Analysis of Balanced Stiffness Valve by using Transient Finite Element Analysis

In chemical industries there is necessary to control the flow of liquids between chambers, where it is necessary that valve will be opened when a certain pressure of fluid is reached. To control this fluid flow electronically actuated valves are generally used. Sometimes there is also need of mechanical actuated valve. A single valve will connect three chambers and will control inter flow between these chambers using a balanced stiffness approach where in flow will switch automatically operating at pressure. This paper basically focused on the transient finite element analysis of Balanced Stiffness valve. This transient analysis is generally used to determine the dynamic response of a structure under the action of any general time-dependent loads. It is used to determine the time-varying displacements, stresses, strains, and forces in valve parts as it responds to any transient loads. Here performance of the Balanced Stiffness Valve, i.e. movement of pressure plates observed. Pressure Plate area is exposing to the fluid flow instantaneously as the supply pressure given to pressure plate. Hence it is essential to examine time dependent dynamic response of the valv

On the Static Instability of Liquid Poppet Valves

This paper focuses on flow induced static instabilities occur-ring in poppet valves. Computational fluid dynamics simula-tion were performed to gain static characteristics of the poppet valve and to demonstrate the unstable behaviour of the valve. Based on theoretical considerations, a necessary condition for the stable operation is derived. The study indicates that stabil-ity can be obtained with proper geometrical design of the valve or by limiting the total compression of the spring. The paper discusses the possible steps to prevent instability and proper spring selection. Keywords application of momentum theory, flow induced instability, force coefficient, static instability

Modelo predictivo para la determinación del flujo de descarga en válvulas de alivio de presión en aplicaciones de vapor

This article presents the development of a predictive model which quantify the flow discharge of steam in safety valves, based on tests conducted with Nitrogen in a test bench. The proposed model was built with experimental data obtained through test bench measurements that meet the requirement of the current ASME / API regulations. Simulations were performed in the CFD tool of the ANSYS® software, which was validated using the experimental data obtained, to increase the sample size within the operating range of the valves and thus reduce the costs of experimentation. These results were related to the variables that influence the phenomenon through a multivariate regression, which yielded an expression capable of predicting the steam flow through the safety valve. The proposed correlation calculates the correction factor to predict the flow discharged by the valve operating in the steam generator and based on the measurement of the Nitrogen discharge flow in the test bench. The reproducibility of the developed model was validated through a Durbin-Watson test for residues, a hypothesis test for the model and a normality test, where the predictive capacity of the correlations was verified.Este artículo presenta el desarrollo de un modelo predictivo para cuantificar el flujo de descarga de vapor enválvulas de seguridad, a partir de ensayos realizados con Nitrógeno en un banco de prueba. El modelo propuesto se construyó con datos experimentales obtenidos a través de mediciones en banco de prueba que cumplen los lineamientos de la normativa ASME/API vigente. Se realizaron simulaciones en la herramienta CFD del software ANSYS®, las cuales fueron validadas con los datos experimentales obtenidos, con el fin deaumentar los puntos de muestreo dentro del rango de operación de las válvulas y de esta forma reducir los costos de experimentación. Estos resultados se relacionaron con las variables que influyen el fenómeno en estudio a través de una regresión multivariable, con lo que se obtuvo una expresión capaz de predecir el flujo de vapor a través de la válvula de seguridad. La correlación propuesta calcula el factor de corrección parapredecir el flujo desalojado por la válvula operando en el generador de vapor, pero basado en la medición del flujo de descarga de Nitrógeno en el banco de prueba. Se validó la reproducibilidad del modelo desarrollado a través de una prueba de Durbin-Watson para residuos, una prueba de hipótesis para el modelo y una prueba de normalidad, en donde se verificó la alta capacidad de predicción de las correlaciones desarrolladas en el presente estudio

An assessment of eddy viscosity models on predicting performance parameters of valves

