Prediction Of Leakage Research Articles

Prediction of Leak Rates Through Porous Gaskets at High Temperature

The ability of a gasket to maintain tightness under different operating conditions has been studied extensively in recent years. However, most of the research studies conducted on leakage predictions was performed at room temperature. The aim of this work is to predict leakage through gaskets taking into account the effect of the temperature on the fluid properties and gasket internal structural characteristics. The analytical model of slip flow regime to evaluate the mass leak rates through a porous gasket developed by Grine and Bouzid (2011, “Correlation of Gaseous Mass Leak Rates Through Micro and Nano-Porous Gaskets,” ASME J. Pressure Vessel Technol.) was used in this study. The results from the model were validated and compared with the experimental data obtained from tests conducted on the Universal Gasket Rig with two different gases (helium and nitrogen). The leak rates measured are in the range of 1 to 0.0001 mg/s, which are measurable using the pressure rise technique. As a second objective, the influence of the gasket displacements caused by stress and temperature on the flow leakage was studied. A relationship between displacement or void thickness and leakage is clearly demonstrated. The slip flow regime model is capable of predicting leakage at temperature with reasonable accuracy.

A model for predicting pancreatic leakage after pancreaticoduodenectomy based on the international study group of pancreatic surgery classification.

Backgrounds/AimsWith recent advances in pancreatic surgery, pancreaticoduodenectomy (PD) has become increasingly safe. However, pancreatic leakage is still one of the leading postoperative complications. An accurate prediction model for pancreatic leakage after PD can be helpful for pancreas surgeons. The aim of this study was to provide a new model that was simple and useful with high accuracy for predicting pancreatic leakage after PD.MethodsTo predict the occurrence of pancreatic leakage, several factors were selected using bivariate analysis and univariate logistic regression analysis. The final model was developed using multivariable logistic regression analysis in the model construction data set.ResultsOverall, 41 of 100 patients had pancreatic leakage by the International Study Group on Pancreatic Fistula (ISGPF) criteria. Soft pancreatic parenchyma, small pancreatic duct diameter (≤3 mm), and combined resection of SMV and portal vein were independently predictive of pancreatic leakage. The risk score (R) for individual patients can be calculated by combining the 3 prognostic values with the regression test: R=0.5986+(0.5533×pancreatic parenchyma)+(0.5448×pancreatic duct diameter)+(0.8453×combined resection). The overall predictive accuracy of the model, as measured by the receiver operating characteristic (ROC) curve, was 0.728.ConclusionsAlthough continued refinements and improvements in the model are needed, the present model may assist pancreatic surgeons in the prediction of pancreatic leakage after PD.

The Relation Between Perfusion Pattern of Hepatic Artery Perfusion Scintigraphy and Response to Y-90 Microsphere Therapy

Objective: Hepatic artery perfusion scintigraphy is a routine procedure for patient evaluation before Y-90 radiomicrosphere therapy and mostly used for prediction of extrahepatic leakage. Moreover, it also displays perfusion pattern of tumours, which is an important parameter on success of the therapy. The aim of this study is to assess the relation between the perfusion pattern on hepatic artery perfusion scintigraphy and radiomicrosphere therapy response.Methods: A total of 99 radiomicrosphere therapy applications were carried out in 80 patients (M/F: 55/25).Results: Heterogeneous and diffuse perfusion patterns were observed in 47 patients and 52 patients, respectively. The patients with diffuse perfusion pattern had better therapy response both on FDG PET/CT (p= 0.04) and CT (p=0.008) when compared to those with heterogenous perfusion pattern.Conclusion: Perfusion pattern observed on hepatic artery perfusion scintigraphy may be a successful predictor of early response to radiomicrosphere therapy. Conflict of interest:None declared.

