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1.
In technical applications, static seals are sometimes also subjected to dynamic loadings. Therefore, the leakage behaviour under dynamic conditions has to be evaluated as well. For this purpose, FKM elastomer seals have been tested by using newly designed equipment that allows for rapid partial release of the seal and simultaneous leakage rate measurement at a wide range of test temperatures. Furthermore, material characterisation was done by using Dynamic Mechanical Analysis, Differential Scanning Calorimetry and Compression Set. It was shown that, under static conditions, the leakage rate increased significantly during cooling at temperatures around 18 K lower than the glass transition range. On reheating, the seal's functionality was restored in the high temperature region of the glass rubber transition. In the subsequent dynamic release tests, that comprised a reduction of the seal compression within 1 s from 25% to 23%, increased leakage rates were observed in the high temperature region of the glass transition range. It was shown that the temperature that is critical for increased leakage is significantly lower under static conditions compared to dynamic conditions. The obtained leakage rates for static tests and dynamic release tests at different temperatures were analysed with reference to results of the material characterisation.  相似文献   

2.
Seal assemblies are critical elements in a variety of drilling and completion equipment such as wellhead casing hangers, packers, and liner hangers. Zonal isolation is accomplished by seal compression (energization) which generates contact pressure at the seal-pipe interface. The performance of a seal is evaluated based on its mechanical and hydraulic integrity as well as its resistance to failure mechanisms. Objective of this study is to evaluate the performance of a seal assembly at varying compressions, seal and pipe properties, and chemical swelling.In this paper, numerical modeling approach validated by a lab-scale experimental work has been presented. Finite element model and experimental setup consisting of liner, casing, compression plates, and elastomer seal are used. In the model, seal performance was evaluated in terms of contact pressure generated at seal-pipe interface. Experimental setup was used to verify the modelling results. In experiments, sealability was evaluated by injecting gas and observing leakage.Modelling results indicate that elastomer sealability is linearly dependent on amount of seal compression. Numerical model also demonstrated that pipe material can have notable impact on elastomer sealability. Simulation results show that seal-pipe friction has insignificant impact on seal performance. Exposure to surfactant caused volumetric swelling of investigated elastomer materials. Despite reduction in hardness, volumetric swelling was high enough to generate additional seal compression and provide improved sealability as demonstrated by model.Performance evaluation of liner hangers is considered a challenge for industry and regulators because of limited testing protocols, standards, or regulatory guidelines for evaluating this type of barrier system. Information generated in this work will help further advance performance evaluation and qualification guidelines for liner hanger seal assembly.  相似文献   

3.
Since aging is an inevitable phenomenon during storage of a radial lip seal, this study aims to investigate the effect of aging on the seal performance. An air oven aging test is conducted to produce aged rubber samples and seal products. An aging life prediction model is constructed to predict the equivalent material properties at any storage temperature. The material property parameters of aged rubber samples are measured in a uniaxial compression experiment. The pumping rate and friction torque of the seal are calculated through numerical simulation by using a mixed elastohydrodynamic lubrication (EHL) model. A bench test is used to verify the aging life prediction model and the simulation results of the EHL model. Finally, the verified EHL model is used to study how aging during storage affects the lip seal performance, as characterized by the leakage and friction torque.  相似文献   

4.
Metal closures with a polymer-based sealing for beer bottles have been known since the late nineteen-sixties. However, to what extent which parameter of the polymer sealing gasket plays a role in closure performance to keep the beer quality to a highest level possible is not fully understood. For this purpose three thermoplastic elastomer (TPE) liners were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectrometry, dynamical mechanical analysis (DMA), scanning electron microscopy (SEM) and surface roughness in order to understand the effect of relative humidity (RH) and carbon dioxide (CO2) on their physical and chemical properties as well as their macromolecular structures. The TPEs’ viscoelasticity in the frequency domain under different isothermal conditions was evaluated. RH and CO2 were effective for changes in thermomechanical and surface properties. Liner C was found to have lower seal performance attributed to its relatively higher crystallinity, stiffness, weaker bond structure and rougher surface. Vibrations can lead to seal leakage in Liner B due to its higher damping behavior during production and transportation. Liner A outperforms others due to stabile behavior within the operational temperature range.  相似文献   

