Experimental investigation on flow and heat transfer characteristics of eutectic Sn-Bi alloy in a circular tube

• Systematic experimental study on ESnBi flow and heat transfer in a circular tube. • New Nu–Pe and f–Re correlations proposed for turbulent ESnBi flow. • ESnBi correlations comprehensively compared with existing liquid metal correlations. • Results provide a theoretical basis for engineering applications of ESnBi. Compared with conventional liquid metals such as sodium (Na) and lead–bismuth eutectic (LBE), eutectic tin–bismuth alloy (ESnBi) exhibits notable advantages including higher volumetric heat capacity, moderate thermal conductivity, lead-free with lower toxicity, and chemical inertness in air, making it a promising candidate for medium-to-high temperature heat transfer applications (T > 150 °C). However, studies on its thermal hydraulic behavior remain scarce. To address this research gap, the present work experimentally investigates the flow and heat transfer characteristics of ESnBi under turbulent flow conditions in a circular tube with an inner diameter of 14 mm. Experiments were conducted under uniform wall heat fluxes ranging from 12.2 kW/m 2 to 83.6 kW/m 2 , corresponding to Reynolds numbers ( Re ) between 5,000 and 25,000 and Peclet numbers ( Pe ) between 200 and 1,000. The convective heat transfer coefficient and pressure drop were measured, and empirical correlations were developed. The proposed Nusselt number ( Nu ) correlation, Nu = 4.47 + 0.016 Pe 0.78 , exhibits close agreement with established correlations for LBE and demonstrates strong predictive capability across heavy liquid metals, as confirmed by relative standard deviation (RSD) analysis. Additionally, a frictional resistance coefficient ( f ) correlation for the hydraulically smooth regime was established: f = 0.3716/ Re 0.21 , which is approximately 1.7 times greater than the classical Blasius equation, indicating flow resistance behavior similar to that of LBE in the transitionally rough regime. This deviation may result from oxide inclusions and corrosion effects within ESnBi, which merit further investigation. Overall, this study provides essential experimental data to support the engineering application and thermal system design of ESnBi as a promising heat transfer fluid.