Simulation and Evaluation of Respirator Faceseal Leaks Using Computational Fluid Dynamics and Infrared Imaging

This paper presents a computational fluid dynamics (CFD) simulation approach for the prediction of leakage between an N95 filtering facepiece respirator (FFR) and a headform and an infrared camera (IRC) method for validating the CFD approach. The CFD method was used to calculate leak location(s) and 'filter-to-faceseal leakage' (FTFL) ratio for 10 headforms and 6 FFRs.The computational geometry and leak gaps were determined from analysis of the contact simulation results between each headform-N95 FFR combination. The volumetric mesh was formed using a mesh generation method developed by the authors. The breathing cycle was described as a time-dependent profile of the air velocity through the nostril. Breathing air passes through both the FFR filter medium and the leak gaps. These leak gaps are the areas failing to achieve a seal around the circumference of the FFR. The CFD approach was validated by comparing facial temperatures and leak sites from IRC measurements with eight human subjects. Most leaks appear at the regions of the nose (40%) and right (26%) and left cheek (26%) sites. The results also showed that, with N95 FFR (no exhalation valves) use, there was an increase in the skin temperature at the region near the lip, which may be related to thermal discomfort. The breathing velocity and the viscous resistance coefficient of the FFR filter medium directly impacted the FTFL ratio, while the freestream flow did not show any impact on the FTFL ratio. The proposed CFD approach is a promising alternative method to study FFR leakage if limitations can be overcome.

Early prediction of anastomotic leakage after free jejunal flap reconstruction of circumferential pharyngeal defects

Anastomotic leakage from the free jejunal flap, if diagnosed late, can result in catastrophes. Our study aims to look for clinical parameters that allow early identification of leakage so that appropriate interventions can be taken. Between 1980 and 2011, consecutive patients with free jejunal flap reconstruction of circumferential pharyngeal defects were included. A retrospective chart review was then performed comparing the clinical parameters (body temperature, heart rate, serum albumin, haemoglobin and white cell count) between patients with no leakage and those with clinical and radiological leakage. 4. Ninety-six patients were included in the study. The median age was 62 years. Majority (69.8%) of the defects were created after resection of tumours in the hypopharynx. Five (5.2%) patients had clinical leakage and 12 (12.5%) had radiological leakage. There was no significant difference in body temperature, heart rate, incidence of atrial fibrillation and haemoglobin level between those with and without leakage. The serum white cell count was higher in the patients who leaked, but it became statistically significant only after day 7 postoperatively. The serum albumin level was significantly lower in patients with anastomotic leakage starting as early as day 3 after surgery, and the difference persisted until the leak was controlled. However, there was no significant difference in the plasma albumin level between those with clinical or radiological leak. Both serum albumin level and white cell count identified the presence of anastomotic leakage from the free jejunal flap. Serum albumin allows early prediction of leakage so that early interventions can be taken to avoid the damage resulting from the delay in diagnosis.

Gas Leakage Prediction Model of Large-Scale Explosions in Hard Rock Based on Quantification Theory

The toxic gas produced by the underground large-scale contained explosions have a great impact on the surrounding environment safety of the explosion project, so it is of great significance for the safety protection design to predict the leakage of the explosion gases to the environment. Based on the study of the one-dimensional spherically (axially) symmetric fluid dynamic model for seepage of the underground contained explosion gases, the qualitative and quantitative variables which impact the gas seepage, such as the explosion cavity, the gas pressure in the cavity and the rock mass permeability, among which the qualitative variables can describe the uncertainty of the geological mass, were analyzed. In accordance with the physical significance of variables and the quantification theory, the qualitative variables were quantified and such details as the principle for variable selection, significance assessment and recurrence test to establish a quantification prediction model, etc. were discussed. Based on 15 test samples on the hard rock conditions, we have established a quantification model for prediction of the contained explosion gases leakage at the specific site. The prediction accuracy of this model can meet the requirement of this project, and according to this model, it is known that such qualitative factors as groundwater status and rock properties have significant influence on the gas leakage. In this study, the prediction model is established based on physical analysis so that the quantitative prediction model could have its rationality and effectiveness well ensured, and the research methods and results in this paper could be promoted and applied in the similar engineering practices.

