Oscillations auto-entretenues dans les écoulements diphasiques chauffés

Self-sustained oscillations in heated two-phase flows

¹ Service des Transferts Thermiques, Centre d'Etudes Nucléaires de Grenoble.
² Institut de Physique Atomique de Bucarest, Stagiaire de l'A.I.E.A. auprès du Service des Transferts Thermiques.

Résumé

The spontaneous occurrence of oscillations in heated two-phase flows can be explained by lags in the system. The process considered in this paper as a 'density effect' results in lags because of the propagation of a density disturbance in the channel at finite velocity (An initial description of this process was given in a paper to Société Hydrotechnique de France in 1964 [8]). It is shown first of all that the density effect is sufficient to cause oscillations whose thresholds, frequencies and other properties are consistent with those of real-life phenomena. It is then shown with the aid of a mathematical model that the density effect provides a satisfactory explanation for the influences observed experimentally and thus seems to be the main "mechanism" at play in the oscillatory behaviour of real systems. Finally, the quantitative results obtained with the mathematical model are compared with the experimental data.