Previous experiments were conducted and reported in a safety relief valve. It was noticed that in presence of a cavitating two-phase flow, the mass flux tends to be reduced due to the two-phase mixture compressibility. Moreover, the forces acting on the valve are dependent on the dynamic pressure and therefore, characteristics may be affected by the presence of a gas phase. The goal of this study is to propose a mathematical model capable of predicting the mass flux and forces acting on a safety relief valve experiencing cavitation at initial high subcooling conditions. For the mass flux prediction, an extension of the actual recommended sizing equations of IEC 60534-2-3 is proposed, including a formulation of the semi-critical region based on the hypothesis that compressibility of a two-phase mixture may be considered as an ellipse. It is verified that at chocking flow conditions, the critical section is partially filled by vapor as the fluid velocity equals the local speed of sound. Finally, a theoretical analysis is proposed to estimate the hydrodynamic fluid forces acting on the disk of a safety relief valve, using a simplified axisymmetric system of a plate over a nozzle. Results show a good agreement against experimental data and underline the influence of the backpressure in the SRV flow characteristics.

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