Leakage Performance Research Articles

Numerical investigations on leakage performance and flow mechanism of spiral groove seal for shrouded blade in axial turbine

Flow field of shroud leakage flow for a single-stage axial turbine has been investigated in this article. The spiral groove seal (SGS) is adopted for shrouded rotor blade to reduce tip leakage and improve turbine aerodynamic performance. A series of three-dimensional (3D) computational fluid dynamics (CFD) simulations are performed to investigate leakage characteristics and flow mechanism of various configurations with different angle, depth, width, and grooves number of the SGS. The original staggered labyrinth seal (LS) is also calculated for comparison. The results illustrate that small spiral groove angle can create more axial flow resistance; meanwhile, it will increase grooves number existing in the axial direction. Groove depth and tooth width will influence the number, shape, and strength of vortex in the groove. The leakage mass flow can be reduced by 36% and isentropic efficiency of the turbine can be increased by 0.26% when spiral groove angle, depth, and width of the SGS are 1.5°, 1.8 mm, and 0.8 mm, respectively. Overall, the optimal SGS can influence vortex generation and enhance energy dissipation in shroud cavity to reduce the leakage and suppress mixing loss of leakage flow with the main flow to some extent. It can be attributed to the combination of throttling effect and pumping effect of the SGS that realize leakage reduction and efficiency improvement. As a result, the SGS can effectively improve tip leakage flow of shrouded blade in axial turbine.

Enhancement of thermal energy absorption/storage performance of paraffin wax (PW) phase change material by means of chemically synthesized Ethylene Propylene Diene Monomer (EPDM) rubber network

Phase change materials (PCMs) are kind of energy storage systems utilized for thermal energy storage (TES) by virtue of high fusion latent heat property. In this research, Paraffin wax (PW) PCM and Ethylene-Propylene-Diene-Monomer (EPDM) were Vulcanized together by using various Benzoyl Peroxide contents to determine EPDM rubber network characteristics required for low leakage and high thermal performance. PCM systems were developed using vulcanized EPDM impregnation in high temperature molten PW. It is depicted that PW PCM system containing 5 wt.% Benzoyl Peroxide for EPDM curing has resulted in significantly higher thermal characteristics, while leakage was merely 0.81%, which is negligible and achieved along with PW shape stability in rubber network. Time -temperature performance of optimum PCM denotes that PW PCM presence could decrease rate of temperature change significantly. Furthermore, for adequate PCM system, more than 60% of inflow heat flux was absorbed.

Rotordynamic characteristics prediction for scallop damper seals using computational fluid dynamics

Enhancing damping characteristic is one of the effective methods to solve the instability problem of the rotor system. The three-dimensional numerical analysis model of scallop damper seal was established, and the effects of inlet pressures, preswirl ratios, rotational speeds, interlaced angles and seal cavity depths on the rotordynamic characteristics of scallop damper seal were studied based on dynamic mesh method and multi-frequencies elliptic whirling model. Results show that the direct stiffness of the scallop damper seal increases with decreasing inlet pressure and increasing rotational speed and cavity depth. When the seal cavity is interlaced by a certain angle, which shows positive direct stiffness. The effective damping of the scallop damper seal increases with the increasing inlet pressure, the decreasing preswirl ratio and the rotational speed and cavity depth. There exists an optimal interlaced angle to maximize the effective damping and the system stability. The leakage of the scallop damper seal is significantly reduced with decreasing inlet pressure. The preswirl will reduce the leakage flowrate, and the rotational speed has a slight effect on the leakage performance. The leakage of the scallop damper seal decreases with increasing seal cavity depth.