Clock-Phase-Noise-Induced TX Leakage Estimation of a Baseband Wireless Transmitter DAC

In many wireless systems, the transmit (TX) signal could leak to the receiver input through the antenna duplexer, and this leakage could raise the noise level in the receive (RX) band. Therefore, it is important to be able to accurately predict the noise spectrum that leaks into the RX band from a TX digital-to-analog converter (DAC) in order to optimize the noise performance. This study analyzes the DAC output noise that is caused by the phase noise of the DAC clock. First, a closed-form equation is derived to account for both the phase noise and noise aliasing. Then, the proposed TX leakage prediction in the RX band is verified with both simulation and measurement. A clear understanding of the relationship between the clock phase noise and the DAC output noise spectrum could enable both the DAC and phase-locked loop designs to be optimized for the lowest RX band noise performance with low cost and power consumption at the same time.

Design of 65nm Sub-Threshold SRAM Using the Bitline Leakage Prediction Scheme and the Non-trimmed Sense Amplifier

In this paper we present a 0.25-1.0V, 0.1-200MHz, 256×32, 65nm SRAM macro. The main design techniques include a bitline leakage prediction scheme and a non-trimmed non-strobed sense amplifier to deal with process and runtime variations and data dependence.

Trend Prediction of Hydraulic Liquid Leakage Based on ES-LSSVM

A novel prediction method which combined evolutionary strategy with least-square support vector machine is presented and applied to the trend prediction of hydraulic liquid leakage in this paper. In order to improve the prediction performance, the evolutionary strategy is employed to optimize the internal parameters of least-square support vector machine. Through the experiment study, the result validated the effectiveness of the prediction method, and it is also demonstrated that the method is able to do the short-term fault prediction for the hydraulic system.

Investigating leakage and bypass flows in an HTR using a CFD methodology

An area that has been identified as significantly important in the development of a high temperature reactor (HTR) is the prediction of leakage and bypass flows. It is therefore essential to understand the influence of leakage and bypass flows on the thermal performance of an HTR. A methodology was developed to conduct an integral thermal analysis of a reactor using a CFD approach. One of the main objectives was to include leakage and bypass flow paths in order to provide a capability for simulating these very detailed flows. This paper investigates leakage and bypass flows through the PBMR reactor unit. It was found that, although these flows are dependent on the pressure drop through the pebble bed, a change in pebble bed pressure drop does not result in a similar change in the predicted leakages flows. It is also shown that the ability to account for leakage and bypass flows in an integral manner can help designers to focus their efforts on the specific regions that need to be targeted for the improvement of the life expectancy of the graphite blocks. Furthermore, leakage and bypass flows were found to reduce the pressure drop across the reactor unit while increasing the peak fuel temperatures.

Numerical modelling of hydraulic seals by inverse lubrication theory

This article describes a methodology used to achieve a numerical analysis of hydraulic seals by the inverse hydrodynamic lubrication method. The main novelties consist of taking into account the influence of the shear stresses in the lubricant film and in the treatment of hydrodynamic effects on the seal inlet. Each step is detailed and discussed in terms of possible error over the predicted seal performances. It has been shown that the pressure field computed directly from the structure model does not give a realistic approximation of the hydrodynamic pressure in the inlet zone, and a hydrodynamic correction is necessary. Furthermore, it has been shown that if the tangential friction due to the shear stress in the lubricant film is not taken into account, error of about 5 per cent can be made, concerning the predictions of leakage and friction force.

Prediction of leakage of a pressure-relief valve based on support vector regression with auxiliary input information

It is significant if the gas leakage of pressure-relief valve (PRV) can be accurately predicted in advance, because gas leakage may destroy the PRV's stability and result in a potential damage to the entire pneumatic circuit. This article puts forward a model based on support vector regression (SVR) to predict the gas leakage of PRV. The experimental data of three identical PRVs are employed to evaluate the performance of the leakage prediction model with different input information. The experimental results demonstrate the superiority of the proposed model, proved especially when the pressure difference between inlet and outlet pressures of PRV is chosen as the auxiliary input information. The SVR prediction model which only uses leakage data as input information can perform better than the artificial neural network prediction model, but the prediction accuracy can be further improved if the proper auxiliary input information is taken.

