Leak Rate Computation: Flow Resistance vs. Thermal-Hydraulic Aspect

2018 ◽  
Author(s):  
Klaus Heckmann ◽  
Jürgen Sievers ◽  
Fabian Weyermann
Keyword(s):  
Flow Resistance ◽  
Discharge Rate ◽  
Crack Opening ◽  
Hydraulic Modeling ◽  
Leak Rate ◽  
Equilibrium Models ◽  
Flow Rates ◽  
Flow Models ◽  
Critical Discharge ◽  
Non Equilibrium

The computation of mass flow rates through crack-like defects in piping systems of light water reactors requires typically the description of two-phase flow conditions. The computed discharge rate depends on the crack opening area, the thermal-hydraulic modeling of the flow, and the flow resistance of the crack. Several models have been proposed to characterize the critical flow through crack-like defects. An evaluation of advantages and shortcomings of the different models with regard to the interaction of the three different parts (crack opening area, thermal-hydraulic modeling, flow resistance) has been performed. In this paper, the flow resistance modeling from several approaches is discussed, and compared with a database from eight different testing programs. Five different flow models are applied to analyze a database of more than 800 leak rate measurements for subcooled water from twelve different experimental programs. It is shown that the correct modeling of the flow resistance is crucial for a best estimate reproduction of the measured data. It turns out that generally, equilibrium models are about as good as non-equilibrium models. The data were processed with the GRS software WinLeck which includes different analytical approaches for the calculation of crack sizes and leak rates in piping components. The most reliable results within the model selection are produced by the CDR model (Critical Discharge Rate) of the ATHLET code (Analysis of Thermal-hydraulics of Leaks and Transients) developed by GRS. As a conclusion, the accurate modeling of form losses and frictional pressure losses for critical discharge flow rates through crack-like leaks are essential for a reliable prediction of flow rates. Uncertainties in leak rate computations results arise due to the lack of information about the flow geometry and its associated drag. The assumed flow resistance of a through-wall crack influences the computed leak rate as significant as the phase-change- and flow-models. The manifest difference between equilibrium models (Pana, Estorf) and non-equilibrium models (Henry, ATHLET-CDR) seems to be less significant than the pressure loss issue. One can conjecture that, for crack-like through-wall defects, friction effects play a more important role than non-equilibrium effects.

Applicability of Choking Flow Models for Subcooled Flashing Flow Through Tube Cracks

2011 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Mechanistic Model ◽  
Channel Length ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Flow Models ◽  
Model Predictions ◽  
Flow Through ◽  
The Difference ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. These data are used in assessing the key choking flow models. Based on this assessment a mechanistic choking model is developed. The model is used to predict the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values (∼5) to large values (100). Results are presented on the effects of thermal and mechanical non-equilibrium on the choking flow for small L/D channels. A mechanistic model was developed to model two-phase choking flow through slits. A comparison of model results to experimental data shows that the homogeneous equilibrium based models markedly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases.

scholarly journals Automated Compartment Model Development Based on Data from Flow-Following Sensor Devices

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1651
Author(s):  
Jonas Bisgaard ◽  
Tannaz Tajsoleiman ◽  
Monica Muldbak ◽  
Thomas Rydal ◽  
Tue Rasmussen ◽  
...  
Keyword(s):  
Large Scale ◽  
Model Development ◽  
Axial Flow ◽  
Compartment Model ◽  
Mixing Times ◽  
Flow Rates ◽  
Stirred Vessel ◽  
Compartment Models ◽  
Flow Models ◽  
Sensor Devices

Due to the heterogeneous nature of large-scale fermentation processes they cannot be modelled as ideally mixed reactors, and therefore flow models are necessary to accurately represent the processes. Computational fluid dynamics (CFD) is used more and more to derive flow fields for the modelling of bioprocesses, but the computational demands associated with simulation of multiphase systems with biokinetics still limits their wide applicability. Hence, a demand for simpler flow models persists. In this study, an approach to develop data-based flow models in the form of compartment models is presented, which utilizes axial-flow rates obtained from flow-following sensor devices in combination with a proposed procedure for automatic zoning of volume. The approach requires little experimental effort and eliminates the necessity for computational determination of inter-compartmental flow rates and manual zoning. The concept has been demonstrated in a 580 L stirred vessel, of which models have been developed for two types of impellers with varying agitation intensities. The sensor device measurements were corroborated by CFD simulations, and the performance of the developed compartment models was evaluated by comparing predicted mixing times with experimentally determined mixing times. The data-based compartment models predicted the mixing times for all examined conditions with relative errors in the range of 3–27%. The deviations were ascribed to limitations in the flow-following behavior of the sensor devices, whose sizes were relatively large compared to the examined system. The approach provides a versatile and automated flow modelling platform which can be applied to large-scale bioreactors.