Effects of Front Plate Geometry on Brush Seal in Highly Swirling Environments of Gas Turbine

Advanced brush seal technology has a significant impact on the performance and efficiency of gas turbine engines. However, in highly inlet swirling environments, the bristles of a brush seal tend to circumferentially slip, which may lead to aerodynamic instability and seal failure. In this paper, seven different front plate geometries were proposed to reduce the impact of high inlet swirl on the bristle pack, and a three-dimensional porous medium model was carried out to simulate the brush seal flow characteristics. Comparisons of a plane front plate with a relief cavity, plane front plate with axial drilled holes, anti-“L”-type plate and their relative improved configurations on the pressure and flow fields as well as the leakage behavior were conducted. The results show that the holed front plate can effectively regulate and control the upstream flow pattern of the bristle pack, inducing the swirl flow to move radially inward, which results in decreased circumferential velocity component. The anti-“L” plate with both axial holes and one radial hole was observed to have the best effect on reducing the swirl of those investigated. The swirl velocity upstream the bristle pack can decline 50% compared to the baseline model with plane front plate, and the circumferential aerodynamic forces on the bristles, which scale with the swirl dynamic head, are reduced by a factor of 4. This could increase the bristle stability dramatically. Moreover, the front plate geometry does not influence the leakage performance significantly, and the application of the axial hole on the front plate will increase the leakage slightly by around 3.5%.

Improving performance of triboelectric nanogenerators by dielectric enhancement effect

<h2>Summary</h2> As an emerging energy-harvesting technology, enhancing the output performance of triboelectric nanogenerators (TENGs) is crucial for its practical application. Here, a dielectric enhancement effect is firstly proposed to improve the output performance of TENGs. It is found that the dielectric enhancement layer greatly elevates the triboelectrification effect, and the enhanced performance is verified by all types of TENGs. Thus, the output power of alternative current TENG (AC-TENG) and direct current TENG (DC-TENG) realizes 8.5-fold and 2.6-fold enhancement of normal devices, respectively. Besides this, the dielectric enhancement layer with leakage performance is proven to be necessary for DC-TENG to produce a continuous output. Our work provides a simple and universal strategy for elevating the performance of all types of TENGs, which is beneficial to the promotion of large-scale energy harvesting by TENGs.

Characterisation of trocar associated gas leaks during laparoscopic surgery

BackgroundDuring laparoscopy, the abdominal cavity is insufflated with carbon dioxide (CO2) that could become contaminated with viruses and surgical smoke. Medical staff is potentially exposed when this gas leaks into the operating room through the instruments and past trocar valves. No detailed studies currently exist that have quantified these leakage pathways. Therefore, the goal of this study was to quantify the gas leakages through trocars and instruments, during minimally invasive procedures.MethodsA model of the surgical environment was created, consisting of a rigid container with an interface for airtight clamping of laparoscopic equipment such as trocars and surgical instruments. The model was insufflated to 15 mm Hg using a pressure generator and a pneumotachograph measured the equipment gas leak. A protocol of several use cases was designed to simulate the motions and forces the surgeon exerts on the trocar during surgery.ResultsTwenty-three individual trocars and twenty-six laparoscopic instruments were measured for leakage under the different conditions of the protocol. Trocar leakages varied between 0 L/min and more than 30 L/min, the instruments revealed a range of leakages between 0 L/min and 5.5 L/min. The results showed that leakage performance varied widely between trocars and instruments and that the performance and location of the valves influenced trocar leakage.ConclusionsWe propose trocar redesigns to overcome specific causes of gas leaks. Moreover, an international testing standard for CO2 leakage for all new trocars and instruments is needed so surgical teams can avoid this potential health hazard when selecting new equipment.

Numerical investigation on leakage and rotordynamic performance of the honeycomb seal with swirl-reverse rings

Honeycomb seals are a crucial component to restrict the leakage flow and improve system stability for the turbomachines and aero-engines. In this work, the leakage and rotordynamic performance of honeycomb seals with the Swirl-Reverse Ring (SRR) is predicted by employing the approach of Computational Fluid Dynamics (CFD) and the multifrequency whirling model theory. Numerical results show that the positive preswirl flow and circumferential velocity can be effectively weakened for the honeycomb seal as SRR is introduced. The obtained results also suggest that the direct stiffness, direct damping, and effective stiffness will not reduce, for the honeycomb seal is introduced to SRR. However, the honeycomb seal with SRR can significantly reduce the cross-coupled stiffness and remarkably enhance the effective damping. Meanwhile, the absolute value of negative tangential force acting on the rotor surface significantly increased for the honeycomb seal introduced SRR. Therefore, the whirling velocity of the rotor would be weakened. This phenomenon would be conducive to improve the stability of the rotor. Besides, the performance of SRR can be further enhanced when SRR possesses a smaller bending angle, and a higher arrangement density and height.