5.
程璇  彭程  游梦迪  刘晶  张颖 《电化学》2005,11(3):254-261
设计并组装单电池寿命测试系统,测试直接甲醇燃料电池(DMFC)的运行寿命,获得不同运行时间下单电池的极化和功率曲线.测试结束后,分别对运行过的膜电极(MEA)催化剂(铂黑和铂钌黑)和Nafion117(膜作XRD,HRTEM,FTIR及Raman等表征.考察在长期运行条件下电池寿命性能与膜电极中催化剂的颗粒大小、分布、形态、表面物种以及膜的结构之间的关系.寿命测试结果表明,单电池在不同运行阶段其性能变化也不同.运行前200 h,电池性能衰减较显著;运行200~704 h性能较稳定,运行1 002 h后电池性能恶化.波谱实验发现,单电池长期运行后,其膜电极的阴、阳极催化剂颗粒变大.电池寿命性能的衰退伴随膜电极微结构、表面组成、催化剂/膜界面结构的变化以及Nafion 117(膜的老化.  相似文献   

6.
A strong lightweight material (X-VOx) was formulated by nanocasting a conformal 4 nm thin layer of an isocyanate-derived polymer on the entangled worm-like skeletal framework of typical vanadia aerogels. The mechanical properties were characterized under both quasi-static loading conditions (dynamic mechanical analysis, compression and flexural bending testing) as well as high strain rate loading conditions using a split Hopkinson pressure bar (SHPB). The effects of mass density, moisture concentration and low temperature on the mechanical properties were determined and evaluated. Digital image correlation was used to measure the surface strains through analysis of images acquired by ultra-high speed photography, indicating nearly uniform compression at all stages of deformation during compression. The energy absorption of X-VOx was plotted as a function of the density, strain rate and temperature, and compared with that of plastic foams. X-VOx remains ductile even at ?180 °C, a characteristic not found in most materials. This unusual ductility is derived from interlocking and sintering-like fusion of nanoworms during compression. X-VOx emerges as an ideal material for force protection under impact.  相似文献   

7.
Impregnation mode in wood plastic composite   总被引:1,自引:0,他引:1  
Bulk monomer MMA was impregnated into simul, a fuel wood of Bangladesh, under vacuum and under normal temperature and pressure conditions in order to compare the mode of impregnation and its effect on various characteristic parameters of wood plastic composites. Methanol (MeOH) was used as the swelling solvent with methylmethacrylate (MMA) at MMA: MeOH = 70:30, v/v. Impregnation of the bulk monomer was very high under vacuum compared to that at normal condition; but the difference of grafting of MMA to the wood cellulose under these two impregnating conditions was much lower as compared to that of the uptakes of impregnating solution MMA + MeOH under these two modes of impregnation. Incorporation of additives to MMA + MeOH has substantially enhanced grafting, tensile strength, bending strength and compression strength of thcomposite of such an extent that there is virtually very little difference between vacuum impregnation and normal impregnation. Considering the available data it is suggested that the impregnation under normal condition is preferable beacuse different substrates of various sizes and shapes can be suitably impregnated under normal condition while vacuum impregnation has several limitations in this respect.  相似文献   

8.
Lifetime-resolved imaging measurements of chlorophyll a fluorescence were made on leaves of avocado plants to study whether rapidly reversible ΔpH-dependent (transthylakoid H(+) concentration gradient) thermal energy dissipation (qE) and slowly reversible ΔpH-independent fluorescence quenching (qI) are modulated by lutein-epoxide and violaxanthin cycles operating in parallel. Under normal conditions (without inhibitors), analysis of the chlorophyll a fluorescence lifetime data revealed two major lifetime pools (1.5 and 0.5 ns) for photosystem II during the ΔpH build-up under illumination. Formation of the 0.5-ns pool upon illumination was correlated with dark-retention of antheraxanthin and photo-converted lutein in leaves. Interconversion between the 1.5- and 0.5-ns lifetime pools took place during the slow part of the chlorophyll a fluorescence transient: first from 1.5 ns to 0.5 ns in the P-to-S phase, then back from 0.5 ns to 1.5 ns in the S-to-M phase. When linear electron transport and the resulting ΔpH build-up were inhibited by treatment with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), the major fluorescence intensity was due to a 2.2-ns lifetime pool with a minor faster contribution of approximately 0.7 ns. In the presence of DCMU, neither the intensity nor the lifetimes of fluorescence were affected by antheraxanthin and photo-converted lutein. Thus, we conclude that both antheraxanthin and photo-converted lutein are able to enhance ΔpH-dependent qE processes that are associated with the 0.5-ns lifetime pool. However, unlike zeaxanthin, retention of antheraxanthin and photo-converted lutein may not by itself stabilize quenching or cause qI.  相似文献   

