Supercritical CO2 flow instability in natural circulation loop: CFD analysis

Abstract

Three-dimensional computational fluid dynamics (CFD) simulation on a supercritical CO2 based natural circulation loop (scCO2-NCL) is carried out to explore the effects of various parameters (i.e., pressure and heat inputs) on the loop’s transient and stability behaviour. Results show that for supercritical CO2, there is a threshold point that decides the flow’s nature. Lower than threshold heat inputs flow shows repetitive-reversal flow while at higher heat input the flow changes to stable or single-direction flow. With an increase in heat input, the system attains stability for a given operating pressure. In addition, a possible mechanism for continuous flow oscillation and measurement of instability with different pressure in unstable loops is also proposed in this study. It is found that the Nusselt number decreases with an increase in operating pressure for given heat input. Obtained simulation results are validated with the two existing correlations and found a good agreement.