Flow control valves may experience localized cavitation when the local static pressure drops to the liquid vapor pressure. Localized damage to the valve and surrounding area can occur when the vapor cavity collapses. Valve designs that reduce cavitation are based on empirical evidence and accumulated experience, but there are still considerable cavitation problems in industry. Valve designers may use computational fluid dynamics (CFD) to simulate cavitation in flow control valves, but model validation is challenging because there are limited data of local cavitation from the valve surface. Typically, the intensity of cavitation in a control valve is inferred from measurements of observable side effects of cavitation such as valve noise, vibration, or damage to the valve assembly. Such an indirect approach to characterizing cavitation yields little information about the location, degree, and extent of the cavitation flow field that can be used in CFD validation studies. This study uses 3D X-ray computed tomography (CT) imaging to visualize cavitation from a 5.1 cm diameter butterfly valve and compares the resulting vapor cloud to that predicted by CFD simulations. Qualitative comparisons reveal that the resulting cavitation structures are captured by the simulations when a small amount of non-condensable gas is introduced into the fluid and the simulations are completed in a transient mode. Proceedings of the ASME-JSME-KSME ABSTRACT Flow control valves may experience localized cavitation when the local static pressure drops to the liquid vapor pressure. Localized damage to the valve and surrounding area can occur when the vapor cavity collapses. Valve designs that reduce cavitation are based on empirical evidence and accumulated experience, but there are still considerable cavitation problems in industry. Valve designers may use computational fluid dynamics (CFD) to simulate cavitation in flow control valves, but model validation is challenging because there are limited data of local cavitation from the valve surface. Typically, the intensity of cavitation in a control valve is inferred from measurements of observable side effects of cavitation such as valve noise, vibration, or damage to the valve assembly. Such an indirect approach to characterizing cavitation yields little information about the location, degree, and extent of the cavitation flow field that can be used in CFD validation studies. This study uses 3D X-ray computed tomography (CT) imaging to visualize cavitation from a 5.1 em diameter butterfly valve and compares the resulting vapor cloud to that predicted by CFD simulations. Qualitative comparisons reveal that the resulting cavitation structures are captured by the simulations when a small amount of noncondensable gas is introduced into the fluid and the simulations are completed in a transient mode.

Process fluids flowing through control valves undergo thermodynamic throttling that induces a decrease in the mean fluid pressure. Substantial pressure reduction can result in the formation of a stable, secondary compressible phase within the liquid continuum. Without distinction this phenomenon is generally referred to as flashing, and may have a significant impact on the magnitude of flow through the control valve. The formation of the compressible phase may be the result of two different underlying sources: vaporization, wherein a small portion of the liquid undergoes a phase change from liquid to vapor; or out-gassing, wherein dissolved or entrained gases come out of solution. The industry standard equations used to determine an appropriate process control valve size include an adjustment for the effect of vaporization. Implicit in this method is the assumption that the fluid is vaporizing according to a corresponding states model. This paper distinguishes between the two compressible phase forming mechanisms and derives a comparable methodology that is appropriate to the out-gassing process. A revised prediction of the choked or limiting flow pressure differential is presented and density corrections are incorporated into the industry standard methodology.