Two-phase flow in orifice plates and valves

Abstract

The pressure drop that occurs when a two-phase flow passes through a pipeline component is usually found by calculating the single-phase value and multiplying it by a two-phase multiplier. Little or no consideration is given to what occurs within that component. For example, if the valve seat area is sufficiently small, the fluid velocity will approach, or even reach, the critical velocity. In these circumstances, compressibility effects should be accounted for—they rarely are. This study was initiated to develop a technique that would allow pressure drops to be predicted for pipe fittings, whether the flow is compressible or not, and to allow the critical mass flux to be estimated, thus allowing the method to be applied to the design of venting systems. The model developed can be used for all pipe fittings of the contraction-expansion type, like orifice plates and valves, up to and including the choking point, provided the single-phase loss coefficient is known.