Prediction of the Flow and Force Characteristics of Safety Relief Valves

2006 ◽  
Author(s):  
W. Dempster ◽  
C. K. Lee ◽  
J. Deans
Keyword(s):  
Operating Conditions ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Relief Valve ◽  
Good Correspondence ◽  
Geometry Modeling ◽  
Valve Opening ◽  
Satisfactory Prediction ◽  
Force Characteristics

The design of safety relief valves depends on knowledge of the expected force-lift and flow-lift characteristics at the desired operating conditions of the valve. During valve opening the flow conditions change from seal-leakage type flows to combinations of sub-sonic and supersonic flows It is these highly compressible flow conditions that control the force and flow lift characteristics. This paper reports the use of computational fluid dynamics techniques to investigate the valve characteristics for a conventional spring operated 1/4” safety relief valve designed for gases operating between 10 and 30 bar. The force and flow magnitudes are highly dependent on the lift and geometry of the valve and these characteristics are explained with the aid of the detailed information available from the CFD analysis. Experimental determination of the force and flow lift conditions has also been carried out and a comparison indicates good correspondence between the predictions and the experiment. However, attention requires to be paid to specific aspects of the geometry modeling including corner radii and edge chamfers to ensure satisfactory prediction.

Flowforce in Safety Relief Valve Under Incompressible, Compressible and Two-Phase Flow Conditions

2011 ◽  
Author(s):  
Vasilios Kourakos ◽  
Sai¨d Chabane ◽  
Patrick Rambaud ◽  
Jean-Marie Buchlin
Keyword(s):  
Power Plants ◽  
Two Phase Flow ◽  
Valve Lift ◽  
Phase Flow ◽  
Relief Valve ◽  
Two Phase ◽  
Valve Opening ◽  
Experimental Findings ◽  
Static Conditions

The use of relief valves is crucial for the safety of power plants. Indeed, these simple and robust in their design valves are the ultimate protection when all other systems are insufficient. This study is focused on valve opening characteristics which can be concluded through the determination of flowforces applied at the valve disk. A spring loaded safety relief valve (1 1/2″ G 3″) and transparent model of this valve are tested under static conditions. The spring is removed and the forces exerted at the valve disk for different inlet pressures and lift positions are measured. Compressible, incompressible and two-phase flow behaviors are investigated and compared. Inversed force of air and water is noticed above a certain value of valve lift. Numerical simulations are performed to verify experimental findings.

Flowforce in a Safety Relief Valve Under Incompressible, Compressible, and Two-Phase Flow Conditions (PVP-2011-57896)

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Vasilios Kourakos ◽  
Patrick Rambaud ◽  
Jean-Marie Buchlin ◽  
Saïd Chabane
Keyword(s):  
Power Plants ◽  
Flow Behavior ◽  
Valve Lift ◽  
Relief Valve ◽  
Two Phase ◽  
Precise Adjustment ◽  
Valve Opening ◽  
Static Conditions ◽  
Safety Systems

The use of relief valves is crucial for the safety of power plants. Indeed, these valves, simple but robust in their design, provide the ultimate protection when all other safety systems are inadequate. This study is focused on valve opening characteristics which can be studied through the determination of flowforces applied on the valve disk. A spring-loaded safety relief valve (SRV) (1½ in. G 3 in.) and its transparent model are tested under static conditions. The spring is removed and the forces, exerted at the valve disk for different inlet pressures and lift positions, are measured in compressible, incompressible, and two-phase flows. Results indicate that even for relatively small qualities (i.e., 5–10%), two-phase mixtures approach compressible flow behavior (especially for the higher lifts) in terms of disk force. Additionally, an inverse flowforce of air and water is noticed above a certain value of valve lift. Numerical simulations with a commercial computation fluid dynamics (CFD) code are performed in a 2D axisymmetric model of the valve for validation purposes. The main motivation of these computations is to obtain the qualitative physical explanation of this phenomenon revealing the displacement of the sonic line which occurs in air flow simulations. Finally, the importance of precise adjustment of the valve ring (in the smallest valve opening) for its optimal use is stressed by quantitative analysis using CFD simulations.

