The analysis of density wave instability phenomena of supercritical water in two parallel channels

•An automation threshold power detection method was applied in the system analysis code which shows good accuracy.•When density wave instability happens, the out-of-phase oscillation of mass flow from inlet to outlet and from one channel to the other channel is observed.•The dimensionless parameters for supercritical water were analyzed which showed good results in converging the scattered data into one line. The density wave instability is a very important thermal hydraulic phenomenon in water reactors design. The supercritical water is a kind of special fluid state which has both the characteristics of single-phase and two-phase fluids. Due to the sharp fluid properties variation near the pseudocritical point, the density wave instability of supercritical water has its own peculiarities. The stability analysis of supercritical fluid has been performed by some researchers. Some experimental results are available now to verify the numerical tools and promote the knowledge of flow instability phenomena at supercritical pressure. In this paper, the system analysis code Relap5 is used as the tool to help explain the mechanism of the density wave instability. The calculation method was verified with the experiments. Parametric effects on flow instability were discussed and stability boundaries were presented. The dimensionless parameters were analyzed which showed good potential to be used for the instability analysis of supercritical water.