COMPUTATIONAL FLUID DYNAMICS BASED DIAGNOSTICS AND PREDICTION TOOL FOR OPTIMAL DESIGN OF MULTISTAGE TRIM CONTROL VALVES

Control valves form an integral part of many industrial applications such as in the manufacturing, energy generation, aerospace, medical, civil, and environmental sectors. It is overly important and critical that accurate and explicit information on the local pressure and flow structure within a multi-stage trim control valve is known. Currently there is no known universal and scalable characterization methodology of local geometry of varying multiple aperture shape and size arrangements along a valve or flow handling device flow path, with local and Global flow and pressure parameters. Furthermore, at present the local pressure and flow structure within the vicinity of singularities, or flow passages within control valves is experimentally inscrutable with current experimental apparatus, mainly due to flow field intrusion, and impracticability of measuring probe or instrument insertion presented by complex local geometry. Extensive research is being carried out to improve the hydrodynamic performance efficiency and safe operation of control valves, as well as to develop viable and accurate scalable hydrodynamic performance prediction models within multiple flow passage trim control valves. Hence, the in-depth knowledge and understanding of the complex local pressure and flow phenomenon within multi-stage or multi-flow passage control valve trims is still an active subject of research. This is because most of the studies carried out on multi-stage control valve trims have severely limited information on the local geometric and flow field hydrodynamic interactive performance characteristics, or are based on globally derived empirical parameters for specific control valve types, and from which locally unquantified approximations of the local flow and pressure structure have been reported. The current hydrodynamic characterization methodologies presents a high risk of misrepresentation of the local and global flow and pressure structure. In addition, the current excessive empiricism presents ambiguity in selection of suitable and applicable methods and equations for a given flow restriction geometric shape, flow passages arrangement configuration, and flow physics. This leads to incorrect trim hydrodynamic design, and specification for an application. Consequently, this results in performance failures through cavitation and flashing damage, and inefficiency through choked flow and excessive pumping energy requirements. Hence this is the reason why this work is important.

The advent of advanced numerical flow analysis techniques has made it possible to simulate the complex local flow characteristics within multi-stage or multi-flow passage control valves and gain more detailed and in-depth information on the underlying local complex flow phenomenon. The work in this study is focused on the implementation of advanced numerical modelling tools to simulate flow inside multi-stage trim control valves with the objective of quantifying currently unmeasurable local geometric, flow and pressure characteristics within multi-stage trim control valves. The terminology control valves allude to devices that are used to critically regulate flow and pressure for designated downstream process requirements. Novel characterization methods of geometric, flow and pressure parameters have been developed and used to carry out investigations under various geometric and flow conditions within multi-stage or multi-flow passage trim control valves. Comprehensive diagnostics have been performed qualitatively and quantitatively on the flow and pressure structure within multi-stage trims in control valves. A new and novel geometric based pressure loss coefficient (KL) has been developed which is characteristic of geometry alone and independent of the current pressure loss coefficient prerequisites of pre-known pressure drop and flow rate across a flow passage or singularity. The pressure loss coefficient has been incorporated in the development of new and novel prediction tools that account for the observed combined effects of multiple apertures on the flow field, and as a function of the sequence of arrangement of their effective flow areas.

The prediction tools developed in this work have been incorporated to accurately predict local flow exit pressure, flow coefficient (CV), velocity, Pressure drop, and cavitation index and pumping energy requirements at each flow passage in a multi-stage trim, and as well as the global flow rate, pressure drop, and flow coefficient (CV), and pumping energy requirements. The flow coefficient is at present defined as a global parameter that characterises the flow and pressure drop across a flow restriction, and defines the efficiency at which flow is permitted through a flow restriction. It is practically expressed as the flow of water in US gallons/min at 60° Fahrenheit with a 1 PSI Global pressure drop across a valve.

From the developed hydrodynamic prediction tools, an optimization methodology based on the reduced gradient principle has been developed. The optimization model presented in this work is scalable, robust, and easily applicable. From the optimization model, the following determinations can be made:
➢ Optimal flow passages effective flow areas and their configuration of sequence of arrangement along the flow path can be simultaneously determined for optimal local flow Coefficient (CV) at any flow passage along a multi-stage trim flow path.
➢ Optimal flow passages effective flow areas and their configuration of sequence of arrangement along the flow path can be simultaneously determined for desired or prescribed local pressure drop at any flow passage along the flow path.
➢ Optimal flow passages effective flow areas and their configuration of sequence of arrangement along the flow path can be simultaneously determined for desired or prescribed cavitation characteristics at any flow passage along the flow path.
➢ Optimal flow passages effective flow areas and their configuration of sequence of arrangement along the flow path can be simultaneously determined for prescribed, desired and optimal local pumping energy requirements at any flow passage along the flow path.