Numerical simulation analysis of flow boiling heat transfer in internal micro-finned tubes

Internal micro-finned tubes are widely used in modern air conditioning and refrigeration systems due to their excellent thermal performance during two-phase flow conditions. This study begins with a numerical simulation that examines the boiling heat transfer and two-phase flow characteristics of different refrigerants—R32, R410A, and R1234ze—inside a micro-finned tube with a 3.32 mm internal diameter. Subsequently, the paper presents a numerical analysis of R32’s behavior in micro-fin tubes of identical diameter under heat flux densities of 10 kW/m2, 50 kW/m2, and 100 kW/m2, respectively. The results show that as various refrigerants flow and boil in the tubes, there is a sequential occurrence of bubble flow, slug flow, and wavy-annular flow. The boiling heat transfer coefficient is highest for R32 and lowest for R1234ze, with a direct proportionality to the refrigerant’s latent heat of vaporization and liquid thermal conductivity. The local pressure drop escalates with increasing tube length, with R32 experiencing the highest average pressure drop, followed by R1234ze and R410A. Furthermore, the heat transfer coefficient diminishes as the heat flux density increases, while the pressure drop surges in response to rising heat flux density.