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

Abstract

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.