A Numerical Investigation on the Choking Phenomenon in a Commercial Safety Relief Valve

Safety relief valves are used in various industries including oil and gas, power plants, water distribution, etc. to protect vessels and pipelines from overpressure. An important parameter in a safety valve which is used in the sizing procedure, is the required/maximum discharge capacity. At a certain upstream pressure, by reducing the discharge pressure it is expected to have higher discharge capacity. However, the mass flow rate passing through the safety valve is limited at a certain downstream pressure which is referred to as critical pressure. This phenomenon is called “choking” and it affects the valve sizing and selection significantly. In this study, the choking phenomenon for a commercial KIASA ۲”x۳” safety valve with an orifice of H is investigated numerically using Ansys Fluent software. At the set pressure and over pressure of ۴۴ barg and ۲۱%, it was demonstrated that the flow through the KIASA’s ۲”x۳” valve will be choked at gauge backpressures of below ۷۲%. Also, it was shown that the outlet flow is supersonic with a Mach number of ۱.۲۱ when the gauge backpressure is set at ۰%, but the flow will be subsonic for higher gauge backpressures. Finally, by employing an experimental-evaluated discharge coefficient for KIASA’s ۲”x۳” valves, our simulation results were compared to the results of the American Petroleum Institute (API) ۵۲۰ standard for critical and subcritical flows.

کلیدواژه ها:

Safety Relief Valve ، PSV ، CFD ، Numerical Analysis ، Choking