A model of critical boiling flow with account of wall boiling-up

A model for simulation of critical flows of boiling liquids is proposed, which takes into account the existence of two vapor phases: α-bubbles “attached” to the channel walls and β-bubbles moving in the flow. The model takes into account the possibility of breakdown of both groups of the bubbles due to both the Kelvin-Helmholtz instability caused by the flow around the bubbles and the Rayleigh-Taylor instability induced by the increase in the expansion rate of the vapor-water mixture. It is shown that the experiments on depressurization of high-pressure vessels can be explained by assuming that the initial boiling centers are located only on the walls, and in the flow core the bubbles appear only after the injection of the fragments of broken wall bubbles into the flow. The experimental oscillograms are compared with the calculated curves obtained using the model proposed and the models which take into account only one instability mode, i.e. the Kelvin-Helmholtz or Rayleigh-Taylor instability. The waves which accompany the vessel depressurization process are described.