Abstract
Experiments were carried out to observe the vapor-liquid two-phase flow of a refrigerant R 410A in small diameter glass tubes. The cross-sectional shapes of the glass tubes were circular, rectangular, and triangular, and their hydraulic diameters were 1.03, 0.97, and 0.82 mm, respectively. Flow directions were vertical upward, downward, and horizontal. Two-phase flow patterns were observed with a high-speed camera for mass velocity ranges from 30 to 400 kg/(m2·s) and qualities between 0.05 and 0.9 at the saturation temperature of 10 ℃ under adiabatic condition. The vapor and liquid superficial velocities were taken as 0.036 - 8.588 m/s, and 0.003 - 0.337 m/s, respectively. Based on the present observations, flow patterns were classified into several flow regimes, and the effects of the cross-sectional shape and flow direction on the flow pattern were clarified. Furthermore, conventional flow pattern maps for mini-channels were compared with the present observation results, and new flow pattern maps were proposed. In addition, the evaporation heat transfer through thin liquid film was confirmed through the observation with heating.
