Two-phase flow through safety/relief valves, nozzles, orifices

A careful design of the pressure safety valves (PSV) is an essential requirement for safeguarding of industrial plants; reliable correlations are available for PSV design in the cases of liquid or gas discharge. Instead, if two-phase flow is possible, especially for low vapour quality (less than 10%), PSV design becomes very difficult owing to complex thermal hydraulic phenomena that happen between the two phases; moreover, in this situation, the prediction of the critical flow onset (which occurs when the fluid velocity becomes equal to the sound velocity in the fluid) is very important for a correct design because it involves a choked flow situation.
Currently there are some calculation methods, based on different simplifying hypotheses, that try to predict the two-phase flow rate through a PSV knowing the inlet fluid conditions (pressure, quality or temperature) and the outlet pressure; however none of them is acknowledged as being reliable for every situation and, therefore, there are not standards for PSV design in two-phase conditions.
The ITFD has an experimental facility for the studying of two-phase flows through safety systems or other geometry as nozzles and orifices. The research aims to providing with useful information on performance of the most used  calculation methods by the comparison with experimental data. The experimental programme will be carried out on the VASIB facility.