Natural convective flow and heat transfer of supercritical CO₂ in a rectangular circulation loop

Fluid dynamics and heat transfer of supercritical CO₂ natural convection are important for nuclear engineering and new energy system design etc. In this paper, in order to study the flow and heat transfer behavior of supercritical CO₂ natural circulation system, a computational simulation on a closed natural circulation loop (NCL) model has been carried out. The fluid temperature in the loop varies between 298.15K and 323.15K, which is across the CO₂ critical temperature, and the density is found to be in the range of 250-800kg/m³. The results show a small temperature difference of 25°C between heating and cooling sources can induce a mass flow with the Reynolds number up to 6×10⁴ using supercritical CO₂ fluid. A periodic reversal flow pattern is found and presented in this paper. Enhanced heat transfer phenomenon is also found for the supercritical CO₂ natural convective flow. The mechanisms to this enhancement and the heating effect on the flow are also discussed in detail in the present study.