Seal performance analysis and lifetime evaluation of capsule plugging glue

The capsule plugging glue as a repair tool is used to block the leak of the space station in orbit. Therefore the stringent requirements of its seal performance and life are put forward to ensure that the space station has excellent seal performance in orbit. It protects the life of cosmonaut, and maintains the lifetime of the space station. But the seal performance analysis and lifetime evaluation of capsule plugging glue has not carried out at present. Based on this, the mechanics performance parameters of the capsule plugging glue before and after the aging test are obtained by the correlative experiment. And then the thermal oxygen aging models of the capsule plugging glue are established in the storage and service status based on the time-temperature equivalence theory respectively, and realized to predict the lifetime of the capsule plugging glue in the two working status. In addition, the leakage performance of the capsule plugging glue, which is used to block the leak, is measured by the spray probe method. And then the change law of the seal performance of capsule plugging glue with the increase of aging time is obtained in the storage and service status.

Study on preparation and thermal performance improvements of composite phase change material for asphalt steel bridge deck

Phase change materials (PCMs) have the capabilities of thermal energy storage and temperature regulation. However, the application of PCMs in asphalt pavements is still limited due to the severe leakage and low thermal performance problem. In this research work, the phase change asphalt mixture (PCAM) with Polyethylene glycol/hydrophobic fumed silica composite phase change material (PEG/HFS) and Polyethylene glycol/SiO2 composite phase change material (PEG/SiO2) replacing mineral filler and fine aggregate was prepared and tested. The leakage experiment illustrated that the PEG/HFS with PEG content of 45% (wt) and PEG/SiO2 with PEG content of 70% (wt) had good thermal exudation stability. The results of XRD and FTIR showed that the preparation process of composite phase change materials (CPCMs) was a pure physical mixing process without chemical reactions. In addition, based on the results of the indoor radiation test, Marshall test, and rutting test, we found that when mineral filler and fine aggregate were replaced by 25% of the same volume of CPCMs, the PCAM exhibited a better cooling effect and relatively small decrease in mechanical strength. Therefore, the PCAM developed in this research has great potential for improving the thermal performance of asphalt steel bridge deck.

The protective performance of reusable cloth face masks, disposable procedure masks, KN95 masks and N95 respirators: Filtration and total inward leakage.

Face coverings are a key component of preventive health measure strategies to mitigate the spread of respiratory illnesses. In this study five groups of masks were investigated that are of particular relevance to the SARS-CoV-2 pandemic: re-usable, fabric two-layer and multi-layer masks, disposable procedure/surgical masks, KN95 and N95 filtering facepiece respirators. Experimental work focussed on the particle penetration through mask materials as a function of particle diameter, and the total inward leakage protection performance of the mask system. Geometric mean fabric protection factors varied from 1.78 to 144.5 for the fabric two-layer and KN95 materials, corresponding to overall filtration efficiencies of 43.8% and 99.3% using a flow rate of 17 L/min, equivalent to a breathing expiration rate for a person in a sedentary or standing position conversing with another individual. Geometric mean total inward leakage protection factors for the 2-layer, multi-layer and procedure masks were <2.3, while 6.2 was achieved for the KN95 masks. The highest values were measured for the N95 group at 165.7. Mask performance is dominated by face seal leakage. Despite the additional filtering layers added to cloth masks, and the higher filtration efficiency of the materials used in disposable procedure and KN95 masks, the total inward leakage protection factor was only marginally improved. N95 FFRs were the only mask group investigated that provided not only high filtration efficiency but high total inward leakage protection, and remain the best option to protect individuals from exposure to aerosol in high risk settings. The Mask Quality Factor and total inward leakage performance are very useful to determine the best options for masking. However, it is highly recommended that testing is undertaken on prospective products, or guidance is sought from impartial authorities, to confirm they meet any implied standards.

