Industrial-process control valves - Part 2-1: Flow capacity - Sizing equations for fluid flow under installed conditions (Endorsed by AENOR in September of 2011.)

2Scope / Description

This part of IEC 60534 contains equations for predicting the flow of compressible and incompressible fluids through control valves. The equations for incompressible flow are based on the standard fluid dynamics equations for Newtonian, incompressible fluids. They are not applicable to non-Newtonian fluids, fluid mixtures, slurries, or liquid-solid transport systems. The equations for incompressible flow can be used with caution for non-vaporizing multicomponent liquid mixtures. For more information, see Section 6. At very low differential pressures relative to the absolute inlet pressure ratio (Δp/p1), compressible fluids behave like incompressible fluids. In this case, the sizing equations for compressible flow can be traced back to the standard fluid dynamics equations for Newtonian, incompressible fluids. However, increasing the value of Δp/p1 introduces compressibility effects, requiring the basic equations to be modified using appropriate correction factors. The equations for compressible flows apply to ideal gases or vapors and are not applicable to multiphase flows such as gas-liquid, vapor-liquid, or gas-solid mixtures. Reasonable accuracy is maintained only when the ratio of specific heats, γ, is limited to 1.08 < γ < 1.65. For more information, see Section 7.2. For compressible flow applications, this standard applies to valves with xT ≤ 0.84 (see Table D.2). For valves with xT > 0.84 (e.g., some multi-stage valves), lower accuracy of flow prediction can be expected. Reasonable accuracy for control valves can only be maintained when the following conditions are met: 047, 0218 < dNC Note that while the equation structure used in this document is fundamentally different from previous versions of the standard, the basic techniques remain relatively unchanged. The revised equation format is intended to simplify the presentation of the various equations and improve the readability of the document.