Fracture Prevention Following Offshore Well Blowouts: Selecting the Appropriate Capping Stack Shut-In Strategy

2020 ◽  
pp. 1-13
Author(s):  
Andreas Michael ◽  
Ipsita Gupta
Keyword(s):  
Fracture Initiation ◽  
Loss Of Control ◽  
Flow Rates ◽  
Discharge Flow ◽  
Well Control ◽  
Wellbore Integrity ◽  
Discharge Flow Rate ◽  
Critical Discharge ◽  
Control Situations

Summary Following uncontrolled discharge during loss of well control events, fracture initiation occurring during the post-blowout capping stage can lead to reservoir fluids broaching to the seafloor. A classic example is Union Oil's 1969 oil spill in Santa Barbara Channel, where fracture initiation at various locations caused thousands of gallons per hour to broach onto the ocean floor over a month before it could be controlled (Mullineaux 1970; Easton 1972). Disasters such as these could be prevented if the effects of the post-blowout loss of well control stages (uncontrolled discharge and capping) are incorporated into the shut-in procedures, and the wellbore architectures are modified accordingly. In this study, analytical models are used to simulate the loads on the wellbore during the different stages of loss of control. Capping pressure buildup during the shut-in is modeled to indicate fracture initiation points during the capping stage. Using these models, the critical capping pressure for a well is determined, and subsequent critical discharge flow rates are calculated. Fracture initiation would occur if the actual discharge flow rate is below the calculated critical discharge flow rate. A hypothetical case study using typical deepwater Gulf of Mexico (GOM) parameters is performed demonstrating the likelihood of fracture initiation during different discharge flow rates, discharge periods, and capping stack shut-in methods (single-step/“abrupt” or multistep/“incremental”). An abrupt shut-in for this case study leads to fracture initiation at approximately 8 hours after shut-in, while a five-step incremental shut-in is shown to prevent any fracture initiation during the 48 hours after the beginning of the shut-in. Reservoir depletion through longer discharge periods or higher discharge flow rates, despite the adverse environmental effect, can delay or even prevent fracture initiations during post-blowoutcapping. The ability to model these fracture failures enhances the understanding of wellbore integrity problems induced during loss of control situations and helps create workflows for predicting possible broaching scenarios during the post-blowout capping stage. Dimensionless plots are used to present fracture initiation for different cases—this is useful for drilling and wellbore integrity engineers for making contingency plans for dealing with loss of well control situations.

scholarly journals Experimental Investigation of Diffuser Hub Injection to Improve Centrifugal Compressor Stability

2005 ◽  
Vol 127 (1) ◽  
pp. 107-117 ◽  
Author(s):  
Gary J. Skoch
Keyword(s):  
Centrifugal Compressor ◽  
Surface Resistance ◽  
Flow Resistance ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Injection Rate ◽  
Flow Rates ◽  
Injection Flow ◽  
Air Supply ◽  
Series Of Experiments

Results from a series of experiments to investigate whether centrifugal compressor stability could be improved by injecting air through the diffuser hub surface are reported. The research was conducted in a 4:1 pressure ratio centrifugal compressor configured with a vane-island diffuser. Injector nozzles were located just upstream of the leading edge of the diffuser vanes. Nozzle orientations were set to produce injected streams angled at −8, 0, and +8 degrees relative to the vane mean camber line. Several injection flow rates were tested using both an external air supply and recirculation from the diffuser exit. Compressor flow range did not improve at any injection flow rate that was tested, and generally diminished as injection rate increased. Compressor flow range did improve slightly at zero injection due to the flow resistance created by injector openings on the hub surface. Resistance and flow range both increased as the injector orientation was turned toward radial. Leading edge loading and semivaneless space diffusion showed trends that are similar to those reported earlier from shroud surface experiments that did improve compressor range. Opposite trends are seen for hub injection cases where compressor flow range decreased. The hub injection data further explain the range improvement provided by shroud-side injection and suggest that stability factors cited in the discussion of shroud surface techniques are valid. The results also suggest that a different application of hub-side techniques may produce a range improvement in centrifugal compressors.

