10 Multistage severe service control valves are extensively used in various energy systems, such 11 as oil & gas, nuclear etc. The primary purpose of such valves is to control the amount of fluid 12 flow passing through them under extreme pressure changes. As opposed to the conventional 13 valves (butterfly, gate etc.), control valves are often installed in energy systems with 14 geometrically complex trims, comprising of various geometrical features, formed by a 15 complex arrangement of cylindrical arrays. The pressure within the trim varies in controlled 16 steps and hence, cavitation resistance can be embedded in the trim through improved design 17 process for the trim for severe service applications in energy systems. The flow 18 characteristics within a control valve are quite complex, owing to complex geometrical 19 features inherent in such designs, which makes it extremely difficult to isolate and quantify 20 contribution of these features on the flow characteristics. One of the most important design 21 parameters of such trims is the flow coefficient (also known as flow capacity) of the trim 22 which depends on the geometrical features of the trim. The design of valves for particular 23 performance envelop within the energy systems depends on effects of complex trim 24 geometrical features on performance characteristics; hence, the focus of recent research is on 25 quantifying the hydrodynamic behaviour of severe service control valves, including the trims. 26 This includes the estimation of the local flow capacity contributions of the geometrical 27 features of the trim through detailed numerical investigations. In this work, a tool has been 28 developed that can be used to predict the local contribution of geometrical features on the 29 flow coefficient of the trim. It is expected that this work will result in better performance of 30 the energy systems where these valves are used. 31 32 Capacity, Energy Systems 34 35 1.0 Introduction 36 Valves are an integral part of any piping network and are used in a variety of industries for 37 various process control applications. The design of valves is a specialist area and the 38 performance of valves is integral to the performance of the energy systems. The severe 39 service control vales typically have very complex flow paths and it is necessary to have 40 understanding of flow characteristics through the complex pathways to eliminate undesirable 41 effects such as vibrations, noise and cavitation in energy systems. The designs of such valves 42 are carried out with the help of well-known standards but many times undesirable local flow 43 effects cannot be eliminated through such designs. The standards are continuously updated to 44 incorporate state of the art knowledge into the design process through extensive experimental 45 and numerical research work carried out all over the world. Newer designs are continuously 46 * Corresponding Author Tel.: +44 1484 472323 1 only partially applicable. In such cases a thorough fluid dynamic analysis is necessary to 2...

For safety-critical industrial applications, severe-service valves are often used, and the conditions during operations can be either single phase or multiphase. The design requirements for valves handling multiphase flows can be very different to the single-phase flow and depend on the flow regime within valves. The variation in flow conditions during the operation of such valves can have a significant effect on performance, particularly in oil and gas applications where multiphase behaviour can rapidly change within the valve causing unwanted flow conditions. Current practices in designing and sizing such valves are based solely on global phase properties such as pressure drop of the bulk fluid across the valve and overall phase ratio. These do not take into account local flow conditions, as with multiphase fluids, the flow behaviour across the valve becomes more complex. In this work, wellvalidated computational fluid dynamics (CFD) tools were used to locally and globally quantify the performance characteristics of a severe service valve handling multiphase gas and liquid flow. Such flows are frequently encountered in process equipment found in vital energy industries e.g. process and oil & gas. The CFD model was globally validated with benchmark experiments. Two valve opening positions of 60% and 100% were considered each with 5, 10, and 15% inlet air volume fractions to simulate real life conditions. The results show that while the non-uniformity in pressure field is along expected lines, there is severe non-uniformity in the local air, water and void fraction distributions within the valve trim. To quantify the phase non-uniformities observed, an equation for the distribution parameter was defined and used to calculate its value in each localised quarter within the trim. Phase velocity and void fraction data extracted from the CFD results were also used to obtain relationships for the local void fraction distribution and flow coefficient. The detailed investigation that has been carried out allows for local flow characteristics to be determined and embedded in sizing methodology for severe-service control valve systems with multiphase gas and liquid flow.

Control valves are an integral part of a number of energy systems, such as those used in chemical and nuclear industries. These valves are used to regulate the amount of fluid flow passing through these systems. A key component of a control valve is its trim, which in case of a multi-stage continuous-resistance trim consists of a staggered arrangement of columns.Flow passing through the channels formed between adjacent columns (also called as flow paths), loses a significant amount of its energy and regulates the pressure field. As the geometrical features of these flow paths dictate the flow capacity of the trim, systematic investigations have been carried out to analyse the complex flow behaviour within these flow paths. Well-verified computational fluid dynamics based solver has been used to investigate the effects of the geometrical features of flow paths on the flow capacity of the trim, at various valve opening positions. It has been noticed that reducing the size of flow paths increases the flow capacity of the trim, however, at a critical flow path size, the inherent opening characteristics of a trim have been observed to alter. In order to recover the original opening behaviour of the trim, careful manipulation of the flow paths is required, which has been successfully achieved in the present investigation.

Control valves that are used in severe service applications have trim cages that are geometrically quite complex. Most of these trims are manufactured using traditional manufacturing methods which are expensive and time-consuming. In order to reduce manufacturing costs and shorten the product development cycles, Additive Manufacturing (AM) methods have been gaining popularity over the traditional manufacturing methods. Selective Laser Melting (SLM) is one of the most popular AM techniques. In this paper, the effect of the conventional Electron Discharge Machining (EDM) method and the SLM method on the performance characteristics of a complex multi-stage disc stack trim is investigated. Experimental tests conducted on the SLM trim showed that the flow capacity reduced in comparison to the EDM manufactured trim. Surface profile measurements indicated that the surface roughness of the SLM trim was significantly higher than the EDM trim. In order to evaluate the effect of surface roughness on performance in detail, well validated numerical simulations were conducted to compare the local performance of the valve trims manufactured by the two methods. The simulation results showed that the wall shear stress increases by 1.9 times on the trim manufactured by the SLM method due to the increased roughness.

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