Flow instability in parallel-channel systems with ultra-supercritical water

In this study, a numerical code that applies a time-domain method is established to analyze the flow instability of a uniformly heated parallel-channel system. Nonlinear dynamics of the ultra-supercritical flow in the water wall are discussed. Results show that the inlet and outlet mass flow rates demonstrate antiphase. The mass flow rates with heat flux perturbations imposed on either single channel decline gradually with time, suggesting that flow stability can be maintained at normal operation. In addition, the effects of heat flux perturbation on transient responses of the typical parallel channels are studied. Results illustrate that the maximum of the inlet mass flow rate in both channels are high when perturbation is imposed on a strong heated channel. Moreover, flow in the stronger heated channel reveals more remarkable dynamic characteristics than in the weaker one. Approximately 141.6 and 139.8 s are needed for perturbation.1 and perturbation.2 to restore to steady state, respectively. Furthermore, data under different inlet temperatures and mass flow rates are calculated to generate the dimensionless instability boundary. When the inlet temperature is low, the inlet mass flow rate should be increased to stabilize the system. Otherwise, the effect of the mass flow rate on the instability boundary is almost negligible.