Abstract:

Supercritical CO₂ plays an important role in many applications such as nuclear power generation, solar power generation, cryogenic refrigeration, and aerospace. Currently, the majority of studies on supercritical CO₂ convective heat transfer in tubes focus on the temperature range near the critical point, while the heat transfer patterns at high temperature and pressure far from the critical point remain unclear and need to be further studied. In this study, numerical simulations were performed to analyze the effects of mass flow, inlet temperature, system pressure, heat flux density, and tube diameter on the convective heat transfer coefficient at high temperature and pressure, as well as the effects of buoyancy and flow acceleration caused by operating conditions on the heat transfer characteristics. The results show that the convective heat transfer coefficient increases with increasing mass flow, inlet temperature, system pressure, and heat flux density. The difference in convective heat transfer coefficient gradually grows along the flow direction under different heat flux densities. Convective heat transfer coefficient decreases with increasing tube diameter. Compared with the heat transfer patterns near the critical point, heat flux density and tube diameter exert different effects on the convective heat transfer coefficient. In general, the effects of pressure on the convective heat transfer coefficient are small. This study provides significant values to understand the law of supercritical fluid heat transfer and guide the design of efficient and safe heat exchanger.

Key words: supercritical CO₂, far critical point, vertical tube, heat transfer characteristics, numerical simulation