Effects of double-humped axial heat flux variation on the stability of two-phase flow in heated channels

Stability analysis of two-phase flow in heated channels with double-humped axial heat flux variation, relevant to boiling water nuclear reactors, has been carried out. Single-phase and two-phase flow equations are linearized about the steady-state solution, and the stability of the fixed points is studied in frequency domain. Effects of symmetric and asymmetric double-humped axial heat flux variation on stability has been determined. Results are presented as stability boundaries in parameter space and as bifurcation diagrams. It is found that whether a channel with single-humped heat flux variation becomes more or less stable as the heat flux is replaced by an equivalent double-humped profile, actually depends upon other system parameters, such as the channel inlet subcooling. For example, for low inlet subcooling, a channel with symmetric double-humped heat flux variation is less stable than another channel with single-humped heat flux variation (same total heat flux), whereas, the trend is reversed for high inlet subcooling.