Exploring Diabatic Flow Patterns Maps and Factors Affecting Flow Boiling Heat Transfer Coefficients of R134a and R513A Refrigerants Through Microfin Tube

This study investigates the evaporation heat transfer performance of environmentally friendly refrigerant R513A compared to conventional R134a in horizontal micro-fin tubes, addressing the urgent need for sustainable alternatives to high-GWP (global warming potential) refrigerants. Experiments were conducted across mass fluxes (75–275 kg/(m2·s)), saturation temperatures (17–27 °C), and heat fluxes (up to 36 kW·m−2). Results demonstrate that R513A achieves 10–25% higher heat transfer coefficients than R134a under identical conditions, maintaining stable annular/wavy-annular flow patterns without premature dry-out. In contrast, R134a exhibited early dry-out initiation at 36 kW/m2, reducing its thermal efficiency. Increasing heat flux amplified dry-out tendencies in both refrigerants, as evidenced by flow pattern transitions. R513A’s superior performance is attributed to its favorable thermophysical properties and enhanced interaction with micro-fin geometry, which promote efficient convective and nucleate boiling. Notably, R513A combines a 56% lower GWP with thermodynamic performance comparable to R134a, positioning it as a viable eco-friendly replacement. The study underscores the critical role of micro-fin tubes in optimizing heat transfer and highlights the tradeoffs between thermal efficiency, operational stability, and environmental impact in refrigeration system design. These insights provide actionable guidelines for transitioning to sustainable refrigerants without compromising performance in high-demand applications.