A careful design of 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 under two-phase conditions. This paper shows the results of an experimental research carried out through a PSV with steam-water two-phase flow. The experimental data are compared with the results of a calculation method based on the homogeneous model with non equilibrium hypotheses and an other one presented in API Racomanded Practice 520, devoloped with equilibrium hypotheses. The performance of the models is evaluated as a function of inlet and outlet parameters; an analysis of model critical flow prediction capability is presented too, with some uncertainties caused by the test procedures (here the mass flow-rate is imposed)
Water two-phase flow through pressure safety valve with variable backpressure: check of calculation methods to estimate mass flow-rate and critical flow conditions / G., Boccardi; Bubbico, Roberto; G. P., Celata; M., Cumo; F., Di Tosto. - STAMPA. - (2003). (Intervento presentato al convegno 3rd European Multiphase Systems Institute Meeting and 41st European Two-Phase Flow Group Meeting tenutosi a Trondheim, Norway nel May 2003).
Water two-phase flow through pressure safety valve with variable backpressure: check of calculation methods to estimate mass flow-rate and critical flow conditions
BUBBICO, Roberto;
2003
Abstract
A careful design of 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 under two-phase conditions. This paper shows the results of an experimental research carried out through a PSV with steam-water two-phase flow. The experimental data are compared with the results of a calculation method based on the homogeneous model with non equilibrium hypotheses and an other one presented in API Racomanded Practice 520, devoloped with equilibrium hypotheses. The performance of the models is evaluated as a function of inlet and outlet parameters; an analysis of model critical flow prediction capability is presented too, with some uncertainties caused by the test procedures (here the mass flow-rate is imposed)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
