Two-phase flow characteristics of R32 in horizontal multiport minichannels: Flow visualization and development of flow regime map

Abstract The two-phase flow characteristics of R32 were experimentally investigated for horizontal multiport rectangular minichannels with hydraulic diameters of 0.5 and 1.0 mm. The two-phase flow was observed using a high-speed camera, with a mass velocity range of 30–400 kgm −2 s −1 at a saturation temperature of 15 °C. The effects of mass velocity, quality, and channel size on the two-phase flow were clarified. The observed two-phase flow was classified into intermittent, transition, and annular flow regimes. The intermittent flow regime was observed at a lower quality region. The quality of transition from intermittent to transition flow regimes decreased with increasing mass velocity and channel size. Previously proposed flow regime maps could not predict the two-phase flow regime in multiport rectangular minichannels with sufficient accuracy. Thus, a new prediction method of flow regimes for multiport minichannels, considering channel size, was developed.