Water Distribution System Modeling and Smart Grid Technology

In order to study how information and technology can be used to improve water management, smart grid technologies were introduced into the water industry. This paper describes a project to integrate GIS, SCADA and online hydraulic model to assist water engineers in assessing the water distribution system. The integrated system simulates the flow and concentration of chemical contaminants online in municipality's water distribution system. The integrated system is a powerful tool for routine planning and emergency response and also for remote leakage detection and prediction of pipe burst. The capabilities of the integrated system can greatly assist in the decision making processes for network asset inventory, rehabilitation requirements, and financial planning.

Investigation of Leakage Characteristics of Straight and Stepped Labyrinth Seals

Leakage characteristics of two labyrinth seals with different configurations (straight vs stepped) were investigated. Leakage flows were predicted by computational fluid dynamics (CFD) for the two configurations and compared with test data. A semi-analytical leakage prediction tool was also tried to predict the leakage. It was confirmed that the CFD gives quite good agreements with test data. The analytical tool also yielded similar leakage behaviors with test results, but the overall agreement with test data was not as good as that of the CFD. The effect of flow direction in the stepped seal on leakage flow was examined. The dependence of leakage performance, in terms of flow function, on the seal clearance size was investigated. Flow function decreased with decreasing clearance in the straight seal, while the trend was reversed in the stepped seal.

A CFD method to evaluate the integrated influence of leakage and bypass flows on the PBMR Reactor Unit

An area that has been identified as significantly important in the development of a High Temperature Reactor (HTR) is the prediction of leakage and bypass flows through such a reactor. It is therefore essential to understand the causes of bypass flows and to determine the effect on the predicted fuel and component temperatures.This paper discusses the identification of leakage flows that are applicable to the Pebble Bed Modular Reactor (Pty) Ltd. (PBMR) design and the ranking of these leakage flows. The modeling methodology and results are also discussed.Similar to previous HTR's, it was found that leakage and bypass flows are important parameters to consider for safe and efficient operation of the PBMR. Through a focused approach, it is shown that PBMR is able to improve the understanding of this phenomenon and quantify the flows and subsequent influence on the operation of the system. This has resulted in a reduction of leakage and bypass from approximately 46% to 20%. The improved understanding of leakage and bypass flows allows PBMR to address this issue during the design phase of the project, which subsequently results in a vast improvement over historical HTR designs. This gives PBMR a distinct advantage over previous High Temperature Reactors.

Leakage Prediction Method for Contacting Mechanical Seals with Parallel Faces

Since the beginning of the 20th century, many researches on the sealing characteristic of mechanical seals were carried out broadly and in depth by various methods and some leakage models were built. But due to the lack of the way to characterize the main factors of influence on the leakage, most of the early researches were based on the assumptions that the seal faces topography and the frictional conditions were invariant. In the early built models, the effect of the surface topography change of the seal face on the leakage rate was neglected. Based on the fractal theory, the contact of end faces of the rotary and stationary rings was simplified to be the contact of a rough surface and an ideal rigid smooth surface, and the contact interface’s cavity size-distribution function as well as the fractal characteristic of the cavity profile curve was discussed. By analyzing the influence of abrasion on the seal face topography and the leakage channel, the time-correlation leakage prediction model of mechanical seals based on the fractal theory was established and the method for predicting the leakage rate of mechanical seals with parallel plane was proposed. The values of the leakage rate predicted theoretically are similar to the measured values of the leakage rate in the model test and in situ test. The experimental results indicate that the leakage rate of mechanical seals is a transient value. The surface topography of the end faces of the seal rings and its change during the frictional wear of mechanical seals can be accurately characterized by the fractal parameters. Under the work conditions of changeless frictional mechanism, the fractal parameters measured or calculated based on the accelerated testing equation can be used to predict the leakage rate of mechanical seal in service. The proposed research provides the basis for determining the leakage state and predicting working life of mechanical seal.

