Dynamic heat transfer characteristics of R-410A refrigerant in saturated flow boiling under oscillating mass flux conditions

The study investigates the unsteady saturated flow boiling heat transfer of R-410A in a horizontal annular channel , focusing on the effects of oscillating mass flux. Key parameters, including mean mass flux, amplitude and period of oscillation, input thermal flux, and saturation temperature , are examined to determine their influence on boiling curves and heat transfer coefficients (HTC). Baseline steady-state experiments show that mass flux oscillation has minimal effect on boiling curves beyond nucleate boiling , where fully developed nucleate boiling governs heat transfer. Under oscillatory flow conditions, three distinct flow regimes are identified: single-phase flow, sporadic boiling flow, and persistent boiling flow. Periodic variations in mass flux induce corresponding oscillations in both wall temperature ( T w ) and boiling HTC , with larger amplitude and frequency of oscillation enhancing thermal response. At higher thermal flux, wall temperature decreases with reduced mass flux, opposite to the trend observed in single-phase flow. For moderate heat flux levels, oscillations in T w and HTC are minimal, while larger oscillation periods result in more pronounced fluctuations in temperature and HTC. These findings offer valuable insights into the dynamic heat transfer behavior of R-410A, contributing to the optimization of thermal management systems for industrial applications operating under unsteady flow conditions.