Study on the influence of tube type and fluid flow channel on cooling heat transfer characteristics of supercritical CO2 in spirally grooved casing tubes

Abstract

This study investigates the heat transfer characteristics of supercritical CO₂ (SCO₂) in five different spirally grooved casing tubes and proposes a comprehensive evaluation factor to assess their overall performance, aiming to improve heat exchanger efficiency through optimizing tube designs. The Finite Volume Method is employed to simulate and compare five different spirally grooved configurations: three-start circular arc (Case A), four-start circular arc (Case B), four-start trapezoidal (Case C), four-start triangular (Case D), and six-start circular arc (Case E). The results show that when SCO₂ flows through the channel between the inner and outer tubes (channel 1), Case E exhibits the highest heat transfer coefficient, with a value of 2537.91 W·(m²·K)⁻¹. This is significantly higher than the other designs, with a maximum increase of 19.20 %, demonstrating its optimal performance in enhancing heat transfer efficiency. In the inner tube channel (channel 2), the average heat transfer coefficients for Case D and Case E are approximately equal, around 2410 W·(m²·K)⁻¹, which is 3.22 % higher on average than the other three designs, indicating impressive potential for optimizing the groove shape in channel 2. The pattern of SCO₂ flowing in channel 2 can effectively reduce the pressure drop gradient, with a maximum reduction of 27.60 %, thereby significantly improving the safety of the system. The flow pattern of SCO₂ in channel 2 of Case A exhibits the optimal comprehensive evaluation factor value (2.03). These scientific findings provide conducive insights for optimizing design of the SCO₂ heat exchangers.