Novel Correlations for flow and heat transfer processes in S-CO2 Brayton cycle with different roughness by experimental and simulation methods

Abstract

This study comprehensively examines heat transfer performance of supercritical carbon dioxide (S-CO2) in horizontal tubes under actual operating conditions of precooler, regenerator and heater, with a focus on the impact of tube roughness. By employing both experimental and numerical methods, it aims to bridge the gap in current research regarding S-CO2 heat exchanger performance that incorporates the effect of roughness. The results indicate that roughness height can suppress the influence of buoyancy effects. As roughness height increases from 1.5 μm to 100 μm, average temperature difference of heater at an outlet temperature of 1000 K decreases from 134.9 K to 61.1 K. Although roughness height can significantly enhance heat transfer, yet the rate of this enhancement diminishes when the roughness height surpasses 50 μm. To address the need for accurate heat transfer and flow correlations considering roughness, high-precision correlations are proposed and validated. The correlations of precooler, regenerator and heater exhibit average absolute deviations of within 8 %, 10 % and 12 %, respectively. The proposed correlations not only enrich theoretical framework of related fields but also provide a solid foundation for optimizing the design and operation of S-CO2 Brayton cycle, enabling more efficient energy conversion and reduced carbon emissions.