Numerical investigation on coupled heat transfer of an immersed tube with sCO2 working fluid in a fluidized bed at high temperature and pressure

•A bed-tube-sCO2 coupled heat transfer model is developed and validated.•The bed-tube-sCO2 coupled heat transfer is numerical studied for the first time.•The effect of immersed tube on coupled heat transfer is investigated.•A new heat transfer correlation with an accuracy of ±25% is proposed. Supercritical CO2 (sCO2) power cycle driven by pressurized fluidized bed (FB) boiler, reactor or heat exchanger is an advanced thermal power generation technology due to higher electrical efficiency and more compact system. However, as the main heating surface, the coupled heat transfer behavior of immersed tubes loaded within sCO2 is unclear. In this work, we developed a bed-tube-sCO2 heat transfer model and explored the effects of tube wall, furnace pressure, particle properties, bed temperature and fluidization medium on heat transfer of sCO2 loaded immersed tube in a FB at high temperature and pressure. Results showed that the thermal buffering effect of the immersed tube improved the heat transfer stability of sCO2. The bed-to-tube heat transfer coefficient (HTC) would not increase continuously with the furnace pressure. Therefore, using bed materials with better properties was an effective way to enhance the heat transfer of immersed tubes in high-pressure FBs. CO2 as a fluidization medium affected heat transfer mainly through convection rather than radiation. A new heat transfer correlation with an accuracy of ± 25% was proposed, which can be used to design and optimize immersed tubes in this advanced technology.