Extractive distillation modeling of the ternary system 2-methoxy-2-methylpropane-methanol-butan-1-ol

2012 ◽  
Vol 66 (6) ◽  
Author(s):  
Zuzana Labovská ◽  
Pavol Steltenpohl ◽  
Elena Graczová
Keyword(s):  
Extractive Distillation ◽  
Model Complexity ◽  
Transfer Coefficients ◽  
Equilibrium Models ◽  
Nrtl Equation ◽  
Equilibrium Data ◽  
Real Behavior ◽  
Separation Equipment ◽  
Equilibrium Phases ◽  
Non Equilibrium

AbstractInfluence of model complexity on the separation equipment performance was investigated. As an example, separation of azeotrope formed by 2-methoxy-2-methylpropane and methanol was considered using butan-1-ol as an extractive solvent. Non-equilibrium model of a column for extractive distillation accounting for the mass and heat transfer rates was composed according to the rigorous Maxwell-Stefan theory. An empirical AICHE correlation was adopted for the calculation of binary mass transfer coefficients at column trays. Results of the column steady-state operation were compared with those obtained assuming different equilibrium models. Effect of the quality of the vapor-liquid equilibrium (VLE) description on the results of the separation simulation considering real behavior of either liquid or both equilibrium phases was tested. Real behavior of the liquid phase was computed according to the NRTL equation taking into account binary and, in some cases, also ternary equilibrium data. In case of real behavior of the vapor phase, the equation of state in the form of virial expansion was employed. Qualitative agreement was found comparing the simulation results calculated by equilibrium and non-equilibrium models of the extractive distillation column while using the same description of ternary VLE.

Crack-Opening Displacement and Leak-Rate Calculations for Full Structural Weld Overlays

2009 ◽  
Author(s):  
D.-J. Shim ◽  
E. Kurth ◽  
F. Brust ◽  
G. Wilkowski ◽  
A. Csontos ◽  
...  
Keyword(s):  
Crack Opening ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Opening Displacement ◽  
Primary Coolant ◽  
Pressurized Water ◽  
Weld Overlay ◽  
Water Reactors ◽  
The Impact ◽  
Weld Overlays

Full structural weld overlays have been used in the U.S. nuclear power industry for over twenty years in boiling water reactors (BWRs). Primary water stress corrosion cracking (PWSCC) in nickel-based dissimilar metal welds (DMWs) has been experienced in pressurized water reactors (PWRs) since the early 1990s. As a result, the nuclear industry is implementing full structural weld overlays (FSWOL) as a PWSCC mitigation technique that may be used on primary coolant lines previously approved for Leak-Before-Break (LBB). This work investigates the effect of the FSWOL on the leakage behavior of these lines with postulated defects. In this paper, finite element (FE) based crack-opening displacements (CODs) were developed for pipes with a FSWOL with postulated complex cracks. The COD solutions were then employed in standard leak-rate calculations, where equivalent crack morphology parameters were developed to consider a flow through two different crack morphologies, i.e., PWSCC through the DMW and corrosion fatigue through the weld overlay. The results of the sensitivity study and a discussion on the impact of the weld overlay on the leakage behavior concludes this paper.

Experimental and Analytical Leak Characterization for Axial Through-Wall Cracks in a Liquids Pipeline

2014 ◽  
Author(s):  
Mohamed R. Chebaro ◽  
Nader Yoosef-Ghodsi ◽  
David M. Norfleet ◽  
Jason H. Bergman ◽  
Aaron C. Sutton
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Internal Pressure ◽  
Crack Opening ◽  
Full Scale ◽  
Leak Rate ◽  
Propagation Mechanism ◽  
Element Analysis ◽  
Fea Model ◽  
Experimental Findings

Three pipeline sections containing defects of interest were non-destructively tested in the field, cut out and shipped to a structural laboratory to undergo full-scale testing. The common objectives of the experiments were to determine (1) the leak initiation pressure and (2) the leak rate at various specified internal pressures. While two spools (Specimens A and B) contained through-wall cracks, the third (Specimen C) had a partial through-wall crack with similar characteristics. The capacity of through-wall defects to withstand a level of internal pressure without leaking is due to the resultant local, compressive hoop residual stresses. Specimen C underwent full-scale pressure cycling to further comprehend the crack propagation mechanism in order to correlate it to field operation and analytical fatigue life predictions. To enhance the understanding of the physical crack behaviour as a function of internal pressure, a comprehensive finite element analysis (FEA) model was built using SIMULIA’s Abaqus software. The model inputs incorporated results from the above-mentioned laboratory tests, in addition to extensive radial, circumferential and axial residual stress measurements using the X-ray diffraction (XRD) technique, obtained on three pipe spools cut out from the same line. The resulting crack opening parameters from FEA were input into a closed-form fluid mechanics (FM) model, which was calibrated against a computational fluid dynamics (CFD) model, to determine the corresponding leak initiation pressures and leak rates. These outcomes were then compared to experimental findings. The FEA and FM models were subsequently employed to carry out a parametric study for plausible combinations of feature geometries, material properties, operational pressures and residual stresses to replicate field conditions. The key outcome from this study is the experimental and analytical demonstration that, for given fluid properties and pressures, the leak threshold and leak rate for through-wall cracks are primarily dependent upon the crack geometry and local residual stress distributions.

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