9.
A miniaturised lab-in-a-pill device has been produced incorporating a temperature and pH sensor with wireless communication using the 433.92 MHz ISM band. The device has been designed in order to enable real time in situ measurements in the gastrointestinal (GI) tract, and accordingly, issues concerning the resolution and accuracy of the data, and the lifetime of the device have been considered. The sensors, which will measure two key parameters reflecting the physiological environment in the GI (as indicators for disease) were both controlled by an application specific integrated circuit (ASIC). The data were sampled at 10-bit resolution prior to communication off chip as a single interleaved data stream. This incorporated a power saving serial bitstream data compression algorithm that was found to extend the service lifetime of the pill by 70%. An integrated on-off keying (OOK) radio transmitter was used to send the signal to a local receiver (base station), prior to acquisition on a computer. A permanent magnet was also incorporated in the device to enable non-visual tracking of the system. We report on the implementation of this device, together with an initial study sampling from within the porcine GI tract, showing that measurements from the lab-on-a-pill, in situ, was within 90% of literature values.  相似文献   

10.
Ceramic hydroxyapatite (CHT) chromatography offers unique selectivity for protein purification. However, columns composed of CHT, a crystalline form of calcium phosphate, often suffer from short column lifetimes, particularly under acidic operating conditions. In this paper, CHT was used under slightly acidic conditions (pH 6) for the production scale purification of a recombinant protein. Under these conditions, the packing quality of production scale CHT columns (45 cm diameter) degraded after 5-10 cycles of operation. This was not reproduced using a conventional scale-down chromatography model, in which a constant column bed height was maintained across scales. Thus, an alternative scale-down model was developed to better predict the lifetime of large scale CHT columns. The alternative approach, which utilized a constant column diameter-to-height aspect ratio, was able to predict column failure that approximated that of the manufacturing scale column. The alternative scale-down approach was then used to test alternate buffer formulations that significantly improved the CHT column lifetime. Screening studies, which assessed the effects of mobile phase pH and composition on the dissolution (weight loss) of CHT, were used to identify the alternative mobile phase formulations. Results from the study showed that slight changes to the existing mobile phase compositions significantly increased the column lifetime, from approximately 10 cycles to approximately 65 cycles of use, without altering the purification of the recombinant protein. The alternative scale-down model, together with relatively rapid mobile phase screening studies, provides a practical approach for predicting and optimizing the useful lifetime of CHT columns for large scale applications.  相似文献   

11.
Nitrous oxide (N2O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N2O stable isotope investigations can help to characterize the N2O sources and N2O production mechanisms. N2O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N2O emitted from Antarctic tundra ecosystems have been reported although the coastal ice-free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N2O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using in situ field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N2O. For all the field sites, the soil-emitted N2O was 15N- and 18O-depleted compared with N2O in local ambient air. The mean delta values of the soil-emitted N2O were delta15N = -13.5 +/- 3.2 per thousand and delta18O = 26.2 +/- 1.4 per thousand for the penguin colony, delta15N = -11.5 +/- 5.1 per thousand and delta18O = 26.4 +/- 3.5 per thousand for the skua colony and delta15N = -18.9 +/- 0.7 per thousand and delta18O = 28.8 +/- 1.3 per thousand for the seal colony. In the soil incubations, the isotopic composition of N2O was measured under N2 and under ambient air conditions. The soils incubated under the ambient air emitted very little N2O (2.93 microg N2O--N kg(-1)). Under N2 conditions, much more N2O was formed (9.74 microg N2O--N kg(-1)), and the mean delta15N and delta18O values of N2O were -19.1 +/- 8.0 per thousand and 21.3 +/- 4.3 per thousand, respectively, from penguin colony soils, and -17.0 +/- 4.2 per thousand and 20.6 +/- 3.5 per thousand, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the predominant N2O source from Antarctic sea animal colonies.  相似文献   