Novel gate air cavity GaN HEMTs design for improved RF and DC performance

Studies are performed to develop physical insights into the RF and DC behavior of GaN HEMTs. In purpose of improving the current gain cutoff frequency (fT) and power gain cutoff frequency (fmax), an air cavity structure was proposed, which efficiently decreases the gate–drain capacitance and gate–source capacitance. As a result, the proposed HEMTs with air cavity offers over 2× improvements in cutoff frequency comparing with the design without, which increases the fT and fmax to 14.9 GHz and 33.1 GHz, respectively. It breaks through the performance bottleneck limited by the length of gate, realizing a relatively high scaling factor that Lg × fT = 20.86 GHz μm when compared with previous reports. Besides, in order to realize both DC and RF performance improvement we proposed another kind of air cavity design, the fT and fmax can be increased by 82% and 37.6% respectively. The maximum saturation drain current approximately increased by 50%, maximum transconductance (gm, max) raise from 209 to 237 mS/mm and the gate current leakage performance is improved to a certain extent. Furthermore, forth bias sweep C–V (capacitance–voltage) curves and current density are also extracted to discuss the mechanism accompany with the reported physical model, based on which 2 simplified capacitive networks are proposed.

Brush seal contact force theory and correlation with tests

Brush seals are leakage performance systems that are operating against turbine shafts and bucket tips. Flexible bristle structure can compensate the rotor interference during transients, which enables closer clearance control in turbine and turbo-engine applications. During turbomachinery transients, contacting bristles exert force on turbine shaft, which in turn result in wear, frictional heat generation, counter torque and power loss. Brush seal design with proper stiffness has crucial importance since high bristle tip force levels during rotor contact may result in rotor instability, bristle tip melting or thermo-mechanical fatigue due to large amount of local frictional heat input. Counter torque applied by the contacting brush seal with improperly excessive tip force may result in turbine stall and overall efficiency losses. High levels of bristle contact forces may induce elevated wear rates, which degrades the leakage performance of the brush seal during its life cycle. Brush seal contact force evaluation under operating conditions has critical importance and has to be conducted before turbine integration to avoid performance losses and possible turbine failure in some extreme cases. In this paper, ‘Bristle Contact Force Theory’ is developed and closed form bristle tip force (BTF) function is derived where rotor-bristle, inter-bristle and bristle-back plate interactions are included. BTF measurements under pressurized and unpressurized air environment are conducted for the selected test seals by using the custom ‘Rotary Test Rig’. BTF function of bristle contact force theory show high level of correlation with the test data. The effect of cant angle manufacturing tolerance on bristle tip force levels is also examined through bristle tip contact force theory, and compared with the test seal measurements. Methodology for number of bristle row calculation and comparison with the geometric inspection of test seals are also detailed within the content of this paper.

Water Transport and Ion Diffusion Investigation of an Amphotericin B-Based Channel Applied to Forward Osmosis: A Simulation Study.

The use of an Amphotericin B_Ergosterol (AmBEr) channel as an artificial water channel in forward osmosis filtration (FO) was studied via molecular dynamics (MD) simulation. Three channel models were constructed: a common AmBEr channel and two modified C3deOAmB_Ergosterol (C3deOAmBEr) channels with different diameters (12 Å and 18 Å). During FO filtration simulation, the osmotic pressure of salt-water was a driving force for water permeation. We examined the effect of the modified C3deOAmBEr channel on the water transport performance. By tracing the change of the number of water molecules along with simulation time in the saltwater region, the water permeability of the channel models could be calculated. A higher water permeability was observed for a modified C3deOAmBEr channel, and there was no ion permeation during the entire simulation period. The hydrated ions and water molecules were placed into the channel to explore the ion leakage behavior of the channels. The mean squared displacement (MSD) of ions and water molecules was obtained to study the ion leakage performance. The Amphotericin B-based channels showed excellent selectivity of water molecules against ions. The results obtained on an atomistic scale could assist in determining the properties and the optimal filtration applications for Amphotericin B-based channels.

