The gravitational effect in the linear and non-linear dynamics of boiling channels

Abstract

The effect of gravity on the dynamics of flow boiling channels is studied using linear and non-linear stability analysis tools. The developed tools are used to predict experimental results showing good agreement. The linear stability analysis shows that gravity enhances the density wave instability mechanism, enlarging the linear unstable region. Non-linear effects are then investigated by using Hopf bifurcation characterization, allowing identifying meta-stable operating conditions, associated with subcritical bifurcations. In addition, different dynamic basins have been found numerically, which correspond to sub and supercritical Hopf bifurcations. From the results obtained with the model presented here, it is concluded the gravitational effect is found to enhance the density wave instability mechanism, for both the linear and the non-linear domain. This result indicates neglecting gravity in stability studies may lead to non-conservative results. Furthermore, the gravitational effect tends to expand the region where the system exhibits a subcritical behavior.