12.
A thermally activated delayed fluorescence (TADF)-type exciplex host employing a novel electron-transport type (n-type) type host managing positive polarons and stabilizing excitons was developed to elongate the device lifetime of deep blue phosphorescent organic light-emitting diodes (PhOLEDs). The bipolar n-type host was designed to prevent hole leakage and secure hole stability while being stabilized under excitons by introducing a CN-modified carbazole moiety as a weak donor. The TADF-type exciplex host-based blue PhOLEDs showed high (above 20 %) quantum efficiency with a deep blue color coordinate of (0.14, 0.16) and elongated device lifetime. The device operational lifetime of the blue PhOLEDs bearing the TADF-type exciplex host was extended by more than twice compared to that of the exciplex-free unipolar host. This work suggested a design concept of the n-type host to develop the TADF-type exciplex host for deep blue phosphors to reach a long lifespan in the deep blue PhOLEDs.  相似文献   

13.
A critical failure mechanism in long-term applications of plastic structures, such as piping systems, is considered to be crack initiation and subsequent Slow Crack Growth (SCG). Thus, safe installation and operation during service lifetime of such structures are not conceivable without the knowledge of the resistance against SCG for any new material, like Unplasticized PolyAmide 12 (PA-U12). Unfortunately, long-term static tests at elevated temperatures lead to unreasonably long test times and measurements may also be affected by thermal aging and hydrolysis. Against this backdrop, the current study examines two accelerated test methods, namely the cyclic Cracked Round Bar (CRB) test as well as the Strain Hardening (SH) test, in order to characterize the SCG behavior. Both were originally developed for PolyEthylene (PE) and successfully implemented in recent years. While the cyclic CRB test measures SCG directly, accelerated through cyclic loading, the SH test quantifies the molecular disentanglement resistance, which determines craze formation and breakdown. The focus of this work was initially put on the extension of the CRB test towards PA-U12 grades, checking the occurrence of actual crack initiation and propagation. Afterwards a correlation to SH test results was done in terms of SCG resistance. Thereby, adequate test conditions were developed and the influence of the Molecular Weight (MW), expressed by the Viscosity Number (VN) of the PA-U12 grades, was considered. Results confirm the suitability of each method to rank SCG resistance and show a good correlation of the abovementioned SMall scale Accelerated Reliable Test (SMART) methods, highlighting their sensitivity to long-term relevant molecular parameters.  相似文献   

14.
A long-term(about nine months) isothermal degradation experiment of two different commercial polylactide(PLA) samples used for food packaging was carried out at a relatively low temperature(423 K). Thermooxidative degradations of the same polymers were carried out in a thermogravimetric(TG) analyser, at higher temperatures(453 K ≤ T ≤ 523 K), under isothermal heating conditions. The obtained set of experimental TG data was used to determine the apparent activation energy(Ea) of degradation through two isothermal kinetic methods. The results from long-term experiment evidenced considerable mass loss for both PLA samples in the investigated period, but the experimental data were not in agreement with those from the short-term degradations at higher temperatures, thus suggesting a different degradation kinetics, and, then a low reliability of the lifetime predictions for polymers in service or degradation forecasts for the end of their life based on experiments at higher temperatures.  相似文献   

15.
Dissipative particle dynamics (DPD) was used to investigate the behavior of two opposing end-grafted charged polymer brushes in aqueous media under normal compression and lateral shear. The effect of polymer molecular weight, degree of ionization, grafting density, ionic strength, and compression on the polymer conformation and the resulting shear force between the opposing polymer layers were investigated. The simulations were carried out for the poly(tert-butyl methacrylate)-block-poly(sodium sulfonate glycidyl methacrylate) copolymer, referred as PtBMA-b-PGMAS, end-attached to a hydrophobic surface for comparison with previous experimental data. Mutual interpenetration of the opposing end-grafted chains upon compression is negligible for highly charged polymer brushes for compression ratios ranging from 2.5 to 0.25. Under electrostatic screening effects or for weakly charged polymer brushes, a significant mutual interpenetration was measured. The variation of interpenetration thickness with separation distance, grafting density, and polymer size follows the same scaling law as the one observed for two opposing grafted neutral brushes in good solvent. However, compression between two opposing charged brushes results in less interpenetration relative to neutral brushes when considering equivalent grafting density and molecular weight. The friction coefficient between two opposing polymer-coated surfaces sliding past each other is shown to be directly correlated with the interpenetration thickness and more specifically to the number of polymer segments within the interpenetration layer.  相似文献   

