An Experimental and Numerical Analysis on the Dynamical Behavior of a Safety Valve in the Case of Two-phase Non-flashing Flow

Abstract

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.

An Experimental Study on the Force Coefficient and the Discharge Coefficient of a Safety Valve in Air-water Mixture Flow

“…Burhani and Hős [26] discussed the flow behavior of a poppet valve (only) experimentally in the case of non-flashing flow (i.e. frozen flow) under the assumption of the steady-state condition and a studied interval of water injection up to 30.8 % to a pressurized airflow.…”

“…(1) stands for the unsteady part resulting from the change of the deformable volume, while the second and the third terms refer to the momentum force and pressure force. The unsteady term can usually be neglected, see [9,14,26,27]. Furthermore, the impulse and pressure forces should be evaluated on the boundary ∂Ω of the control volume, and Eq.…”

“…The pressure force A v ( p 0 − p b ) represents the pressure difference between the upper surface and the lower surface of the valve disc. The pressure profile on the remaining surfaces of the disc is assumed to be uniformly distributed, and the axial component of the pressure force at the outer surfaces of the control volume is trivial; for details, see [26,27].…”

Study on the Influencing Factors of the Response Characteristics of the Slide Valve-Type Direct-Acting Relief Valve with External Orifice

“…Song et al [1] developed a numerical model using CFD techniques to investigate the fluid and dynamic characteristics of a direct-operated safety relieve valve (SRV), and examined the comparison of the effects of the design parameters, including the adjusting ring position, vessel volume and spring stiffness. Burhani and Hos [2] addressed the static and dynamic behavior of a direct spring-operated PRV of conical shape in the presence of two-phase non-flashing flow, and recorded the effect of the system parameters, such as spring stiffness and reservoir capacity. Zong et al [3] established the accuracy of CFD models for the prediction of the flow force exerted on the disk of a direct-operated pressure safety valve in energy system.…”