Leak rate calibration with gas flow standard apparatus

Vacuum ◽  
1996 ◽  
Vol 47 (6-8) ◽  
pp. 515-517 ◽  
Author(s):  
Zhang Dixin ◽  
Liu Shiliang ◽  
Li Detian ◽  
Meng Yang ◽  
Liu Qiang ◽  
...  
Keyword(s):  
Gas Flow ◽  
Leak Rate ◽  
Standard Apparatus

Experimental Investigation of Interfacial and Permeation Leak Rates in Sheet Gaskets and Valve Stem Packing

2018 ◽  
Author(s):  
Ali Salah Omar Aweimer ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Gas Flow ◽  
Experimental Testing ◽  
High Stress ◽  
Design Criterion ◽  
Leak Rate ◽  
Environment And Health ◽  
Valve Stem ◽  
Packing Rings ◽  
Order Of Magnitude ◽  
Hazardous Pollutants

The quantities of leak rate through sealing systems are being regulated because of the global concern on the hazardous pollutants being released into the atmosphere and their consequences on the environment and health. The maximum tolerated leak is becoming a design criterion, and the leak rate for an application under specific conditions is required to be estimated with reasonable accuracy. In this respect, experimental and theoretical studies are being conducted to characterize the gas flow through gaskets and packing rings. The amount of the total leak that is present in a gasketed joint or a valve stem packing is the sum of the permeation leak through the sealing material and the interfacial leak at the mating surfaces between the sealing element and mechanical clamp assembly. The existing models used to predict leakage do not separate these two types of leaks. This paper deals with a study based on experimental testing that quantifies the amount of these two types of leaks in bolted gasketed joints and packed stuffing boxes. It shows the contribution of interfacial leak for low and high contact surface stresses and the influence of the surface finish as a result of a 32 and 250 micro-inch RAAH phonographic finish in the case of a bolted flange joint. The results indicate that most of the leak is interfacial reaching 99% at the low stress while the interfacial leak is in the same order of magnitude of the permeation leak at high stress reaching 10−6 and 10−8 mg/s in both packing and gaskets, respectively.

Leak Before Break: Studies in Support of New R6 Guidance on Leak Rate Evaluation

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
J. P. Taggart ◽  
P. J. Budden
Keyword(s):  
Gas Flow ◽  
Flow Direction ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Effective Roughness ◽  
Crack Morphology ◽  
Morphology Model ◽  
Flow Through ◽  
Rate Evaluation ◽  
Leak Before Break

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly, in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a program of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks and a global value (i.e., the overall crack contours) for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. (1991, “Leakage Flow Through Small Cracks—Report of Second Stage of Experimental Work,” unpublished) gives better agreement with measured flow rates than that due to Button et al. (1978, “Gas Flow Through Cracks,” ASME J. Fluids Eng., 100, pp. 453–458), which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified.

A gas flow standard apparatus

Vacuum ◽  
1996 ◽  
Vol 47 (6-8) ◽  
pp. 519-522 ◽  
Author(s):  
Li Wangkui ◽  
Zhang Dixin ◽  
Liu Qiang ◽  
Lu Shiliang ◽  
Li Detian ◽  
...  
Keyword(s):  
Gas Flow ◽  
Standard Apparatus

On the Use of Gas Flow Models to Predict Leak Rates Through Sheet Gasket Materials

2017 ◽  
Author(s):  
Abdel-Hakim Bouzid ◽  
Ali Salah Omar Aweimer
Keyword(s):  
Flow Regime ◽  
Gas Flow ◽  
Stokes Equations ◽  
Pressure Rise ◽  
Second Order ◽  
Leak Rate ◽  
Molecular Flow ◽  
Flow Models ◽  
Micro Channels ◽  
Different Gases

The prediction of leak rate through porous gaskets for different gases based on test conducted on a reference gas can prevent bolted joint leakage failure and save the industry a lot of money. This work gives a basic comparison between different gas flow models that can be used to predict leak rates through porous gasket materials. The ability of a model to predict the leak rate at the micro and nano levels in tight gaskets relies on its capacity to incorporate different flow regimes that can be present under the different working conditions. Four models based on Navier-Stokes equations and incorporate the boundary conditions of the appropriate flow regime considered. The first and second order slip, diffusivity and molecular flow models are used to predict and correlate leak rates of gases namely helium, nitrogen, SF6, methane, argon and air passing through three frequently used nanoporous gasket materials which are flexible graphite, PTFE and compressed fiber. The methodology is based on the determination experimentally of the porosity parameter (N and R) of the micro channels assumed to simulate the leak paths present in the gasket using helium as the reference gas. The predicted leak rates of different gases at the different stresses and pressure levels are confronted to the results obtained experimentally by measurements of leak rates using pressure rise and mass spectrometry techniques. The results show that the predictions depend on the type of flow regime that predominates. Nevertheless the second order slip model is the one that gives better agreements with the measured leaks in all cases.