Simulation and Contrast Analysis of tem Images of Cracks

1990 ◽  
Vol 48 (1) ◽  
pp. 578-579
Author(s):  
D. Goyal ◽  
A. H. King
Keyword(s):  
Displacement Vector ◽  
Crack Tip ◽  
Perfect Crystal ◽  
Operating Conditions ◽  
Displacement Fields ◽  
Fringe Contrast ◽  
Orthogonal Geometry ◽  
Moire Fringe ◽  
Moiré Fringe

TEM images of cracks have been found to give rise to a moiré fringe type of contrast. It is apparent that the moire fringe contrast is observed because of the presence of a fault in a perfect crystal, and is characteristic of the fault geometry and the diffracting conditions in the TEM. Various studies have reported that the moire fringe contrast observed due to the presence of a crack in an otherwise perfect crystal is distinctive of the mode of crack. This paper describes a technique to study the geometry and mode of the cracks by comparing the images they produce in the TEM because of the effect that their displacement fields have on the diffraction of electrons by the crystal (containing a crack) with the corresponding theoretical images. In order to formulate a means of matching experimental images with theoretical ones, displacement fields of dislocations present (if any) in the vicinity of the crack are not considered, only the effect of the displacement field of the crack is considered.The theoretical images are obtained using a computer program based on the two beam approximation of the dynamical theory of diffraction contrast for an imperfect crystal. The procedures for the determination of the various parameters involved in these computations have been well documented. There are three basic modes of crack. Preliminary studies were carried out considering the simplest form of crack geometries, i. e., mode I, II, III and the mixed modes, with orthogonal crack geometries. It was found that the contrast obtained from each mode is very distinct. The effect of variation of operating conditions such as diffracting vector (), the deviation parameter (ω), the electron beam direction () and the displacement vector were studied. It has been found that any small change in the above parameters can result in a drastic change in the contrast. The most important parameter for the matching of the theoretical and the experimental images was found to be the determination of the geometry of the crack under consideration. In order to be able to simulate the crack image shown in Figure 1, the crack geometry was modified from a orthogonal geometry to one with a crack tip inclined to the original crack front. The variation in the crack tip direction resulted in the variation of the displacement vector also. Figure 1 is a cross-sectional micrograph of a silicon wafer with a chromium film on top, showing a crack in the silicon.

Cake Formation in Cross-Flow Microfiltration Systems

1992 ◽  
Vol 25 (10) ◽  
pp. 149-162 ◽  
Author(s):  
V. L. Pillay ◽  
C. A. Buckley
Keyword(s):  
Cross Flow ◽  
Operating Conditions ◽  
Waste Waters ◽  
Domestic Waste ◽  
Time Curve ◽  
Good Correspondence ◽  
Operating Variables ◽  
Start Up ◽  
Turbulent Flow Regime ◽  
Cake Formation

Cross-flow microfiltration (CFMF) has potentially wide application in the processing of industrial and domestic waste waters. Optimum design and operation of CFMF systems necessitates a knowledge of the characteristic system behaviour, and an understanding of the mechanisms governing this behaviour. This paper is a contribution towards the elucidation and understanding of the behaviour of a woven fibre CFMF operated in the turbulent flow regime. The characteristic flux-time curve and effects of operating variables on flux are presented for a limestone suspension cross-flow filtered in a 25 mm woven fibre tube. The phenomena contributing to the shape of the flux-time curve are discussed. A model of the mechanisms governing cake growth and limit is presented. Predicted steady-state fluxes show a notably good correspondence with experimentally measured values. It is also found that the flux may not be uniquely defined by the operating conditions, but may also be a function of the operating path taken to reach the operating point. This is of significance in the start-up and operation of CFMF units.

Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Static Stability ◽  
Operating Conditions ◽  
Eccentricity Ratio ◽  
Static Stiffness ◽  
Flow Conditions ◽  
Experiment Data ◽  
High Eccentricity ◽  
Stiffness Coefficients ◽  
Direct Stiffness ◽  
Gas Seals

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor–stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines. The paper deals with the leakage and static stability behavior of a fully partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360 deg mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces, and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-averaged Navier–Stokes solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7000 rpm, 11,000 rpm, and 15,000 rpm) including the nonrotating condition, three pressure ratios (0.17, 0.35, and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions; no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal (PDS) would be statically unstable.

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