Pulsations of the mass flow rate during pressure relief

During two-phase flow blowdown from pressure vessels considerable pulsations of the discharged mass flow rate were found. Regions of mass flow rate instability were predicted by a linear stability analysis. The pulsations are caused by the following closed feedback circuit: boil up – level swell – void fraction of the discharged mixture – critical discharge rate – velocity of pressure decrease – boil up. They were also observed in transient simulations of the depressurization. Finally, the regions of instability were confirmed by experiments. The possibility of the occurrence of pulsations increases with the volume of the ventline and the volume void fraction of the discharged mixture. They may influence the rate of pressure relief from pressure vessels as well as from chemical reactors.