Viscosity correction factor for safety relief valves

A commercial computation fluid dynamics (CFD) code was used to compute the discharge coefficient for a representative relief valve configuration and various nozzle sizes, for Newtonian liquids with various viscosities. The results are compared with values of the viscosity correction factor, K v , from the API Recommended Practice 520, and equations are proposed to represent both the K v curve and the computational results in a correspondings form, which also includes the effect of the dimensionless nozzle diameter on the valve K v .