16.
ABSTRACT

The viscoelastic behavior of elastomers manifests itself in numerous ways depending on the application. In seals, the viscoelastic response of an elastomer is complex as it depends upon the specific combination of loading pressures, loading rates, chemical environment, temperature and time of loading, and ultimately long-term effects such as creep or stress relaxation can result in seal failure. One specific mechanism encountered in seals under large pressures is extrusion damage. When a seal is pressurized by a fluid, the elastomer is highly constrained; however, there is typically a very small gap between the inner and outer sealing surfaces. Over time viscoelastic creep causes the elastomer to gradually extrude into this gap until the seal ruptures. In this paper the viscoelastic creep behavior of a typical sealing elastomer, NBR, was studied. Compression creep tests were carried out over a range of strains and the measured data were used to develop a strain-dependent viscoelastic material model. The model was then implemented into a finite element analysis (FEA) simulation to study the extrusion creep behavior of an O-Ring seal. Data from the FEA model were then compared against physical test data from equivalent extrusion tests. The FEA model correlated well to the physical test data, with the strain-dependent viscoelastic material model allowing compression creep data to be used to accurately predict extrusion creep.  相似文献   

17.
A novel thermo- and pH-sensitive nanogel particle, which is a core-shell structured particle with a poly(N-isopropylacrylamide) (p(NIPAAm)) hydrogel core and a poly(ethylene glycol) monomethacrylate grafted poly(methacrylic acid) (p(MMA-g-EG)) shell, is of interest as a vehicle for the controlled release of peptide drugs. The interactions between such nanogel particles and artificial mucin layers during both approach and separation were successfully measured by using colloid probe atomic force microscopy (AFM) under various compression forces, scan velocities, and pH values. While the magnitudes of the compression forces and scan velocities did not affect the interactions during the approach process, the adhesive force during the separation process increased with these parameters. The pH values significantly influenced the interactions between the nanogel particles and a mucin layer. A large steric repulsive force and a long-range adhesive force were measured at neutral pH due to the swollen p(MMA-g-EG) shell. On the other hand, at low pH values, the steric repulsive force disappeared and a short-range adhesive force was detected, which resulted from the collapse of the shell layer. The nanogel particles possessed a pH response that was sufficient to protect the incorporated peptide drug under the harsh acidic conditions in the stomach and to effectively adhere to the mucin layer of the small intestine, where the pH is neutral. The relationships among the nanogel particle-mucin layer interactions, pH conditions, scan velocities, and compression forces were systemically investigated and discussed.  相似文献   

18.
《Analytical letters》2012,45(1-2):217-227
Abstract

We have successfully installed and tested the first direct insertion probe (DIP) fast atom bombardment (FAB) gun on a Kratos MS-80 mass spectrometer. the installation requires only minor modifications on the standard EI/CI source which do not interfere with normal EI or CI operation. A small 2 inch extender must be added to the solid inlet to accomodate the extra length of the probe tip; this can be replaced in a few minutes by the standard seal to accept the regular solid probe. We have operated the source under simultaneous EI/FAB conditions with excellent results. The use of sorbitol syrup helps to keep source contamination and background spectrum to a minimum making it possible to operate at sufficiently high resolution in order to make exact mass operation routine. The performance evaluation has been carried out with synthetic peptides and the results are presented here.  相似文献   

19.
Park T  Song IH  Park DS  You BH  Murphy MC 《Lab on a chip》2012,12(16):2799-2802
A novel thermoplastic fusion bonding method using a pressure-assisted boiling point (PABP) control system was developed to apply precise temperatures and pressures during bonding. Hot embossed polymethyl methacrylate (PMMA) components containing microchannels were sealed using the PABP system. Very low aspect ratio structures (AR = 1/100, 10 μm in depth and 1000 μm in width) were successfully sealed without collapse or deformation. The integrity and strength of the bonds on the sealed PMMA devices were evaluated using leakage and rupture tests; no leaks were detected and failure during the rupture tests occurred at pressures greater than 496 kPa. The PABP system was used to seal 3D shaped flexible PMMA devices successfully.  相似文献   

20.
Despite of the hazardous risk of Pb2+leakage,lead dioxide has been attributed as a quasi-ideal anode material with high oxygen evolution potential,excellent conductivity,good stability and low cost in electrochemical oxidation wastewater treatment technique.In this study,a novel Ti/PbO2 anode was fabricated by embedding raw materials that are readily and cheaply available,i.e.,hairs.The structure-activity relationship of the new electrode was firstly revealed by material an...  相似文献   

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