Sealing smothering method is an important approach to control large fire in channels. This paper experimentally studied the fire behaviors after the sealing in a reduced-scale channel model, ...considering different initial sealing time under different sealing rates. A series of characteristic parameters, such as the temperature over fire source, mass loss rate of fuel, CO concentration at channel entrance as well as smoke temperature at channel entrance were measured. The results showed that for complete sealing, the earlier the initial sealing time is, the better the fire can be suppressed with a shorter burning duration and lower temperature. However, for incomplete sealing, although the sealing implemented before violent burning stage can reduce the temperature effectively, it causes a much longer burning duration and induces a higher CO concentration at the channel entrance. Especially during violent burning stage, the sealing not only does not restrict fire growth but also exacerbates the channel fire with an extremely high CO concentration at the channel entrance and a longer ceiling flame jet. Besides, as long as one of the channel entrances is not sealed completely, the temperature above the ceiling at channel entrance increases immediately after the sealing, which should be noticed for firefighters during fire rescue.
•Fabrication methods, structure design and durability analysis of advanced sealing materials in proton exchange membrane fuel cells.•The sealing structures and assembly methods of Proton exchange ...membrane fuel cell are summarized.•Detailed durability analysis of the sealing material was carried out.•For the first time, the durability test and test methods of the seal are summarized.
In a proton exchange membrane fuel cell (PEMFC) stack, there are many cells and each single cell has a multi-layer structure. The bipolar plates, membrane electrode assembly (MEA) and other components must be strongly sealed with gaskets and/or glue. The stable and reliable sealing is crucial for PEMFC stacks in terms of the lifetime. However, the expansion, shrinkage and aging of the sealing leads to the failure of fuel cell due to the complex operation environment. Thus, the function of sealing components plays important roles in fuel cell. In this work, the recent research of fabrication methods, structure design and durability analysis of the sealing materials are comprehensively reviewed and analyzed considering the key properties, including surface morphology, density, hardness, mechanical properties and chemical properties of the sealing materials under various test environments. The novelty of this study is that the failure mechanisms of PEMFC seal materials are also discussed from the perspective of both experimental examination and theoretical modeling. At last, technical challenges are summarized and the possible future research directions are proposed, which may contribute to overcome the challenges of prolonging the durability of the PEMFC stacks in the future researches.
The low gas extraction concentration is one of the main factors that affect the prevention and control effect of coal and gas outburst. Based on this, the factors of air leakage around the roadway ...and borehole are analyzed. The effect of extraction time, seal length and air leakage on the gas concentration is discussed by the fluid-solid coupling model, which is proved by the borehole environmental parameter instrument.The research findings show :(1) Influenced by roadway excavation and drilling, a large number of cracks are created inside the coal around the roadway and the boreholes, which are the main air leakage channels for the air to flow from roadway into borehole; (2) Inside the borehole, the closer it is to the bottom of the borehole, the fewer the cracks in the coal seam, the higher the gas concentration. The critical point of air leakage in which the gas concentration is 100 % moves continuously to the bottom of the borehole with extraction time, until it is stable. The effective sealing length must exceed the position of critical point of air leakage; (3) The gas concentration is related to the sealing length and the amount of air leakage. Increasing the sealing length, and reducing the air leakage can greatly improve the extraction efficiency. Based on the above results, combined bag-type segmented grouting technique, which is to inject different sealing materials into different regions divided by the stress, is proposed to block the air leakage channel by comparing the crack characteristics of the coal surface in the abnormal stress zone and the normal stress zone by SEM technology. According to the field test results, the application of the new sealing technology blocks the crack channel, improves gas concentration and reduces the risk of coal and gas outburst. The results have important guiding significance for improving gas utilization rate, reducing greenhouse gas emission and enhancing safety in production.
Endodontic sealers for non-surgical root canal treatment (NSRCT) span many compositions and attributes. This comprehensive review discusses current types of endodontic sealers by their setting ...reaction type, composition, and properties: zinc oxide-eugenol, salicylate, fatty acid, glass ionomer, silicone, epoxy resin, tricalcium silicate, and methacrylate resin sealers. Setting time, solubility, sealing ability, antimicrobial, biocompatibility, and cytotoxicity are all aspects key to the performance of endodontic sealers. Because sealing ability is so important to successful outcomes, the relative degree of microleakage among all the relevant sealers was calculated by way of a meta-analysis of relevant literature. Compared to AH Plus, tricalcium silicate sealers show the lowest relative microleakage among the sealers assessed, followed by silicone sealers and other non-AH Plus epoxy resin sealers. Tricalcium silicate sealers also exhibit the most favorable antimicrobial effect and excellent biocompatibility. Future sealers developed should ideally combine a hermetic seal with therapeutic effects.
Magnetic fluids are the suspensions composed of magnetic nanoparticles, surfactants, and non-magnetic carrier liquids. Magnetic fluids are widely used in various fields, especially in sealing, ...because of their excellent features, including rapid magnetic response, flexible flow ability, tunable magneto-viscous effect, and reliable self-repairing capability. Here, we provide an in-depth, comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories: static sealing, rotary sealing, and reciprocating sealing. We summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present, particularly focusing on the recent progress of magnetic fluid seals. Although magnetic fluid sealing technology has been commercialized and industrialized, many difficulties still exist in its applications. At the end of the review, the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.