The major objective of the present study is to evaluate the performance of a range of turbulent eddy viscosity models in the prediction of macro-parameters (flow coefficient (CQ) and force coefficient (CF)), for certain types of valve, including the conic valve, the disk valves, and the compensated valve. This has been achieved by comparison of numerical predictions with experimental measurements available in the literature. The examined turbulence models include most of the available turbulent eddy viscosity models in STAR-CCM+ 12.04. They are the standard k-ε model, realizable k-ε model, k-ω-sst model, V2F model, EB k-ε model and the Lag EB k-ε models. The low-Re turbulence models (k-ω-sst, V2F, EB k-ε and Lag EB k-ε) perform worse than the high-Re models (standard k-ε and realizable k-ε). For the conic valve, the performance of different turbulent models varies little; the standard k-ε model shows a marginal advantage over the others. The performance of the turbulence models changed greatly, however, for prediction of CQ and CF of the disk and compensated valves. In general, the realizable k-ε model is demonstrated to be a robust choice for both valve types. Although the EB k-ε may marginally outperform it in the prediction of CF at large disk valve opening. The effects of the unknown entry flow and initialization conditions are also studied. The predictions are more sensitive to the entry flow condition when the valve opening is large. Additionally, the uncertainties caused by unknown entry conditions are comparable to overall modelling errors in some cases. For flow systems with multiple stable flow-states coexisting in the flow domain, the output of the numerical models can also be affected by the initialization conditions. When the streamline curvature and secondary flow is modest like conical valve flow, the nonlinear modification of the standard k-ε model and k-ω-sst model, as well as the curvature correction in the realizable k-ε model, will not have visible effects on the numerical prediction. Once the strong streamline curvature and secondary flow exit in the domain, such as the disk valve flow, the non-linear modification of the standard k-ε model will greatly improve the numerical outputs, however, the non-linear modifications of k-ω-sst model only have minor effects. Moreover, the curvature correction in the realizable k-ε model will jeopardise the accuracy of outputs in the same case

Study of mechanical aspects of leak tightness in a pressure relief valve using advanced FE-analysis

This paper presents a numerical study involving the deformation of contact faces in the metal-to-metal seal in a typical pressure relief valve. The valve geometry is simplified to an axisymmetric problem, which comprises a simple geometry consisting of only 3 components. A cylindrical nozzle, which has a valve seat on top, contacts with a disk, which is preloaded by a compressed linear spring. All the components are made of AISI type 316N(L) steel defined using the multilinear kinematic hardening model based on monotonic and cyclic tests at 20°C. In-service observations show that there is a limited fluid leakage through the valve seat at operational pressures about 90% of the set pressure, which is caused by the fluid penetrating into surface asperities at the microscale. Nonlinear FEA in ANSYS using the fluid pressure penetration (FPP) technique revealed that there is a limited amount of fluid penetrating into gap, which is caused by the plastic deformation of the valve seat at the macroscale. Prediction of the fluid pressure distribution over the valve seat just before the valve lift is addressed in this study considering the FPP interaction on multiscale. This is the principal scope, since it allows adjustment of the valve spring force in order to improve the leak tightness

Design optimisation of a safety relief valve to meet ASME BPVC section I performance requirements

The understanding of fluid flow behaviour within safety relief valves invariably requires knowledge of strong pressure and velocity gradients with significant levels of turbulence in three-dimensional flow environments. In the case of gas service valves - the focus of this thesis - these flows will be super-sonic with multidimensional shock formations resulting in challenging design conditions. This thesis takes advantage of the development and validation of computational fluid dynamic (CFD) techniques in recent years to reliably predict such flows and investigate how the techniques can be used to produce better performing safety valves. Historically OEMs will have relied on an experimental based design approach using feedback from test data to guide the evolution of a valve design. Unfortunately, due to the complexity of these devices this method could require much iteration. However, it is now possible to combine CFD techniques and optimisation algorithms to search for improved designs with reduced development times. To date these techniques have had limited exposure within valve design studies. This thesis investigates the development of a numerical based design procedure by combining validated CFD models optimisation techniques to seek valve trim geometries that improve opening and closing behaviour. The approach is applied to an ASME Section VIII certified valve and seeks to modify the internal trim to satisfy the improved performance requirements stipulated in Section I of the ASME Boiler and Pressure Vessel Code.The understanding of fluid flow behaviour within safety relief valves invariably requires knowledge of strong pressure and velocity gradients with significant levels of turbulence in three-dimensional flow environments. In the case of gas service valves - the focus of this thesis - these flows will be super-sonic with multidimensional shock formations resulting in challenging design conditions. This thesis takes advantage of the development and validation of computational fluid dynamic (CFD) techniques in recent years to reliably predict such flows and investigate how the techniques can be used to produce better performing safety valves. Historically OEMs will have relied on an experimental based design approach using feedback from test data to guide the evolution of a valve design. Unfortunately, due to the complexity of these devices this method could require much iteration. However, it is now possible to combine CFD techniques and optimisation algorithms to search for improved designs with reduced development times. To date these techniques have had limited exposure within valve design studies. This thesis investigates the development of a numerical based design procedure by combining validated CFD models optimisation techniques to seek valve trim geometries that improve opening and closing behaviour. The approach is applied to an ASME Section VIII certified valve and seeks to modify the internal trim to satisfy the improved performance requirements stipulated in Section I of the ASME Boiler and Pressure Vessel Code