Numerical Study on Flow and Heat Transfer of Supercritical CO₂ in Narrow Rectangular Channel with Sinusoidal Rib

The efficient heat transfer of supercritical CO₂ (SCO₂) is crucial for the design and operation of compact heat exchangers in advanced energy systems, such as solar thermal power plants and nuclear reactors. Sinusoidal rib structures are promising for enhancing heat transfer in narrow rectangular channels, yet their comprehensive influence on the flow and heat transfer characteristics of SCO₂ remains insufficiently explored. This study aims to investigate the effect of sinusoidal ribs and operating conditions on flow dynamics and heat transfer performance of SCO₂ in narrow rectangular channels. A numerical simulation was conducted to analyze the flow and heat transfer processes of SCO₂ in a narrow rectangular channel equipped with sinusoidal ribs. The SST k-ω turbulence model was adopted to accurately capture the turbulent flow features and near-wall heat transfer behaviors, considering the strong thermophysical property variations of SCO₂ near the critical point. The parameters of the sinusoidal rib structure were analyzed, including amplitude A ranging from 2 mm to 4 mm, period p ranging from 20 mm to 60 mm and operating parameters, including mass flux G ranging from300 kg/(m²·s) to 500 kg/(m²·s), inlet temperature T_in ranging from 300 K to 320 K, heat flux q ranging from 20 kW/m² to 40 kW/m² and operating pressure P ranging from 8 MPa to10 MPa. Detailed flow field and temperature distribution data were obtained through numerical simulations to evaluate key performance indicators, such as average heat transfer coefficient (h_ave), average wall temperature (T_w,ave), maximum wall temperature (T_w,max), and performance evaluation criterion (PEC). Results indicate that the h_ave increases with rising G due to stronger turbulent convection. In relation to T_in, h_ave shows a non-monotonic trend, initially increasing as T_in approaches the pseudo-critical temperature (T_pc) and then decreasing. Both increased q and P generally lead to a reduction in h_ave, attributed to the alteration of thermophysical properties. The sinusoidal rib structures enhance heat transfer performance primarily by intensifying near-wall turbulence and disrupting the thermal boundary layer, which promotes the convective heat transfer between SCO₂ and the channel wall. Comparative analysis of different rib configurations reveals that the configuration with A=4 mm and p=40 mm achieves the optimal enhanced heat transfer performance in terms of T_w,ave and h_ave. However, when considering T_w,max and PEC, the configuration A=2 mm and p=20 mm outperforms others, yielding the lowest T_w,max=342.29 K and the optimal PEC=1.20. These findings provide a crucial theoretical basis and practical design references for the application of sinusoidal rib structures in high-efficiency compact SCO₂ heat exchangers, facilitating the optimization of energy conversion efficiency in advanced energy systems.