•A new numerical simulation method is proposed to obtain the magnetic fluid boundary and thermal deformation of the sealing gap.•The thermal expansion displacement of magnetic materials was deduced ...by using the thermal resistance model.•Research on the effects of thermal expansion on magnetic fluid rotary seal.
Magnetic fluid seal is the most mature application of magnetic fluid at present. However, some deficiencies limit the application of magnetic liquid seals at high rotation speeds, including the thermal expansion under different temperatures. The sealing gap width is affected by thermal expansion significantly, which leads to a change in the sealing performance. This paper proposes a new numerical simulation method to obtain the magnetic fluid boundary and the thermal deformation of the sealing gap. The dynamic mesh and thermo-hydro-mechanical coupling methods are used to calculate the thermal deformation in the two-dimensional axisymmetric model. Numerical results show the fluid temperature and sealing gap change under different rotation speeds, which influences the sealing performance.
Controversy arises whenever and wherever the sealing industry is discussed. But the modern-day anti-sealing movement is very new in comparison with the industry it opposes. This comprehensive history ...begins with the opening of American trade with China, and follows the industry wherever North Americans have sought seals for their fat or their skins, from New England to Australia, from Cape Horn to the California coast. All the many species of seals hunted received due consideration, as do walruses and sea otters, also part of the larger sealing industry. Above all, this book studies the fur seals of the Bering Sea and the harp seals of the Newfoundland hunt, detailing the consequences of an industry's killing of more than 50,000,000 seals in 150 years. Busch weighs this toll against the economic benefits that sealing brought to a great many people in cities along both North American coasts. Based on extensive research into primary and published sources, Busch's history provides conservationists, naturalists, historians, and general readers with new information and new perspectives on a subject of continuing world interest.
High-performance sealing materials that can guard key components against high pressure gases and liquid chemicals while withstanding mechanical deformation are of utmost importance in a number of ...industries. In this present work, graphene nanoplatelets (GNPs) were introduced into a fluoroelastomer (FKM) matrix to improve its mechanical and barrier properties and test its suitability for sealing applications. Nanocomposites filled with different loadings of GNPs were prepared and compared with their counterparts loaded with carbon black (CB). GNPs were dispersed homogeneously with a high degree of in-plane alignment. The tensile and barrier properties of the FKM were improved significantly by the addition of GNPs. Micromechanical modelling based on the shear-lag/rule-of-mixtures theory was used to analyse the reinforcing efficiency of the GNPs. Upon the addition of the GNPs, the elastomer was able to swell anisotropically in liquids, a fact that can be used to tune the swelling properties for sealing applications. In terms of gas permeability, a modification of the well-established Nielsen's theory was introduced to analyse the CO2 permeability for the bulk composite samples. The significantly improved mechanical, thermal and barrier properties at relatively low filler loadings, reveal that the FKM/GNP nanocomposites produced are very promising for use in advanced sealing applications.
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Air leakage is the principal reason for low methane concentrations during coal seam gas drainage. To investigate the air leakage mechanism, a coupled model of coal deformation and air-CH4 flow in ...coal seams was developed, considering gas adsorption and the elastoplasticity of coal. The model was first validated by comparing model results with field data. Subsequently, the model was implemented to analyze air flow distribution in the seam, and discuss the impacts of time, active support pressure and drainage pressure on the air leakage. Modeling results reveal that (1) air flow is distributed widely in the seam near the roadway side, and in the area away from the roadway, the air flow is concentrated around the gas drainage borehole; (2) air leakage is notably affected by time, and increases rapidly initially, then tends to gradually stabilize; and (3) the air leakage decreases with an increase in the active support pressure acting on the drainage borehole wall, or when the drainage pressure (absolute pressure) is improved. Therefore, an active support sealing method was proposed with a double-expansive (DE) material as the sealing material. The expansion pressure of the DE material provides an active support onto the hole-wall, inhibiting coal deformation to control air leakage. Furthermore, field test results prove that the air leakage can be reduced effectively by the active support sealing method, and that the average methane concentration is 21.5% higher than that of the boreholes sealed by the traditional sealing method.
•Experimental and numerical study about sealing on tunnel fire were conducted.•Maximum gas temperature data beneath ceiling in a sealing tunnel fire was obtained.•A model for predicting maximum gas ...temperature is purposed including sealing ratio.•Modified equations agree well with the measured data.
Sealing the tunnel portal is one of practical strategies for tunnel fire extinguishing. In order to better comprehend the sealing effects on tunnel fire and help with sealing strategies scientifically, the maximum gas temperature beneath ceiling in a sealing fire was investigated theoretically, experimentally and numerically in this paper. The results show that maximum ceiling gas temperature is greatly affected by sealing ratio, which probably due to the comprehensive effect between fresh air supply and the reduction of heat loss significantly related to vent area of tunnel portal. Moreover, there always exists a critical sealing ratio, at which ceiling temperature would reach the maximum, and when beyond the critical sealing ratio, maximum gas temperature would drop gradually, which is expected in firefighting. Also, it is found that critical sealing ratio is a function of dimensionless heat release rate, and the greater the heat release rate is, the smaller the critical sealing ratio would be. Finally, an empirical model determining maximum ceiling gas temperature is developed to modify the current models by taking sealing effect into account. The predictions calculated by modified equations agree well with experimental and numerical date in maximum ceiling gas temperature.
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