Effect of Axial Power Distributions on Supercritial Water Flow Instability

The control equations of the calculation model on flow instability for a supercritical water parallel channel system were established. Semi-implicit finite-difference method with staggered mesh was used to discretize the control equations solved by the main element Gauss-Jordan elimination method. The accuracy of this model was verified by the experiment data. Uniform power distribution was selected as the reference axial power distribution, and cosine, bottom-peaked and top-peaked power distributions were used to simulate the axial non-uniform power distribution. The marginal stability boundaries (MSBs) for those four different axial power distributions were obtained by the transient calculation. The results show that compared with the uniform power distribution, the bottom-peaked power distribution will destabilize the system stability, while the top-peaked power distribution can enhance the system stability in the whole pseudo-subcooling number region. In high pseudo-subcooling number region, cosine power distribution will decrease the system stability, while the system stability will be enhanced in low pseudo-subcooling number region. In addition, a concept of pseudo-single-phase pressure drop ratio was proposed to analyze the influence mechanism for axial power distributions on the flow instability of the supercritical water in parallel channels.