Impact of Supply Chain Information Integration on Operational Performance of Pharmaceutical Firms: Mediating Role of Information Leakage

Aims: The aim of the current study is to investigate the mediating role of information leakage on the relationship between supply chain information integration and operational performance of pharmaceutical firms.&#x0D; Study Design: Survey approach was used. Primary cross-sectional data was collected from 151 firms.&#x0D; Place and Duration of Study: Unit of analysis was organizations; population of the study was managerial staff, territory managers, field managers, area managers of firms. Total 200 questionnaires were distributed and 150 completed questionnaires were used in the analysis. Data was collected from Pfizer, Abbot, GSK, Mark, and Sanofi Aventis in 2020-2021.&#x0D; Methodology: Partial Least Square Structural Modeling Equation (PLS-SEM) was used for analysis. Measurement model and structural model were developed and tested. Majority of the respondents were male followed by female staff members. All the respondents belong to managerial and administration side/positions.&#x0D; Results: results of measurement model consist of loadings &gt;0.7, Cronbach alpha &gt;0.7, AVE&gt;0.5, CR&gt;0.7, revealed that scales used in the current study are reliable and valid. Results of structural model revealed that there is direct impact of supply chain information integration on information leakage and operational performance as well as indirect effect of information leakage upon supply chain information integration and operational performance of pharmaceutical firms.&#x0D; Conclusion: it is concluded that in pharmaceutical firms there is leakage of information. Accidental information leakage has some consequences as well as intentional leak of information is more harmful. Firms have to strengthen their network in order to attain competitive advantage over their competitors and sustainable operational performance.

Friction Mechanism and Application of PTFE Coating in Finger Seals

Due to their special flexible structure, finger seals show good wear and leakage characteristics and has a great application prospects. Under the condition of high speed, the sealing and wear performance of finger seals is directly related to the characteristics of the friction pair between the finger foot and rotor. As a kind of high polymer material with a lower friction coefficient, polytetrafluoroethylene (PTFE) has potential application value in finger seals. Therefore, based on the previous theoretical analysis and optimization design, in this study pin-on-disc tests between the metals applied in finger seals and the PTFE coating and bench-scale performance tests of finger seals with the PTFE coating were carried out. The results show that for finger seals made of the cobalt-base alloy GH605, the friction coefficient of finger seals with PTFE coating is only 0.15, which is 50% lower than that without the PTFE coating; after a 50-h durability test, the leakage performance of finger seals with the PTFE coating was more stable, and its leakage rate and wear rate were reduced by 30 and 39%, respectively, compared to without the PTFE coating. The test results in this article indicate that the PTFE coating has excellent wear resistance characteristics and good application potential for finger seals, which provides valuable reference for the design of the friction pair of finger seals.

Threshold Voltage Engineering of Enhancement-Mode AlGaN/GaN Metal-Oxide-Semiconductor High Electron Mobility Transistors with Different Doping Concentration of In Situ Cl− Doped Al2O3

This work used mist chemical vapor deposition to deposit an in situ Cl− doped Al2O3 film. 0.05 vol%, 0.1 vol%, and 0.15 vol% HCl were added to the precursor solutions for Cl− doping. The recess and Cl− doped Al2O3 gate dielectrics were used to form enhancement-mode AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors. The Cl− doping was confirmed by X-ray photoelectron spectroscopy and the negative charge concentration was extracted by capacitance-voltage method. It was found that the doping concentration affects the gate leakage performance and the carrier transportation mechanisms of the gate leakage were investigated. By using the Cl− doped Al2O3 as the gate dielectric layer, the device performance was improved, including more positive threshold voltage, higher output current at the same overdrive voltage, and over 600 V off-state breakdown voltage. In addition, the temperature-dependent threshold voltage characteristics were investigated to estimate the Cl− dopant runaway.

A Study on the Leakage Characteristics of a Stepped Labyrinth Seal with a Ribbed Casing

A new type of stepped seal with a ribbed casing is proposed to efficiently reduce the leakage at the tips of turbine blades. The leakage characteristics of two different types of labyrinth seals (conventional seal vs. ribbed seal) were compared and analyzed through computational fluid dynamics (CFD) in a wide operating range of pressure ratios and clearances. The analysis showed that the ribbed seal has superior leakage performance to the conventional seal at all clearance sizes. With the same clearance size (S/H = 1.0), the flow function of the ribbed seal was approximately 21.5–42.6% less than that of the conventional seal. Also, different trends of variation in the flow function according to the increase of the clearance were found between the conventional and ribbed seals. The leakage flow inside the labyrinth seal was analyzed to explain the cause of this difference in tendency, and it was confirmed that the added ribs cause collision between the leakage flow and the tooth wall, even with the increase of the clearance. Also, the ribbed seal enables operation at a larger clearance with the same leakage performance when comparing the absolute leakage flow rate of the two seals. In addition, a parametric study on the influence of the rib height and rib inclination angle revealed that the flow function generally decreases as both parameters increase.

Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals Operating in Supercritical CO2 Turbomachinery

Abstract The balance piston seal in multiple-stage centrifugal compressors and axial turbines sustains the largest pressure drop through the machines and therefore plays an important role in successful full load operation at high rotational speed. This is especially true for power dense turbomachines in supercritical CO2 power cycles that generate or expend higher fluid pressures (above the critical value 7.3 MPa) and density (close to water 1000 kg/m3), because the fluid forces generated by the balance piston seals are directly proportional to the fluid density and the pressure drop across the seal. This paper presents a comprehensive assessment and comparison on the leakage and rotordynamic performance of three types of annular gas seals for application in a 14 MW supercritical CO2 turbine. These three seals represent the main seal types used in high-speed rotating machines at the balance piston location in efforts to limit internal leakage flow and achieve rotordynamic stability, including a labyrinth seal (LABY), a fully partitioned pocket damper seal (FPDS), and a hole-pattern damper seal (HPS). These three seals were designed to have the same sealing clearance and similar axial lengths. To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake was also designed and employed at seal entrance for each type seal to reduce the seal inlet preswirl velocity. Numerical results of leakage flow rates, rotordynamic force coefficients, cavity dynamic pressure, and swirl velocity developments were analyzed and compared for three seal designs at high positive inlet preswirl (in the direction of shaft rotation), using a proposed transient computational fluid dynamic (CFD)-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the National Institute of Standards and Technology reference fluid properties database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions. Results show that the inlet swirl brake can significantly reduce the preswirl velocity at seal entrance, lowering the effective damping crossover frequency fco (or even fco = 0) to maximize the full operational frequency range of the machines. In stability analysis phase of a MW-scale supercritical CO2 turbine/compressor, the seal stiffness effects on the rotor mode shape must be evaluated carefully, where the seal stiffness is sufficiently large (comparable to the bearing stiffness). From a rotordynamic viewpoint, the HPS seal with entrance swirl brake is a better seal concept for the balance piston seal in supercritical CO2 turbomachinery, which possesses the largest positive effective damping throughout the entire subsynchronous frequency range.

Subharmonic single-balanced LMV with bottom LO injection

This paper proposes a subharmonic single-balanced RF receiver front-end (called LMV) where low noise amplifier is stacked on top of a differential voltage-controlled oscillator (VCO) to re-use the dc bias current. In this subharmonic (SH) LMV, the VCO itself plays the role of the single-balanced subharmonic mixer while generating an LO signal. This bottom LO SH LMV has good LO to IF and LO to RF leakage performances. Also, it can reduce the die size on a chip since it requires only one inductor for the VCO instead of two in the case of top LO LMV.Oscillating at around 2.4 GHz band, the proposed SH LMV is designed using a 65 nm CMOS technology and compared to the top LO SH LMV in terms of phase noise, conversion gain and double sideband noise figure. The SH LMVs consume about 160 μW dc power from a 1-V supply.

Suppression of Stress-Induced Defects in FinFET by Implantation and STI Co-Optimization

Defects originated from the stress-induced fin dislocation in FinFET have become critical in taller and narrower fin structures at advanced technology nodes that can easily form a leakage path between the source and the drain, leading to direct short failure. In this work, the correlation between the stress-induced defect and device leakage current has been studied using 14-nm FinFET devices with different fin structures. A novel method to detect and quantify the fin dislocation defect has been developed by characterizing the leakage performance, which can be used to evaluate the process effects. The asymmetric stress from shallow trench isolation (STI) oxide film and fin damage by ion implantation are verified as the primary causes through statistical analysis, which have been further co-optimized to achieve a higher yield.