Condensation heat transfer of pure refrigerants R1234yf and R32 inside multiple circular minichannels

This study experimentally investigated condensation heat transfer coefficients inside horizontal multiple circular minichannels with inner diameters of 0.81 and 0.49 mm, using pure refrigerants R1234yf and R32. The effects of mass flux, vapor quality, channel size, heat flux, and refrigerant properties on condensation flow characteristics within a mass flux range of 50-400 kgm(-2)s(-1) were clarified. Annular, churn, slug-annular, and plug (intermittent) flows were visualized inside multiple circular minichannels. It was determined that the heat transfer coefficients of R1234yf and R32 were affected by mass flux, vapor quality, and heat flux. At lower mass fluxes, the contribution of surface tension to heat transfer was dominant relative to that of forced convection. The heat transfer coefficient increased with decreasing channel size, and R32 exhibited higher values of the heat transfer coefficient compared to those exhibited by R1234yf. The proposed heat transfer correlation, accounting for the effects of forced convection and surface tension, predicted heat transfer coefficients for circular minichannels with a mean absolute deviation of 15.2%. (C) 2022 Elsevier Ltd. All rights reserved.