A review of heat transfer deterioration mechanisms and mitigation strategies of supercritical CO2 heat transfer

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As a non-toxic, non-combustible natural working fluid, CO2 is widely used in kinds of new power generation systems and low-grade waste heat recovery due to its stable chemical properties and excellent thermophysical properties, which not only significantly reduces the volume of the thermal system, but also effectively improves the circulating thermal efficiency. The thermophysical properties of supercritical CO2 change drastically with temperature near the pseudo-critical point (Tpc), generating a complex boundary layer structure that triggers heat transfer enhancement and deterioration. Heat transfer deterioration typically manifests as a sudden increase in wall temperature and a corresponding decline in the heat transfer coefficient. This leads to irreversible losses in the heat transfer process, resulting in heightened system circulation, reduced thermal efficiency, accelerated tube corrosion, and, in severe instances, poses a significant threat to system safety, potentially resulting in tube bursting and considerable harm. Therefore, understanding and mastering the flow and convective heat transfer characteristics of supercritical fluids in tubes is the basis for designing more efficient heat transfer structures. This paper provides a comprehensive overview of the mechanisms underlying heat transfer deterioration in supercritical CO2 systems, along with various strategies to enhance heat transfer efficiency. Additionally, it discusses the current state of research on Helmholtz self-oscillating cavities, which can serve to inhibit heat transfer deterioration in supercritical fluid tubes. This research not only serves as a reference for improving system performance but also offers new insights into the exploration of more efficient heat transfer technologies.