Thermal-hydraulic performance of R1234yf in brazed plate heat exchanger at low saturation temperature and mass flux conditions: Experimental investigation

Abstract

This study investigated the heat transfer coefficient (h_r) and two-phase frictional pressure drop during the evaporation of R1234yf within an offset strip fin (OSF)-structured brazed plate heat exchanger (BPHE). The work is conducted at a saturation temperature (T_s) of −3 to 3 °C, with mass flux (G) ranging from 25 to 45 kg m⁻² s⁻¹ and heat flux (q) between 15 and 23 kW m⁻² across a vapor quality (x) range of 0.1–0.8. Understanding these behaviors is critical for optimizing BPHEs in low-temperature applications, such as heat pumps, where energy efficiency is essential. The novelty of this work lies in its exploration of operating conditions that are less studied in the literature, particularly the impact of low T_s, low G, and high q on h_r and two-phase frictional pressure drop in an OSF-BPHE with R1234yf. Unlike prior studies focusing on convection-dominated boiling, our findings reveal a coexistence of nucleate and convective boiling mechanisms, especially at different vapor qualities. The h_r is significantly influenced by q at x  < 0.6, G at x  > 0.6, and T_s across all x. In contrast, evidence of dryout at high x highlights the importance of these parameters in managing heat transfer efficiency. The results indicate a strong correlation between the two-phase frictional pressure drop and G, with a marked increase in it at higher G. Besides, this study reveals flow characteristics commonly linked with both macrochannel and minichannel flows, enhancing novelty by bridging the gap between these two regimes. These findings challenge existing literature correlations that predominantly emphasize convection-dominated behavior and contribute to a better understanding of the dual boiling mechanisms in BPHEs.