On the analogies in the dynamic behaviour of heated channels with boiling and supercritical fluids

In this paper, the origin and the consequences of a new dimensionless formalism recently introduced for analysing the dynamic behaviour of heated channels with fluids at supercritical pressures are discussed. A unified view of boiling and supercritical fluid instabilities is proposed, basing on the argument that, despite the strong differences in their operating conditions, in both cases the relevant dynamics results from the changes in density that the fluid undergoes along the channel. The discussion is presently supported only by modelling, performed both by a simplified program and a system code; however, considering the complete independence of these modelling tools, the close agreement observed between their results provides a reasonable level of confidence in the proposed conclusions. Interesting thermodynamic relationships, devised as a by-product of the introduction of the new dimensionless parameters, are also presented, in the aim to stimulate further studies capable to provide greater insight into the fascinating aspects raised by recognising the intimate similarity of these two classes of phenomena, which have such a remarkable relevance for present and future nuclear reactor technology.