On the Use of Gas Flow Models to Predict Leak Rates Through Sheet Gasket Materials

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Abdel-Hakim Bouzid ◽  
Ali Salah Omar Aweimer
Keyword(s):  
Flow Regime ◽  
Gas Flow ◽  
Stokes Equations ◽  
Pressure Rise ◽  
Second Order ◽  
Leak Rate ◽  
Molecular Flow ◽  
Specific Flow ◽  
Flow Models ◽  
Different Gases

The prediction of leak rate through porous gaskets for different gases based on test conducted on a reference gas can prevent bolted joint leakage failure and save the industry lots of money. This work gives a basic comparison between different gas flow models that can be used to predict leak rates through porous gasket materials. The ability of a model to predict the leak rate at the micro- and nanolevels in tight gaskets relies on its capacity to incorporate different flow regimes that can be present under different working conditions. Four models based on Navier–Stokes equations that incorporate different boundary conditions and characterize specific flow regime are considered. The first- and second-order slip, diffusivity, and molecular flow models are used to predict and correlate leak rates of gases namely helium, nitrogen, SF6, methane, argon, and air passing through three frequently used porous gasket materials which are flexible graphite, polytetrafluoroethylene (PTFE), and compressed fiber. The methodology is based on the determination experimentally of the porosity parameter (N and R) of the microchannels assumed to simulate the leak paths present in the gasket using helium as the reference gas. The predicted leak rates of different gases at different stresses and pressure levels are confronted to the results obtained experimentally by measurements of leak rates using pressure rise and mass spectrometry techniques. The results show that the predictions depend on the type of flow regime that predominates. Nevertheless, the second-order slip model is the one that gives better agreements with the measured leaks in all cases.

TEM evaluation of graded SixGe1-x heterolayers

1991 ◽  
Vol 49 ◽  
pp. 894-895
Author(s):  
N. David Theodore ◽  
Mamoru Tomozane ◽  
Ming Liaw
Keyword(s):  
Heterojunction Bipolar Transistors ◽  
Gas Flow ◽  
Field Effect Transistors ◽  
Chemical Vapor ◽  
Dark Field ◽  
Bipolar Transistors ◽  
Structural Quality ◽  
Weak Beam ◽  
Transmission Electron ◽  
And Behavior

There is extensive interest in SiGe for use in heterojunction bipolar transistors. SiGe/Si superlattices are also of interest because of their potential for use in infrared detectors and field-effect transistors. The processing required for these materials is quite compatible with existing silicon technology. However, before SiGe can be used extensively for devices, there is a need to understand and then control the origin and behavior of defects in the materials. The present study was aimed at investigating the structural quality of, and the behavior of defects in, graded SiGe layers grown by chemical vapor deposition (CVD).The structures investigated in this study consisted of Si1-xGex[x=0.16]/Si1-xGex[x= 0.14, 0.13, 0.12, 0.10, 0.09, 0.07, 0.05, 0.04, 0.005, 0]/epi-Si/substrate heterolayers grown by CVD. The Si1-xGex layers were isochronally grown [t = 0.4 minutes per layer], with gas-flow rates being adjusted to control composition. Cross-section TEM specimens were prepared in the 110 geometry. These were then analyzed using two-beam bright-field, dark-field and weak-beam images. A JEOL JEM 200CX transmission electron microscope was used, operating at 200 kV.

Electron Microscopy/Diffraction Study of the Ternary Mn-Er-S System

1990 ◽  
Vol 48 (1) ◽  
pp. 76-77
Author(s):  
A. R. Landa Canovas ◽  
L.C. Otero Diaz ◽  
T. White ◽  
B.G. Hyde
Keyword(s):  
Electron Microscopy ◽  
Gas Flow ◽  
Graphite Crucible ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
Alumina Crucible ◽  
X Ray ◽  
Intermediate Phases ◽  
Twin Band ◽  
Ar Gas

X-Ray diffraction revealed two intermediate phases in the system MnS+Er2S3,:MnEr2S4= MnS.Er2S3, and MnEr4S7= MnS.2Er2S3. Their structures may be described as NaCl type, chemically twinned at the unit cell level, and isostructural with CaTi2O4, and Y5S7 respectively; i.e. {l13} NaCl twin band widths are (4,4) and (4,3).The present study was to search for structurally-related (twinned B.) structures and or possible disorder, using the more sensitive and appropiate technigue of electron microscopy/diffraction.A sample with nominal composition MnEr2S4 was made by heating Mn3O4 and Er2O3 in a graphite crucible and a 5% H2S in Ar gas flow at 1500°C for 4 hours. A small amount of this material was thenannealed, in an alumina crucible, contained in sealed evacuated silica tube, for 24 days at 1100°C. Both samples were studied by X-ray powder diffraction, and in JEOL 2000 FX and 4000 EX microscopes.

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