Density wave instability analysis in a parallel channel natural circulation loop of supercritical pressure fluid

Abstract

To analyse the steady state behaviour and dynamic density wave instabilities (DWIs) of super-critical pressure fluid (SCF) inside a natural circulation loop (NCL) for a heated section with parallel channels, a numerical thermal-hydraulic (TH) model is developed. The capability of the TH model to simulate the above mentioned aspects for a two channel heated section is validated with the existing numerical results and experimental data points. Steady state analysis is performed mainly to find the loop mass flow rate at different operating conditions. It is also aimed to correlate the loop mass flow rate with the driving head, i.e., with the difference in pressure drops due to gravity and friction. Next, the transient model is integrated with that of the steady state to analyse DWI. The model accounts for compressible flow dynamics of SCF and can deal with any number of parallel channels in the heated section while analysing DWIs. With the transient simulations, it is aimed to bifurcate the operating regime into stable and unstable regions, and find the marginal stability boundary (MSB). Extensive simulations are, next, performed to determine the effect of different parameters on the MSB and the findings are reported accordingly.