An Experimental and Numerical Analysis on the Dynamical Behavior of a Safety Valve in the Case of Two-phase Non-flashing Flow
Pressure Relief Valves (PRVs) are key elements of any hydraulic system in the process industry, especially in chemical plants or hydraulic power transmission systems. Their task is to maintain the system pressure beneath a prescribed maximum pressure and vent the excessive fluid in an emergency scenario. This paper addresses the static and dynamic behavior of a Direct Spring-Operated PRV of conical shape in the presence of two-phase non-flashing flow, that is, water-air mixture. First, experimental results on the force and discharge characteristics of such a valve in a wide range of the air-to-water mass fraction are presented. Our test facility includes a custom-designed PRV with 42.5 mm inlet pipe diameter, an inlet pressure up to 6.6 bar(g) and a maximum lift of 10 mm. Additionally, the empirical results on the static characteristics, notably fluid force on the valve disc and discharge coefficients are reported as a function of the liquid mass fraction and valve lift. In the second part of the paper, we present the development of a Matlab-based simulation tool that is capable of predicting the dynamics and stability of such a valve in the case of two-phase, non-flashing, frozen-mixture flow. Moreover, the effect of system parameters, such as spring stiffness and reservoir capacity are recorded. Finally, we also present results on the stability of the opening and closing the multi-phase flow influence on the stability of the blowdown process.