Theoretical study on the flow instability of supercritical water in the parallel channels

Super Critical Water (SCW) will experience considerable changes on the thermal and transport properties such as density, enthalpy, specific heat and thermal conductivity at normal operating condition. The flow instability in the parallel channels with SCW was studied in this paper. Mathematical and physical models were established to simulate the flow and the heat transfer characteristics of supercritical water with semi-implicit scheme and staggered mesh scheme. The flow instability of SCW was analyzed using the tiny perturbation method. Pseudo-subcooling number (N_SPC) and pseudo-phase change number (N_TPC) which can be used to distinguish the system instability were derived based on the property of SCW. The marginal stability boundary (MSB) was then obtained by using the N_SPC and N _TPC. The effects of different parameters, such as mass flow rate, heat flux, inlet temperature and system pressure, on the flow instability boundary were also investigated. When increasing the mass flow rate and the system pressure, decreasing the heat flux, the flow stability in the parallel channels increases. The effect of inlet temperature in the low pseudo-subcooling number region is different from that in high pseudo-subcooling number region.