Nonlinear dynamics of two-phase flow in multiple parallel heated channels

Some basic aspects of bifurcation phenomena in two-phase flow and the related nonlinear dynamics of single and multiple parallel, uniformly and nonuniformly heated channels are studied. Specifically, the effects of several two-phase-flow system features on the stability of equilibria are determined. These features include: (1) unheated sections, or risers, at the tops of the heated channels; (2) a return feedback loop that relates the fluid properties at the channel inlets to those at the channel exits at an earlier time; and (3) the flow interaction among multiple parallel channels subjected to fixed total mass flow rate boundary conditions and alternatively to fixed external pressure drop boundary conditions. It is shown that the addition of unheated riser sections at the tops of the heated channels has a destabilizing effect, and that as the lengths of the risers at the tops of otherwise stable heated channels are increased, a supercritical Hopf bifurcation occurs resulting in stable limit cycle density-wave oscillations. It also is demonstrated that the addition of a simple return feedback loop is destabilizing, and that the complex interaction among multiple channels enables one unstable channel to drive the multiple channel system unstable.