System pressure effect on density-wave instability; Simplified model analysis and experiments

Shibamoto, Yasuteru ; Iguchi, Tadashi; Nakamura, Hideo  ; Kukita, Yutaka*

The pressure effect on the onset of flow instability in a vertical upflow through a boiling channel is studied both analytically and experimentally. The analytical model is based on the Wallis-Heasley model for linear analysis of one-dimensional homogeneous two-phase flow in thermal equilibrium. The dead-time elements commonly used to represent the time lag in the responses of variables to the inlet velocity perturbation is replaced by first-order lag elements to allow the system characteristic equation to be solved analytically. This approach, although approximate, makes it much easier to identify the main contributor to the instability because the individual components are represented by separate terms in the characteristic equation. The predictions are in reasonable agreement with the data when the system pressure effect on the irreversible pressure loss in the two-phase region is appropriately considered based on calibration experiments.