Computational fluid dynamic analysis of a supercritical CO2 based natural circulation loop with end heat exchangers

Abstract

Steady state simulation of a 3D model of supercritical CO2 based natural circulation loop with end heat exchangers has been carried out employing the commercial CFD (computational fluid dynamics) code, FLUENT. The simulation considers phenomena such as viscous dissipation in fluid, axial conduction in fluid as well as in solid wall. Study has been carried out at a constant CO2 operating pressure of 80 bar. Results are obtained for various inlet temperatures of water in the hot heat exchanger, within the range of 323–353 K, for a fixed inlet temperature of cooling water in the cold heat exchanger (305 K). Results show that heat transfer rate increases with increase in HHX water inlet temperature whereas mass flow rate of loop fluid decreases. Due to the presence of bends and strong buoyancy effects, fluid parameters such as local velocity and temperature vary in all three dimensions which justifies the use of 3D model for this study. Results also show that even for a small temperature difference of 18 K, Reynolds number reaches a high value of the order of 105. Validation of simulation results against experimental results reported in the literature with respect to modified Grashof number (Grm) and Reynolds number (Re) exhibit good agreement.