predicted within a ± 10% error band.