Uncertainty Analysis for Assessing Leakage Through Water Tunnels: A Case from Nepal Himalaya

Water leakage problems in unlined or shotcrete lined water tunnels are not new issues. In many occasions severe water leakage problems have been faced that not only have reduced the stability of the rock mass, but also have caused valuable water to be lost from it, causing safety risk as well as huge economic loss to the projects. Hence, making tunnels water tight plays an important role in improving stability and safety of underground excavations. The real challenge is however accurate prediction and quantification of possible water leakage, so that cost consequences can be incorporated during planning of a water conveying tunnel project. The main purposes of this paper are to analyze extensive data on leakage test carried out through exploratory drillhole used to define the need for pre-injection grouting of Khimti headrace tunnel and to carry out probabilistic approach of uncertainty analysis based on relationship established between leakage, hydrostatic head and selected Q-value parameters. The authors believe that the new approach regarding uncertainty analysis of leakage presented in this paper will improve the understanding of leakage characteristics of the rock mass, and hope this will lead to a better understanding concerning quantification of possible water leakage from unlined and shotcrete lined water tunnels.

Quantitative prediction of junction leakage in bulk-technology CMOS devices

Junction leakage becomes more significant as metal-oxide-semiconductor (MOS) technologies scale down in bulk-silicon. In this work we quantify the four key elements to junction leakage generation through a combination of experiment and device simulation. These elements are: (i) ultra-shallow junction steepness, (ii) channel and pocket concentrations, (iii) junction curvature, and (iv) the presence of residual defects. We first characterize n+/p and p+/n diodes to quantify how changes in doping profiles affect reverse bias leakage. Diodes with end-of-range (EOR) silicon defects intentionally located in the junction depletion region are also characterized to quantify their contribution. This feeds into a device simulation study to gain insight in the experimental results and in the capabilities of available physical models. Thereafter simulation is used to predict leakage in future generation bulk-silicon MOS devices. In summary, band-to-band tunneling (BBT) due to aggressively scaled doping profiles and trap-assisted tunneling (TAT) due to the increased presence of defects make off-state low-standby-power leakage targets difficult to meet. With the increase of junction leakage from aggressively scaled ultra-shallow junctions, the assumption that the subthreshold leakage component dominates off-state current is no longer valid.

Intraoperative assessment of microperfusion with visible light spectroscopy for prediction of anastomotic leakage in colorectal anastomoses

Anastomotic leakage is associated with increased morbidity and mortality. However, there is no accurate tool to predict its occurrence. We evaluated the predictive value of visible light spectroscopy (VLS), a novel method to measure tissue oxygenation [saturated O(2) (StO(2) )], for anastomotic leakage of the colon and the rectum. Oxygen saturation in the bowel was measured in 77 colorectal resections. The anastomosis was between 2 and 30 cm (mean 13 cm) from the anal verge. The oxygen saturation was measured in the colon and rectum before and after anastomosis construction. This was compared with a reference measurement in the caecum. Data on postoperative complications were prospectively collected. Anastomotic leakage occurred in 14 (18%) patients. When compared with a leaking anastomosis, normal anastomoses showed rising O(2) values during the operation (mean StO(2) 72.1 ± 9.0-76.7 ± 8.0 vs 73.9 ± 7.9-73.1 ± 7.4) (P ≤ 0.05). There were also higher StO(2) values in the caecum compared with those which ultimately leaked (73.6 ± 5.7 normal anastomoses, 69.6 ± 5.6 anastomotic leaks) (P ≤ 0.05). Both StO(2) values were predictive of anastomotic leakage. Tissue oxygenation O(2) appears to be a potentially useful means of predicting anastomotic leakage after colorectal anastomosis.

Two-dimensional thermal analysis of liquid hydrogen tank insulation

Abstract Liquid hydrogen (LH 2 ) storage has the advantage of high volumetric energy density, while boil-off losses constitute a major disadvantage. To minimize the losses, complicated insulation techniques are necessary. In general, Multi Layer Insulation (MLI) and a Vapor-Cooled Shield (VCS) are used together in LH 2 tanks. In the design of an LH 2 tank with VCS, the main goal is to find the optimum location for the VCS in order to minimize heat leakage. In this study, a 2D thermal model is developed by considering the temperature dependencies of the thermal conductivity and heat capacity of hydrogen gas. The developed model is used to analyze the effects of model considerations on heat leakage predictions. Furthermore, heat leakage in insulation of LH 2 tanks with single and double VCS is analyzed for an automobile application, and the optimum locations of the VCS for minimization of heat leakage are determined for both cases.