Numerical study on the density wave oscillation of supercritical water in parallel multichannel system

A time-domain model is proposed to study the density wave instability of supercritical water in parallel multichannel system. The present model splits the flow domain along each channel based on the collocated mesh method, and adopts an iterative solution to solve the coupling among multiple channels. The model is verified firstly by the experimental data obtained in open literature. After that, the model is used to study the effect of the key parameters on the density wave instability of supercritical water in parallel multichannel system (such as, adding different perturbations, inlet fluid temperature, and so on). Moreover, the influence mechanisms of these key parameters on the density wave oscillation of supercritical water are also explained. It is found that out-of-phase oscillation occurs between the perturbation channels (which are added with the perturbation) and the rest other channels, and the amount of perturbation channels has little effect on oscillation period and system stability. The system stability first decreases and then increases with the inlet fluid temperature, and the system has the worst stability when the inlet fluid temperature is equal to a critical value, denoted by T_in-cr. This is because that the variation of the fluid density along the system will reach the maximum when the inlet fluid temperature is near T_in-cr, which makes the system most unstable. T_in-cr is always lower than the pseudo-critical temperature of supercritical water at the corresponding pressure. T_in-cr has no obvious change with system pressure.