Experimental study on heat transfer characteristics of supercritical carbon dioxide in a vertical circular tube

Supercritical carbon dioxide (S-CO₂) nuclear energy and power systems have garnered significant attention for flow and heat transfer experiments because of their compact design, advanced circulation methods, and high thermal efficiency, aligning with future trends in nuclear power plant development. However, the dramatic change in physical properties of S-CO₂ near its pseudo-critical point can lead to heat transfer deterioration (HTD) in heat exchangers, potentially damaging the S-CO₂ Brayton system. This paper presents an experimental study on the HTD of S-CO₂ in a vertical circular tube under forced circulation, examining how heat flux, inlet temperature, and system pressure influence HTD. The analysis delves into the mechanisms of HTD, focusing on the buoyancy and flow acceleration effects. Additionally, the study explores the instability of single-tube flow under forced circulation conditions. Ultimately, the research summarizes the flow and heat transfer characteristics of S-CO₂ and proposes a new heat transfer correlation formula, demonstrating an error margin within ±25 %, which meets practical engineering requirements. This experimental study contributes valuable data to the understanding of flow and heat transfer phenomena in S-CO₂, offering significant insights for future applications.