Flow and heat transfer characteristics of liquid metal and supercritical CO2 in a twisted tube heat exchanger

Abstract

The Lead-cooled Fast Reactors (LFRs) are fast neutron spectrum reactors cooled by molten lead or lead alloys, which are recommended as one of candidates for the next generation of nuclear reactors due to high performance in sustainability, thermal-hydraulics, and security features. As the critical equipment linking the primary circuit and secondary circuit in LFR, the performance of the main heat exchanger plays a significant role in the operating efficiency of the reactor. In order to improve the heat transfer efficiency and optimize the temperature distribution between the coolant in the primary circuit and secondary circuit of LFR, the flow and heat transfer characteristics of fluids in twisted elliptical tube are investigated in the present study, since the specific spiral cross flow is expected occurring in both inside of the tubes and the interfering area outside the tubes. Theoretical calculation is conducted firstly based on the periodical unit model of the twisted tube heat exchanger. Then the numerical simulation is carried out to study the characteristics of fluid and heat transfer in both shell and tube sides. The results show that the cross flow in twisted tubes improves the overall heat transfer performance of the heat exchanger by strengthening the mixing and turbulence of working fluid. Compared with straight tubes, the entire performance evaluating factor of twisted tubes is around 1.596 times. The theoretical and numerical studies are helpful to the design of the main heat exchanger in LFR.